bencode

A netstring and bencode implementation for Clojure.

This particular implementation was extracted from nREPL, so it could be reused by other applications and be made ClojureScript-compatible as well.

There are other netstring/bencode libraries for Clojure out there, but this one has the distinct advantage that it's certainly going to work well with nREPL. ;-)

Motivation

In each and every application, which contacts peer processes via some communication channel, the handling of the communication channel is obviously a central part of the application. Unfortunately introduces handling of buffers of varying sizes often bugs in form of buffer overflows and similar.

A strong factor in this situation is of course the protocol which goes over the wire. Depending on its design it might be difficult to estimate the size of the input up front. This introduces more handling of message buffers to accomodate for inputs of varying sizes. This is particularly difficult in languages like C, where there is no bounds checking of array accesses and where errors might go unnoticed for considerable amount of time.

To address these issues D. Bernstein developed the so called netstrings. They are especially designed to allow easy construction of the message buffers, easy and robust parsing.

BitTorrent extended this to the bencode protocol which also includes ways to encode numbers and collections like lists or maps.

wire is based on these ideas.

Usage

Just add bencode as a dependency to your project and start hacking.

[nrepl/bencode "1.1.0"]

The API is documented in great detail here.

The main functions in the API are:

• read-netsring
• write-nestring
• read-bencode
• write-bencode

Here are some usage examples for each of the functions available:

• read-netstring

(-> (.getBytes "13:Hello, World!," "UTF-8")
    ByteArrayInputStream.
    read-netstring
    (String. "UTF-8"))

=> Hello, World!

• write-netstring

(-> (doto (ByteArrayOutputStream.)
       (write-netstring (.getBytes "Hello, World!" "UTF-8")))
    .toString)

=> "13:Hello, World!,"

• read-bencode

(vec
  (map
    #(String. % "UTF-8")
    (-> (.getBytes "5:nrepl2:is7:awesomee" "UTF-8")
        ByteArrayInputStream.
        PushbackInputStream.
        read-bencode)))

=> ["nrepl" "is" "awesome"]

• write-bencode

(-> (doto (ByteArrayOutputStream.)
     (write-bencode {:foo "bar"}))
   .toString)

=> "d3:foo3:bare"

Additionally, you can check this document to learn more about it's usage.

Use Cases

Obviously you can use this library whenever you need to deal with netstrings or bencode, but I assume that in practice most people will end up using it for building alternative Clojure nREPL clients or servers. babashka.nrepl is one notable user of the library.

There's also the potential to have the library support ClojureScript and ClojureCLR down the road, so it could be leveraged in even more contexts. Sky is the limit!

License

Copyright © 2018-2021 Meikel Brandmeyer, Bozhidar Batsov and nREPL contributors

Distributed under the Eclipse Public License either version 1.0 or (at your option) any later version.