redis-plus-plus

• Overview
  • Features
  • Branches
• Installation
  • Install hiredis
  • Install redis-plus-plus
  • Run Tests (Optional)
  • Use redis-plus-plus In Your Project
• Getting Started
• API Reference
  • Connection
  • Send Command to Redis Server
  • Exception
  • Generic Command Interface
  • Publish/Subscribe
  • Pipeline
  • Transaction
  • Redis Cluster
  • Redis Sentinel
  • Redis Stream
• Redis Recipes
  • Redlock
• Author

Overview

This is a C++ client for Redis. It's based on hiredis, and written in C++ 11 / C++ 17.

NOTE: I'm not a native speaker. So if the documentation is unclear, please feel free to open an issue or pull request. I'll response ASAP.

Features

• Most commands for Redis.
• Connection pool.
• Redis scripting.
• Thread safe unless otherwise stated.
• Redis publish/subscribe.
• Redis pipeline.
• Redis transaction.
• Redis Cluster.
• Redis Sentinel.
• STL-like interfaces.
• Generic command interface.
• Redis Stream.
• Redlock.
• Redis ACL.
• TLS/SSL support.

Branches

The master branch is the stable branch, which passes all tests. The dev branch is unstable. If you want to contribute, please create pull request on dev branch.

Installation

Install hiredis

Since redis-plus-plus is based on hiredis, you should install hiredis first. The minimum version requirement for hiredis is v0.12.1. However, the latest stable release of hiredis is always recommended.

NOTE: You must ensure that there's only 1 version of hiredis is installed. Otherwise, you might get some wired problems. Check the following issues for example: issue 135, issue 140 and issue 158.

git clone https://github.com/redis/hiredis.git

cd hiredis

make

make install

By default, hiredis is installed at /usr/local. If you want to install hiredis at non-default location, use the following commands to specify the installation path.

make PREFIX=/non/default/path

make PREFIX=/non/default/path install

Install redis-plus-plus

redis-plus-plus is built with CMAKE.

git clone https://github.com/sewenew/redis-plus-plus.git

cd redis-plus-plus

mkdir build

cd build

cmake ..

make

make install

cd ..

If hiredis is installed at non-default location, you should use CMAKE_PREFIX_PATH to specify the installation path of hiredis. By default, redis-plus-plus is installed at /usr/local. However, you can use CMAKE_INSTALL_PREFIX to install redis-plus-plus at non-default location.

cmake -DCMAKE_PREFIX_PATH=/path/to/hiredis -DCMAKE_INSTALL_PREFIX=/path/to/install/redis-plus-plus ..

By default, redis-plus-plus is built with -std=c++11 standard. If you want to use the std::string_view and std::optional features, you can also build redis-plus-plus with -std=c++17 standard by specifying the following cmake flag: -DREDIS_PLUS_PLUS_CXX_STANDARD=17.

cmake -DCMAKE_PREFIX_PATH=/path/to/hiredis -DCMAKE_INSTALL_PREFIX=/path/to/install/redis-plus-plus -DREDIS_PLUS_PLUS_CXX_STANDARD=17 ..

When compiling redis-plus-plus, it also compiles a test program, which might take a while. However, you can disable building test with the following cmake option: -DREDIS_PLUS_PLUS_BUILD_TEST=OFF.

cmake -DCMAKE_PREFIX_PATH=/path/to/hiredis -DCMAKE_INSTALL_PREFIX=/path/to/install/redis-plus-plus -DREDIS_PLUS_PLUS_BUILD_TEST=OFF ..

By default, redis-plus-plus builds both a static library and a shared library. If you only want to build one of them, you can disable the other with -DREDIS_PLUS_PLUS_BUILD_STATIC=OFF or -DREDIS_PLUS_PLUS_BUILD_SHARED=OFF.

redis-plus-plus builds static library with -fPIC option, i.e. Position Independent Code, by default. However, you can disable it with -DREDIS_PLUS_PLUS_BUILD_STATIC_WITH_PIC=OFF.

Windows Support

Now hiredis has Windows support, and since Visual Studio 2017, Visual Studio has built-in support for CMake. So redis-plus-plus also supports Windows platform now. It has been fully tested with Visual Studio 2017 and later on Win 10. I'm not familiar with Visual Studio environment, and the following doc might not be accurate. If you're familiar with the Windows platform, feel free to update this doc on how to install redis-plus-plus on Windows.

CMake Support On Visual Studio

The following are some links on how to build CMake project with Visual Studio 2017 or later. If you're not familiar with it, you'd better read these instructions first:

• CMake support in Visual Studio
• CMake projects in Visual Studio
• CMakeSettings.json schema reference
• Open a project from a GitHub repo

NOTE: IMHO, Visual Studio 2017's support for CMake project is not very mature, and I recommend you to build hiredis and *redis-plus-plus with Visual Studio 2019.

Build hiredis

First of all, you need to get the latest code of hiredis on master branch. Older version might not support Windows platform. hiredis' CMakeLists.txt uses add_compile_definitions method, which is only supported by cmake 3.12 or later. However, Visual Studio 2017's cmake version is older than that. So if you're using Visual Studio 2017, you need to comment the following line in the CMakeLists.txt file:

#IF(WIN32)
#    ADD_COMPILE_DEFINITIONS(_CRT_SECURE_NO_WARNINGS WIN32_LEAN_AND_MEAN)
#ENDIF()

You can use the Open Folder feature to open hiredis project, and build it with the instructions (links) mentioned above.

Build redis-plus-plus

Since redis-plus-plus depends on hiredis, we need to specify the installation paths of hiredis before building it. You can use the Open Folder feature to open redis-plus-plus project. You need to edit the CMakeSetting.json file (automatically generated by Visual Studio) to set HIREDIS_HEADER, HIREDIS_LIB and HIREDIS_STATIC_LIB variables to specify the installation path of hiredis headers, installation path of hiredis dynamic library and installation path of hiredis static library. The following is an example of CMakeSetting.json file:

{
    "configurations": [
      {
        "name": "x64-Release",
        "generator": "Visual Studio 15 2017 Win64",
        "configurationType": "Release",
        "buildRoot": "${env.LOCALAPPDATA}\\CMakeBuild\\${workspaceHash}\\build\\${name}",
        "cmakeCommandArgs": "",
        "buildCommandArgs": "-m -v:minimal",
        "variables": [
          {
            "name": "HIREDIS_HEADER",
            "value": "installation path of hiredis header files",
            "type": "PATH"
          },
          {
            "name": "HIREDIS_LIB",
            "value": "installation path of dynamic library of hiredis",
            "type": "FILEPATH"
          },
          {
            "name": "TEST_HIREDIS_LIB",
            "value": "installation path of static library of hiredis",
            "type": "FILEPATH"
          }
        ]
      }
    ]
}

Then you can build it the instructions (links) mentioned above. If you're building with Visual Studio 2017 in debug mode, you might get /bigobj error when building the test. In this case, you can disable building test by setting -DREDIS_PLUS_PLUS_BUILD_TEST=OFF or build it in Release mode.

NOTE: REDIS_PLUS_PLUS_CXX_STANDARD is not supported on Windows so far, and TLS/SSL support has not been tested on Windows yet.

Run Tests (Optional)

redis-plus-plus has been fully tested with the following compilers:

gcc version 4.8.5 20150623 (Red Hat 4.8.5-39) (GCC)
gcc version 5.5.0 20171010 (Ubuntu 5.5.0-12ubuntu1)
gcc version 6.5.0 20181026 (Ubuntu 6.5.0-2ubuntu1~18.04)
gcc version 7.4.0 (Ubuntu 7.4.0-1ubuntu1~18.04.1)
gcc version 8.3.0 (Ubuntu 8.3.0-6ubuntu1~18.04.1)
gcc version 9.2.1 20191008 (Ubuntu 9.2.1-9ubuntu2)
clang version 3.9.1-19ubuntu1 (tags/RELEASE_391/rc2)
clang version 4.0.1-10 (tags/RELEASE_401/final)
clang version 5.0.1-4 (tags/RELEASE_501/final)
clang version 6.0.0-1ubuntu2 (tags/RELEASE_600/final)
clang version 7.0.0-3~ubuntu0.18.04.1 (tags/RELEASE_700/final)
clang version 8.0.1-3build1 (tags/RELEASE_801/final)
Apple clang version 11.0.0 (clang-1100.0.33.12)
Visual Studio 2017 (Win 10)
Visual Studio 2019 (Win 10)

If you build redis-plus-plus with -DREDIS_PLUS_PLUS_BUILD_TEST=ON (the default behavior, and you can disable building test with -DREDIS_PLUS_PLUS_BUILD_TEST=OFF), you'll get a test program in compile/test directory: compile/test/test_redis++.

In order to run the tests, you need to set up a Redis instance, and a Redis Cluster. Since the test program will send most of Redis commands to the server and cluster, you need to set up Redis of the latest version (by now, it's 5.0). Otherwise, the tests might fail. For example, if you set up Redis 4.0 for testing, the test program will fail when it tries to send the ZPOPMAX command (a Redis 5.0 command) to the server. If you want to run the tests with other Redis versions, you have to comment out commands that haven't been supported by your Redis, from test source files in redis-plus-plus/test/src/sw/redis++/ directory. Sorry for the inconvenience, and I'll fix this problem to make the test program work with any version of Redis in the future.

NOTE: The latest version of Redis is only a requirement for running the tests. In fact, you can use redis-plus-plus with Redis of any version, e.g. Redis 2.0, Redis 3.0, Redis 4.0, Redis 5.0.

NEVER run the test program in production envronment, since the keys, which the test program reads or writes, might conflict with your application.

In order to run tests with both Redis and Redis Cluster, you can run the test program with the following command:

./compile/test/test_redis++ -h host -p port -a auth -n cluster_node -c cluster_port

• host and port are the host and port number of the Redis instance.
• cluster_node and cluster_port are the host and port number of Redis Cluster. You only need to set the host and port number of a single node in the cluster, redis-plus-plus will find other nodes automatically.
• auth is the password of the Redis instance and Redis Cluster. The Redis instance and Redis Cluster must be configured with the same password. If there's no password configured, don't set this option.

If you only want to run tests with Redis, you only need to specify host, port and auth options:

./compile/test/test_redis++ -h host -p port -a auth

Similarly, if you only want to run tests with Redis Cluster, just specify cluster_node, cluster_port and auth options:

./compile/test/test_redis++ -a auth -n cluster_node -c cluster_port

By default, the test program will not test running redis-plus-plus in multi-threads environment. If you want to do multi-threads test, which might cost a long time, you can specify the -m option:

./compile/test/test_redis++ -h host -p port -a auth -n cluster_node -c cluster_port -m

If all tests have been passed, the test program will print the following message:

Pass all tests

Otherwise, it prints the error message.

Performance

redis-plus-plus runs as fast as hiredis, since it's a wrapper of hiredis. You can run test_redis++ in benchmark mode to check the performance in your environment.

./compile/test/test_redis++ -h host -p port -a auth -n cluster_node -c cluster_port -b -t thread_num -s connection_pool_size -r request_num -k key_len -v val_len

• -b option turns the test program into benchmark mode.
• thread_num specifies the number of worker threads. 10 by default.
• connection_pool_size specifies the size of the connection pool. 5 by default.
• request_num specifies the total number of requests sent to server for each test. 100000 by default.
• key_len specifies the length of the key for each operation. 10 by default.
• val_len specifies the length of the value. 10 by default.

The bechmark will generate 100 random binary keys for testing, and the size of these keys is specified by key_len. When the benchmark runs, it will read/write with these keys. So NEVER run the test program in your production environment, otherwise, it might inaccidently delete your data.

Use redis-plus-plus In Your Project

After compiling the code, you'll get both shared library and static library. Since redis-plus-plus depends on hiredis, you need to link both libraries to your Application. Also don't forget to specify the -std=c++11 and thread-related option.

Use Static Libraries

Take gcc as an example.

g++ -std=c++11 -o app app.cpp /path/to/libredis++.a /path/to/libhiredis.a -pthread

If hiredis and redis-plus-plus are installed at non-default location, you should use -I option to specify the header path.

g++ -std=c++11 -I/non-default/install/include/path -o app app.cpp /path/to/libredis++.a /path/to/libhiredis.a -pthread

Use Shared Libraries

g++ -std=c++11 -o app app.cpp -lredis++ -lhiredis -pthread

If hiredis and redis-plus-plus are installed at non-default location, you should use -I and -L options to specify the header and library paths.

g++ -std=c++11 -I/non-default/install/include/path -L/non-default/install/lib/path -o app app.cpp -lredis++ -lhiredis -pthread

When linking with shared libraries, and running your application, you might get the following error message:

error while loading shared libraries: xxx: cannot open shared object file: No such file or directory.

That's because the linker cannot find the shared libraries. In order to solve the problem, you can add the path where you installed hiredis and redis-plus-plus libraries, to LD_LIBRARY_PATH environment variable. For example:

export LD_LIBRARY_PATH=$LD_LIBRARY_PATH:/usr/local/lib

Check this StackOverflow question for details on how to solve the problem.

Build With Cmake

If you're using cmake to build your application, you need to add hiredis and redis-plus-plus dependencies in your CMakeLists.txt:

# <------------ add hiredis dependency --------------->
find_path(HIREDIS_HEADER hiredis)
target_include_directories(target PUBLIC ${HIREDIS_HEADER})

find_library(HIREDIS_LIB hiredis)
target_link_libraries(target ${HIREDIS_LIB})

# <------------ add redis-plus-plus dependency -------------->
# NOTE: this should be *sw* NOT *redis++*
find_path(REDIS_PLUS_PLUS_HEADER sw)
target_include_directories(target PUBLIC ${REDIS_PLUS_PLUS_HEADER})

find_library(REDIS_PLUS_PLUS_LIB redis++)
target_link_libraries(target ${REDIS_PLUS_PLUS_LIB})

See this issue for a complete example of CMakeLists.txt.

Also, if you installed hiredis and redis-plus-plus at non-default location, you need to run cmake with CMAKE_PREFIX_PATH option to specify the installation path of these two libraries.

cmake -DCMAKE_PREFIX_PATH=/installation/path/to/the/two/libs ..

Getting Started

#include <sw/redis++/redis++.h>

using namespace sw::redis;

try {
    // Create an Redis object, which is movable but NOT copyable.
    auto redis = Redis("tcp://127.0.0.1:6379");

    // ***** STRING commands *****

    redis.set("key", "val");
    auto val = redis.get("key");    // val is of type OptionalString. See 'API Reference' section for details.
    if (val) {
        // Dereference val to get the returned value of std::string type.
        std::cout << *val << std::endl;
    }   // else key doesn't exist.

    // ***** LIST commands *****

    // std::vector<std::string> to Redis LIST.
    std::vector<std::string> vec = {"a", "b", "c"};
    redis.rpush("list", vec.begin(), vec.end());

    // std::initializer_list to Redis LIST.
    redis.rpush("list", {"a", "b", "c"});

    // Redis LIST to std::vector<std::string>.
    vec.clear();
    redis.lrange("list", 0, -1, std::back_inserter(vec));

    // ***** HASH commands *****

    redis.hset("hash", "field", "val");

    // Another way to do the same job.
    redis.hset("hash", std::make_pair("field", "val"));

    // std::unordered_map<std::string, std::string> to Redis HASH.
    std::unordered_map<std::string, std::string> m = {
        {"field1", "val1"},
        {"field2", "val2"}
    };
    redis.hmset("hash", m.begin(), m.end());

    // Redis HASH to std::unordered_map<std::string, std::string>.
    m.clear();
    redis.hgetall("hash", std::inserter(m, m.begin()));

    // Get value only.
    // NOTE: since field might NOT exist, so we need to parse it to OptionalString.
    std::vector<OptionalString> vals;
    redis.hmget("hash", {"field1", "field2"}, std::back_inserter(vals));

    // ***** SET commands *****

    redis.sadd("set", "m1");

    // std::unordered_set<std::string> to Redis SET.
    std::unordered_set<std::string> set = {"m2", "m3"};
    redis.sadd("set", set.begin(), set.end());

    // std::initializer_list to Redis SET.
    redis.sadd("set", {"m2", "m3"});

    // Redis SET to std::unordered_set<std::string>.
    set.clear();
    redis.smembers("set", std::inserter(set, set.begin()));

    if (redis.sismember("set", "m1")) {
        std::cout << "m1 exists" << std::endl;
    }   // else NOT exist.

    // ***** SORTED SET commands *****

    redis.zadd("sorted_set", "m1", 1.3);

    // std::unordered_map<std::string, double> to Redis SORTED SET.
    std::unordered_map<std::string, double> scores = {
        {"m2", 2.3},
        {"m3", 4.5}
    };
    redis.zadd("sorted_set", scores.begin(), scores.end());

    // Redis SORTED SET to std::unordered_map<std::string, double>.
    scores.clear();
    redis.zrangebyscore("sorted_set",
            UnboundedInterval<double>{},            // (-inf, +inf)
            std::inserter(scores, scores.begin()));

    // Only get member names:
    // pass an inserter of std::vector<std::string> type as output parameter.
    std::vector<std::string> without_score;
    redis.zrangebyscore("sorted_set",
            BoundedInterval<double>(1.5, 3.4, BoundType::CLOSED),   // [1.5, 3.4]
            std::back_inserter(without_score));

    // Get both member names and scores:
    // pass an inserter of std::unordered_map<std::string, double> as output parameter.
    std::unordered_map<std::string, double> with_score;
    redis.zrangebyscore("sorted_set",
            BoundedInterval<double>(1.5, 3.4, BoundType::LEFT_OPEN),    // (1.5, 3.4]
            std::inserter(with_score, with_score.end()));

    // ***** SCRIPTING commands *****

    // Script returns a single element.
    auto num = redis.eval<long long>("return 1", {}, {});

    // Script returns an array of elements.
    std::vector<long long> nums;
    redis.eval("return {ARGV[1], ARGV[2]}", {}, {"1", "2"}, std::back_inserter(nums));

    // mset with TTL
    auto mset_with_ttl_script = R"(
        local len = #KEYS
        if (len == 0 or len + 1 ~= #ARGV) then return 0 end
        local ttl = tonumber(ARGV[len + 1])
        if (not ttl or ttl <= 0) then return 0 end
        for i = 1, len do redis.call("SET", KEYS[i], ARGV[i], "EX", ttl) end
        return 1
    )";

    // Set multiple key-value pairs with TTL of 60 seconds.
    auto keys = {"key1", "key2", "key3"};
    std::vector<std::string> args = {"val1", "val2", "val3", "60"};
    redis.eval<long long>(mset_with_ttl_script, keys.begin(), keys.end(), vals.begin(), vals.end());

    // ***** Pipeline *****

    // Create a pipeline.
    auto pipe = redis.pipeline();

    // Send mulitple commands and get all replies.
    auto pipe_replies = pipe.set("key", "value")
                            .get("key")
                            .rename("key", "new-key")
                            .rpush("list", {"a", "b", "c"})
                            .lrange("list", 0, -1)
                            .exec();

    // Parse reply with reply type and index.
    auto set_cmd_result = pipe_replies.get<bool>(0);

    auto get_cmd_result = pipe_replies.get<OptionalString>(1);

    // rename command result
    pipe_replies.get<void>(2);

    auto rpush_cmd_result = pipe_replies.get<long long>(3);

    std::vector<std::string> lrange_cmd_result;
    pipe_replies.get(4, back_inserter(lrange_cmd_result));

    // ***** Transaction *****

    // Create a transaction.
    auto tx = redis.transaction();

    // Run multiple commands in a transaction, and get all replies.
    auto tx_replies = tx.incr("num0")
                        .incr("num1")
                        .mget({"num0", "num1"})
                        .exec();

    // Parse reply with reply type and index.
    auto incr_result0 = tx_replies.get<long long>(0);

    auto incr_result1 = tx_replies.get<long long>(1);

    std::vector<OptionalString> mget_cmd_result;
    tx_replies.get(2, back_inserter(mget_cmd_result));

    // ***** Generic Command Interface *****

    // There's no *Redis::client_getname* interface.
    // But you can use *Redis::command* to get the client name.
    val = redis.command<OptionalString>("client", "getname");
    if (val) {
        std::cout << *val << std::endl;
    }

    // Same as above.
    auto getname_cmd_str = {"client", "getname"};
    val = redis.command<OptionalString>(getname_cmd_str.begin(), getname_cmd_str.end());

    // There's no *Redis::sort* interface.
    // But you can use *Redis::command* to send sort the list.
    std::vector<std::string> sorted_list;
    redis.command("sort", "list", "ALPHA", std::back_inserter(sorted_list));

    // Another *Redis::command* to do the same work.
    auto sort_cmd_str = {"sort", "list", "ALPHA"};
    redis.command(sort_cmd_str.begin(), sort_cmd_str.end(), std::back_inserter(sorted_list));

    // ***** Redis Cluster *****

    // Create a RedisCluster object, which is movable but NOT copyable.
    auto redis_cluster = RedisCluster("tcp://127.0.0.1:7000");

    // RedisCluster has similar interfaces as Redis.
    redis_cluster.set("key", "value");
    val = redis_cluster.get("key");
    if (val) {
        std::cout << *val << std::endl;
    }   // else key doesn't exist.

    // Keys with hash-tag.
    redis_cluster.set("key{tag}1", "val1");
    redis_cluster.set("key{tag}2", "val2");
    redis_cluster.set("key{tag}3", "val3");

    std::vector<OptionalString> hash_tag_res;
    redis_cluster.mget({"key{tag}1", "key{tag}2", "key{tag}3"},
            std::back_inserter(hash_tag_res));

} catch (const Error &e) {
    // Error handling.
}

API Reference

You can also see redis.h for doxygen style documentation.

Connection

Redis class maintains a connection pool to Redis server. If the connection is broken, Redis reconnects to Redis server automatically.

You can initialize a Redis instance with ConnectionOptions and ConnectionPoolOptions. ConnectionOptions specifies options for connection to Redis server, and ConnectionPoolOptions specifies options for conneciton pool. ConnectionPoolOptions is optional. If not specified, Redis maintains a single connection to Redis server.

ConnectionOptions connection_options;
connection_options.host = "127.0.0.1";  // Required.
connection_options.port = 6666; // Optional. The default port is 6379.
connection_options.password = "auth";   // Optional. No password by default.
connection_options.db = 1;  // Optional. Use the 0th database by default.

// Optional. Timeout before we successfully send request to or receive response from redis.
// By default, the timeout is 0ms, i.e. never timeout and block until we send or receive successfuly.
// NOTE: if any command is timed out, we throw a TimeoutError exception.
connection_options.socket_timeout = std::chrono::milliseconds(200);

// Connect to Redis server with a single connection.
Redis redis1(connection_options);

ConnectionPoolOptions pool_options;
pool_options.size = 3;  // Pool size, i.e. max number of connections.

// Optional. Max time to wait for a connection. 0ms by default, which means wait forever.
// Say, the pool size is 3, while 4 threds try to fetch the connection, one of them will be blocked.
pool_options.wait_timeout = std::chrono::milliseconds(100);

// Optional. Max lifetime of a connection. 0ms by default, which means never expire the connection.
// If the connection has been created for a long time, i.e. more than `connection_lifetime`,
// it will be expired and reconnected.
pool_options.connection_lifetime = std::chrono::minutes(10);

// Connect to Redis server with a connection pool.
Redis redis2(connection_options, pool_options);

NOTE: if you set ConnectionOptions::socket_timeout, and try to call blocking commands, e.g. Redis::brpop, Redis::blpop, Redis::bzpopmax, Redis::bzpopmin, you must ensure that ConnectionOptions::socket_timeout is larger than the timeout specified with these blocking commands. Otherwise, you might get TimeoutError, and lose message.

See ConnectionOptions and ConnectionPoolOptions for more options. Also see issue 80 for discussion on connection pool.

NOTE: Redis class is movable but NOT copyable.

// auto redis3 = redis1;    // this won't compile.

// But it's movable.
auto redis3 = std::move(redis1);

redis-plus-plus also supports connecting to Redis server with Unix Domain Socket.

ConnectionOptions options;
options.type = ConnectionType::UNIX;
options.path = "/path/to/socket";
Redis redis(options);

You can also connect to Redis server with a URI:

tcp://[[username:][email protected]]host[:port][/db]

unix://[[username:][email protected]]path-to-unix-domain-socket[/db]

The scheme and host parts are required, and others are optional. If you're connecting to Redis with Unix Domain Socket, you should use the unix scheme, otherwise, you should use tcp scheme. The following is a list of default values for those optional parts:

• username: default
• password: empty string, i.e. no password
• port: 6379
• db: 0

NOTE: If your password or username contains '@', or your username contains ':', you cannot construct Redis object with URI. Because redis-plus-plus will incorrectly parse the URI. In this case, you need to use ConnectionOptions to construct Redis object.

NOTE: Redis 6.0 supports ACL, and you can specify a username for the connection. However, before Redis 6.0, you cannot do that.

Also, the following connection options can be specified with the query string of URI, e.g. tcp://127.0.0.1?keep_alive=true&socket_timeout=100ms&connect_timeout=100ms:

• ConnectionOptions::keep_alive: false by default.
• ConnectionOptions::socket_timeout: 0ms by default.
• ConnectionOptions::connect_timeout: 0ms by default.

NOTE: Options specified in query string are case-sensitive, i.e. all key-value pairs must be in lowercase.

So far, you cannot specify connection pool options with URI, e.g. ConnectionPoolOptions::size.

// Single connection to the given host and port.
Redis redis1("tcp://127.0.0.1:6666");

// Use default port, i.e. 6379.
Redis redis2("tcp://127.0.0.1");

// Connect to Redis with password, and default port.
Redis redis3("tcp://[email protected]");

// Connect to Redis and select the 2nd (db number starts from 0) database.
Redis redis4("tcp://127.0.0.1:6379/2");

// Set keep_alive option to true with query string.
Redis redis5("tcp://127.0.0.1:6379/2?keep_alive=true");

// Set socket_timeout to 50 milliseconds, and connect_timeout to 1 second with query string.
Redis redis6("tcp://127.0.0.1?socket_timeout=50ms&connect_timeout=1s");

// Connect to Unix Domain Socket.
Redis redis7("unix://path/to/socket");

Lazily Create Connection

Connections in the pool are lazily created. When the connection pool is initialized, i.e. the constructor of Redis, Redis does NOT connect to the server. Instead, it connects to the server only when you try to send command. In this way, we can avoid unnecessary connections. So if the pool size is 5, but the number of max concurrent connections is 3, there will be only 3 connections in the pool.

Connection Failure

You don't need to check whether Redis object connects to server successfully. If Redis fails to create a connection to Redis server, or the connection is broken at some time, it throws an exception of type Error when you try to send command with Redis. Even when you get an exception, i.e. the connection is broken, you don't need to create a new Redis object. You can reuse the Redis object to send commands, and the Redis object will try to reconnect to server automatically. If it reconnects successfully, it sends command to server. Otherwise, it throws an exception again.

See the Exception section for details on exceptions.

Reuse Redis object As Much As Possible

It's NOT cheap to create a Redis object, since it will create new connections to Redis server. So you'd better reuse Redis object as much as possible. Also, it's safe to call Redis' member functions in multi-thread environment, and you can share Redis object in multiple threads.

// This is GOOD practice.
auto redis = Redis("tcp://127.0.0.1");
for (auto idx = 0; idx < 100; ++idx) {
    // Reuse the Redis object in the loop.
    redis.set("key", "val");
}

// This is VERY BAD! It's very inefficient.
// NEVER DO IT!!!
for (auto idx = 0; idx < 100; ++idx) {
    // Create a new Redis object for each iteration.
    auto redis = Redis("tcp://127.0.0.1");
    redis.set("key", "val");
}

TLS/SSL Support

redis-plus-plus also has TLS support. However, in order to use this feature, you need to enable it when building hiredis and redis-plus-plus.

NOTE: So far, TLS feature has not been tested on Windows platform. I'll fix it in the future.

Enable TLS/SSL support

When building hiredis with TLS support, you need to download hiredis of version v1.0.0 or latter, and specify USE_SSL=1 flag:

make PREFIX=/non/default/path USE_SSL=1

make PREFIX=/non/default/path USE_SSL=1 install

Then you can build redis-plus-plus to enable TLS support by specifying the -DREDIS_PLUS_PLUS_USE_TLS=ON option:

cmake -DREDIS_PLUS_PLUS_USE_TLS=ON ..

Connection Options

In order to connect to Redis with TLS support, you need to specify the following connection options:

ConnectionOptions opts;
opts.host = "127.0.0.1";
opts.port = 6379;

opts.tls.enabled = true;    // Required. `false` by default.
opts.tls.cert = "/path/to/client/certificate";  // Optional
opts.tls.key = "/path/to/private/key/file"; // Optional
opts.tls.cacert = "/path/to/CA/certificate/file";   // You can also set `opts.tls.cacertdir` instead.
opts.tls.sni = "server-name-indication";    // Optional

Although tls.cert and tls.key are optional, if you specify one of them, you must also specify the other. Instead of specifying tls.cacert, you can also specify tls.cacertdir to the directory where certificates are stored.

These options are the same as redis-cli's TLS related command line arguments, so you can also run redis-cli --help to get the detailed explanation of these options.

Then you can use this ConnectionOptions to create a Redis object to connect to Redis server with TLS support.

NOTE: When building your application code, you also need to link it with libhiredis.a, libhiredis_ssl.a, libredis++.a (or the corresponding shared libraries), -lssl and -lcrypto.

Automatically Initialize OpenSSL Library

By default, redis-plus-plus automatically initializes OpenSSL library, i.e. calls SSL_library_init and initializes locks if needed. However, your application code might already initialize OpenSSL library. In this case, you can call tls::disable_auto_init() to disable the initialization. You should call this function only once and call it before any other redis-plus-plus operation. Otherwise, the behavior is undefined.

Send Command to Redis Server

You can send Redis commands through Redis object. Redis has one or more (overloaded) methods for each Redis command. The method has the same (lowercased) name as the corresponding command. For example, we have 3 overload methods for the DEL key [key ...] command:

// Delete a single key.
long long Redis::del(const StringView &key);

// Delete a batch of keys: [first, last).
template <typename Input>
long long Redis::del(Input first, Input last);

// Delete keys in the initializer_list.
template <typename T>
long long Redis::del(std::initializer_list<T> il);

With input parameters, these methods build a Redis command based on Redis protocol, and send the command to Redis server. Then synchronously receive the reply, parse it, and return to the caller.

Let's take a closer look at these methods' parameters and return values.

Parameter Type

Most of these methods have the same parameters as the corresponding commands. The following is a list of parameter types:

Parameter Type	Explaination	Example	Note
StringView	Parameters of string type. Normally used for key, value, member name, field name and so on	bool Redis::hset(const StringView &key, const StringView &field, const StringView &val)	See the StringView section for details on StringView
long long	Parameters of integer type. Normally used for index (e.g. list commands) or integer	void ltrim(const StringView &key, long long start, long long stop) long long decrby(const StringView &key, long long decrement)
double	Parameters of floating-point type. Normally used for score (e.g. sorted set commands) or number of floating-point type	double incrbyfloat(const StringView &key, double increment)
std::chrono::duration std::chrono::time_point	Time-related parameters	bool expire(const StringView &key, const std::chrono::seconds &timeout) bool expireat(const StringView &key, const std::chrono::time_point<std::chrono::system_clock, std::chrono::seconds> &tp)
std::pair<StringView, StringView>	Used for Redis hash's (field, value) pair	bool hset(const StringView &key, const std::pair<StringView, StringView> &item)
std::pair<double, double>	Used for Redis geo's (longitude, latitude) pair	OptionalLongLong georadius(const StringView &key, const std::pair<double, double> &location, double radius, GeoUnit unit, const StringView &destination, bool store_dist, long long count)
pair of iterators	Use a pair of iterators to specify a range of input, so that we can pass the data in a STL container to these methods	template < typename Input > long long del(Input first, Input last)	Throw an exception, if it's an empty range, i.e. first == last
std::initializer_list< T >	Use an initializer list to specify a batch of input	template < typename T > long long del(std::initializer_list< T > il)
some options	Options for some commands	UpdateType, template < typename T > class BoundedInterval	See command_options.h for details

StringView

std::string_view is a good option for the type of string parameters. However, by now, not all compilers support std::string_view. So if you build redis-plus-plus with -std=c++11 standard (i.e. the default behavior), we wrote a simple version, i.e. StringView. Instead, if you build redis-plus-plus with -std=c++17 standard (i.e. by specifying -DREDIS_PLUS_PLUS_CXX_STANDARD=17 with cmake command), you can use std::string_view, and we have a typedef for it: using StringView = std::string_view.

Since there are conversions from std::string and c-style string to StringView, you can just pass std::string or c-style string to methods that need a StringView parameter.

// bool Redis::hset(const StringView &key, const StringView &field, const StringView &val)

// Pass c-style string to StringView.
redis.hset("key", "field", "value");

// Pass std::string to StringView.
std::string key = "key";
std::string field = "field";
std::string val = "val";
redis.hset(key, field, val);

// Mix std::string and c-style string.
redis.hset(key, field, "value");

Return Type

Redis protocol defines 5 kinds of replies:

• Status Reply: Also known as Simple String Reply. It's a non-binary string reply.
• Bulk String Reply: Binary safe string reply.
• Integer Reply: Signed integer reply. Large enough to hold long long.
• Array Reply: (Nested) Array reply.
• Error Reply: Non-binary string reply that gives error info.

Also these replies might be NULL. For instance, when you try to GET the value of a nonexistent key, Redis returns a NULL Bulk String Reply.

As we mentioned above, replies are parsed into return values of these methods. The following is a list of return types:

Return Type	Explaination	Example	Note
void	Status Reply that should always return a string of "OK"	RENAME, SETEX
std::string	Status Reply that NOT always return "OK", and Bulk String Reply	PING, INFO
bool	Integer Reply that always returns 0 or 1	EXPIRE, HSET	See the Boolean Return Value section for the meaning of a boolean return value
long long	Integer Reply that not always return 0 or 1	DEL, APPEND
double	Bulk String Reply that represents a double	INCRBYFLOAT, ZINCRBY
std::pair	Array Reply with exactly 2 elements. Since the return value is always an array of 2 elements, we return the 2 elements as a std::pair's first and second elements	BLPOP
std::tuple	Array Reply with fixed length and has more than 2 elements. Since length of the returned array is fixed, we return the array as a std::tuple	BZPOPMAX
output iterator	General Array Reply with non-fixed/dynamic length. We use STL-like interface to return this kind of array replies, so that you can insert the return value into a STL container easily	MGET, LRANGE	Also, sometimes the type of output iterator decides which options to send with the command. See the Examples section for details
Optional< T >	For any reply of type T that might be NULL	GET, LPOP, BLPOP, BZPOPMAX	See the Optional section for details on Optional<T>
Variant< Args... >	For reply that might be of serval different types	MEMORY STATS	NOTE: so far, this type is only supported when compiling redis-plus-plus with C++ 17 standard. This is normally used with generic command interface. See the Variant section for details on Variant<Args...>
STL container	General Array Reply	CONFIG GET	Both output iterator and STL container are used for array reply. The difference is that STL container is normally used with generic command interface. See the STL container section for example

Boolean Return Value

The return type of some methods, e.g. EXPIRE, HSET, is bool. If the method returns false, it DOES NOT mean that Redis failed to send the command to Redis server. Instead, it means that Redis server returns an Integer Reply, and the value of the reply is 0. Accordingly, if the method returns true, it means that Redis server returns an Integer Reply, and the value of the reply is 1. You can check Redis commands manual for what do 0 and 1 stand for.

For example, when we send EXPIRE command to Redis server, it returns 1 if the timeout was set, and it returns 0 if the key doesn't exist. Accordingly, if the timeout was set, Redis::expire returns true, and if the key doesn't exist, Redis::expire returns false.

So, never use the return value to check if the command has been successfully sent to Redis server. Instead, if Redis failed to send command to server, it throws an exception of type Error. See the Exception section for details on exceptions.

Optional

std::optional is a good option for return type, if Redis might return NULL REPLY. Again, since not all compilers support std::optional so far, if you build redis-plus-plus with -std=c++11 standard (i.e. the default behavior), we implement our own simple version, i.e. template Optional<T>. Instead, if you build redis-plus-plus with -std=c++17 standard (i.e. by specifying -DREDIS_PLUS_PLUS_CXX_STANDARD=17 with cmake command), you can use std::optional, and we have a typedef for it: template <typename T> using Optional = std::optional<T>.

Take the GET and MGET commands for example:

// Or just: auto val = redis.get("key");
Optional<std::string> val = redis.get("key");

// Optional<T> has a conversion to bool.
// If it's NOT a null Optional<T> object, it's converted to true.
// Otherwise, it's converted to false.
if (val) {
    // Key exists. Dereference val to get the string result.
    std::cout << *val << std::endl;
} else {
    // Redis server returns a NULL Bulk String Reply.
    // It's invalid to dereference a null Optional<T> object.
    std::cout << "key doesn't exist." << std::endl;
}

std::vector<Optional<std::string>> values;
redis.mget({"key1", "key2", "key3"}, std::back_inserter(values));
for (const auto &val : values) {
    if (val) {
        // Key exist, process the value.
    }
}

We also have some typedefs for some commonly used Optional<T>:

using OptionalString = Optional<std::string>;

using OptionalLongLong = Optional<long long>;

using OptionalDouble = Optional<double>;

using OptionalStringPair = Optional<std::pair<std::string, std::string>>;

Variant

std::variant is a good option for return type, if the reply might be of different types. For example, the MEMORY STATS command returns an array reply, which is, in fact, a map of key-value pairs of configurations:

127.0.0.1:6379> memory stats
 1) "peak.allocated"
 2) (integer) 4471104
 ...
17) "db.0"
18) 1) "overhead.hashtable.main"
    2) (integer) 104
    3) "overhead.hashtable.expires"
    4) (integer) 32
...
27) "dataset.percentage"
28) "9.70208740234375"
...

However, as you can see, the value part of the result might be of type long long (key: peak.allocated), double (key: dataset.percentage) or even a map (key: db.0). So you cannot simply parse the result into a std::unordered_map<std::string, long long> or std::unordered_map<std::string, double>. A workaround is to parse the result into a tuple, however, this tuple solution is ugly and error-prone. Check this issue for detail.

In this case, Variant, which is a typedef of std::variant if you build redis-plus-plus with C++17 standard, is very helpful. You can parse the result into a std::unordered_map<std::string, Variant<double, long long, std::unordered_map<std::string, long long>>>.

using Var = Variant<double, long long, std::unordered_map<std::string, long long>>;
auto r = Redis("tcp://127.0.0.1");
auto v = r.command<std::unordered_map<std::string, Var>>("memory", "stats");

There're some limitations on Variant support:

• The type arguments of Variant, cannot have duplicate items, e.g. Variant<double, long long, double> won't work.
• double must be placed before std::string. Because double reply is, in fact, string reply, and when parsing variant, we try to parse the reply into the first matched type, specified with the type arguments from left to right. So if double is placed after std::string, i.e. on the right side of std::string, the reply will always be parsed into std::string.

Also check the generic command section for more examples on generic command interface.

STL container

When using generic command interface, instead of parsing the reply to output iterator, you can also parse it into a STL container.

auto r = Redis("tcp://127.0.0.1");
auto v = r.command<std::unordered_map<std::string, std::string>>("config", "get", "*");

Also check the generic command section for more examples on generic command interface.

Examples

Let's see some examples on how to send commands to Redis server.

Various Parameter Types

// ***** Parameters of StringView type *****

// Implicitly construct StringView with c-style string.
redis.set("key", "value");

// Implicitly construct StringView with std::string.
std::string key("key");
std::string val("value");
redis.set(key, val);

// Explicitly pass StringView as parameter.
std::vector<char> large_data;
// Avoid copying.
redis.set("key", StringView(large_data.data(), large_data.size()));

// ***** Parameters of long long type *****

// For index.
redis.bitcount(key, 1, 3);

// For number.
redis.incrby("num", 100);

// ***** Parameters of double type *****

// For score.
redis.zadd("zset", "m1", 2.5);
redis.zadd("zset", "m2", 3.5);
redis.zadd("zset", "m3", 5);

// For (longitude, latitude).
redis.geoadd("geo", std::make_tuple("member", 13.5, 15.6));

// ***** Time-related parameters *****

using namespace std::chrono;

redis.expire(key, seconds(1000));

auto tp = time_point_cast<seconds>(system_clock::now() + seconds(100));
redis.expireat(key, tp);

// ***** Some options for commands *****

if (redis.set(key, "value", milliseconds(100), UpdateType::NOT_EXIST)) {
    std::cout << "set OK" << std::endl;
}

redis.linsert("list", InsertPosition::BEFORE, "pivot", "val");

std::vector<std::string> res;

// (-inf, inf)
redis.zrangebyscore("zset", UnboundedInterval<double>{}, std::back_inserter(res));

// [3, 6]
redis.zrangebyscore("zset",
    BoundedInterval<double>(3, 6, BoundType::CLOSED),
    std::back_inserter(res));

// (3, 6]
redis.zrangebyscore("zset",
    BoundedInterval<double>(3, 6, BoundType::LEFT_OPEN),
    std::back_inserter(res));

// (3, 6)
redis.zrangebyscore("zset",
    BoundedInterval<double>(3, 6, BoundType::OPEN),
    std::back_inserter(res));

// [3, 6)
redis.zrangebyscore("zset",
    BoundedInterval<double>(3, 6, BoundType::RIGHT_OPEN),
    std::back_inserter(res));

// [3, +inf)
redis.zrangebyscore("zset",
    LeftBoundedInterval<double>(3, BoundType::RIGHT_OPEN),
    std::back_inserter(res));

// (3, +inf)
redis.zrangebyscore("zset",
    LeftBoundedInterval<double>(3, BoundType::OPEN),
    std::back_inserter(res));

// (-inf, 6]
redis.zrangebyscore("zset",
    RightBoundedInterval<double>(6, BoundType::LEFT_OPEN),
    std::back_inserter(res));

// (-inf, 6)
redis.zrangebyscore("zset",
    RightBoundedInterval<double>(6, BoundType::OPEN),
    std::back_inserter(res));

// ***** Pair of iterators *****

std::vector<std::pair<std::string, std::string>> kvs = {{"k1", "v1"}, {"k2", "v2"}, {"k3", "v3"}};
redis.mset(kvs.begin(), kvs.end());

std::unordered_map<std::string, std::string> kv_map = {{"k1", "v1"}, {"k2", "v2"}, {"k3", "v3"}};
redis.mset(kv_map.begin(), kv_map.end());

std::unordered_map<std::string, std::string> str_map = {{"f1", "v1"}, {"f2", "v2"}, {"f3", "v3"}};
redis.hmset("hash", str_map.begin(), str_map.end());

std::unordered_map<std::string, double> score_map = {{"m1", 20}, {"m2", 12.5}, {"m3", 3.14}};
redis.zadd("zset", score_map.begin(), score_map.end());

std::vector<std::string> keys = {"k1", "k2", "k3"};
redis.del(keys.begin(), keys.end());

// ***** Parameters of initializer_list type *****

redis.mset({
    std::make_pair("k1", "v1"),
    std::make_pair("k2", "v2"),
    std::make_pair("k3", "v3")
});

redis.hmset("hash",
    {
        std::make_pair("f1", "v1"),
        std::make_pair("f2", "v2"),
        std::make_pair("f3", "v3")
    });

redis.zadd("zset",
    {
        std::make_pair("m1", 20.0),
        std::make_pair("m2", 34.5),
        std::make_pair("m3", 23.4)
    });

redis.del({"k1", "k2", "k3"});

Various Return Types

// ***** Return void *****

redis.save();

// ***** Return std::string *****

auto info = redis.info();

// ***** Return bool *****

if (!redis.expire("nonexistent", std::chrono::seconds(100))) {
    std::cerr << "key doesn't exist" << std::endl;
}

if (redis.setnx("key", "val")) {
    std::cout << "set OK" << std::endl;
}

// ***** Return long long *****

auto len = redis.strlen("key");
auto num = redis.del({"a", "b", "c"});
num = redis.incr("a");

// ***** Return double *****

auto real = redis.incrbyfloat("b", 23.4);
real = redis.hincrbyfloat("c", "f", 34.5);

// ***** Return Optional<std::string>, i.e. OptionalString *****

auto os = redis.get("kk");
if (os) {
    std::cout << *os << std::endl;
} else {
    std::cerr << "key doesn't exist" << std::endl;
}

os = redis.spop("set");
if (os) {
    std::cout << *os << std::endl;
} else {
    std::cerr << "set is empty" << std::endl;
}

// ***** Return Optional<long long>, i.e. OptionalLongLong *****

auto oll = redis.zrank("zset", "mem");
if (oll) {
    std::cout << "rank is " << *oll << std::endl;
} else {
    std::cerr << "member doesn't exist" << std::endl;
}

// ***** Return Optional<double>, i.e. OptionalDouble *****

auto ob = redis.zscore("zset", "m1");
if (ob) {
    std::cout << "score is " << *ob << std::endl;
} else {
    std::cerr << "member doesn't exist" << std::endl;
}

// ***** Return Optional<pair<string, string>> *****

auto op = redis.blpop({"list1", "list2"}, std::chrono::seconds(2));
if (op) {
    std::cout << "key is " << op->first << ", value is " << op->second << std::endl;
} else {
    std::cerr << "timeout" << std::endl;
}

// ***** Output iterators *****

std::vector<OptionalString> os_vec;
redis.mget({"k1", "k2", "k3"}, std::back_inserter(os_vec));

std::vector<std::string> s_vec;
redis.lrange("list", 0, -1, std::back_inserter(s_vec));

std::unordered_map<std::string, std::string> hash;
redis.hgetall("hash", std::inserter(hash, hash.end()));
// You can also save the result in a vecotr of string pair.
std::vector<std::pair<std::string, std::string>> hash_vec;
redis.hgetall("hash", std::back_inserter(hash_vec));

std::unordered_set<std::string> str_set;
redis.smembers("s1", std::inserter(str_set, str_set.end()));
// You can also save the result in a vecotr of string.
s_vec.clear();
redis.smembers("s1", std::back_inserter(s_vec));

SCAN Commands

auto cursor = 0LL;
auto pattern = "*pattern*";
auto count = 5;
std::unordered_set<std::string> keys;
while (true) {
    cursor = redis.scan(cursor, pattern, count, std::inserter(keys, keys.begin()));
    // Default pattern is "*", and default count is 10
    // cursor = redis.scan(cursor, std::inserter(keys, keys.begin()));

    if (cursor == 0) {
        break;
    }
}

Command Overloads

Sometimes the type of output iterator decides which options to send with the command.

// If the output iterator is an iterator of a container of string,
// we send *ZRANGE* command without the *WITHSCORES* option.
std::vector<std::string> members;
redis.zrange("list", 0, -1, std::back_inserter(members));

// If it's an iterator of a container of a <string, double> pair,
// we send *ZRANGE* command with *WITHSCORES* option.
std::unordered_map<std::string, double> res_with_score;
redis.zrange("list", 0, -1, std::inserter(res_with_score, res_with_score.end()));

// The above examples also apply to other command with the *WITHSCORES* options,
// e.g. *ZRANGEBYSCORE*, *ZREVRANGE*, *ZREVRANGEBYSCORE*.

// Another example is the *GEORADIUS* command.

// Only get members.
members.clear();
redis.georadius("geo",
            std::make_pair(10.1, 11.1),
            100,
            GeoUnit::KM,
            10,
            true,
            std::back_inserter(members));

// If the iterator is an iterator of a container of tuple<string, double>,
// we send the *GEORADIUS* command with *WITHDIST* option.
std::vector<std::tuple<std::string, double>> mem_with_dist;
redis.georadius("geo",
            std::make_pair(10.1, 11.1),
            100,
            GeoUnit::KM,
            10,
            true,
            std::back_inserter(mem_with_dist));

// If the iterator is an iterator of a container of tuple<string, double, string>,
// we send the *GEORADIUS* command with *WITHDIST* and *WITHHASH* options.
std::vector<std::tuple<std::string, double, std::string>> mem_with_dist_hash;
redis.georadius("geo",
            std::make_pair(10.1, 11.1),
            100,
            GeoUnit::KM,
            10,
            true,
            std::back_inserter(mem_with_dist_hash));

// If the iterator is an iterator of a container of
// tuple<string, string, pair<double, double>, double>,
// we send the *GEORADIUS* command with *WITHHASH*, *WITHCOORD* and *WITHDIST* options.
std::vector<std::tuple<std::string, double, std::string>> mem_with_hash_coord_dist;
redis.georadius("geo",
            std::make_pair(10.1, 11.1),
            100,
            GeoUnit::KM,
            10,
            true,
            std::back_inserter(mem_with_hash_coord_dist));

Please see redis.h for doxygen style API references and examples, and see the tests for other examples.

Exception

Redis throws exceptions if it receives an Error Reply or something bad happens, e.g. failed to create a connection to server, or connection to server is broken. All exceptions derived from Error class. See errors.h for details.

• Error: Generic error. It's derived from std::exception, and it's also the base class of other exceptions.
• IoError: There's some IO error with the connection.
• TimeoutError: Read or write operation was timed out. It's a derived class of IoError.
• ClosedError: Redis server closed the connection.
• ProtoError: The command or reply is invalid, and we cannot process it with Redis protocol.
• OomError: hiredis library got an out-of-memory error.
• ReplyError: Redis server returned an error reply, e.g. we try to call redis::lrange on a Redis hash.
• WatchError: Watched key has been modified. See Watch section for details.

NOTE: NULL REPLY is not taken as an exception. For example, if we try to GET a non-existent key, we'll get a NULL Bulk String Reply. Instead of throwing an exception, we return the NULL REPLY as a null Optional<T> object. Also see Optional section.

Normally, when exception happens, you don't need to create a Redis object. It's exception safe, and you can reuse the Redis object. Even if the connection to Redis server is broken, and it throws some exception, say, IoError. The next time when you send command with the Redis object, it will try to reconnect to Redis server automatically. This rule also applies to RedisCluster. However, if Pipeline, Transcation and Subscriber throws exception, you need to destroy the object, and create a new one. See the corresponding documentation for details.

Examples

The following is an example on how to catch these exceptions:

try {
    redis.set("key", "value");

    // Wrong type error
    redis.lpush("key", {"a", "b", "c"});
} catch (const ReplyError &err) {
    // WRONGTYPE Operation against a key holding the wrong kind of value
    cout << err.what() << endl;
} catch (const TimeoutError &err) {
    // reading or writing timeout
} catch (const ClosedError &err) {
    // the connection has been closed.
} catch (const IoError &err) {
    // there's an IO error on the connection.
} catch (const Error &err) {
   // other errors
}

Generic Command Interface

There're too many Redis commands, we haven't implemented all of them. However, you can use the generic Redis::command methods to send any commands to Redis. Unlike other client libraries, Redis::command doesn't use format string to combine command arguments into a command string. Instead, you can directly pass command arguments of StringView type or arithmetic type as parameters of Redis::command. For the reason why we don't use format string, please see this discussion.

auto redis = Redis("tcp://127.0.0.1");

// Redis class doesn't have built-in *CLIENT SETNAME* method.
// However, you can use Redis::command to send the command manually.
redis.command<void>("client", "setname", "name");
auto val = redis.command<OptionalString>("client", "getname");
if (val) {
    std::cout << *val << std::endl;
}

// NOTE: the following code is for example only. In fact, Redis has built-in
// methods for the following commands.

// Arguments of the command can be strings.
// NOTE: for SET command, the return value is NOT always void, I'll explain latter.
redis.command<void>("set", "key", "100");

// Arguments of the command can be a combination of strings and integers.
auto num = redis.command<long long>("incrby", "key", 1);

// Argument can also be double.
auto real = redis.command<double>("incrbyfloat", "key", 2.3);

// Even the key of the command can be of arithmetic type.
redis.command<void>("set", 100, "value");

val = redis.command<OptionalString>("get", 100);

// If the command returns an array of elements.
std::vector<OptionalString> result;
redis.command("mget", "k1", "k2", "k3", std::back_inserter(result));

// Or just parse it into a vector.
result = redis.command<std::vector<OptionalString>>("mget", "k1", "k2", "k3");

// Arguments of the command can be a range of strings.
auto set_cmd_strs = {"set", "key", "value"};
redis.command<void>(set_cmd_strs.begin(), set_cmd_strs.end());

auto get_cmd_strs = {"get", "key"};
val = redis.command<OptionalString>(get_cmd_strs.begin(), get_cmd_strs.end());

// If it returns an array of elements.
result.clear();
auto mget_cmd_strs = {"mget", "key1", "key2"};
redis.command(mget_cmd_strs.begin(), mget_cmd_strs.end(), std::back_inserter(result));

NOTE: The name of some Redis commands is composed with two strings, e.g. CLIENT SETNAME. In this case, you need to pass these two strings as two arguments for Redis::command.

// This is GOOD.
redis.command<void>("client", "setname", "name");

// This is BAD, and will fail to send command to Redis server.
// redis.command<void>("client setname", "name");

As I mentioned in the comments, the SET command not always returns void. Because if you try to set a (key, value) pair with NX or XX option, you might fail, and Redis will return a NULL REPLY. Besides the SET command, there're other commands whose return value is NOT a fixed type, you need to parse it by yourself. For example, Redis::set method rewrite the reply of SET command, and make it return bool type, i.e. if no NX or XX option specified, Redis server will always return an "OK" string, and Redis::set returns true; if NX or XX specified, and Redis server returns a NULL REPLY, Redis::set returns false.

So Redis class also has other overloaded command methods, these methods return a ReplyUPtr, i.e. std::unique_ptr<redisReply, ReplyDeleter>, object. Normally you don't need to parse it manually. Instead, you only need to pass the reply to template <typename T> T reply::parse(redisReply &) to get a value of type T. Check the Return Type section for valid T types. If the command returns an array of elements, besides calling reply::parse to parse the reply to an STL container, you can also call template <typename Output> reply::to_array(redisReply &reply, Output output) to parse the result into an array or STL container with an output iterator.

Let's rewrite the above examples:

auto redis = Redis("tcp://127.0.0.1");

redis.command("client", "setname", "name");
auto r = redis.command("client", "getname");
assert(r);

// If the command returns a single element,
// use `reply::parse<T>(redisReply&)` to parse it.
auto val = reply::parse<OptionalString>(*r);
if (val) {
    std::cout << *val << std::endl;
}

// Arguments of the command can be strings.
redis.command("set", "key", "100");

// Arguments of the command can be a combination of strings and integers.
r = redis.command("incrby", "key", 1);
auto num = reply::parse<long long>(*r);

// Argument can also be double.
r = redis.command("incrbyfloat", "key", 2.3);
auto real = reply::parse<double>(*r);

// Even the key of the command can be of arithmetic type.
redis.command("set", 100, "value");

r = redis.command("get", 100);
val = reply::parse<OptionalString>(*r);

// If the command returns an array of elements.
r = redis.command("mget", "k1", "k2", "k3");
// Use `reply::to_array(redisReply&, OutputIterator)` to parse the result into an STL container.
std::vector<OptionalString> result;
reply::to_array(*r, std::back_inserter(result));

// Or just call `reply::parse` to parse it into vector.
result = reply::parse<std::vector<OptionalString>>(*r);

// Arguments of the command can be a range of strings.
auto get_cmd_strs = {"get", "key"};
r = redis.command(get_cmd_strs.begin(), get_cmd_strs.end());
val = reply::parse<OptionalString>(*r);

// If it returns an array of elements.
result.clear();
auto mget_cmd_strs = {"mget", "key1", "key2"};
r = redis.command(mget_cmd_strs.begin(), mget_cmd_strs.end());
reply::to_array(*r, std::back_inserter(result));

In fact, there's one more Redis::command method:

template <typename Cmd, typename ...Args>
auto command(Cmd cmd, Args &&...args)
    -> typename std::enable_if<!std::is_convertible<Cmd, StringView>::value, ReplyUPtr>::type;

However, this method exposes some implementation details, and is only for internal use. You should NOT use this method.

Publish/Subscribe

You can use Redis::publish to publish messages to channels. Redis randomly picks a connection from the underlying connection pool, and publishes message with that connection. So you might publish two messages with two different connections.

When you subscribe to a channel with a connection, all messages published to the channel are sent back to that connection. So there's NO Redis::subscribe method. Instead, you can call Redis::subscriber to create a Subscriber and the Subscriber maintains a connection to Redis. The underlying connection is a new connection, NOT picked from the connection pool. This new connection has the same ConnectionOptions as the Redis object.

With Subscriber, you can call Subscriber::subscribe, Subscriber::unsubscribe, Subscriber::psubscribe and Subscriber::punsubscribe to send SUBSCRIBE, UNSUBSCRIBE, PSUBSCRIBE and PUNSUBSCRIBE commands to Redis.

Thread Safety

Subscriber is NOT thread-safe. If you want to call its member functions in multi-thread environment, you need to synchronize between threads manually.

Exception

If any of the Subscriber's method throws an exception other than ReplyError or TimeoutError, you CANNOT use it any more. Instead, you have to destroy the Subscriber object, and create a new one.

Subscriber Callbacks

There are 6 kinds of messages:

• MESSAGE: message sent to a channel.
• PMESSAGE: message sent to channels of a given pattern.
• SUBSCRIBE: message sent when we successfully subscribe to a channel.
• UNSUBSCRIBE: message sent when we successfully unsubscribe to a channel.
• PSUBSCRIBE: message sent when we successfully subscribe to a channel pattern.
• PUNSUBSCRIBE: message sent when we successfully unsubscribe to a channel pattern.

We call messages of SUBSCRIBE, UNSUBSCRIBE, PSUBSCRIBE and PUNSUBSCRIBE types as META MESSAGEs.

In order to process these messages, you can set callback functions on Subscriber:

• Subscriber::on_message(MsgCallback): set callback function for messages of MESSAGE type, and the callback interface is: void (std::string channel, std::string msg).
• Subscriber::on_pmessage(PatternMsgCallback): set the callback function for messages of PMESSAGE type, and the callback interface is: void (std::string pattern, std::string channel, std::string msg).
• Subscriber::on_meta(MetaCallback): set callback function for messages of META MESSAGE type, and the callback interface is: void (Subscriber::MsgType type, OptionalString channel, long long num). type is an enum, it can be one of the following enum: Subscriber::MsgType::SUBSCRIBE, Subscriber::MsgType::UNSUBSCRIBE, Subscriber::MsgType::PSUBSCRIBE, Subscriber::MsgType::PUNSUBSCRIBE, Subscriber::MsgType::MESSAGE, and Subscriber::MsgType::PMESSAGE. If you haven't subscribe/psubscribe to any channel/pattern, and try to unsubscribe/punsubscribe without any parameter, i.e. unsubscribe/punsubscribe all channels/patterns, channel will be null. So the second parameter of meta callback is of type OptionalString.

All these callback interfaces pass std::string by value, and you can take their ownership (i.e. std::move) safely.

Consume Messages

You can call Subscriber::consume to consume messages published to channels/patterns that the Subscriber has been subscribed.

Subscriber::consume waits for message from the underlying connection. If the ConnectionOptions::socket_timeout is reached, and there's no message sent to this connection, Subscriber::consume throws a TimeoutError exception. If ConnectionOptions::socket_timeout is 0ms, Subscriber::consume blocks until it receives a message.

After receiving the message, Subscriber::consume calls the callback function to process the message based on message type. However, if you don't set callback for a specific kind of message, Subscriber::consume will consume the received message and discard it, i.e. Subscriber::consume returns without running the callback.

Examples

The following example is a common pattern for using Subscriber:

// Create a Subscriber.
auto sub = redis.subscriber();

// Set callback functions.
sub.on_message([](std::string channel, std::string msg) {
            // Process message of MESSAGE type.
        });

sub.on_pmessage([](std::string pattern, std::string channel, std::string msg) {
            // Process message of PMESSAGE type.
        });

sub.on_meta([](Subscriber::MsgType type, OptionalString channel, long long num) {
            // Process message of META type.
        });

// Subscribe to channels and patterns.
sub.subscribe("channel1");
sub.subscribe({"channel2", "channel3"});

sub.psubscribe("pattern1*");

// Consume messages in a loop.
while (true) {
    try {
        sub.consume();
    } catch (const Error &err) {
        // Handle exceptions.
    }
}

If ConnectionOptions::socket_timeout is set, you might get TimeoutError exception before receiving a message:

while (true) {
    try {
        sub.consume();
    } catch (const TimeoutError &e) {
        // Try again.
        continue;
    } catch (const Error &err) {
        // Handle other exceptions.
    }
}

The above examples use lambda as callback. If you're not familiar with lambda, you can also set a free function as callback. Check this issue for detail.

Pipeline

Pipeline is used to reduce RTT (Round Trip Time), and speed up Redis queries. redis-plus-plus supports pipeline with the Pipeline class.

Create Pipeline

You can create a pipeline with Redis::pipeline method, which returns a Pipeline object.

ConnectionOptions connection_options;
ConnectionPoolOptions pool_options;

Redis redis(connection_options, pool_options);

auto pipe = redis.pipeline();

When creating a Pipeline object, by default, Redis::pipeline method creates a new connection to Redis server. This connection is NOT picked from the connection pool, but a newly created connection. This connection has the same ConnectionOptions as other connections in the connection pool. Pipeline object maintains the new connection, and all piped commands are sent through this connection.

NOTE: By default, creating a Pipeline object is NOT cheap, since it creates a new connection. So you'd better reuse the Pipeline object as much as possible. Check this to see how to create a Pipeline object without creating a new connection.

Send Commands

You can send Redis commands through the Pipeline object. Just like the Redis class, Pipeline has one or more (overloaded) methods for each Redis command. However, you CANNOT get the replies until you call Pipeline::exec. So these methods do NOT return the reply, instead they return the Pipeline object itself. And you can chain these methods calls.

pipe.set("key", "val").incr("num").rpush("list", {0, 1, 2}).command("hset", "key", "field", "value");

Get Replies

Once you finish sending commands to Redis, you can call Pipeline::exec to get replies of these commands. You can also chain Pipeline::exec with other commands.

pipe.set("key", "val").incr("num");
auto replies = pipe.exec();

// The same as:
replies = pipe.set("key", "val").incr("num).exec();

In fact, these commands won't be sent to Redis, until you call Pipeline::exec. So Pipeline::exec does 2 work in order: send all piped commands, then get all replies from Redis.

Also you can call Pipeline::discard to discard those piped commands.

pipe.set("key", "val").incr("num");

pipe.discard();

Parse Replies

Pipeline::exec returns a QueuedReplies object, which contains replies of all commands that have been sent to Redis. You can use QueuedReplies::get method to get and parse the ith reply. It has 3 overloads:

• template <typename Result> Result get(std::size_t idx): Return the ith reply as a return value, and you need to specify the return type as tempalte parameter.
• template <typename Output> void get(std::size_t idx, Output output): If the reply is of type Array Reply, you can call this method to write the ith reply to an output iterator. Normally, compiler will deduce the type of the output iterator, and you don't need to specify the type parameter explicitly.
• redisReply& get(std::size_t idx): If the reply is NOT a fixed type, call this method to get a reference to redisReply object. In this case, you need to call template <typename T> T reply::parse(redisReply &) to parse the reply manually.

Check the Return Type section for details on the return types of the result.

auto replies = pipe.set("key", "val").incr("num").lrange("list", 0, -1).exec();

auto set_cmd_result = replies.get<bool>(0);

auto incr_cmd_result = replies.get<long long>(1);

std::vector<std::string> list_cmd_result;
replies.get(2, std::back_inserter(list_cmd_result));

Exception

If any of Pipeline's method throws an exception other than ReplyError, the Pipeline object enters an invalid state. You CANNOT use it any more, but only destroy the object, and create a new one.

Thread Safety

Pipeline is NOT thread-safe. If you want to call its member functions in multi-thread environment, you need to synchronize between threads manually.

Create Pipeline Without Creating New Connection

YOU MUST CAREFULLY READ ALL WORDS IN THIS SECTION AND THE VERY IMPORTANT NOTES BEFORE USING THIS FEATURE!!!

In fact, you can also create a Pipeline object with a connection from the underlying connection pool, so that calling Redis::pipeline method can be much cheaper (since it doesn't need to create a new connection).

The prototype of Redis::pipeline is as follows: Pipeline pipeline(bool new_connection = true);. If new_connection is false, the Pipeline object will be created with a connection from the underlying pool.

ConnectionOptions connection_options;
ConnectionPoolOptions pool_options;

Redis redis(connection_options, pool_options);

// Create a Pipeline without creating a new connection.
auto pipe = redis.pipeline(false);

VERY IMPORTANT NOTES

However, in this case, you MUST be very careful, otherwise, you might get bad performance or even dead lock. Because when you run command with Pipeline object, it will hold the connection until Pipeline::exec, Pipeline::discard or Pipeline's destructor is called (the connection will also be released if any method of Pipeline throws Exception). If the Pipeline object holds the connection for a long time, other Redis methods might not be able to get a connection from the underlying pool.

Check the following dead lock example:

// By defaul, create a `Redis` object with only ONE connection in pool.
// Also by default, the `ConnectionPoolOptions::wait_timeout` is 0ms,
// which means if the pool is empty, `Redis` method will be blocked until
// the pool is not empty.
Redis redis("tcp://127.0.0.1");

// Create a `Pipeline` with a connection in the underlying pool.
// In fact, the connection hasn't been fetched from the pool
// until some method of `Pipeline` has been called.
auto pipe = redis.pipeline(false);

// Now the `Pipeline` object fetches a connection from the pool.
pipe.set("key1", "val");

// `Pipeline` object still holds the connection until `Pipeline::exec`,
// `Pipeline::discard` or the destructor is called.
pipe.set("key2", "val");

// Try to send a command with `Redis` object.
// However, the pool is empty, since the `Pipeline` object still holds
// the connection, and this call will be blocked forever.
// DEAD LOCK!!!
redis.get("key");

// NEVER goes here.
pipe.exec();

BEST PRACTICE:

When creating Pipeline without creating a new connection:

• Always set ConnectionPoolOptions::wait_timeout larger than 0ms (i.e. when pool is empty, never block forever).
• Avoid doing slow operation between Pipeline's methods.
• Better chain Pipeline methods and the Pipeline::exec in one statements.
• Better leave Pipeline related code in a block scope.

ConnectionOptions opts;
opts.host = "127.0.0.1";
opts.port = 6379;
opts.socket_timeout = std::chrono::milliseconds(50);

ConnectionPoolOptions pool_opts;
pool_opts.size = 3;

// Always set `wait_timeout` larger than 0ms.
pool_opts.wait_timeout = std::chrono::milliseconds(50);

auto redis = Redis(opts, pool_opts);

{
    // Better put `Pipeline` related code in a block scope.
    auto pipe = redis.pipeline(false);

    pipe.set("key1", "val");

    // DON'T run slow operations here, since `Pipeline` object still holds
    // the connection, other threads using this `Redis` object, might be blocked.

    pipe.set("key2", "val");

    // When `Pipeline::exec` finishes, `Pipeline` releases the connection, and returns it to pool.
    auto replies = pipe.exec();

    // This is even better, i.e. chain `Pipeline` methods with `Pipeline::exec`.
    replies = pipe.set("key1", "val").set("key2", "val").exec();
}

for (auto i = 0; i < 10; ++i) {
    // This operation, i.e. creating a `Pipeline` object with connection in pool, is cheap
    auto pipe = redis.pipeline(false);

    // Fetch a connection from the underlying pool, and hold it.
    pipe.set("key1", "val").set("key2", "val");

    // Although `Pipeline::exec` and `Pipeline::discard` haven't been called,
    // when `Pipeline`'s destructor is called, the connection will also be
    // returned to the pool.
}

Transaction

Transaction is used to make multiple commands runs atomically.

Create Transaction

You can create a transaction with Redis::transaction method, which returns a Transaction object.

ConnectionOptions connection_options;
ConnectionPoolOptions pool_options;

Redis redis(connection_options, pool_options);

auto tx = redis.transaction();

As the Pipeline class, Transaction maintains a newly created connection to Redis. This connection has the same ConnectionOptions as the Redis object.

NOTE: Creating a Transaction object is NOT cheap, since it creates a new connection. So you'd better reuse the Transaction as much as possible. Check this to see how to create a Transaction object without creating a new connection.

Also you don't need to send MULTI command to Redis. Transaction will do that for you automatically.

Send Commands

Transaction shares most of implementation with Pipeline. It has the same interfaces as Pipeline. You can send commands as what you do with Pipeline object.

tx.set("key", "val").incr("num").lpush("list", {0, 1, 2}).command("hset", "key", "field", "val");

Execute Transaction

When you call Transaction::exec, you explicitly ask Redis to execute those queued commands, and return the replies. Otherwise, these commands won't be executed. Also, you can call Transaction::discard to discard the execution, i.e. no command will be executed. Both Transaction::exec and Transaction::discard can be chained with other commands.

auto replies = tx.set("key", "val").incr("num").exec();

tx.set("key", "val").incr("num");

// Discard the transaction.
tx.discard();

Parse Replies

See Pipeline's Parse Replies section for how to parse the replies.

Piped Transaction

Normally, we always send multiple commnds in a transaction. In order to improve the performance, you can send these commands in a pipeline. You can create a piped transaction by passing true as parameter of Redis::transaction method.

// Create a piped transaction
auto tx = redis.transaction(true);

With this piped transaction, all commands are sent to Redis in a pipeline.

Exception

If any of Transaction's method throws an exception other than WatchError or ReplyError, the Transaction object enters an invalid state. You CANNOT use it any more, but only destroy the object and create a new one.

Thread Safety

Transacation is NOT thread-safe. If you want to call its member functions in multi-thread environment, you need to synchronize between threads manually.

Watch

WATCH is used to provide a check-and-set(CAS) behavior to Redis transactions.

The WATCH command must be sent in the same connection as the transaction. And normally after the WATCH command, we also need to send some other commands to get data from Redis before executing the transaction. Take the following check-and-set case as an example:

WATCH key           // watch a key
val = GET key       // get value of the key
new_val = val + 1   // incr the value
MULTI               // begin the transaction
SET key new_val     // set value only if the value is NOT modified by others
EXEC                // try to execute the transaction.
                    // if val has been modified, the transaction won't be executed.

However, with Transaction object, you CANNOT get the result of commands until the whole transaction has been finished. Instead, you need to create a Redis object from the Transaction object. The created Redis object shares the connection with Transaction object. With this created Redis object, you can send WATCH command and any other Redis commands to Redis server, and get the result immediately.

Let's see how to implement the above example with redis-plus-plus:

auto redis = Redis("tcp://127.0.0.1");

// Create a transaction.
auto tx = redis.transaction();

// Create a Redis object from the Transaction object. Both objects share the same connection.
auto r = tx.redis();

// If the watched key has been modified by other clients, the transaction might fail.
// So we need to retry the transaction in a loop.
while (true) {
    try {
        // Watch a key.
        r.watch("key");

        // Get the old value.
        auto val = r.get("key");
        auto num = 0;
        if (val) {
            num = std::stoi(*val);
        } // else use default value, i.e. 0.

        // Incr value.
        ++num;

        // Execute the transaction.
        auto replies = tx.set("key", std::to_string(num)).exec();

        // Transaction has been executed successfully. Check the result and break.

        assert(replies.size() == 1 && replies.get<bool>(0) == true);

        break;
    } catch (const WatchError &err) {
        // Key has been modified by other clients, retry.
        continue;
    } catch (const Error &err) {
        // Something bad happens, and the Transaction object is no longer valid.
        throw;
    }
}

NOTE: in the example above, we create Transaction object outside the while loop, in order to avoid creating new connection again and again.

Create Transaction Without Creating New Connection

NOTE: YOU MUST CAREFULLY READ ALL WORDS AND THE VERY IMPORTANT NOTES LINK IN THIS SECTION BEFORE USING THIS FEATURE!!!

In fact, you can also create a transaction object with a connection from the underlying connection pool, so that calling Redis::transaction method can be much cheaper (since it doesn't need to create a new connection).

The prototype of Redis::transaction is as follows: Transaction transaction(bool piped = false, bool new_connection = true);. If new_connection is false, the Transaction object will be created with a connection from the underlying pool.

ConnectionOptions connection_options;
ConnectionPoolOptions pool_options;

Redis redis(connection_options, pool_options);

// Create a Transaction without creating a new connection.
auto tx = redis.transaction(false, false);

However, in this case, you MUST be very careful, otherwise, you might get bad performance or even dead lock. Please carefully check the similar pipeline's VERY IMPORTANT NOTES section, before you use it!

Besides those very important notes, there's another important note for Transaction:

• Limit the scope of Redis object created by Transaction::Redis, i.e. destroy it ASAP.

Check the following example:

auto redis = Redis(opts, pool_opts);

// Create a `Transaction` object without creating a new connection.
auto tx = redis.Transaction(false, false);

// Create a `Redis`, and this `Redis` object shares the same connection with the `Transaction` object.
auto r = tx.redis();

// Other code here...

// Execute the transaction.
auto replies = tx.set("key", "val").exec();

// Although `Transaction::exec` has been called, the connection has not been returned to pool.
// Because the `Redis` object, i.e. `r`, still holds the connection.

So the above watch example should be modified as follows:

auto redis = Redis(opts, pool_opts);

// If the watched key has been modified by other clients, the transaction might fail.
// So we need to retry the transaction in a loop.
while (true) {
    try {
        // Create a transaction without creating a new connection.
        auto tx = redis.transaction(false, false);

        // Create a Redis object from the Transaction object. Both objects share the same connection.
        auto r = tx.redis();

        // Watch a key.
        r.watch("key");

        // Get the old value.
        auto val = r.get("key");
        auto num = 0;
        if (val) {
            num = std::stoi(*val);
        } // else use default value, i.e. 0.

        // Incr value.
        ++num;

        // Execute the transaction.
        auto replies = tx.set("key", std::to_string(num)).exec();

        // Transaction has been executed successfully. Check the result and break.

        assert(replies.size() == 1 && replies.get<bool>(0) == true);

        break;
    } catch (const WatchError &err) {
        // Key has been modified by other clients, retry.
        continue;
    } catch (const Error &err) {
        // Something bad happens, and the Transaction object is no longer valid.
        throw;
    }
}

NOTE: The difference is that we create the Transaction object in the while loop (it's cheap, since it doesn't need to create a new connection). When the Transaction object and the Redis object created by Transaction::redis have been destroyed, the connection will be return to pool.

Redis Cluster

redis-plus-plus supports Redis Cluster. You can use RedisCluster class to send commands to Redis Cluster. It has similar interfaces as Redis class.

Connection

By default, RedisCluster connects to all master nodes in the cluster. For each master node, it maintains a connection pool. If you want to read from slave nodes, you need to explicitly set an option (see below for reference).

You can initialize a RedisCluster instance with ConnectionOptions and ConnectionPoolOptions. You only need to set one master node's host & port in ConnectionOptions, and RedisCluster will get other nodes' info automatically (with the CLUSTER SLOTS command). For each master node, it creates a connection pool with the specified ConnectionPoolOptions. If ConnectionPoolOptions is not specified, RedisCluster maintains a single connection to every master node.

// Set a master node's host & port.
ConnectionOptions connection_options;
connection_options.host = "127.0.0.1";  // Required.
connection_options.port = 7000; // Optional. The default port is 6379.
connection_options.password = "auth"; // Optional. No password by default.

// Automatically get other nodes' info,
// and connect to every master node with a single connection.
RedisCluster cluster1(connection_options);

ConnectionPoolOptions pool_options;
pool_options.size = 3;

// For each master node, maintains a connection pool of size 3.
RedisCluster cluster2(connection_options, pool_options);

You can also specify connection option with an URI. However, in this way, you can only use default ConnectionPoolOptions, i.e. pool of size 1, and CANNOT specify password.

// Specify a master node's host & port.
RedisCluster cluster3("tcp://127.0.0.1:7000");

// Use default port, i.e. 6379.
RedisCluster cluster4("tcp://127.0.0.1");

Read From Replica

If you want to scale read by reading (possible stale) data from slave nodes, you can specifiy Role::SLAVE as the third parameter of RedisCluster's constructor. In this case, redis-plus-plus will randomly pick a replica node for each master node of the cluster, and create a connection pool for the replica node.

RedisCluster cluster(connection_options, pool_options, Role::SLAVE);

auto val = cluster.get("key");

In this case, you can only send readonly commands to Redis Cluster. If you try to send a write command, e.g. set, hset, redis-plus-plus will throw an exception. Currently, redis-plus-plus doesn't handle this case, i.e. sending write command in Role::SLAVE mode, elegantly, and you might get some performance problem. So, NEVER send write command in Role::SLAVE mode. I'll fix this issue in the future.

NOTE: In Role::SLAVE mode, you don't need to manually send READONLY command to slave nodes. Instead, redis-plus-plus will send READONLY command to slave nodes automatically.

Note

• RedisCluster only works with tcp connection. It CANNOT connect to Unix Domain Socket. If you specify Unix Domain Socket in ConnectionOptions, it throws an exception.
• All nodes in the cluster should have the same password.
• Since Redis Cluster does NOT support multiple databses, ConnectionOptions::db is ignored.

Interfaces

As we mentioned above, RedisCluster's interfaces are similar to Redis. It supports most of Redis' interfaces, including the generic command interface (see Redis' API Reference section for details), except the following:

• Not support commands without key as argument, e.g. PING, INFO.
• Not support Lua script without key parameters.

Since there's no key parameter, RedisCluster has no idea on to which node these commands should be sent. However there're 2 workarounds for this problem:

• If you want to send these commands to a specific node, you can create a Redis object with that node's host and port, and use the Redis object to do the work.
• Instead of host and port, you can also call Redis RedisCluster::redis(const StringView &hash_tag) to create a Redis object with a hash-tag specifying the node. In this case, the returned Redis object creates a new connection to Redis server. NOTE: the returned Redis object, IS NOT THREAD SAFE!. Also, when using the returned Redis object, if it throws exception, you need to destroy it, and create a new one with the RedisCluster::redis method.

Also you can use the hash tags to send multiple-key commands.

See the example section for details.

Publish/Subscribe

You can publish and subscribe messages with RedisCluster. The interfaces are exactly the same as Redis, i.e. use RedisCluster::publish to publish messages, and use RedisCluster::subscriber to create a subscriber to consume messages. See Publish/Subscribe section for details.

Pipeline and Transaction

You can also create Pipeline and Transaction objects with RedisCluster, but the interfaces are different from Redis. Since all commands in the pipeline and transaction should be sent to a single node in a single connection, we need to tell RedisCluster with which node the pipeline or transaction should be created.

Instead of specifing the node's IP and port, RedisCluster's pipeline and transaction interfaces allow you to specify the node with a hash tag. RedisCluster will calculate the slot number with the given hash tag, and create a pipeline or transaction with the node holding the slot.

Pipeline RedisCluster::pipeline(const StringView &hash_tag, bool new_connection = true);

Transaction RedisCluster::transaction(const StringView &hash_tag, bool piped = false, bool new_connection = true);

With the created Pipeline or Transaction object, you can send commands with keys located on the same node as the given hash_tag. See Examples section for an example.

NOTE: By default, Pipeline and Transaction will be created with a new connection. In order to avoid creating new connection, you can pass false as the last parameter. However, in this case, you MUST be very careful, otherwise, you might get bad performance or even dead lock. Please carefully check the related pipeline section before using this feature.

Examples

#include <sw/redis++/redis++.h>

using namespace sw::redis;

auto redis_cluster = RedisCluster("tcp://127.0.0.1:7000");

redis_cluster.set("key", "value");
auto val = redis_cluster.get("key");
if (val) {
    std::cout << *val << std::endl;
}

// With hash-tag.
redis_cluster.set("key{tag}1", "val1");
redis_cluster.set("key{tag}2", "val2");
redis_cluster.set("key{tag}3", "val3");
std::vector<OptionalString> hash_tag_res;
redis_cluster.mget({"key{tag}1", "key{tag}2", "key{tag}3"},
        std::back_inserter(hash_tag_res));

redis_cluster.lpush("list", {"1", "2", "3"});
std::vector<std::string> list;
redis_cluster.lrange("list", 0, -1, std::back_inserter(list));

// Pipeline.
auto pipe = redis_cluster.pipeline("counter");
auto replies = pipe.incr("{counter}:1").incr("{counter}:2").exec();

// Transaction.
auto tx = redis_cluster.transaction("key");
replies = tx.incr("key").get("key").exec();

// Create a Redis object with hash-tag.
// It connects to the Redis instance that holds the given key, i.e. hash-tag.
auto r = redis_cluster.redis("hash-tag");

// And send command without key parameter to the server.
r.command("client", "setname", "connection-name");

NOTE: By default, when you use RedisCluster::redis(const StringView &hash_tag, bool new_connection = true) to create a Redis object, instead of picking a connection from the underlying connection pool, it creates a new connection to the corresponding Redis server. So this is NOT a cheap operation, and you should try to reuse this newly created Redis object as much as possible. If you pass false as the second parameter, you can create a Redis object without creating a new connection. However, in this case, you should be very careful, otherwise, you might get bad performance or even dead lock. Please carefully check the related pipeline section before using this feature.

// This is BAD! It's very inefficient.
// NEVER DO IT!!!
// After sending PING command, the newly created Redis object will be destroied.
cluster.redis("key").ping();

// Then it creates a connection to Redis, and closes the connection after sending the command.
cluster.redis("key").command("client", "setname", "hello");

// Instead you should reuse the Redis object.
// This is GOOD!
auto redis = cluster.redis("key");

redis.ping();
redis.command("client", "setname", "hello");

// This is GOOD! Create `Redis` object without creating a new connection. Use it, and destroy it ASAP.
cluster.redis("key", false).ping();

Details

RedisCluster maintains the newest slot-node mapping, and sends command directly to the right node. Normally it works as fast as Redis. If the cluster reshards, RedisCluster will follow the redirection, and it will finally update the slot-node mapping. It can correctly handle the following resharding cases:

• Data migration between exist nodes.
• Add new node to the cluster.
• Remove node from the cluster.

redis-plus-plus is able to handle both MOVED and ASK redirections, so it's a complete Redis Cluster client.

If master is down, the cluster will promote one of its replicas to be the new master. redis-plus-plus can also handle this case:

• When the master is down, redis-plus-plus losts connection to it. In this case, if you try to send commands to this master, redis-plus-plus will try to update slot-node mapping from other nodes. If the mapping remains unchanged, i.e. new master hasn't been elected yet, it fails to send command to Redis Cluster and throws exception.
• When the new master has been elected, the slot-node mapping will be updated by the cluster. In this case, if you send commands to the cluster, redis-plus-plus can get an update-to-date mapping, and sends commands to the new master.

Redis Sentinel

Redis Sentinel provides high availability for Redis. If Redis master is down, Redis Sentinels will elect a new master from slaves, i.e. failover. Besides, Redis Sentinel can also act like a configuration provider for clients, and clients can query master or slave address from Redis Sentinel. So that if a failover occurs, clients can ask the new master address from Redis Sentinel.

redis-plus-plus supports getting Redis master or slave's IP and port from Redis Sentinel. In order to use this feature, you only need to initialize Redis object with Redis Sentinel info, which is composed with 3 parts: std::shared_ptr<Sentinel>, master name and role (master or slave).

Before using Redis Sentinel with redis-plus-plus, ensure that you have read Redis Sentinel's doc.

Sentinel

You can create a std::shared_ptr<Sentinel> object with SentinelOptions.

SentinelOptions sentinel_opts;
sentinel_opts.nodes = {{"127.0.0.1", 9000},
                        {"127.0.0.1", 9001},
                        {"127.0.0.1", 9002}};   // Required. List of Redis Sentinel nodes.

// Optional. Timeout before we successfully connect to Redis Sentinel.
// By default, the timeout is 100ms.
sentinel_opts.connect_timeout = std::chrono::milliseconds(200);

// Optional. Timeout before we successfully send request to or receive response from Redis Sentinel.
// By default, the timeout is 100ms.
sentinel_opts.socket_timeout = std::chrono::milliseconds(200);

auto sentinel = std::make_shared<Sentinel>(sentinel_opts);

SentinelOptions::connect_timeout and SentinelOptions::socket_timeout CANNOT be 0ms, i.e. no timeout and block forever. Otherwise, redis-plus-plus will throw an exception.

See SentinelOptions for more options.

Role

Besides std::shared_ptr<Sentinel> and master name, you also need to specify a role. There are two roles: Role::MASTER, and Role::SLAVE.

With Role::MASTER, redis-plus-plus will always connect to current master instance, even if a failover occurs. Each time when redis-plus-plus needs to create a new connection to master, or a connection is broken, and it needs to reconnect to master, redis-plus-plus will ask master address from Redis Sentinel, and connects to current master. If a failover occurs, redis-plus-plus can automatically get the address of the new master, and refresh all connections in the underlying connection pool.

Similarly, with Role::SLAVE, redis-plus-plus will always connect to a slave instance. A master might have several slaves, redis-plus-plus will randomly pick one, and connect to it, i.e. all connections in the underlying connection pool, connect to the same slave instance (check this discussion on why redis-plus-plus not connect to all slaves). If the connection is broken, while this slave instance is still an alive slave, redis-plus-plus will reconnect to this slave. However, if this slave instance is down, or it has been promoted to be the master, redis-plus-plus will randomly connect to another slave. If there's no slave alive, it throws an exception.

Create Redis With Sentinel

When creating a Redis object with sentinel, besides the sentinel info, you should also provide ConnectionOptions and ConnectionPoolOptions. These two options are used to connect to Redis instance. ConnectionPoolOptions is optional, if not specified, it creates a single connection the instance.

ConnectionOptions connection_opts;
connection_opts.password = "auth";  // Optional. No password by default.
connection_opts.connect_timeout = std::chrono::milliseconds(100);   // Required.
connection_opts.socket_timeout = std::chrono::milliseconds(100);    // Required.

ConnectionPoolOptions pool_opts;
pool_opts.size = 3; // Optional. The default size is 1.

auto redis = Redis(sentinel, "master_name", Role::MASTER, connection_opts, pool_opts);

You might have noticed that we didn't specify the host and port fields for ConnectionOptions. Because, Redis will get these info from Redis Sentinel. Also, in this case, ConnectionOptions::connect_timeout and ConnectionOptions::socket_timeout CANNOT be 0ms, otherwise, it throws an exception. So you always need to specify these two timeouts manually.

After creating the Redis object with sentinel, you can send commands with it, just like an ordinary Redis object.

If you want to write to master, and scale read with slaves. You can use the following pattern:

auto sentinel = std::make_shared<Sentinel>(sentinel_opts);

auto master = Redis(sentinel, "master_name", Role::MASTER, connection_opts, pool_opts);

auto slave = Redis(sentinel, "master_name", Role::SLAVE, connection_opts, pool_opts);

// Write to master.
master.set("key", "value");

// Read from slave.
slave.get("key");

Redis Stream

Since Redis 5.0, it introduces a new data type: Redis Stream. redis-plus-plus has built-in methods for all stream commands except the XINFO command (of course, you can use the Generic Command Interface to send XINFO command).

However, the replies of some streams commands, i.e. XPENDING, XREAD, are complex. So I'll give some examples to show you how to work with these built-in methods.

Examples

auto redis = Redis("tcp://127.0.0.1");

using Attrs = std::vector<std::pair<std::string, std::string>>;

// You can also use std::unordered_map, if you don't care the order of attributes:
// using Attrs = std::unordered_map<std::string, std::string>;

Attrs attrs = { {"f1", "v1"}, {"f2", "v2"} };

// Add an item into the stream. This method returns the auto generated id.
auto id = redis.xadd("key", "*", attrs.begin(), attrs.end());

// Each item is assigned with an id: pair<id, attributes>.
using Item = std::pair<std::string, Attrs>;
using ItemStream = std::vector<Item>;

// If you don't care the order of items in the stream, you can also use unordered_map:
// using ItemStream = std::unordered_map<std::string, Attrs>;

// Read items from a stream, and return at most 10 items.
// You need to specify a key and an id (timestamp + offset).
std::unordered_map<std::string, ItemStream> result;
redis.xread("key", id, 10, std::inserter(result, result.end()));

// Read from multiple streams. For each stream, you need to specify a key and an id.
std::unordered_map<std::string, std::string> keys = { {"key", id}, {"another-key", "0-0"} };
redis.xread(keys.begin(), keys.end(), 10, std::inserter(result, result.end()));

// Block for at most 1 second if currently there's no data in the stream.
redis.xread("key", id, std::chrono::seconds(1), 10, std::inserter(result, result.end()));

// Block for multiple streams.
redis.xread(keys.begin(), keys.end(), std::chrono::seconds(1), 10, std::inserter(result, result.end()));

// Read items in a range:
ItemStream item_stream;
redis.xrange("key", "-", "+", std::back_inserter(item_stream));

// Trim the stream to a given number of items. After the operation, the stream length is NOT exactly
// 10. Instead, it might be much larger than 10.
// `XTRIM key MAXLEN 10`
redis.xtrim("key", 10);

// In order to trim the stream to exactly 10 items, specify the third argument, i.e. approx, as false.
// `XTRIM key MAXLEN ~ 10`
redis.xtrim("key", 10, false);

// Delete an item from the stream.
redis.xdel("key", id);

// Create a consumer group.
redis.xgroup_create("key", "group", "$");

// If the stream doesn't exist, you can set the fourth argument, i.e. MKSTREAM, to be true.
// redis.xgroup_create("key", "group", "$", true);

id = redis.xadd("key", "*", attrs.begin(), attrs.end());

// Read item by a consumer of a consumer group.
redis.xreadgroup("group", "consumer", "key", ">", 1, std::inserter(result, result.end()));

using PendingItem = std::tuple<std::string, std::string, long long, long long>;
std::vector<PendingItem> pending_items;

// Get pending items of a speicified consumer.
redis.xpending("key", "group", "-", "+", 1, "consumer", std::back_inserter(pending_items));

redis.xack("key", "group", id);

redis.xgroup_delconsumer("key", "group", "consumer");
redis.xgroup_destroy("key", "group");

If you have any problem on sending stream commands to Redis, please feel free to let me know.

Redis Recipes

We can create many interesting data structures and algorithms based on Redis, such as Redlock. We call these data structures and algorithms as Redis Recipes. redis-plus-plus will support some of these recipes.

NOTE: These recipes will be first implemented on the recipes branch. I'd like to hear your feedback on the API of these recipes, and when these APIs become stable, I'll merge the code into the master branch. So APIs on the recipes branch are NOT stable, and might be changed in the future.

Redlock

Redlock is a distributed lock based on Redis. Thanks to @wingunder's suggestion, redis-plus-plus supports Redlock now. @wingunder and I made two different implementation of Redlock: one based on Lua script, and the other based on transaction. The Lua script version should be faster, and also it has many other parameters to control the behavior. However, if you are not allowed to, or don't want to run Lua scripts inside Redis, you could try using the transaction version.

Examples

auto redis1 = Redis("tcp://127.0.0.1:7000");
auto redis2 = Redis("tcp://127.0.0.1:7001");
auto redis3 = Redis("tcp://127.0.0.1:7002");

// Lua script version:
{
    RedLockMutex mtx({redis1, redis2, redis3}, "resource");

    // Not locked.
    RedLock<RedLockMutex> lock(mtx, std::defer_lock);

    // Try to get the lock, and keep 30 seconds.
    // It returns the validity time of the lock, i.e. the lock is only
    // valid in *validity_time*, after that the lock might be acquired by others.
    // If failed to acquire the lock, throw an exception of Error type.
    auto validity_time = lock.try_lock(std::chrono::seconds(30));

    // Extend the lock before the lock expired.
    validity_time = lock.extend_lock(std::chrono::seconds(10));

    // You can unlock explicitly.
    lock.unlock();
} // If unlock() is not called, the lock will be unlocked automatically when it's destroied.

// Transaction version:
{
    RedMutex mtx({redis1, redis2, redis3}, "resource");

    RedLock<RedMutex> lock(mtx, std::defer_lock);
    auto validity_time = lock.try_lock(std::chrono::seconds(30));
    validity_time = lock.extend_lock(std::chrono::seconds(30));

    // You can unlock explicitly.
    lock.unlock();
}

Please refer to the code for detail. I'll enhance the doc in the future.

Author

redis-plus-plus is written by sewenew, who is also active on StackOverflow.