From 9a9efb854659420a83b4e9d52f1b0c8011aa5d12 Mon Sep 17 00:00:00 2001
From: winlin <winlin@vip.126.com>
Date: Sun, 7 Feb 2021 15:48:46 +0800
Subject: [PATCH] RTC: Parse TWCC SN fastly.

---
 trunk/src/app/srs_app_rtc_conn.cpp      |  9 +---
 trunk/src/kernel/srs_kernel_rtc_rtp.cpp | 62 +++++++++++++++++++++++++
 trunk/src/kernel/srs_kernel_rtc_rtp.hpp |  2 +
 3 files changed, 65 insertions(+), 8 deletions(-)

diff --git a/trunk/src/app/srs_app_rtc_conn.cpp b/trunk/src/app/srs_app_rtc_conn.cpp
index 103a53319..5ec60865e 100644
--- a/trunk/src/app/srs_app_rtc_conn.cpp
+++ b/trunk/src/app/srs_app_rtc_conn.cpp
@@ -1132,19 +1132,12 @@ srs_error_t SrsRtcPublishStream::on_rtp(char* data, int nb_data)
 
     // Decode the header first.
     if (twcc_id_) {
-        SrsRtpHeader h;
-        SrsBuffer b(data, nb_data);
-        h.ignore_padding(true); h.set_extensions(&extension_types_);
-        if ((err = h.decode(&b)) != srs_success) {
-            return srs_error_wrap(err, "twcc decode header");
-        }
-
         // We must parse the TWCC from RTP header before SRTP unprotect, because:
         //      1. Client may send some padding packets with invalid SequenceNumber, which causes the SRTP fail.
         //      2. Server may send multiple duplicated NACK to client, and got more than one ARQ packet, which also fail SRTP.
         // so, we must parse the header before SRTP unprotect(which may fail and drop packet).
         uint16_t twcc_sn = 0;
-        if ((err = h.get_twcc_sequence_number(twcc_sn)) == srs_success) {
+        if ((err = srs_rtp_fast_parse_twcc(data, nb_data, &extension_types_, twcc_sn)) == srs_success) {
             if((err = on_twcc(twcc_sn)) != srs_success) {
                 return srs_error_wrap(err, "on twcc");
             }
diff --git a/trunk/src/kernel/srs_kernel_rtc_rtp.cpp b/trunk/src/kernel/srs_kernel_rtc_rtp.cpp
index 355b02c61..04a17d154 100644
--- a/trunk/src/kernel/srs_kernel_rtc_rtp.cpp
+++ b/trunk/src/kernel/srs_kernel_rtc_rtp.cpp
@@ -70,6 +70,68 @@ uint8_t srs_rtp_fast_parse_pt(char* buf, int size)
     }
     return buf[1] & 0x7f;
 }
+srs_error_t srs_rtp_fast_parse_twcc(char* buf, int size, SrsRtpExtensionTypes* ext_types, uint16_t& twcc_sn)
+{
+    srs_error_t err = srs_success;
+
+    int need_size = 12 /*rtp head fix len*/ + 4 /* extension header len*/ + 3 /* twcc extension len*/;
+    if(size < (need_size)) {
+        return srs_error_new(ERROR_RTC_RTP_MUXER, "required %d bytes, actual %d", need_size, size);
+    }
+
+    uint8_t first = buf[0];
+    bool extension = (first & 0x10);
+    uint8_t cc = (first & 0x0F);
+
+    if(!extension) {
+        return srs_error_new(ERROR_RTC_RTP, "no extension in rtp");
+    }
+
+    need_size += cc * 4; // csrc size
+    if(size < (need_size)) {
+        return srs_error_new(ERROR_RTC_RTP_MUXER, "required %d bytes, actual %d", need_size, size);
+    }
+    buf += 12 + 4*cc;
+
+    uint16_t value = *((uint16_t*)buf);
+    value = ntohs(value);
+    if(0xBEDE != value) {
+        return srs_error_new(ERROR_RTC_RTP_MUXER, "no support this type(0x%02x) extension", value);
+    }
+    buf += 2;
+    
+    uint16_t extension_length = ntohs(*((uint16_t*)buf));
+    buf += 2;
+    extension_length *= 4;
+    need_size += extension_length; // entension size
+    if(size < (need_size)) {
+        return srs_error_new(ERROR_RTC_RTP_MUXER, "required %d bytes, actual %d", need_size, size);
+    }
+
+    while(extension_length > 0) {
+        uint8_t v = buf[0];
+        buf++;
+        extension_length--;
+        if(0 == v) {
+            continue;
+        }
+
+        uint8_t id = (v & 0xF0) >>4;
+        uint8_t len = (v & 0x0F) + 1;
+
+        SrsRtpExtensionType xtype = ext_types->get_type(id);
+        if(xtype == kRtpExtensionTransportSequenceNumber) {
+            twcc_sn = ntohs(*((uint16_t*)buf));
+            return err;
+        } else {
+            buf += len;
+            extension_length -= len;
+        }
+    }
+
+
+    return err;
+}
 
 // If value is newer than pre_value，return true; otherwise false
 bool srs_seq_is_newer(uint16_t value, uint16_t pre_value)
diff --git a/trunk/src/kernel/srs_kernel_rtc_rtp.hpp b/trunk/src/kernel/srs_kernel_rtc_rtp.hpp
index 4b5761b4a..b843dc201 100644
--- a/trunk/src/kernel/srs_kernel_rtc_rtp.hpp
+++ b/trunk/src/kernel/srs_kernel_rtc_rtp.hpp
@@ -57,10 +57,12 @@ class SrsBuffer;
 class SrsRtpRawPayload;
 class SrsRtpFUAPayload2;
 class SrsSharedPtrMessage;
+class SrsRtpExtensionTypes;
 
 // Fast parse the SSRC from RTP packet. Return 0 if invalid.
 uint32_t srs_rtp_fast_parse_ssrc(char* buf, int size);
 uint8_t srs_rtp_fast_parse_pt(char* buf, int size);
+srs_error_t srs_rtp_fast_parse_twcc(char* buf, int size, SrsRtpExtensionTypes* types, uint16_t& twcc_sn);
 
 // 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