rtcp 接收部分

rtcp 接收是在rtcp 初始化时注册个scheduler的一个handler，具体调用如下函数

void RTCPInstance::incomingReportHandler1() {  do {    Boolean callByeHandler = False;    int tcpReadStreamSocketNum = fRTCPInterface.nextTCPReadStreamSocketNum();    unsigned char tcpReadStreamChannelId = fRTCPInterface.nextTCPReadStreamChannelId();    unsigned packetSize = 0;    unsigned numBytesRead;    struct sockaddr_in fromAddress;    Boolean packetReadWasIncomplete;    if (fNumBytesAlreadyRead >= maxRTCPPacketSize) {      envir() << "RTCPInstance error: Hit limit when reading incoming packet over TCP. Increase \"maxRTCPPacketSize\"\n";      break;    }    Boolean readResult      = fRTCPInterface.handleRead(&fInBuf[fNumBytesAlreadyRead], maxRTCPPacketSize - fNumBytesAlreadyRead,  numBytesRead, fromAddress, packetReadWasIncomplete);    if (packetReadWasIncomplete) {      fNumBytesAlreadyRead += numBytesRead;      return; // more reads are needed to get the entire packet    } else { // normal case: We've read the entire packet       packetSize = fNumBytesAlreadyRead + numBytesRead;      fNumBytesAlreadyRead = 0; // for next time    }    if (!readResult) break;    // Ignore the packet if it was looped-back from ourself:    Boolean packetWasFromOurHost = False;    if (RTCPgs()->wasLoopedBackFromUs(envir(), fromAddress)) {      packetWasFromOurHost = True;      // However, we still want to handle incoming RTCP packets from      // *other processes* on the same machine.  To distinguish this      // case from a true loop-back, check whether we've just sent a      // packet of the same size.  (This check isn't perfect, but it seems      // to be the best we can do.)      if (fHaveJustSentPacket && fLastPacketSentSize == packetSize) {// This is a true loop-back:fHaveJustSentPacket = False;break; // ignore this packet      }    }    unsigned char* pkt = fInBuf;    if (fIsSSMSource && !packetWasFromOurHost) {      // This packet is assumed to have been received via unicast (because we're a SSM source, and SSM receivers send back RTCP "RR"      // packets via unicast).  'Reflect' the packet by resending it to the multicast group, so that any other receivers can also      // get to see it.      // NOTE: Denial-of-service attacks are possible here.      // Users of this software may wish to add their own,      // application-specific mechanism for 'authenticating' the      // validity of this packet before reflecting it.      // NOTE: The test for "!packetWasFromOurHost" means that we won't reflect RTCP packets that come from other processes on      // the same host as us.  The reason for this is that the 'packet size' test above is not 100% reliable; some packets      // that were truly looped back from us might not be detected as such, and this might lead to infinite forwarding/receiving      // of some packets.  To avoid this possibility, we only reflect RTCP packets that we know for sure originated elsewhere.      // (Note, though, that if we ever re-enable the code in "Groupsock::multicastSendOnly()", then we could remove the test for      // "!packetWasFromOurHost".)      fRTCPInterface.sendPacket(pkt, packetSize);      fHaveJustSentPacket = True;      fLastPacketSentSize = packetSize;    }#ifdef DEBUG    fprintf(stderr, "[%p]saw incoming RTCP packet", this);    if (tcpReadStreamSocketNum < 0) {      // Note that "fromAddress" is valid only if we're receiving over UDP (not over TCP):      fprintf(stderr, " (from address %s, port %d)", AddressString(fromAddress).val(), ntohs(fromAddress.sin_port));    }    fprintf(stderr, "\n");    for (unsigned i = 0; i < packetSize; ++i) {      if (i%4 == 0) fprintf(stderr, " ");      fprintf(stderr, "%02x", pkt[i]);    }    fprintf(stderr, "\n");#endif    int totPacketSize = IP_UDP_HDR_SIZE + packetSize;    // Check the RTCP packet for validity:    // It must at least contain a header (4 bytes), and this header    // must be version=2, with no padding bit, and a payload type of    // SR (200) or RR (201):    if (packetSize < 4) break;    unsigned rtcpHdr = ntohl(*(u_int32_t*)pkt);    if ((rtcpHdr & 0xE0FE0000) != (0x80000000 | (RTCP_PT_SR<<16))) {#ifdef DEBUG      fprintf(stderr, "rejected bad RTCP packet: header 0x%08x\n", rtcpHdr);#endif      break;    }    // Process each of the individual RTCP 'subpackets' in (what may be)    // a compound RTCP packet.    int typeOfPacket = PACKET_UNKNOWN_TYPE;    unsigned reportSenderSSRC = 0;    Boolean packetOK = False;    while (1) {      unsigned rc = (rtcpHdr>>24)&0x1F;      unsigned pt = (rtcpHdr>>16)&0xFF;      unsigned length = 4*(rtcpHdr&0xFFFF); // doesn't count hdr      ADVANCE(4); // skip over the header      if (length > packetSize) break;      // Assume that each RTCP subpacket begins with a 4-byte SSRC:      if (length < 4) break; length -= 4;      reportSenderSSRC = ntohl(*(u_int32_t*)pkt); ADVANCE(4);      Boolean subPacketOK = False;      switch (pt) {        case RTCP_PT_SR: {#ifdef DEBUG  fprintf(stderr, "SR\n");#endif  if (length < 20) break; length -= 20;  // Extract the NTP timestamp, and note this:  unsigned NTPmsw = ntohl(*(u_int32_t*)pkt); ADVANCE(4);  unsigned NTPlsw = ntohl(*(u_int32_t*)pkt); ADVANCE(4);  unsigned rtpTimestamp = ntohl(*(u_int32_t*)pkt); ADVANCE(4);  if (fSource != NULL) {    RTPReceptionStatsDB& receptionStats      = fSource->receptionStatsDB();    receptionStats.noteIncomingSR(reportSenderSSRC,  NTPmsw, NTPlsw, rtpTimestamp);  }  ADVANCE(8); // skip over packet count, octet count  // If a 'SR handler' was set, call it now:  if (fSRHandlerTask != NULL) (*fSRHandlerTask)(fSRHandlerClientData);  // The rest of the SR is handled like a RR (so, no "break;" here)}        case RTCP_PT_RR: {#ifdef DEBUG  fprintf(stderr, "RR\n");#endif  unsigned reportBlocksSize = rc*(6*4);  if (length < reportBlocksSize) break;  length -= reportBlocksSize;          if (fSink != NULL) {    // Use this information to update stats about our transmissions:            RTPTransmissionStatsDB& transmissionStats = fSink->transmissionStatsDB();            for (unsigned i = 0; i < rc; ++i) {              unsigned senderSSRC = ntohl(*(u_int32_t*)pkt); ADVANCE(4);              // We care only about reports about our own transmission, not others'              if (senderSSRC == fSink->SSRC()) {                unsigned lossStats = ntohl(*(u_int32_t*)pkt); ADVANCE(4);                unsigned highestReceived = ntohl(*(u_int32_t*)pkt); ADVANCE(4);                unsigned jitter = ntohl(*(u_int32_t*)pkt); ADVANCE(4);                unsigned timeLastSR = ntohl(*(u_int32_t*)pkt); ADVANCE(4);                unsigned timeSinceLastSR = ntohl(*(u_int32_t*)pkt); ADVANCE(4);                transmissionStats.noteIncomingRR(reportSenderSSRC, fromAddress, lossStats, highestReceived, jitter, timeLastSR, timeSinceLastSR);              } else {                ADVANCE(4*5);              }            }          } else {            ADVANCE(reportBlocksSize);          }  if (pt == RTCP_PT_RR) { // i.e., we didn't fall through from 'SR'    // If a 'RR handler' was set, call it now:    // Specific RR handler:    if (fSpecificRRHandlerTable != NULL) {      netAddressBits fromAddr;      portNumBits fromPortNum;      if (tcpReadStreamSocketNum < 0) {// Normal case: We read the RTCP packet over UDPfromAddr = fromAddress.sin_addr.s_addr;fromPortNum = ntohs(fromAddress.sin_port);      } else {// Special case: We read the RTCP packet over TCP (interleaved)// Hack: Use the TCP socket and channel id to look up the handlerfromAddr = tcpReadStreamSocketNum;fromPortNum = tcpReadStreamChannelId;      }      Port fromPort(fromPortNum);      RRHandlerRecord* rrHandler= (RRHandlerRecord*)(fSpecificRRHandlerTable->Lookup(fromAddr, (~0), fromPort));      if (rrHandler != NULL) {if (rrHandler->rrHandlerTask != NULL) {  (*(rrHandler->rrHandlerTask))(rrHandler->rrHandlerClientData);}      }    }    // General RR handler:    if (fRRHandlerTask != NULL) (*fRRHandlerTask)(fRRHandlerClientData);  }  subPacketOK = True;  typeOfPacket = PACKET_RTCP_REPORT;  break;}        case RTCP_PT_BYE: {#ifdef DEBUG  fprintf(stderr, "BYE\n");#endif  // If a 'BYE handler' was set, arrange for it to be called at the end of this routine.  // (Note: We don't call it immediately, in case it happens to cause "this" to be deleted.)  if (fByeHandlerTask != NULL      && (!fByeHandleActiveParticipantsOnly  || (fSource != NULL      && fSource->receptionStatsDB().lookup(reportSenderSSRC) != NULL)  || (fSink != NULL      && fSink->transmissionStatsDB().lookup(reportSenderSSRC) != NULL))) {    callByeHandler = True;  }  // We should really check for & handle >1 SSRCs being present #####  subPacketOK = True;  typeOfPacket = PACKET_BYE;  break;}// Later handle SDES, APP, and compound RTCP packets #####        default:#ifdef DEBUG  fprintf(stderr, "UNSUPPORTED TYPE(0x%x)\n", pt);#endif  subPacketOK = True;  break;      }      if (!subPacketOK) break;      // need to check for (& handle) SSRC collision! ######ifdef DEBUG      fprintf(stderr, "validated RTCP subpacket (type %d): %d, %d, %d, 0x%08x\n", typeOfPacket, rc, pt, length, reportSenderSSRC);#endif      // Skip over any remaining bytes in this subpacket:      ADVANCE(length);      // Check whether another RTCP 'subpacket' follows:      if (packetSize == 0) {packetOK = True;break;      } else if (packetSize < 4) {#ifdef DEBUGfprintf(stderr, "extraneous %d bytes at end of RTCP packet!\n", packetSize);#endifbreak;      }      rtcpHdr = ntohl(*(u_int32_t*)pkt);      if ((rtcpHdr & 0xC0000000) != 0x80000000) {#ifdef DEBUGfprintf(stderr, "bad RTCP subpacket: header 0x%08x\n", rtcpHdr);#endifbreak;      }    }    if (!packetOK) {#ifdef DEBUG      fprintf(stderr, "rejected bad RTCP subpacket: header 0x%08x\n", rtcpHdr);#endif      break;    } else {#ifdef DEBUG      fprintf(stderr, "validated entire RTCP packet\n");#endif    }    onReceive(typeOfPacket, totPacketSize, reportSenderSSRC);    // Finally, if we need to call a "BYE" handler, do so now (in case it causes "this" to get deleted):    if (callByeHandler && fByeHandlerTask != NULL/*sanity check*/) {      TaskFunc* byeHandler = fByeHandlerTask;      fByeHandlerTask = NULL; // because we call the handler only once, by default      (*byeHandler)(fByeHandlerClientData);    }  } while (0);}