res_pjsip_sdp_rtp: Use negotiated DTMF Payload types on bitrate mismatch

When Asterisk sends an offer to Bob that includes 48K and 8K codecs with
matching 4733 offers, Bob may want to use the 48K audio codec but can not
accept 48K digits and so negotiates for a mixed set.

Asterisk will now check Bob's offer to make sure Bob has indicated this is
acceptible and if not, will use Bob's preference.

Fixes: #847
(cherry picked from commit cf5a6435c2)

include/asterisk/rtp_engine.h

@@ -764,10 +764,15 @@ struct ast_rtp_codecs {
 	unsigned int framing;
 	/*! The preferred format, as the mappings are numerically sorted */
 	struct ast_format *preferred_format;
+	/*! The preferred dtmf sample rate */
+	int preferred_dtmf_rate;
+	/*! The preferred dtmf payload type */
+	int preferred_dtmf_pt;
 };
 
 #define AST_RTP_CODECS_NULL_INIT \
-    { .codecs_lock = AST_RWLOCK_INIT_VALUE, .payload_mapping_rx = { 0, }, .payload_mapping_tx = { 0, }, .framing = 0, .preferred_format = NULL }
+    { .codecs_lock = AST_RWLOCK_INIT_VALUE, .payload_mapping_rx = { 0, }, .payload_mapping_tx = { 0, }, .framing = 0, .preferred_format = NULL, \
+	.preferred_dtmf_rate = -1, .preferred_dtmf_pt = -1}
 
 /*! Structure that represents the glue that binds an RTP instance to a channel */
 struct ast_rtp_glue {
@@ -1710,6 +1715,69 @@ struct ast_format *ast_rtp_codecs_get_preferred_format(struct ast_rtp_codecs *co
  */
 int ast_rtp_codecs_set_preferred_format(struct ast_rtp_codecs *codecs, struct ast_format *format);
 
+/*!
+ * \brief Retrieve rx preferred dtmf format payload type
+ *
+ * \param codecs Codecs structure to look in
+ *
+ * \return Payload type of preferred dtmf format.
+ * \retval -1 if not set.
+ *
+ * Example usage:
+ *
+ * \code
+ * int payload;
+ * payload = ast_rtp_codecs_get_preferred_dtmf_format_pt(codec);
+ * \endcode
+ *
+ * This looks up the preferred dtmf format pt on the codec
+ */
+int ast_rtp_codecs_get_preferred_dtmf_format_pt(struct ast_rtp_codecs *codecs);
+
+/*!
+ * \brief Retrieve rx preferred dtmf format sample rate
+ *
+ * \param codecs Codecs structure to look in
+ *
+ * \return Sample rate of preferred dtmf format.
+ * \retval -1 if not set.
+ *
+ * Example usage:
+ *
+ * \code
+ * int sample_rate;
+ * sample_rate = ast_rtp_codecs_get_preferred_dtmf_format_rate(codec);
+ * \endcode
+ *
+ * This looks up the preferred dtmf format sample rate on the codec
+ */
+int ast_rtp_codecs_get_preferred_dtmf_format_rate(struct ast_rtp_codecs *codecs);
+
+/*!
+ * \brief Set the preferred dtmf format pt and sample rate
+ *
+ * \param codecs Codecs structure to set the preferred format in
+ * \param pt Preferred dtmf payload type to set.
+ * \param rate Preferred dtmf payload rate to set.
+ *
+ * \return 0
+ *
+ * \note The format passed this function has its reference count increased. If an existing
+ * 		 format is set, that format is replaced.
+ *
+ * Example usage:
+ *
+ * \code
+ * int dtmf_code = atoi(dtmf_pt);
+ * int dtmf_rate = clock_rate;
+ * ast_rtp_codecs_set_preferred_dtmf_format(codecs, dtmf_code, dtmf_rate);
+ * \endcode
+ *
+ * This sets the preferred dtmf_code and dtmf_rate on the codec.
+ */
+int ast_rtp_codecs_set_preferred_dtmf_format(struct ast_rtp_codecs *codecs, int pt, int rate);
+
+
 /*!
  * \brief Update the format associated with a tx payload type in a codecs structure
  *
@@ -2977,6 +3045,20 @@ int ast_rtp_get_rate(const struct ast_format *format);
  */
 struct stasis_topic *ast_rtp_topic(void);
 
+/*!
+ * \brief Determine if a type of payload is already present in mappings.
+ * \since 18
+ *
+ * \param codecs Codecs to be checked for mappings.
+ * \param to_match Payload type object to compare against.
+ *
+ * \note It is assumed that codecs is not locked before calling.
+ *
+ * \retval 0 not found
+ * \retval 1 found
+ */
+int ast_rtp_payload_mapping_tx_is_present(struct ast_rtp_codecs *codecs, const struct ast_rtp_payload_type *to_match);
+
 /* RTP debug logging category name */
 #define AST_LOG_CATEGORY_RTP "rtp"
 /* RTP packet debug logging category name */