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RFC 3261 (SIP) implementation in Erlang

This project is implementation Session Initiation Protocol in Erlang (RFC 3261 and related).

General notes

Currently, a lot of the pieces are missing, some are implemented only partially.

Here is a checklist of most important areas:

  • Syntax and enconding layer is mostly implemented. All RFC 3261 headers support is implemented.
  • Message parsing/generation API is somewhat clumsy.
  • Error handling at syntax and encoding layer is not done. i.e., the code can crash on invalid messages, headers, etc, even if such errors are to be ignored/handled according to the RFC.
  • Transport layer is mostly implemented, but only TCP and UDP are supported. TLS is not supported yet.
  • RFC 3263 (Locating SIP Servers) is mostly implemented, but is not tested well.
  • Transaction layer is mostly implemented and tested.
  • Transaction user layer is mostly unimplemented. Only simplest UAC and UAS behaviour is in place. Very simple tests are present. API is far from stable.
  • Minimal dialogs implementation present.
  • No sessions support yet. Offer/answer model is not supported.
  • The code was not tested for performance, concurrency, corner cases. In fact, only the simplest cases are covered by tests.

Hacking the code

Compiling:

$ rebar compile

Running tests for siperl only:

$ rebar eunit ct app=sip

Hacking the code:

$ rebare compile & shell/siperl

Running simplest scenario of UAC and UAS interaction:

$ shell/ct.sh apps/sip/test/ua.spec

Cheatsheet

Add code:load_abs("<PROJECT>/shell/user_default"). to the ~/.erlang to get few helpful commands in the Erlang shell:

  • lm() reload all modified modules
  • mm() print list of all modified modules
  • ctl(Module) run all EUnit tests in the module Module with line level coverage analysis and print the results
  • ctctl(Module) show Module code Coverage after Common Test run

API Notes

  • Parsing, formatting, generating and processing messages is mostly in sip_headers and sip_message. modules The The former is mostly used for individual headers, the latter -- to update message as a whole. Data structures for the supported headers and messages are in sip.hrl
  • Transport layer API is sip_transport module. Transport layer dispatches messages to the transaction layer. If transaction layer cannot handle the message, transport layer lookups core via sip_cores:lookup_core/1 invocation. If core process is found, message is sent to it in form of either {request, Msg} or {response, Msg}.
  • Transaction layer API is in sip_transaction module. When transaction is started, a TU PID is provided to the transaction. Responses from client transactions are sent to TU in form of {response, Msg, TxPid}. Requests from server transactions (the only possible request is ACK) are sent to TU in form of {request, Msg, TxPid}. Transport errors from server transactions are reported in form of {tx_error, Reason, TxPid}.
  • Cores are registered via sip_cores:register_core/1 invocation. Basically, registration is a gproc property added to the core process with value of #sip_core_info{}. For now, it contains single element -- function that returns if core is applicable for given message or not.
  • Utility functions for processing binaries are in sip_binary and sip_syntax.
  • Functions to process supported URIs (for now, only sip scheme is supported) are in sip_uri.

Implemented RFCs

  • RFC 3261 SIP: Session Initiation Protocol (partial support)
  • RFC 6026 Correct Transaction Handling for 2xx Responses to Session Initiation Protocol (SIP) INVITE Requests
  • RFC 3581 An Extension to the Session Initiation Protocol (SIP) for Symmetric Response Routing (only UAS)