【流媒体】RTMPDump—RTMP_Connect函数（握手、网络连接）

RTMP协议相关：
【流媒体】RTMP协议概述
【流媒体】RTMP协议的数据格式
【流媒体】RTMP协议的消息类型
【流媒体】RTMPDump—主流程简单分析
【流媒体】RTMPDump—RTMP_Connect函数（握手、网络连接）
【流媒体】RTMPDump—RTMP_ConnectStream（创建流连接）
【流媒体】RTMPDump—Download（接收流媒体信息）
【流媒体】RTMPDump—AMF编码
【流媒体】基于libRTMP的H264推流器

参考雷博的系列文章（可以从一篇链接到其他文章）：
RTMPdump 源代码分析 1： main()函数

前面进行了RTMPDump主流程的分析，包括初始化和一些解析过程，现在分析RTMPDump是如何进行握手和网络连接，这是进行RTMP通信的第一步

1. RTMP_Connect函数

函数首先添加连接的地址，如果设置socksport，则使用socks连接，否则直接连接；随后，调用了RTMP_Connect0()和RTMP_Connect1()两个函数实现连接

int
RTMP_Connect(RTMP * r, RTMPPacket * cp)
{struct sockaddr_in service;if (!r->Link.hostname.av_len)return FALSE;memset(&service, 0, sizeof(struct sockaddr_in));service.sin_family = AF_INET;if (r->Link.socksport) // 如果设置了socksport，则通过socks连接{/* Connect via SOCKS */if (!add_addr_info(&service, &r->Link.sockshost, r->Link.socksport))return FALSE;}else // 否则直接连接{/* Connect directly */if (!add_addr_info(&service, &r->Link.hostname, r->Link.port))return FALSE;}// 网络层TCP连接if (!RTMP_Connect0(r, (struct sockaddr*) & service))return FALSE;r->m_bSendCounter = TRUE;// 建立RTMP连接return RTMP_Connect1(r, cp);
}

1.1 网络层连接（RTMP_Connect0）

RTMP_Connect0实现了TCP连接功能，使得client和server在网络层能够进行通信，首先使用socket()函数初始化协议为TCP，随后使用connect()进行TCP连接

int
RTMP_Connect0(RTMP * r, struct sockaddr* service)
{int on = 1;r->m_sb.sb_timedout = FALSE;r->m_pausing = 0;r->m_fDuration = 0.0;r->m_sb.sb_socket = socket(AF_INET, SOCK_STREAM, IPPROTO_TCP); // 初始化为TCP连接if (r->m_sb.sb_socket != -1){if (connect(r->m_sb.sb_socket, service, sizeof(struct sockaddr)) < 0) // 进行TCP连接{int err = GetSockError();RTMP_Log(RTMP_LOGERROR, "%s, failed to connect socket. %d (%s)",__FUNCTION__, err, strerror(err));RTMP_Close(r);return FALSE;}if (r->Link.socksport){RTMP_Log(RTMP_LOGDEBUG, "%s ... SOCKS negotiation", __FUNCTION__);if (!SocksNegotiate(r)){RTMP_Log(RTMP_LOGERROR, "%s, SOCKS negotiation failed.", __FUNCTION__);RTMP_Close(r);return FALSE;}}}else{RTMP_Log(RTMP_LOGERROR, "%s, failed to create socket. Error: %d", __FUNCTION__,GetSockError());return FALSE;}/* set timeout */{SET_RCVTIMEO(tv, r->Link.timeout);if (setsockopt(r->m_sb.sb_socket, SOL_SOCKET, SO_RCVTIMEO, (char*)& tv, sizeof(tv))){RTMP_Log(RTMP_LOGERROR, "%s, Setting socket timeout to %ds failed!",__FUNCTION__, r->Link.timeout);}}setsockopt(r->m_sb.sb_socket, IPPROTO_TCP, TCP_NODELAY, (char*)& on, sizeof(on));return TRUE;
}

1.2 RTMP连接（RTMP_Connect1）

该函数主要调用了两个函数：（1）握手（HandShake）；（2）RTMP的NetConnection（SendConnectPacket）

int
RTMP_Connect1(RTMP * r, RTMPPacket * cp)
{if (r->Link.protocol & RTMP_FEATURE_SSL){
#if defined(CRYPTO) && !defined(NO_SSL)TLS_client(RTMP_TLS_ctx, r->m_sb.sb_ssl);TLS_setfd(r->m_sb.sb_ssl, r->m_sb.sb_socket);if (TLS_connect(r->m_sb.sb_ssl) < 0){RTMP_Log(RTMP_LOGERROR, "%s, TLS_Connect failed", __FUNCTION__);RTMP_Close(r);return FALSE;}
#elseRTMP_Log(RTMP_LOGERROR, "%s, no SSL/TLS support", __FUNCTION__);RTMP_Close(r);return FALSE;#endif}if (r->Link.protocol & RTMP_FEATURE_HTTP){r->m_msgCounter = 1;r->m_clientID.av_val = NULL;r->m_clientID.av_len = 0;HTTP_Post(r, RTMPT_OPEN, "", 1);if (HTTP_read(r, 1) != 0){r->m_msgCounter = 0;RTMP_Log(RTMP_LOGDEBUG, "%s, Could not connect for handshake", __FUNCTION__);RTMP_Close(r);return 0;}r->m_msgCounter = 0;}RTMP_Log(RTMP_LOGDEBUG, "%s, ... connected, handshaking", __FUNCTION__);// 1. 握手if (!HandShake(r, TRUE)){RTMP_Log(RTMP_LOGERROR, "%s, handshake failed.", __FUNCTION__);RTMP_Close(r);return FALSE;}RTMP_Log(RTMP_LOGDEBUG, "%s, handshaked", __FUNCTION__);// 2. RTMP的NetConnectionif (!SendConnectPacket(r, cp)){RTMP_Log(RTMP_LOGERROR, "%s, RTMP connect failed.", __FUNCTION__);RTMP_Close(r);return FALSE;}return TRUE;
}

1.2.1 握手（HandShake）

握手是RTMP协议实现的第一个步骤，需要重点分析。值得一提的是，在雷博记录的文章当中（RTMPdump（libRTMP）源代码分析 4： 连接第一步——握手（Hand Shake）），记录的应该是包含加密过程的握手函数，不包含加密过程的握手函数应该在rtmp.c中

前面自己记录的关于握手过程的文章为【流媒体】RTMP协议概述，握手的流程为

RTMPDump中关于非加密握手的代码，如下所示

static int
HandShake(RTMP * r, int FP9HandShake)
{int i;uint32_t uptime, suptime;int bMatch;char type;// clientbuf当中包含了C0和C1数据报，并且同时发出去char clientbuf[RTMP_SIG_SIZE + 1], *clientsig = clientbuf + 1; // RTMP_SIG_SIZE = 1536char serversig[RTMP_SIG_SIZE];// 1. C0数据报// 0x03表示客户端所期望的版本号，即C0clientbuf[0] = 0x03;		/* not encrypted */// 2. C1数据报// 获取当前的timestamp并且转换成为大端存储uptime = htonl(RTMP_GetTime());// 将时间戳拷贝到clientsig当中memcpy(clientsig, &uptime, 4);// 填充4个字节的0值memset(&clientsig[4], 0, 4);#ifdef _DEBUGfor (i = 8; i < RTMP_SIG_SIZE; i++)clientsig[i] = 0xff;
#elsefor (i = 8; i < RTMP_SIG_SIZE; i++) // 填充1536 - 8 = 1528个随机字节clientsig[i] = (char)(rand() % 256);
#endif// 3. 发送C0和C1数据报if (!WriteN(r, clientbuf, RTMP_SIG_SIZE + 1))return FALSE;// 4. 接收S0数据报，即server返回的可以使用的RTMP版本号if (ReadN(r, &type, 1) != 1)	/* 0x03 or 0x06 */return FALSE;RTMP_Log(RTMP_LOGDEBUG, "%s: Type Answer   : %02X", __FUNCTION__, type);// 检查client期望的RTMP版本号是否与server所支持的RTMP版本号匹配if (type != clientbuf[0])RTMP_Log(RTMP_LOGWARNING, "%s: Type mismatch: client sent %d, server answered %d",__FUNCTION__, clientbuf[0], type);// 5. 接收S1数据报if (ReadN(r, serversig, RTMP_SIG_SIZE) != RTMP_SIG_SIZE)return FALSE;/* decode server response */// 解析接收数据报时间戳memcpy(&suptime, serversig, 4);suptime = ntohl(suptime);RTMP_Log(RTMP_LOGDEBUG, "%s: Server Uptime : %d", __FUNCTION__, suptime);RTMP_Log(RTMP_LOGDEBUG, "%s: FMS Version   : %d.%d.%d.%d", __FUNCTION__,serversig[4], serversig[5], serversig[6], serversig[7]);/* 2nd part of handshake */// 6. 发送C2数据报// 发送出去的C2数据报就是接收到的S1数据报if (!WriteN(r, serversig, RTMP_SIG_SIZE))return FALSE;// 7. 读取S2数据报if (ReadN(r, serversig, RTMP_SIG_SIZE) != RTMP_SIG_SIZE)return FALSE;// 检查S2数据报和C1数据报的timestamp是否匹配bMatch = (memcmp(serversig, clientsig, RTMP_SIG_SIZE) == 0);if (!bMatch){RTMP_Log(RTMP_LOGWARNING, "%s, client signature does not match!", __FUNCTION__);}return TRUE;
}

代码基本就是按照标准来写的，唯一需要注意的是C0和C1数据报是同时发送的，C0和C1都存储在clientbuf当中

1.2.2 RTMP的NetConnection（SendConnectPacket）

该函数的主要作用是进行NetConnection，再回顾一下NetConnection的流程图

从流程图中看，client在进行握手成功之后，会向server发送一个 “connect” 的命令，申请进行RTMP连接，而SendConnectPacket实现的功能就是发送一个 “connect” 的命令。另外，也回顾一下connect命令当中可以携带的参数，这些参数在SendConnectPacket当中都有考虑到

RTMPDump会定义所需要使用的命令，例如connect命令会被定义成为 av_connect，如下所示

#define AVC(str)	{str,sizeof(str)-1}
#define SAVC(x)	static const AVal av_##x = AVC(#x)// connect 命令中使用的名值对对象的描述
SAVC(app);
SAVC(connect);	// connect命令，{"connet", sizeof(connect) - 1}
SAVC(flashVer);
SAVC(swfUrl);
SAVC(pageUrl);
SAVC(tcUrl);
SAVC(fpad);
SAVC(capabilities);
SAVC(audioCodecs);
SAVC(videoCodecs);
SAVC(videoFunction);
SAVC(objectEncoding);
SAVC(secureToken);
SAVC(secureTokenResponse);
SAVC(type);
SAVC(nonprivate);

SendConnectPacket函数用于发送一个connect命令，会写入connect当中可能会写入的参数，随后使用RTMP_SendPacket()将信息发送出去

static int
SendConnectPacket(RTMP * r, RTMPPacket * cp)
{RTMPPacket packet;// pend是尾缀char pbuf[4096], * pend = pbuf + sizeof(pbuf);char* enc;if (cp)return RTMP_SendPacket(r, cp, TRUE);// 块流ID设置为3（似乎在标准文档中没有说是多少?）packet.m_nChannel = 0x03;	/* control channel (invoke) *//*#define RTMP_PACKET_SIZE_LARGE    0			// #define RTMP_PACKET_SIZE_MEDIUM   1			// #define RTMP_PACKET_SIZE_SMALL    2			// #define RTMP_PACKET_SIZE_MINIMUM  3			//*/packet.m_headerType = RTMP_PACKET_SIZE_LARGE;	// m_headerType对应于Basic Header中的fmt// RTMP_PACKET_TYPE_INVOKE = 0x14 = 20，表明这是一条命令消息，并且以AMF0的格式进行编码packet.m_packetType = RTMP_PACKET_TYPE_INVOKE;	// m_packetType对应于Messge Header中的message type idpacket.m_nTimeStamp = 0;packet.m_nInfoField2 = 0;packet.m_hasAbsTimestamp = 0;packet.m_body = pbuf + RTMP_MAX_HEADER_SIZE;	// body = 4096 - 18enc = packet.m_body;/*+-----------------+-----------+-------------+------------+------------| RTMP Max Header | Data Type | Data Length | Data Value | 	  xxx|    (18 Bytes)   | (1 Bytes) | (x Bytes)   | (L Bytes)  | (.. Bytes) +-----------------+-----------+-------------+------------+------------pbuf              enc         (packet.m_body)*/// 下面会写入packet.m_body的信息，这些信息用于connect// av_connect = { "connect", sizeof("connect") - 1 };enc = AMF_EncodeString(enc, pend, &av_connect); // 将connect命令写入到enc中enc = AMF_EncodeNumber(enc, pend, ++r->m_numInvokes); // 将呼叫的次数写入到enc中*enc++ = AMF_OBJECT; // 写入data类型为object// 写入app信息enc = AMF_EncodeNamedString(enc, pend, &av_app, &r->Link.app);if (!enc)return FALSE;if (r->Link.protocol & RTMP_FEATURE_WRITE){enc = AMF_EncodeNamedString(enc, pend, &av_type, &av_nonprivate);if (!enc)return FALSE;}if (r->Link.flashVer.av_len){enc = AMF_EncodeNamedString(enc, pend, &av_flashVer, &r->Link.flashVer);if (!enc)return FALSE;}if (r->Link.swfUrl.av_len){enc = AMF_EncodeNamedString(enc, pend, &av_swfUrl, &r->Link.swfUrl);if (!enc)return FALSE;}if (r->Link.tcUrl.av_len){enc = AMF_EncodeNamedString(enc, pend, &av_tcUrl, &r->Link.tcUrl);if (!enc)return FALSE;}if (!(r->Link.protocol & RTMP_FEATURE_WRITE)){enc = AMF_EncodeNamedBoolean(enc, pend, &av_fpad, FALSE);if (!enc)return FALSE;enc = AMF_EncodeNamedNumber(enc, pend, &av_capabilities, 15.0);if (!enc)return FALSE;enc = AMF_EncodeNamedNumber(enc, pend, &av_audioCodecs, r->m_fAudioCodecs);if (!enc)return FALSE;enc = AMF_EncodeNamedNumber(enc, pend, &av_videoCodecs, r->m_fVideoCodecs);if (!enc)return FALSE;enc = AMF_EncodeNamedNumber(enc, pend, &av_videoFunction, 1.0);if (!enc)return FALSE;if (r->Link.pageUrl.av_len){enc = AMF_EncodeNamedString(enc, pend, &av_pageUrl, &r->Link.pageUrl);if (!enc)return FALSE;}}if (r->m_fEncoding != 0.0 || r->m_bSendEncoding){	/* AMF0, AMF3 not fully supported yet */enc = AMF_EncodeNamedNumber(enc, pend, &av_objectEncoding, r->m_fEncoding);if (!enc)return FALSE;}if (enc + 3 >= pend)return FALSE;*enc++ = 0;*enc++ = 0;			/* end of object - 0x00 0x00 0x09 */*enc++ = AMF_OBJECT_END; // 写完object/* add auth string */// 写认证信息if (r->Link.auth.av_len){enc = AMF_EncodeBoolean(enc, pend, r->Link.lFlags & RTMP_LF_AUTH);if (!enc)return FALSE;enc = AMF_EncodeString(enc, pend, &r->Link.auth);if (!enc)return FALSE;}if (r->Link.extras.o_num){int i;for (i = 0; i < r->Link.extras.o_num; i++){enc = AMFProp_Encode(&r->Link.extras.o_props[i], enc, pend);if (!enc)return FALSE;}}packet.m_nBodySize = enc - packet.m_body;return RTMP_SendPacket(r, &packet, TRUE);
}

RTMP_SendPacket()的实现如下所示，基本就是按照标准文档来写入chunk信息并发送，关键位置有注释，大体的步骤为：
（1）确定头信息内容
 （a）确定message header size
 （b）确定basic header size
 （c）确定extended timestamp
（2）写入头信息内容
 （a）写入basic header
 （b）写入message header中的timestamp（3字节）
 （c）写入bodySize（即msg length）（3字节）
 （d）写入packetType（即msg type id）（1字节）
 （e）写入最后4字节（即message stram id）（4字节）
 （f）写入扩展的时间戳（4字节）
（3）发送信息

关于代码的实现，这里有一个小点：

在代码中，是以chunk的格式来存储所有格式的，而不是以message的格式，但最后还有一个分包的操作。按理来说，以message格式存储才需要分包，这里相当于是把一个大的chunk分成了多个小的chunk来发送了

int
RTMP_SendPacket(RTMP * r, RTMPPacket * packet, int queue)
{const RTMPPacket* prevPacket;uint32_t last = 0;int nSize;int hSize, cSize;char* header, * hptr, * hend, hbuf[RTMP_MAX_HEADER_SIZE], c;uint32_t t;char* buffer, * tbuf = NULL, * toff = NULL;int nChunkSize;int tlen;// 检查channel数量if (packet->m_nChannel >= r->m_channelsAllocatedOut){int n = packet->m_nChannel + 10;RTMPPacket** packets = realloc(r->m_vecChannelsOut, sizeof(RTMPPacket*) * n);if (!packets) {free(r->m_vecChannelsOut);r->m_vecChannelsOut = NULL;r->m_channelsAllocatedOut = 0;return FALSE;}r->m_vecChannelsOut = packets;memset(r->m_vecChannelsOut + r->m_channelsAllocatedOut, 0, sizeof(RTMPPacket*) * (n - r->m_channelsAllocatedOut));r->m_channelsAllocatedOut = n;}prevPacket = r->m_vecChannelsOut[packet->m_nChannel];/*Chunk Format:+--------------+----------------+--------------------+-----------------| Basic Header | Message Header | Extended Timestamp | Chunk Data....+--------------+----------------+--------------------+-----------------|<----------------- Chunk Header ------------------->|(1) Basic Header(a) type 10 1 2 3 4 5 6 7+---------------+|fmt|  cs id    | +---------------+(b) type 20				10 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 +---------------+-------------+|fmt|     0     | cs id - 64  |+---------------+-------------+(c) type 30				1               20 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 +---------------+------------------------------+|fmt|     1     |         cs id - 64           |+---------------+------------------------------+(2) Message Header(a) type 0 (11 bytes)0				1               2               30 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+----------------------------------------------+---------------+|					timestamp				   | message length|+----------------------------------------------+---------------+|    message length (cont)    |	message type id| msg stream id |+----------------------------------------------+---------------+|		     message stream id(cont)		   |+----------------------------------------------+(b) type 1 (7 bytes)0				1               2               30 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+----------------------------------------------+---------------+|			     timestamp delta		       | message length|+----------------------------------------------+---------------+|    message length (cont)    |	message type id|+----------------------------------------------+(c) type 2 (3 bytes)0				1               2               0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 +----------------------------------------------+|			     timestamp delta		       |+----------------------------------------------+(d) type 3 (no message header)*/// 1. 确定头信息内容// m_headerType对应于BasicHeader中的fmt字段，表示后续msg的格式// m_packetType对应于Message Header中的message type id，表示消息的类型if (prevPacket && packet->m_headerType != RTMP_PACKET_SIZE_LARGE){// 前面packet的数据是否和当前packet数据有相同之处，如果有，则去掉当前packet的冗余信息/* compress a bit by using the prev packet's attributes */if (prevPacket->m_nBodySize == packet->m_nBodySize&& prevPacket->m_packetType == packet->m_packetType&& packet->m_headerType == RTMP_PACKET_SIZE_MEDIUM)packet->m_headerType = RTMP_PACKET_SIZE_SMALL;if (prevPacket->m_nTimeStamp == packet->m_nTimeStamp&& packet->m_headerType == RTMP_PACKET_SIZE_SMALL)packet->m_headerType = RTMP_PACKET_SIZE_MINIMUM;last = prevPacket->m_nTimeStamp;}if (packet->m_headerType > 3)	/* sanity */{RTMP_Log(RTMP_LOGERROR, "sanity failed!! trying to send header of type: 0x%02x.",(unsigned char)packet->m_headerType);return FALSE;}// static const int packetSize[] = { 12, 8, 4, 1 };/*问：标准当中的msg header size为11, 7, 3, 0，为什么在这里加1？答：RTMP数据报中包括Basic Header、Message Header和Chunk Data，其中Basic Header由fmt和chunk stream id组成，fmt占据2比特，chunk stream id指示当前chunk在当前stream当中位于第几个位置，如果是 (2, 63]，则为1字节，这样packetSize就加1*/// nSize : message header size// (1.a) 确定message header sizenSize = packetSize[packet->m_headerType];hSize = nSize; cSize = 0;t = packet->m_nTimeStamp - last;if (packet->m_body){header = packet->m_body - nSize; // header起始地址hend = packet->m_body; // header结束地址}else{header = hbuf + 6;	// header size = 6hend = hbuf + sizeof(hbuf);}/*stream_id的范围给出了chunk basic header的大小+------------+--------------+|	range	 |	   Bytes	|+------------+--------------+|  (2, 63]	 |	 1  byte	|+------------+--------------+| (63, 319]	 |	 2  Bytes	|+------------+--------------+|(319, 65599]|	 3  Bytes	|+------------+--------------+*/// chunk stream id的检查// cSize描述Basic header的大小// (1.b) 确定basic header sizeif (packet->m_nChannel > 319)cSize = 2;  // chunk basic header为3个字节else if (packet->m_nChannel > 63)cSize = 1;	// chunk basic header为2个字节if (cSize){header -= cSize;hSize += cSize;}// (1.c) 确定extended timestampif (t >= 0xffffff) // 时间戳过大，需要增加额外的extended timestamp{header -= 4;hSize += 4;RTMP_Log(RTMP_LOGWARNING, "Larger timestamp than 24-bit: 0x%x", t);}// 2. 写入头信息hptr = header;c = packet->m_headerType << 6; // 高2位设置为fmtswitch (cSize){// 低6位设置成为stream idcase 0:c |= packet->m_nChannel;break;case 1:break;case 2:c |= 1;break;}// (2.a) 写入basic header*hptr++ = c;// 如果cSize不为0，说明chunk basic header为2字节或者3字节，需要写入0值或者1值if (cSize){int tmp = packet->m_nChannel - 64;*hptr++ = tmp & 0xff;if (cSize == 2)* hptr++ = tmp >> 8;}// (2.b) 写入message header中的timestamp，3字节if (nSize > 1){// 用于编码24位整数值，将其从主机字节序转换为AMF格式所使用的网络字节序hptr = AMF_EncodeInt24(hptr, hend, t > 0xffffff ? 0xffffff : t);}if (nSize > 4){// (2.c) 写入bodySize(msg length)，3字节hptr = AMF_EncodeInt24(hptr, hend, packet->m_nBodySize);// (2.d) 写入packetType(msg type id)，1字节*hptr++ = packet->m_packetType;}// (2.e) 写入最后4字节 (message stram id)if (nSize > 8) // 将一个整数以小端序（little-endian）的方式进行编码为32位的整数hptr += EncodeInt32LE(hptr, packet->m_nInfoField2);// (2.f) 写入扩展的时间戳，4字节if (t >= 0xffffff) // 用于编码32位整数值hptr = AMF_EncodeInt32(hptr, hend, t);nSize = packet->m_nBodySize;buffer = packet->m_body;nChunkSize = r->m_outChunkSize;	// 默认的chunk大小为128个字节RTMP_Log(RTMP_LOGDEBUG2, "%s: fd=%d, size=%d", __FUNCTION__, r->m_sb.sb_socket,nSize);/* send all chunks in one HTTP request */if (r->Link.protocol & RTMP_FEATURE_HTTP){int chunks = (nSize + nChunkSize - 1) / nChunkSize;if (chunks > 1){tlen = chunks * (cSize + 1) + nSize + hSize;tbuf = malloc(tlen);if (!tbuf)return FALSE;toff = tbuf;}}// 3. 发送消息// 前面已经将所需要的信息写入到了packet中，现在需要将packet分成多个chunk发送出去while (nSize + hSize) // nSize = bodySize, hSize = headerSize;{int wrote;if (nSize < nChunkSize) // 当前剩余的size，不需要分成多个chunknChunkSize = nSize;RTMP_LogHexString(RTMP_LOGDEBUG2, (uint8_t*)header, hSize);RTMP_LogHexString(RTMP_LOGDEBUG2, (uint8_t*)buffer, nChunkSize);if (tbuf){memcpy(toff, header, nChunkSize + hSize);toff += nChunkSize + hSize;}else{// 发出信息，大小为nChunkSize + hSize // nChunkSize默认为128字节wrote = WriteN(r, header, nChunkSize + hSize);if (!wrote)return FALSE;}// 更新sizenSize -= nChunkSize;buffer += nChunkSize;hSize = 0;	// 第一次就会把header中的信息全部发完if (nSize > 0) // 还有消息没有发送完，需要将剩余的信息打包成为chunk，用于后续的发送{header = buffer - 1;hSize = 1;// 重新处理头部信息if (cSize){header -= cSize;hSize += cSize;}if (t >= 0xffffff){header -= 4;hSize += 4;}// 取出c中的前2位，即fmt信息*header = (0xc0 | c); // 0xc0 : 1100 0000if (cSize){int tmp = packet->m_nChannel - 64;header[1] = tmp & 0xff;if (cSize == 2)header[2] = tmp >> 8;}if (t >= 0xffffff){char* extendedTimestamp = header + 1 + cSize;AMF_EncodeInt32(extendedTimestamp, extendedTimestamp + 4, t);}}}if (tbuf){int wrote = WriteN(r, tbuf, toff - tbuf);free(tbuf);tbuf = NULL;if (!wrote)return FALSE;}/* we invoked a remote method */if (packet->m_packetType == RTMP_PACKET_TYPE_INVOKE){AVal method;char* ptr;ptr = packet->m_body + 1;AMF_DecodeString(ptr, &method);RTMP_Log(RTMP_LOGDEBUG, "Invoking %s", method.av_val);/* keep it in call queue till result arrives */if (queue) {int txn;ptr += 3 + method.av_len;txn = (int)AMF_DecodeNumber(ptr);AV_queue(&r->m_methodCalls, &r->m_numCalls, &method, txn);}}// 存储前面发送的packetif (!r->m_vecChannelsOut[packet->m_nChannel])r->m_vecChannelsOut[packet->m_nChannel] = malloc(sizeof(RTMPPacket));memcpy(r->m_vecChannelsOut[packet->m_nChannel], packet, sizeof(RTMPPacket));return TRUE;
}

2.小结

记录了RTMPDump中如何以client的视角与对端server建立连接的过程，分为几个步骤：
（1）建立socket连接
（2）建立RTMP连接
 （a）握手
 （b）RTMP的网络连接（会发送connect命令）
基于此，RTMPDump的client就与server进行了正式的连接，后续可以进行互相传输信息了