ESI Tags for Caddy Server (Alpha, WIP

)

This plugin implements partial ESI Edge Side Includes support for the Caddy Webserver to allow data retrieving from heterogeneous backends aka. micro services.

Test Users Wanted!

This plugin has the pre-beta status and we need some users who tests it with various other middlewares on either their test server or even in production. The plugin has been running currently for a couple of weeks on https://cyrillschumacher.com. So far it runs smoothly. Please test it and report bugs in the issue tracker.

Thanks!

Some features:

• Query data from HTTP, HTTPS, HTTP2, gRPC, Redis, Memcache and soon SQL. Default implementation: HTTP/S/2.
• Multiple incoming requests trigger only one single parsing of the ESI tags per page
• Querying multiple backend server parallel and concurrent.
• Coalesce multiple incoming requests into one single request to a backend server
• Forwarding and returning (todo) of HTTP headers from backend servers
• Query multiple backend servers sequentially as a fall back mechanism
• Query multiple backend servers parallel and use the first returned result and discard other responses, an obvious race condition. (todo)
• Support for NoSQL Server to query a key and simply display its value
• Variables support based on Server, Cookie, Header or GET/POST form parameters
• Error handling and fail over. Either display a text from a string or a static file content when a backend server is unavailable.
• If an HTTP/S backend request takes longer than the specified timeout, flip the source URL into an XHR request or an HTTP2 push. (todo)
• No full ESI support, if desired use a scripting language ;-)
• Supports Go >= 1.8

Warning: Project still in beta phase and to enable more backend resources you need to buy a monthly recurring Enterprise maintenance support (Coming soon!)

High level overview

As the above sequence diagram shows, the output of the initial byte starts only then, when all data from the backend resources has been received. This enables us to calculate the correct Content-Length header and also allows to return headers from the backend to the client. So time to first byte "TTFB" depends on the slowest backend resource.

Future versions of CaddyESI provides the additional option of enabling Transfer-Encoding: chunked to start immediately the output and then waiting for all backend resources when the first ESI tag occurs in the page.

Plugin configuration (optional)

https://cyrillschumacher.local:2718 {
    ...
    other caddy directives
    ...
    esi [/path_optional] {
        [timeout 5ms|100us|1m|...]
        [ttl 5ms|100us|1m|...]
        [max_body_size 500kib|5MB|10GB|2EB|etc]
        [page_id_source [host,path,ip, etc]]
        [allowed_methods [GET,POST,etc]]
        [cmd_header_name [X-What-Ever]]
        [cache redis://localhost:6379/0]
        [cache redis://localhost:6380/0]
        [cache memcache://localhost:11211/2]
        [cache inmemory]
        [on_error (filename|"any text")]
        [log_file (filename|stdout|stderr)]
        [log_level (fatal|info|debug)]
        [resources path/to/url_configrations.(xml|json)]
    }
}

Most of the global optional configuration values can be overwritten with a different value in a single ESI tag.

esi defines the namespace in the Caddy configuration file. Reserved keys are:

cmd_header_name current supported values are:

• purge use the value purge with your defined cmd_header_name to purge the ESI tag cache. X-Esi-Cmd: purge
• log-debug enables debug logging. Costs heavily performance.
• log-info enables info logging. Logs some errors and other note worthy informations.
• log-none disables logging.

resources defines the path to a configuration file for more backend resource services. You need this file once CaddyESI has been enabled to work with other plugins as the default HTTP implementation. An example on how the XML or JSON must be coded:

<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
<items>
    <item>
        <alias>redis01</alias>
        <url><![CDATA[redis://127.0.0.1:6379/?db=0&max_active=10&max_idle=4]]></url>
        <!--<query>Unused and hence optional</query>-->
    </item>
    <item>
        <alias>grpc01</alias>
        <url><![CDATA[grpc://127.0.0.1:53044/?timeout=60s&tls=1&ca_file=../path/to/root.pem&server_host_override=my.domain.kom]]></url>
        <!--<query>Unused and hence optional</query>-->
    </item>
    <item>
        <alias>mysql01</alias>
        <url><![CDATA[mysql://user:password@tcp(localhost:5555)/dbname?charset=utf8mb4,utf8&tls=skip-verify]]></url>
        <query><![CDATA[SELECT `value` FROM tableX WHERE key='?']]></query> <!--Creates a long-lived prepared statement-->
    </item>
    <item>
        <alias>mysql02</alias>
        <url>mysql01</url><!--Uses the connection of mysql01-->
        <query><![CDATA[SELECT `value` FROM tableY WHERE another_key=?]]></query> <!--Creates a long-lived prepared statement-->
    </item>
</items>

[
  {
    "alias": "redis01",
    "url": "redis://127.0.0.1:6379/?db=0&max_active=10&max_idle=4"
  },
  {
    "alias": "grpc01",
    "url": "grpc://127.0.0.1:53044/?timeout=60s&tls=1&ca_file=../path/to/root.pem&server_host_override=my.domain.kom"
  },
  {
    "alias": "mysql01",
    "url": "mysql://user:password@tcp(localhost:5555)/dbname?charset=utf8mb4,utf8&tls=skip-verify",
    "query": "SELECT `value` FROM tableX WHERE key='?'"
  },
  {
    "alias": "mysql02",
    "url": "mysql01",
    "query": "SELECT `value` FROM tableY WHERE another_key=?"
  }
]

Please be aware that this file must be stored securely on the hard drive and that the owner of the Caddy process can read it. Other resource credential loading options might be added in the future.

The resource configuration file is only needed when other services besides HTTP are enabled.

The further usage of configuration gets explained in the ESI tag documentation.

Supported ESI Tags and their attributes

Implemented:

• Caddy configuration parsing
• ESI tag parsing
• ESI tag replacement
• Background Fetcher workers
• Basic ESI Tag
• With timeout
• With ttl
• Load local file after timeout for error handling
• Flip src to AJAX call or HTTP2 push after timeout
• Forward all headers
• Forward some headers
• Forward POST,PATCH, PUT data
• Return all headers
• Return some headers
• Forward QUERY STRING and/or POST form data
• Multiple sources
• Multiple sources with race="true"
• Dynamic sources/keys (string replacement)
• Conditional tag loading
• Redis access
• Memcache access
• MySQL access
• PGSQL access
• fCGI access
• gRPC access
• Shell scripts/programs access (stderr|out|in) communication
• Query HTTP/S backend servers
• Handle compressed content from backends (Go http.Client)
• Coalesce multiple requests into one backend request

Only HTTP backend resources are enabled by default.

TL;DR ESI tag options

Quick overview which options are available for two different kinds of ESI tags.

1. Querying an HTTP backend (default enabled)

<esi:include src="https://micro1.service/esi/foo" src="https://microN.service/esi/foo" 
    timeout="time.Duration" ttl="time.Duration" 
    onerror="text or path to file" maxbodysize="bytes"
    forwardheaders="all or specific comma separated list of header names"
    returnheaders="all or specific comma separated list of header names"
    coalesce="true|false" printdebug="true|false"
/>

2. Querying a NOSQL database or gRPC service (not enabled)

<esi:include src="alias_name1" src="alias_nameN" key="key name" 
    onerror="text or path to file" timeout="time.Duration" coalesce="true|false" printdebug="true|false"/>

key or src can contain variables which gets replaced to their corresponding values. See section "Dynamic sources and keys".

Basic tag

The basic tag waits on the src until esi.timeout cancels the loading. If src contains an invalid URL or has not been specified at all, nothing happens.

An unreachable src gets marked as "failed" in the internal cache by a circuit breaker with an exponential back-off strategy: 2ms, 4ms, 8ms, 16ms, 32ms ... or as defined in the esi.timeout or tag based timeout attribute.

ESI tags are getting internally cached after they have been parsed. Changes to ESI tags during development must trigger a cache clearance via restarting or sending the correct cmd_header_name header key.

A page ID defines the internal cache key for a set of ESI tags listed in an HTML page. For each incoming request the ESI processor knows beforehand which ESI tags to load and to process instead of parsing the HTML page sequentially. All ESI src will be loaded parallel before the page output starts. Once the content has been received the Content-Length header gets calculated and the output starts. TODO: Chunked transfer implementation with an immediately starting output.

<esi:include src="https://micro.service/esi/foo" />

With timeout (optional)

The basic tag with the attribute timeout waits for the src until the timeout occurs. After the timeout, the ESI tag gets not rendered and hence displays nothing. The attribute timeout overwrites the default esi.timeout.

<esi:include src="https://micro.service/esi/foo" timeout="time.Duration" />

100% Support with http/s requests to backend services.

With ttl (optional) (TODO)

The basic tag with the attribute ttl stores the returned data from the src in the specified esi.backend. The attribute ttl overwrites the default esi.ttl. If esi.backend has not been set or ttl set to empty, caching is disabled.

esi.backend uses the src as a cache key.

<esi:include src="https://micro.service/esi/foo" ttl="time.Duration" />

Load local file after timeout (optional)

The basic tag with the attribute timeout waits for the src until the timeout occurs. After the timeout, the ESI processor loads the local file or text from the attribute onerror and renders it into the page. If the file does not exists an ugly error gets shown.

Supported file extensions: "html", "htm", "xml", "txt", "json"

<esi:include src="https://micro.service/esi/foo" timeout="time.Duration" onerror="path/to/mylocalFile.html"/>

<esi:include src="https://micro.service/esi/foo" timeout="time.Duration" onerror="Cannot load weather service"/>

Max body size to limit the size of the body returned from a backend (optional)

The basic tag with the attribute maxbodysize="size" takes care that the returned body size has been limited to the provided value. Default body size is 5 MB. Other attributes can be additionally defined. Available size identifiers: https://github.com/dustin/go-humanize/blob/master/bytes.go#L34

<esi:include src="https://micro.service/esi/foo" maxbodysize="3MB"/>

Flip src to AJAX call after timeout (optional) (TODO)

The basic tag with the attribute timeout waits for the src until the timeout occurs. After the timeout, the ESI processor converts the URI in the src attribute to an AJAX call in the frontend. The attribute onerror="ajax" must exists or feature is disabled. TODO: JS code of the template ...

<esi:include src="https://micro.service/esi/foo" timeout="time.Duration" onerror="ajax"/>

Forward POST, PATCH or PUT data (optional)

The basic tag with the attribute forwardpostdata forwards all incoming request POST, PATCH, PUT data to the src. Other attributes can be additionally defined. Default value false which does not forward anything. POST data gets only forwarded to those backend resources which can handle the data.

<esi:include src="https://micro.service/esi/foo" forwardpostdata="true"/>

Forward all headers (optional)

The basic tag with the attribute forwardheaders forwards all incoming request headers to the src. Other attributes can be additionally defined. POST data gets only forwarded to those backend resources which can handle the data.

<esi:include src="https://micro.service/esi/foo" forwardheaders="all"/>

Forward some headers (optional)

The basic tag with the attribute forwardheaders forwards only the specified headers of the incoming request to the src. Other attributes can be additionally defined. POST data gets only forwarded to those backend resources which can handle the data.

<esi:include src="https://micro.service/esi/foo" forwardheaders="Cookie,Accept-Language,Authorization"/>

Return all headers (optional) (TODO)

The basic tag with the attribute returnheaders returns all src headers to the final response. Other attributes can be additionally defined. If duplicate headers from multiple sources occurs, they are getting appended to the response.

<esi:include src="https://micro.service/esi/foo" returnheaders="all"/>

Return some headers (optional) (TODO)

The basic tag with the attribute returnheaders returns the listed headers of the src to the final response. Other attributes can be additionally defined. If duplicate headers from multiple sources occurs, they are getting appended to the response.

<esi:include src="https://micro.service/esi/foo" returnheaders="Set-Cookie"/>

Coalesce multiple requests into one backend request (optional)

The basic tag with the attribute coalesce="boolean" takes care that for multiple incoming requests only one backend request gets fired. Other parallel incoming requests waits until the backend returns from the initializing request. Any returned data from a backend resource gets shared with an unknown number of external requests. This feature limits the pressure onto a backend resource. Other attributes can be additionally defined. Default value false, hence disabled. coalesce="false|true|1|0"

<esi:include src="https://micro.service/esi/foo" coalesce="true"/>

Printdebug (optional)

The basic tag with the attribute printdebug="boolean" allows to print debugging information as an HTML comment. Debugging contains the time taken to complete the backend request, any possible error and the raw tag itself. Be aware that if you store sensitive information in the raw tag they will leak towards the evil internet. Other attributes can be additionally defined. Default value false, hence disabled. printdebug="false|true|1|0"

<esi:include src="https://micro.service/esi/foo" printdebug="true"/>

Multiple sources

The basic ESI tag can contain multiple sources. The ESI processor tries to load src attributes in its specified order. The next src gets called after the esi.timeout or timeout occurs. Other attributes can be additionally defined. Add the attribute race="true" (TODO) to fire all requests at once and the one which is the fastest gets served and the others dropped.

<esi:include 
    src="https://micro1.service/esi/foo" 
    src="http://micro2.service/esi/foo"
    src="https://micro3.service/esi/foo" 
    timeout="time.Duration" 
    race="boolean" />

Dynamic sources and keys (string replacement)

The basic ESI tag can extend all src URLs and key attributes with additional parameters from the http.Request object. A replacement string must be one of the listed below and must consists of the pattern: {[^\}]+}. Replacement strings can occur anywhere and n-times in the src or key attribute.

<esi:include src="http://micro.service/search?query={Fsearch_term}"/>
<esi:include src="https://micro.service/{dir}/{file}/?id={HMy-Header-Key}"/>

The following string replacements are possible:

• {method}
• {scheme}
• {hostname}
• {host} (incl. port)
• {hostonly} (excl. port)
• {path} (header Caddy-Rewrite-Original-URI supported)
• {path_escaped} (header Caddy-Rewrite-Original-URI supported)
• {rewrite_path}
• {rewrite_path_escaped}
• {query}
• {query_escaped}
• {fragment}
• {proto}
• {remote} IP address, might not be the real IP address
• {real_remote} real IP address
• {port}
• {uri} the RequestURI
• {uri_escaped} the RequestURI
• {when}
• {when_iso}
• {file}
• {dir}

To access any value in the header, cookie, GET form or POST form you can write a special crafted replacement string.

• {HMy-Header-Key-Name} must start with H followed by the header key name (case in-sensitive), in this case: My-Header-Key-Name.
• {CMy-Cookie-Name} must start with C followed by the cookie name (case sensitive), in this case: My-Cookie-Name.
• {FMy-Input-Name} must start with F followed by the name of the field (case sensitive), in this case: My-Input-Name.

Conditional tag loading (TODO)

The basic ESI tag can contain the attribute condition. A condition must evaluate an expression to true to trigger the loading of the src.

<esi:include src="http://micro.service/search?query={Fquery}"
    condition="{hostname} eq 'customer.micro.service'"/>

Access via src aliases

The ESI processor can access NoSQL, gRPC and SQL resources which are specified in the Caddy resources configuration file. The src attribute must contain the valid alias name as defined in resources file. The ESI tag must contain a key attribute which accesses the value in the NoSQL server or forwards that value to gRPC or uses it in the SELECT query for a database. The returned value will be rendered unmodified into the HTML page output. You are responsible for secure escaping of your data. If multiple src tags are defined the next src gets used once the key cannot be found in the previous source or the timeout applies. Return and forward headers might not be supported.

<esi:include src="redisAWS1" src="redisLocal1" key="my_redis_key_x" timeout="time.Duration" />
<esi:include src="redisAWS1" key="my_redis_key_x" onerror="myLocalFile.html" timeout="time.Duration" />
<esi:include src="redis1" key="prefix_{host}_{HX-Whatever}" timeout="time.Duration" />

General ESI tag attribute handling

Unrecognized attributes within an <esi:include will trigger a parse error. Protects you from fat fingers ;-)

ProTip: To disable an attribute instead of removing it from the tag you can prepend it with an x. So src="..." will become xsrc="...".

Registered schemes or aliases in the src attribute

The src attribute can contain or refer to the following aliases (defined in the resource configuration file) to fetch content from a resource backend:

• http://
• https://
• sh://
• Name of the aliases as defined in the resources file

To access the next resources you must specify them as an alias in the resources xml|json file. Because those connection lives the whole Caddy process and might never get closed.

• redis://
• memcache://
• sql:// a SQL query (TODO)
• grpc:// a remote procedure call with gRPC

HTTP / HTTPS

http|s allows the usual HTTP requests to a resource.

Always enabled.

sh shell

sh starts a shell program or any other executable script. The incoming HTTP request plus the current arguments gets transformed into a JSON string and will be passed as first argument to the program via stdin. If the program writes to stderr CaddyESI recognizes that and triggers it as an usual error. Too many errors and the circuit breaker opens. To output towards the HTTP response gets written to stdout. The src attribute must look like:

<esi:include src="sh:///path/to/myGoBinary" />
<esi:include src="sh:///path/to/my/slow/php/script.php" />
<esi:include src="sh:///path/to/my/slow/php/script.php --arg1 --arg2=x --argN=y" />

<esi:include src="sh://php /path/to/my/slow/php/script.php" />

ProTip: Provide always the full path to the binary or script because the lookup time in the operation systems environment PATH variable will take long. In general shell execution is pretty slow no matter which kind of program/script you call.

Disabled by default and must be enabled with a new compiled Caddy binary and the build tag esishell.

SQL queries TODO

sql Uses a prepared statement once the ESI tag has been parsed.

<esi:include src="alias_name" key="{FMyFormInputName}" />

key will be used as parameter in the WHERE query part.

Disabled by default and must be enabled with a new compiled Caddy binary and the build tag esisql.

gRPC Remote Procedure Calls

grpc queries another gRPC endpoint. A struct of arguments gets encoded and passed over the wire.

<esi:include src="alias_name" key="cart1" />

You are responsible for building the gRPC server. The .proto file and the corresponding Go file have been placed in package backend/esigrpc. Your gRPC server can run in any programming language you like and is supported by gRPC. https://www.grpc.io

Disabled by default and must be enabled with a new compiled Caddy binary and the build tag esigrpc.

Unsupported ESI Tags

All other tags, as defined in https://www.w3.org/TR/esi-lang, won't be supported. You should switch to a server side scripting language ;-).

Building

The following command enables HTTP/S/2 backends:

$ go get -u github.com/mholt/caddy/...
# maybe checkout different version of caddy. Tested with 0.9.5
$ go get -u github.com/SchumacherDM/caddyesi/...

In file $GOPATH/src/github.com/mholt/caddy/caddy/caddymain/run.go add the line _ "github.com/corestoreio/caddy-esi" after the text // This is where other plugins get plugged in (imported).

In file $GOPATH/src/github.com/mholt/caddy/caddyhttp/httpserver/plugin.go find the variable directives and add the entry "esi", between hugo and mailout. At the moment I'm not quite sure if that is the correct place. If any other middleware fails, you should change the position of the esi entry to somewhere else. Please report back here by opening an issue.

Then you are ready to compile Caddy with ESI support:

$ GOOS=linux GOARCH=amd64 go build -o caddyesi $GOPATH/src/github.com/mholt/caddy/caddy/main.go

Change GOOS and GOARCH to whatever architecture and operating system you are targeting.

Contribute

Send me a pull request or open an issue if you encounter a bug or something can be improved!

Multi-time pull request senders gets collaborator access.

Attribution

github.com/vdobler/ht

Copyright (c) 2014, Volker Dobler All rights reserved.

Redistribution and use in source and binary forms, with or without modification, are permitted provided that the following conditions are met:

• Redistributions of source code must retain the above copyright notice, this list of conditions and the following disclaimer.

• Redistributions in binary form must reproduce the above copyright notice, this list of conditions and the following disclaimer in the documentation and/or other materials provided with the distribution.

• Neither the name of ht nor the names of its contributors may be used to endorse or promote products derived from this software without specific prior written permission.

THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

github.com/dustin/go-humanize

Copyright (c) 2005-2008  Dustin Sallings <[email protected]>

Permission is hereby granted, free of charge, to any person obtaining a copy
of this software and associated documentation files (the "Software"), to deal
in the Software without restriction, including without limitation the rights
to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
copies of the Software, and to permit persons to whom the Software is
furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in
all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
SOFTWARE.

<http://www.opensource.org/licenses/mit-license.php>

github.com/uber-go/zap

Copyright (c) 2016 Uber Technologies, Inc.

Permission is hereby granted, free of charge, to any person obtaining a copy
of this software and associated documentation files (the "Software"), to deal
in the Software without restriction, including without limitation the rights
to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
copies of the Software, and to permit persons to whom the Software is
furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in
all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
THE SOFTWARE.

github.com/bradfitz/gomemcache

Copyright 2011 Google Inc.

Licensed under the Apache License, Version 2.0 (the "License"); you may not use
this file except in compliance with the License. You may obtain a copy of the
License at

     http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software distributed
under the License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR
CONDITIONS OF ANY KIND, either express or implied. See the License for the
specific language governing permissions and limitations under the License.

github.com/gomodule/redigo

Copyright 2012 Gary Burd

Licensed under the Apache License, Version 2.0 (the "License"): you may not use
this file except in compliance with the License. You may obtain a copy of the
License at

    http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software distributed
under the License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR
CONDITIONS OF ANY KIND, either express or implied. See the License for the
specific language governing permissions and limitations under the License.

google.golang.org/grpc

Copyright 2016, Google Inc.
All rights reserved.

Redistribution and use in source and binary forms, with or without
modification, are permitted provided that the following conditions are
met:

    * Redistributions of source code must retain the above copyright
notice, this list of conditions and the following disclaimer.
    * Redistributions in binary form must reproduce the above
copyright notice, this list of conditions and the following disclaimer
in the documentation and/or other materials provided with the
distribution.
    * Neither the name of Google Inc. nor the names of its
contributors may be used to endorse or promote products derived from
this software without specific prior written permission.

THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
"AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
(INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

License

Cyrill Schumacher - My pgp public key

Copyright 2016 Cyrill Schumacher All Rights Reserved.

Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except in compliance with the License. You may obtain a copy of the License at

 http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software distributed under the License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the License for the specific language governing permissions and limitations under the License.