Added support for late SDP negotiation for INVITE and reINVITE.

.github/workflows/ci-linux.yml

@@ -813,6 +813,10 @@ jobs:
         python3 run.py --exe ../../pjsip-apps/src/3rdparty_media_sample/alt_pjsua mod_sipp.py scripts-sipp/alt-pjsua-uas-multiple-amr.xml
         python3 run.py --exe ../../pjsip-apps/src/3rdparty_media_sample/alt_pjsua mod_sipp.py scripts-sipp/alt-pjsua-uas-media-app-managed.xml
         python3 run.py --exe ../../pjsip-apps/src/3rdparty_media_sample/alt_pjsua mod_sipp.py scripts-sipp/alt-pjsua-uas-early-update-app-managed.xml
+        python3 run.py --exe ../../pjsip-apps/src/3rdparty_media_sample/alt_pjsua mod_sipp.py scripts-sipp/alt-pjsua-uac-late-offer.xml
+        python3 run.py --exe ../../pjsip-apps/src/3rdparty_media_sample/alt_pjsua mod_sipp.py scripts-sipp/alt-pjsua-uas-late-offer.xml
+        python3 run.py --exe ../../pjsip-apps/src/3rdparty_media_sample/alt_pjsua mod_sipp.py scripts-sipp/alt-pjsua-uac-late-offer-dummy-codecs.xml
+        python3 run.py --exe ../../pjsip-apps/src/3rdparty_media_sample/alt_pjsua mod_sipp.py scripts-sipp/alt-pjsua-uas-late-offer-dummy-codecs.xml
     - name: upload artifacts on failure
       if: ${{ failure() }}
       uses: actions/upload-artifact@v4

pjsip-apps/src/3rdparty_media_sample/alt_pjsua_aud.c

@@ -1,5 +1,5 @@
 /*
- * Copyright (C) 2008-2011 Teluu Inc. (http://www.teluu.com)
+ * Copyright (C) 2008-2026 Teluu Inc. (http://www.teluu.com)
  *
  * This program is free software; you can redistribute it and/or modify
  * it under the terms of the GNU General Public License as published by
@@ -17,6 +17,7 @@
  */
 #include <pjsua-lib/pjsua.h>
 #include <pjsua-lib/pjsua_internal.h>
+#include "../pjsua/pjsua_app.h"
 
 #if defined(PJSUA_MEDIA_HAS_PJMEDIA) && PJSUA_MEDIA_HAS_PJMEDIA != 0
 #  error The PJSUA_MEDIA_HAS_PJMEDIA should be declared as zero
@@ -173,14 +174,28 @@ static pjmedia_codec_factory_op alt_codec_factory_op =
 /* Initialize third party media library. */
 pj_status_t pjsua_aud_subsys_init()
 {
-    /* Codec registration is intentionally omitted: pjsua now handles an
-     * empty codec registry gracefully, so 3rd-party media stacks do not
-     * need to register dummy codecs.  The alt_codec_factory above is kept
-     * as reference documentation for implementors who do want to register.
-     */
-    (void)alt_codec_factory;
-    (void)alt_codec_factory_op;
-
+    if (app_config.dummy_codecs) {
+        /* Enable dummy codecs if requested in the app config */
+        pjmedia_codec_mgr *codec_mgr;
+        pj_status_t status;
+
+        /* Register our "dummy" codecs */
+        alt_codec_factory.base.op = &alt_codec_factory_op;
+        codec_mgr = pjmedia_endpt_get_codec_mgr(pjsua_var.med_endpt);
+        status = pjmedia_codec_mgr_register_factory(codec_mgr,
+                                                    &alt_codec_factory.base);
+        if (status != PJ_SUCCESS)
+            return status;
+    }
+    else {
+        /* Codec registration is intentionally omitted: pjsua now handles an
+        * empty codec registry gracefully, so 3rd-party media stacks do not
+        * need to register dummy codecs.  The alt_codec_factory above is kept
+        * as reference documentation for implementors who do want to register.
+        */
+        (void)alt_codec_factory;
+        (void)alt_codec_factory_op;
+    }
     /* TODO: initialize your evil library here */
     return PJ_SUCCESS;
 }

pjsip-apps/src/pjsua/pjsua_app_common.h

@@ -205,6 +205,7 @@ typedef struct pjsua_app_config
     /* Custom SDP to inject via on_call_sdp_created (replaces generated SDP).
      * Only available when PJSUA_MEDIA_HAS_PJMEDIA=0 (alt media backend). */
     pj_str_t                custom_sdp;
+    pj_bool_t               dummy_codecs;
 #endif
 
     /* Set PJSUA_CALL_MEDIA_APP_MANAGED on the default call setting used for

pjsip-apps/src/pjsua/pjsua_app_config.c

@@ -206,6 +206,7 @@ static void usage(void)
     puts  ("                     for this account as application-managed from the start,");
     puts  ("                     so pjsua never creates a media transport for them (even");
     puts  ("                     the initial incoming offer). See pjsua_acc_config.");
+    puts  ("  --dummy-codecs      Register dummy codecs for the alternative media backend.");
 #endif
 
 #if PJSUA_HAS_VIDEO
@@ -466,7 +467,8 @@ static pj_status_t parse_args(int argc, char *argv[],
            OPT_USE_CLI, OPT_CLI_TELNET_PORT, OPT_DISABLE_CLI_CONSOLE,
            OPT_SERVER_AFFINITY, OPT_SERVER_FAILOVER, OPT_RESOLVER_FALLBACK
 #if !PJSUA_MEDIA_HAS_PJMEDIA
-           , OPT_CUSTOM_SDP, OPT_SDP_PASSTHROUGH, OPT_ACC_MEDIA_APP_MANAGED
+           , OPT_CUSTOM_SDP, OPT_SDP_PASSTHROUGH, OPT_ACC_MEDIA_APP_MANAGED,
+           OPT_DUMMY_CODECS
 #endif
     };
     struct pj_getopt_option long_options[] = {
@@ -639,6 +641,7 @@ static pj_status_t parse_args(int argc, char *argv[],
         { "acc-media-app-managed", 0, 0, OPT_ACC_MEDIA_APP_MANAGED},
         { "custom-sdp",     1, 0, OPT_CUSTOM_SDP},
         { "sdp-passthrough", 0, 0, OPT_SDP_PASSTHROUGH},
+        { "dummy-codecs", 0, 0, OPT_DUMMY_CODECS},
 #endif
         { NULL, 0, 0, 0}
     };
@@ -1811,6 +1814,9 @@ static pj_status_t parse_args(int argc, char *argv[],
             cfg->custom_sdp.slen = (pj_ssize_t)(dst - cfg->custom_sdp.ptr);
             break;
         }
+        case OPT_DUMMY_CODECS:
+            cfg->dummy_codecs = PJ_TRUE;
+            break;
 #endif /* !PJSUA_MEDIA_HAS_PJMEDIA */
 
         default:
@@ -2914,6 +2920,9 @@ int write_settings(pjsua_app_config *config, char *buf, pj_size_t max)
         cfg_add_str(&cfg, max, &escaped);
         cfg_add(&cfg, max, "\"\n");
     }
+    if (config->dummy_codecs) {
+        cfg_add(&cfg, max, "--dummy-codecs\n");
+    }
 #endif /* !PJSUA_MEDIA_HAS_PJMEDIA */
 
     return (int)cfg.slen;

pjsip/include/pjsua-lib/pjsua.h

@@ -1780,15 +1780,18 @@ typedef struct pjsua_callback
      * Otherwise, by default the re-INVITE will be answered automatically
      * after the callback returns.
      *
-     * For an application-managed call receiving a re-INVITE without SDP,
-     * this callback is also called with a NULL offer. By default, the active
-     * local SDP is re-offered. Application may set \a async to PJ_TRUE and
+     * For a re-INVITE without SDP, this callback is called with a NULL offer.
+     * This also applies to calls that are not application-managed when this
+     * callback is registered. By default, the active local SDP is re-offered.
+     * Application may set \a async to PJ_TRUE and
      * later send the response with #pjsua_call_answer_with_sdp(), supplying
      * its own local SDP offer. On the asynchronous path, a successful final
      * response requires an application-supplied offer; the active local SDP
      * is not automatically re-offered.
      * On the synchronous offerless path, any 2xx callback code is treated
-     * as 200. Codes outside 200-699 are rejected with 500.
+     * as 200, and final rejection codes (300-699) are accepted. Codes outside
+     * 200-699 are rejected with 500. For a re-INVITE containing SDP, only
+     * 200 and 488 are valid callback codes.
      *
      * Remarks: If manually answering at a later timing, application may
      * need to monitor on_call_tsx_state() callback to check whether
@@ -1808,15 +1811,17 @@ typedef struct pjsua_callback
      * as pjsua deactivates it there, see on_call_sdp_created().
      *
      * @param call_id   The call index.
-     * @param offer     Remote offer, or NULL for an application-managed
-     *                  call receiving a re-INVITE without SDP.
+     * @param offer     Remote offer, or NULL for a re-INVITE without SDP.
      * @param rdata     The received re-INVITE request.
      * @param reserved  Reserved param, currently not used.
      * @param async     On input, it is PJ_FALSE. Set to PJ_TRUE if
      *                  app wants to manually answer the re-INVITE.
      * @param code      Status code to be returned for answering the
      *                  offer. On input, it contains status code 200.
-     *                  Currently, valid values are only 200 and 488.
+     *                  For a re-INVITE containing SDP, valid values are 200
+     *                  and 488. For a synchronous offerless re-INVITE, 2xx
+     *                  is treated as 200, 300-699 rejects the request, and
+     *                  values outside 200-699 are changed to 500.
      * @param opt       The current call setting, application can update
      *                  this setting for answering the offer.
      */
@@ -2479,6 +2484,28 @@ typedef struct pjsua_callback
      */
     void (*on_auth_challenge)(pjsua_on_auth_challenge_param *param);
 
+    /**
+     * Notify application when the framework needs to send an ACK request
+     * after it receives an incoming 2xx response for INVITE (e.g. when the
+     * 2xx response carries a late SDP offer). Implementing this callback
+     * alone does not transfer responsibility for sending the ACK. The
+     * framework continues to send it automatically unless this callback
+     * returns PJ_TRUE. When it returns PJ_TRUE, the application is
+     * responsible for creating and sending the ACK itself, using
+     * #pjsua_call_send_ack(). This allows an SDP answer to be attached to
+     * the ACK or the ACK transmission to be delayed, e.g. while waiting for
+     * the SDP answer in 3PCC scenarios.
+     *
+     * @param call_id   The call index.
+     * @param rdata     The received 2xx response that triggered the need to
+     *                  send an ACK request.
+     * @return          PJ_TRUE to suppress the automatic ack request sending.
+     *                  PJ_FALSE (default) to keep current behavior, automatic
+     *                  ACK sending by the framework will proceed as usual.
+     */
+    pj_bool_t (*on_call_send_ack)(pjsua_call_id call_id,
+                                  pjsip_rx_data *rdata);
+
 } pjsua_callback;
 
 
@@ -6934,17 +6961,25 @@ PJ_DECL(pj_status_t) pjsua_call_answer2(pjsua_call_id call_id,
 
 /**
  * Same as #pjsua_call_answer2() but this function will set the local SDP
- * first before sending the response. For application-managed calls
- * (#PJSUA_CALL_MEDIA_APP_MANAGED), the SDP is used as an offer when answering
- * an offerless INVITE or re-INVITE, and as an answer otherwise. For ordinary
- * calls, the SDP is used only as an answer to a pending remote offer.
+ * before sending the response. The SDP is used as an offer when answering
+ * an offerless INVITE or re-INVITE, and as an answer to a pending remote
+ * offer otherwise. For ordinary initial offerless calls, media is initialized
+ * before installing the supplied offer. A pending local offer cannot be
+ * replaced by this function.
+ * Supplying SDP with a final error response (code >= 300) returns
+ * PJ_EINVALIDOP without changing call state.
  * An application-managed answer must have the same media-line count as the
  * remote offer; otherwise PJMEDIA_SDPNEG_EMISMEDIA is returned.
  *
+ * For calls whose media is not application-managed, supplying a local SDP
+ * offer in a provisional (1xx) response requires 100rel to be active
+ * (#PJSIP_INV_REQUIRE_100REL). Otherwise PJ_EINVALIDOP is returned.
+ * Codes 100, 180, and 181 are rejected for such offers even with 100rel active.
+ * These restrictions apply to SDP offers, not answers to remote offers.
+ *
  * @param call_id       Incoming call identification.
- * @param sdp           Local SDP answer, or a local SDP offer for an
- *                      application-managed call answering an offerless
- *                      INVITE or re-INVITE.
+ * @param sdp           Local SDP answer, or a local SDP offer when answering
+ *                      an offerless INVITE or re-INVITE.
  * @param opt           Optional call setting.
  * @param code          Status code, (100-699).
  * @param reason        Optional reason phrase. If NULL, default text
@@ -6965,6 +7000,33 @@ pjsua_call_answer_with_sdp(pjsua_call_id call_id,
                            const pjsua_msg_data *msg_data);
 
 
+/**
+ * Create and send an ACK request for the 2xx response, optionally with an
+ * SDP answer \a sdp attached to it. Application would normally use this
+ * function from within the #pjsua_callback.on_call_send_ack() callback,
+ * to manually take over the ACK transmission, e.g. to attach an SDP answer
+ * to the ACK for a late SDP offer received in the 2xx response.
+ * This function is safe to call synchronously from the
+ * #pjsua_callback.on_call_send_ack() callback when \a call_id identifies the
+ * call whose ACK triggered the callback. A different call ID is rejected with
+ * PJ_EINVALIDOP to avoid acquiring the PJSUA lock while holding the callback
+ * call's dialog lock.
+ *
+ * @param call_id       Call identification.
+ * @param cseq          CSeq of the 2xx response that triggered the need to
+ *                      send an ACK request; normally this is the CSeq of
+ *                      the \a rdata received in the on_call_send_ack()
+ *                      callback.
+ * @param sdp           Optional SDP answer to be attached to the ACK
+ *                      request. May be NULL if no SDP body is required.
+ *
+ * @return              PJ_SUCCESS on success, or the appropriate error code.
+ */
+PJ_DECL(pj_status_t) pjsua_call_send_ack(pjsua_call_id call_id,
+                                        int cseq,
+                                        const pjmedia_sdp_session *sdp);
+
+
 /**
  * Hangup call by using method that is appropriate according to the
  * call state. This function is different than answering the call with

pjsip/include/pjsua-lib/pjsua_internal.h

@@ -298,6 +298,7 @@ struct pjsua_call
                                     /**< Allocated size of siprec_metadata */
 
     pjmedia_av_sync     *av_sync;       /**< Media stream synchronizer      */
+    pjmedia_sdp_session *answer_sdp;/**< Application SDP pending media init.*/
 };
 
 PJ_INLINE(pj_bool_t) pjsua_call_media_is_app_managed(
@@ -941,6 +942,11 @@ pj_status_t pjsua_acc_get_uac_dlg_addr(pjsua_acc_id acc_id,
  */
 pj_bool_t pjsua_call_on_incoming(pjsip_rx_data *rdata);
 
+pj_status_t pjsua_call_validate_initial_local_offer(
+                                      const pjsua_call *call,
+                                      const pjsua_call_setting *opt,
+                                      const pjmedia_sdp_session *sdp);
+
 /*
  * Media channel.
  */
@@ -1057,6 +1063,11 @@ pj_status_t pjsua_call_subsys_init(const pjsua_config *cfg);
  */
 pj_status_t pjsua_call_subsys_start(void);
 
+/**
+ * Destroy call subsystem resources.
+ */
+void pjsua_call_subsys_destroy(void);
+
 /**
  * Init media subsystems.
  */

pjsip/include/pjsua2/call.hpp

@@ -221,6 +221,11 @@ struct SdpSession
     void   *pjSdpSession;
 
 public:
+    /**
+     * Default constructor
+     */
+    SdpSession() : pjSdpSession(nullptr) {}
+
     /**
      * Convert from pjsip
      */
@@ -833,6 +838,36 @@ struct OnCallSdpCreatedParam
     SdpSession remSdp;
 };
 
+/**
+ * This structure contains parameters for Call::onCallSendAck() callback.
+ */
+struct OnCallSendAckParam
+{
+    /**
+     * The 2xx response for INVITE that triggered the need to send an ACK
+     * request.
+     */
+    SipRxData rdata;
+
+    /**
+     * Output: application sets this to true if it has sent (or will send)
+     * the ACK itself, to suppress the automatic ACK sending. Default is false,
+     * i.e. the library sends the ACK after this callback returns.
+     */
+    bool suppressSendAck;
+
+    /**
+     * The CSeq of the 2xx response.
+     */
+    pj_int32_t cseq;
+
+    /**
+     * Default constructor
+     */
+    OnCallSendAckParam() : suppressSendAck(false), cseq(-1)
+    {}
+};
+
 /**
  * This structure contains parameters for Call::onStreamPreCreate()
  * callback.
@@ -1770,6 +1805,27 @@ class Call
      */
     void hangup(const CallOpParam &prm) PJSUA2_THROW(Error);
 
+    /**
+     * Create and send an ACK request for the 2xx response, optionally with
+     * an SDP answer \a sdp attached to it. Application would normally call
+     * this from within onCallSendAck(), to manually take over the ACK
+     * transmission, e.g. to attach an SDP answer to the ACK for a late
+     * SDP offer received in the 2xx response.
+     * When called synchronously from onCallSendAck(), this method may only
+     * be used on the Call whose ACK triggered the callback; another Call
+     * fails with PJ_EINVALIDOP.
+     *
+     * @param cseq      CSeq of the 2xx response that triggered the need to
+     *                  send an ACK request; normally this is the CSeq of
+     *                  the \a rdata received in the onCallSendAck()
+     *                  callback.
+     * @param sdp       Optional SDP answer to be attached to the ACK
+     *                  request. If its wholeSdp is empty, no SDP body
+     *                  will be attached.
+     */
+    void sendAck(int cseq, const SdpSession &sdp = SdpSession())
+                PJSUA2_THROW(Error);
+
     /**
      * Put the specified call on hold. This will send re-INVITE with the
      * appropriate SDP to inform remote that the call is being put on hold.
@@ -2131,6 +2187,22 @@ class Call
     virtual void onCallSdpCreated(OnCallSdpCreatedParam &prm)
     { PJ_UNUSED_ARG(prm); }
 
+    /**
+     * Notify application when the framework needs to send an ACK request
+     * after it receives an incoming 2xx response for INVITE (e.g. when the
+     * 2xx response carries a late SDP offer). The default implementation
+     * does nothing and lets the framework send the ACK. Application can
+     * set prm.suppressSendAck to true and then the application is responsible
+     * for sending the ACK.
+     *
+     * This callback is enabled only when
+     * UaConfig::enableCallSendAckCallback is set before Endpoint::libInit().
+     *
+     * @param prm       Callback parameter.
+     */
+    virtual void onCallSendAck(OnCallSendAckParam &prm)
+    { PJ_UNUSED_ARG(prm); }
+
     /**
      * Notify application when an audio media session is about to be created
      * (as opposed to onStreamCreated(), which is called *after* the session