Sofia SIP User Agent Library - "sdp" - SDP Module

1.12.11

Module Meta Information

The sdp module provides a simple "C" parser interface for SDP [RFC 2327], Session Description Protocol. The parser also implements support for IPv6 addresses as per RFC 3266. The RFC 4566 should be supported, but we have not checked since draft-eitf-mmusic-sdp-new-17 or so.

Contact:

Pekka Pessi <Pekka.Pessi@nokia-email.address.hidden>

Status:

Sofia SIP Core library

License:

LGPL

Contributor(s):

• Pekka Pessi <Pekka.Pessi@nokia-email.address.hidden>
• Jari Selin <Jari.Selin@nokia-email.address.hidden>

SDP Parser

SDP parser parses an SDP message and converts it to internally used SDP structure sdp_session_t.

Typically, the SDP parser is used as follows:

 sdp_parser_t *parser = sdp_parse(home, message, len, 0);

 if (!sdp_session(parser)) {
   show(sdp_parsing_error(parser));
 } else {
   sdp_session_t *sdp = sdp_session(parser);

Act upon session description, then free the parser:

 }
 sdp_parser_free(parser);

There are various flags indicating what kind of SDP variants the sdp_parse() accepts. The sanity check run after parsing can be disabled by including flag sdp_f_insane. The parser can be used to parse syntactically vague configuration files when using flag sdp_f_config. The parser will then accept * for media, protocol and port, for instance.

SDP Printer

SDP printer converts internally used SDP structure sdp_session_t to the standard SDP format.

Typically, the SDP printer is used as follows:

 char buffer[512];
 sdp_printer_t *printer = sdp_print(home, session, buffer, sizeof(buffer), 0);

 if (sdp_message(printer)) {
   char const *msg = sdp_message(printer);
   size_t msgsize = sdp_message_size(printer);

At this point, application can use the SDP message contents, e.g., it can send them to network, and then free the message:

 }
 else {
   show_critical_error(sdp_printing_error(printer));
 }
 sdp_printer_free(printer);

Example

Examples on using SDP parser can be found from test_sdp.c and soa.c. Here is an simple example, which decodes an SDP text in original, increments the version number in the origin line, and encodes the SDP description again to buf.

size_t increment_sdp_version(char buf[], size_t bsize,
                             char const *original, size_t osize)
{
  su_home_t home[1] = { SU_HOME_INIT(home) };
  sdp_parser_t *parser = sdp_parse(home, original, osize, 0);
  sdp_printer_t *printer;
  size_t retval = 0;

  if (sdp_session(parser)) {
    sdp_session_t *sdp = sdp_session(parser);

    sdp->sdp_origin->o_version++;

    printer = sdp_print(home, sdp, buf, bsize, 0);

    if (sdp_message(printer)) {
      retval = sdp_message_size(printer);
    }
    else {
      fprintf(stderr, "increment_sdp_version: %s\n",
              sdp_printing_error(printer));
    }

    sdp_printer_free(printer);
  }
  else {
    fprintf(stderr, "increment_sdp_version: %s\n",
            sdp_parsing_error(parser));
  }

  sdp_parser_free(parser);

  su_home_deinit(home);

  return retval;
}