RTC: Fast parse ssrc and find the publisher

trunk/src/app/srs_app_rtc_conn.cpp

@@ -2095,19 +2095,14 @@ srs_error_t SrsRtcConnection::find_publisher(char* buf, int size, SrsRtcPublishS
         return srs_error_new(ERROR_RTC_RTCP, "no publisher");
     }
 
-    SrsRtpHeader header;
-    if (true) {
-        SrsBuffer* buffer = new SrsBuffer(buf, size);
-        SrsAutoFree(SrsBuffer, buffer);
-        header.ignore_padding(true);
-        if(srs_success != (err = header.decode(buffer))) {
-            return srs_error_wrap(err, "decode rtp header");
-        }
+    uint32_t ssrc = srs_rtp_fast_parse_ssrc(buf, size);
+    if (ssrc == 0) {
+        return srs_error_new(ERROR_RTC_NO_PUBLISHER, "invalid ssrc");
     }
 
-    map<uint32_t, SrsRtcPublishStream*>::iterator it = publishers_ssrc_map_.find(header.get_ssrc());
+    map<uint32_t, SrsRtcPublishStream*>::iterator it = publishers_ssrc_map_.find(ssrc);
     if(it == publishers_ssrc_map_.end()) {
-        return srs_error_new(ERROR_RTC_NO_PUBLISHER, "no publisher for ssrc:%u", header.get_ssrc());
+        return srs_error_new(ERROR_RTC_NO_PUBLISHER, "no publisher for ssrc:%u", ssrc);
     }
 
     *ppublisher = it->second;

trunk/src/kernel/srs_kernel_rtc_rtp.cpp

@@ -33,6 +33,37 @@ using namespace std;
 #include <srs_kernel_utility.hpp>
 #include <srs_kernel_flv.hpp>
 
+uint32_t srs_rtp_fast_parse_ssrc(char* buf, int size)
+{
+    /* @see https://tools.ietf.org/html/rfc1889#section-5.1
+      0                   1                   2                   3
+      0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+     |V=2|P|X|  CC   |M|     PT      |       sequence number         |
+     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+     |                           timestamp                           |
+     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+     |           synchronization source (SSRC) identifier            |
+     +=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+
+     |            contributing source (CSRC) identifiers             |
+     |                             ....                              |
+     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+    */
+    if (size < 12) {
+        return 0;
+    }
+
+    uint32_t value = 0;
+    char* pp = (char*)&value;
+
+    char* p = buf + 8;
+    pp[3] = *p++;
+    pp[2] = *p++;
+    pp[1] = *p++;
+    pp[0] = *p++;
+    return value;
+}
+
 // If value is newer than pre_value，return true; otherwise false
 bool srs_seq_is_newer(uint16_t value, uint16_t pre_value)
 {

trunk/src/kernel/srs_kernel_rtc_rtp.hpp

@@ -58,6 +58,9 @@ class SrsRtpRawPayload;
 class SrsRtpFUAPayload2;
 class SrsSharedPtrMessage;
 
+// Fast parse the SSRC from RTP packet. Return 0 if invalid.
+uint32_t srs_rtp_fast_parse_ssrc(char* buf, int size);
+
 // The "distance" between two uint16 number, for example:
 //      distance(prev_value=3, value=5) === (int16_t)(uint16_t)((uint16_t)3-(uint16_t)5) === -2
 //      distance(prev_value=3, value=65534) === (int16_t)(uint16_t)((uint16_t)3-(uint16_t)65534) === 5