clj-protocol: Declarative Protocols and Binary Formats

clj-protocol enables declarative definition of network protocols and binary formats.

Full API Documentation (generated with codox) is available here.

clj-protocol is primarily designed for use in ClojureScript (due to stronger host networking interfaces), however, the core libraries also support Clojure (JVM).

Quick Tutorial

The following commands can either be executed directly if you have the dependencies on your host. Otherwise, you can use the following command to launch a "dev" container with the build and runtime dependencies:

DOCKER_USER=$(id -u):$(id -g) docker-compose -f docker-compose.yaml -f docker-compose-dev.yaml run dev bash

Install dependencies and then start a REPL either using shadow-cljs or node babashka (nbb):

npm install
npx shadow-cljs node-repl
  # OR
npx nbb -cp src

If you are using Clojure (JVM) then you can use leiningen to start a REPL:

lein repl

Require some clj-protocol namespaces:

cljs.user=> (require '[protocol.platform :as platform])
cljs.user=> (require '[protocol.fields :as fields])
cljs.user=> (require '[protocol.header :as header])

Define binary data in a Buffer (or java.nio.ByteBuffer) that we will read/parse:

user> (def buf (platform/buf-from [0x61 0x62 0x63 0x64]))

Define a data format spec that specifies two 8-bit unsigned integers followed by two 16-bit unsigned integers:

cljs.user=> (def spec1 [[:f1 :uint8] [:f2 :uint8] [:f3 :uint16]])

Use that spec and big-endian field readers to parse the buffer:

cljs.user=> (prn (header/read-header-full
                   buf 0 {:spec spec1 :readers fields/readers-BE}))
{:f1 97, :f2 98, :f3 25444}

Parse using the same spec but using little-endian field readers:

cljs.user=> (prn (header/read-header-full
                   buf 0 {:spec spec1 :readers fields/readers-LE}))
{:f1 97, :f2 98, :f3 25699}

Define an alternate data format spec that specifies a single fixed length (4 byte) UTF-8 encoded string and then use that to parse the buffer:

cljs.user=> (def spec2 [[:s1 :utf8 {:length 4}]])
cljs.user=> (prn (header/read-header-full
                   buf 0 {:spec spec2 :readers fields/readers-BE}))
{:s1 "abcd"}

Define an alternate spec that species a 4-byte bitfield containing three fields: a 7-bit unsigned integer field, a 1-bit boolean field, and a 24-bit unsigned integer field.

cljs.user=> (def spec3 [[:f1 :bitfield {:length 4
                                        :spec [[:b1 :int   7]
                                               [:b2 :bool  1]
                                               [:b3 :int  24]]}]])
cljs.user=> (prn (header/read-header-full
                   buf 0 {:spec spec3 :readers fields/readers-BE}))
{:f1 {:b1 48, :b2 true, :b3 6447972}}

Use the same bitfield spec to encode different values into a buffer starting at offset 2:

cljs.user=> (def msg {:f1 {:b1 5, :b2 false, :b3 16}})
cljs.user=> (def buf2 (header/write-header-full
                        nil msg 2 {:spec spec3 :writers fields/writers-BE}))
cljs.user=> (prn (platform/buf->vec buf2 0))
[0 0 10 0 0 16]

Example Programs

The project includes five working examples:

• A DHCP client
• A DHCP server that uses an IP lease pool
• A DHCP server that uses direct MAC to IP mapping and that supports multiprocess parallel workers
• An ICMP/ping client
• A pcap file parser

Build the examples:

npx shadow-cljs compile simple-client pool-server mac2ip-server ping-client read-pcap

Usage:

• DHCP simple client - Run a DHCP client on eth0. Listening on port 68 requires elevated permissions. WARNING: this will attempt to update your IP address on eth0 if it receives a successful response from a server.

  sudo node ./build/simple-client.js --if-name eth0
  

• DHCP pool server - Run a DHCP server on eth0 that allocates from a pool and stores the leases in a JSON file. This will listen for DHCP DISCOVER/REQUESTS and assign addresses from the pool.

  sudo node ./build/pool-server.js eth0
  

• DHCP mac2ip server - Run a DHCP server on eth0 that does direct MAC to IP assignments (defined in the config file) and runs 5 parallel worker processes.

  sudo node ./build/mac2ip-server.js -processes 5 --if-name eth0 --config-file mac2ip.json
  

• ICMP/ping client - Use the ping client to demonstrate ICMP protocl reading/writing. Elevated permissions are required to send/receive ICMP packets.

  sudo node ./build/ping.js 8.8.8.8
  

• pcap file parser - Use the pcap file parser to print the header and records from the example pcap file.

  node ./build/read-pcap.js test/example.pcap
  

Tests

Build and run the tests:

npx shadow-cljs compile test
chmod +x build/*.js
node build/test.js

If you are using Clojure (JVM) then run tests using leiningen:

lein test

Use docker-compose and conlink to launch a self-contained network environment that runs the DHCP client, server, and ping client.

docker-compose --profile dhcp --profile ping up --force-recreate --build

Test the mac2ip DHCP server:

docker-compose --profile mac2ip up --force-recreate --build

Creating custom reader/writer functions

• Context should be passed to any internal reader/writer calls.

API

All public functions in the protocol namespaces have docstrings that describe the API.

You can use leiningen to generate codox documentation in docs/www like this:

lein codox

TODO

• add signed int value types ?
• :lookup -> :tlv-lookup ?

Running / Testing on NixOS

Run the following on NixOS to get the required node modules (pcap and raw-socket) installed to be able to run the ping and and dhcp commands:

rm -r node_modules
nix-shell -p libpcap --run 'npm install'

Copyright & License

This software is copyright Viasat, Inc and is released under the terms of the Eclipse Public License version 2.0 (EPL.20). A copy of the license is located at in the LICENSE file at the top of the repository.