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.

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

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.

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)