RTMP Handshake(握手协议)

RTMP流播放的流程首先要进行握手操作，才能进行后续的connect和createStream等操作, 本文简单阐述握手基础知识.

Handshake Diagram

**Handshake Diagram in Adobe’s Real Time Messaging Protocol**

wireshark分析握手基本流程

用wireshark对rtmp的包进行抓包分析:

rtmp点播流程

可以看到前三个报文是握手协议:

握手协议

从以上可看出握手的实际流程为三个步骤:

1. Client -> Server
   C0+C1
2. Server -> Client
   S0+S1+S2
3. Client -> Server
   C2
   可以看出握手的起点是Client(RMTP播放器)发送C0+C1, 结束是Server收到Client的C2.
   其中C0 C1 C2 S0 S1 S2的大小都是固定的.
   C2 S2属于用于确认(Ack)的包

Step 1: C0 + C1

C0 + C1一起发送.
其中C0一个字节, 固定为03.
C1为1536个字节.
数据包总长度为:
1 + 1536 = 1537

In C0, this field identifies the RTMP version requested by the client.
In S0, this field identifies the RTMP version selected by the server.
The version defined by this specification is 3.
0-2 are deprecated values used by earlier proprietary products;
4-31 are reserved for future implementations;
32-255 are not allowed (to allow distinguishing RTMP from text-based protocols, which always start with a printable character).

C0

C1

Step 2: S0+S1+S2

S0+S1+S2一起发送.
S0为1个字节，固定为03.
S1和S2都为1536个字节.
整个数据包总长度为:
1 + 1536 + 1536 = 3073

S0

S1

S2

Step 3: C2

C2为1536个字节.
RTMP Server接收到C2意味着握手成功结束.

C2

References:

rtmp_specification_1.0.pdf