写在前面
此系列只追求精简，旨在学习RTSP协议的实现过程，不追求复杂完美，所以这里要实现的RTSP服务器为了简单，实现上同一时间只能有一个客户端，下面开始介绍实现过程
在写一个RTSP服务器之前，我们必须知道一个RTSP服务器最简单的包含两部分，一部分是RTSP的交互，一部分是RTP发送，本文先实现RTSP交互过程
一、创建套接字
想一下我们在vlc输入rtsp://127.0.0.1:8554后发生了什么事？
在这种情况下，vlc其实是一个rtsp客户端，当输入这个url后，vlc知道目的IP为127.0.0.1，目的端口号为8854，这时vlc会发起一个tcp连接取连接服务器，连接成功后就开始发送请求，服务端响应
所以我们要写一个rtsp服务器，第一步肯定是创建tcp服务器
首先创建tcp套接字，绑定端口，监听
//1.创建套接字
serverSockfd = socket(AF_INET, SOCK_STREAM, 0);
setsockopt(serverSockfd, SOL_SOCKET, SO_REUSEADDR, (const char*)&on, sizeof(on));
//2.绑定地址和端口号 这个示例绑定的地址是INADDR_ANY，端口号为8554
bind(serverSockfd, (struct sockaddr *)&addr, sizeof(struct sockaddr)
//3.开始监听
listen(serverSockfd, 10);
RTSP服务器传输音视频数据和信息使用的是RTP和RTCP，所以我们还要为RTP和RTCP创建UDP套接字，并绑定号端口
//1.创建套接字
serverRtpSockfd = createUdpSocket();
serverRtcpSockfd = createUdpSocket();
//2.绑定端口号 当创建好套接字还有绑定号端口后，就可以接收客户端请求了
bindSocketAddr(serverRtpSockfd, "0.0.0.0", SERVER_RTP_PORT);
bindSocketAddr(serverRtcpSockfd, "0.0.0.0", SERVER_RTCP_PORT);
//3.开始accept等待客户端连接
clientfd = accept(serverSockfd, (struct sockaddr *)&addr, &len);
二、解析请求
当rtsp客户端连接成功后就会开始发送请求，服务器这是需要接收客户端请求并开始解析，再采取相应得操作
这里我们做得最简单，首先解析第一行得到方法，对于OPTIONS、DESCRIBE、PLAY、TEARDOWN我们只解析CSeq。对于SETUP，我们讲client_port解析出来
所以我们要做的第一步就是解析请求中的信息
解析完请求命令后，接下来就是更具不同得方法做不同的响应了，如下
/*
* 作者：_JT_
* 博客：https://blog.csdn.net/weixin_42462202
*/
if(!strcmp(method, "OPTIONS"))
{
handleCmd_OPTIONS();
}
else if(!strcmp(method, "DESCRIBE"))
{
handleCmd_DESCRIBE();
}
else if(!strcmp(method, "SETUP"))
{
handleCmd_SETUP();
}
else if(!strcmp(method, "PLAY"))
{
handleCmd_PLAY();
}
else if(!strcmp(method, "TEARDOWN"))
{
handleCmd_TEARDOWN();
}
三、OPTIONS响应
OPTIONS是客户端向服务端请求可用的方法，我们这里就向客户端回复我们当前可用的方法
sprintf(sBuf, "RTSP/1.0 200 OK\r\n"
"CSeq: %d\r\n"
"Public: OPTIONS, DESCRIBE, SETUP, PLAY\r\n"
"\r\n",
cseq);
send(clientSockfd, sBuf, strlen(sBuf));
四、DESCRIBE响应
DESCRIBE是客户端向服务器请求媒体信息，这是服务器需要回复sdp描述文件，这个例子中的媒体是H.264
-
sdp文件生成
sprintf(sdp, "v=0\r\n"
"o=- 9%ld 1 IN IP4 %s\r\n"
"t=0 0\r\n"
"a=control:*\r\n"
"m=video 0 RTP/AVP 96\r\n"
"a=rtpmap:96 H264/90000\r\n"
"a=control:track0\r\n",
time(NULL), localIp);
回复
sprintf(sBuf, "RTSP/1.0 200 OK\r\n"
"CSeq: %d\r\n"
"Content-Base: %s\r\n"
"Content-type: application/sdp\r\n"
"Content-length: %d\r\n\r\n"
"%s",
cseq,
url,
strlen(sdp),
sdp);
send(clientSockfd, sBuf, strlen(sBuf));
五、SETUP响应
SETUP是客户端请求建立会话连接，并发送了客户端的RTP端口和RTCP端口，那么此时服务端需要回复服务端的RTP端口和RTCP端口
六、PLAY响应
PLAY时客户端向服务器请求播放，这时服务端回复完请求后就开始通过setup过程中创建的udp套接字发送RTP包
七、源码
#include <stdio.h>
#include <stdlib.h>
#include <stdint.h>
#include <string.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <time.h>
#define SERVER_PORT 8554
#define SERVER_RTP_PORT 55532
#define SERVER_RTCP_PORT 55533
#define BUF_MAX_SIZE (1024*1024)
static int createTcpSocket()
{
int sockfd;
int on = 1;
sockfd = socket(AF_INET, SOCK_STREAM, 0);
if(sockfd < 0)
return -1;
setsockopt(sockfd, SOL_SOCKET, SO_REUSEADDR, (const char*)&on, sizeof(on));
return sockfd;
}
static int createUdpSocket()
{
int sockfd;
int on = 1;
sockfd = socket(AF_INET, SOCK_DGRAM, 0);
if(sockfd < 0)
return -1;
setsockopt(sockfd, SOL_SOCKET, SO_REUSEADDR, (const char*)&on, sizeof(on));
return sockfd;
}
static int bindSocketAddr(int sockfd, const char* ip, int port)
{
struct sockaddr_in addr;
addr.sin_family = AF_INET;
addr.sin_port = htons(port);
addr.sin_addr.s_addr = inet_addr(ip);
if(bind(sockfd, (struct sockaddr *)&addr, sizeof(struct sockaddr)) < 0)
return -1;
return 0;
}
static int acceptClient(int sockfd, char* ip, int* port)
{
int clientfd;
socklen_t len = 0;
struct sockaddr_in addr;
memset(&addr, 0, sizeof(addr));
len = sizeof(addr);
clientfd = accept(sockfd, (struct sockaddr *)&addr, &len);
if(clientfd < 0)
return -1;
strcpy(ip, inet_ntoa(addr.sin_addr));
*port = ntohs(addr.sin_port);
return clientfd;
}
static char* getLineFromBuf(char* buf, char* line)
{
while(*buf != '\n')
{
*line = *buf;
line++;
buf++;
}
*line = '\n';
++line;
*line = '\0';
++buf;
return buf;
}
static int handleCmd_OPTIONS(char* result, int cseq)
{
sprintf(result, "RTSP/1.0 200 OK\r\n"
"CSeq: %d\r\n"
"Public: OPTIONS, DESCRIBE, SETUP, PLAY\r\n"
"\r\n",
cseq);
return 0;
}
static int handleCmd_DESCRIBE(char* result, int cseq, char* url)
{
char sdp[500];
char localIp[100];
sscanf(url, "rtsp://%[^:]:", localIp);
sprintf(sdp, "v=0\r\n"
"o=- 9%ld 1 IN IP4 %s\r\n"
"t=0 0\r\n"
"a=control:*\r\n"
"m=video 0 RTP/AVP 96\r\n"
"a=rtpmap:96 H264/90000\r\n"
"a=control:track0\r\n",
time(NULL), localIp);
sprintf(result, "RTSP/1.0 200 OK\r\nCSeq: %d\r\n"
"Content-Base: %s\r\n"
"Content-type: application/sdp\r\n"
"Content-length: %d\r\n\r\n"
"%s",
cseq,
url,
strlen(sdp),
sdp);
return 0;
}
static int handleCmd_SETUP(char* result, int cseq, int clientRtpPort)
{
sprintf(result, "RTSP/1.0 200 OK\r\n"
"CSeq: %d\r\n"
"Transport: RTP/AVP;unicast;client_port=%d-%d;server_port=%d-%d\r\n"
"Session: 66334873\r\n"
"\r\n",
cseq,
clientRtpPort,
clientRtpPort+1,
SERVER_RTP_PORT,
SERVER_RTCP_PORT);
return 0;
}
static int handleCmd_PLAY(char* result, int cseq)
{
sprintf(result, "RTSP/1.0 200 OK\r\n"
"CSeq: %d\r\n"
"Range: npt=0.000-\r\n"
"Session: 66334873; timeout=60\r\n\r\n",
cseq);
return 0;
}
static void doClient(int clientSockfd, const char* clientIP, int clientPort,
int serverRtpSockfd, int serverRtcpSockfd)
{
char method[40];
char url[100];
char version[40];
int cseq;
int clientRtpPort, clientRtcpPort;
char *bufPtr;
char* rBuf = malloc(BUF_MAX_SIZE);
char* sBuf = malloc(BUF_MAX_SIZE);
char line[400];
while(1)
{
int recvLen;
recvLen = recv(clientSockfd, rBuf, BUF_MAX_SIZE, 0);
if(recvLen <= 0)
goto out;
rBuf[recvLen] = '\0';
printf("---------------C->S--------------\n");
printf("%s", rBuf);
/* 解析方法 */
bufPtr = getLineFromBuf(rBuf, line);
if(sscanf(line, "%s %s %s\r\n", method, url, version) != 3)
{
printf("parse err\n");
goto out;
}
/* 解析序列号 */
bufPtr = getLineFromBuf(bufPtr, line);
if(sscanf(line, "CSeq: %d\r\n", &cseq) != 1)
{
printf("parse err\n");
goto out;
}
/* 如果是SETUP，那么就再解析client_port */
if(!strcmp(method, "SETUP"))
{
while(1)
{
bufPtr = getLineFromBuf(bufPtr, line);
if(!strncmp(line, "Transport:", strlen("Transport:")))
{
sscanf(line, "Transport: RTP/AVP;unicast;client_port=%d-%d\r\n",
&clientRtpPort, &clientRtcpPort);
break;
}
}
}
if(!strcmp(method, "OPTIONS"))
{
if(handleCmd_OPTIONS(sBuf, cseq))
{
printf("failed to handle options\n");
goto out;
}
}
else if(!strcmp(method, "DESCRIBE"))
{
if(handleCmd_DESCRIBE(sBuf, cseq, url))
{
printf("failed to handle describe\n");
goto out;
}
}
else if(!strcmp(method, "SETUP"))
{
if(handleCmd_SETUP(sBuf, cseq, clientRtpPort))
{
printf("failed to handle setup\n");
goto out;
}
}
else if(!strcmp(method, "PLAY"))
{
if(handleCmd_PLAY(sBuf, cseq))
{
printf("failed to handle play\n");
goto out;
}
}
else
{
goto out;
}
printf("---------------S->C--------------\n");
printf("%s", sBuf);
send(clientSockfd, sBuf, strlen(sBuf), 0);
}
out:
close(clientSockfd);
free(rBuf);
free(sBuf);
}
int main(int argc, char* argv[])
{
int serverSockfd;
int serverRtpSockfd, serverRtcpSockfd;
int ret;
serverSockfd = createTcpSocket();
if(serverSockfd < 0)
{
printf("failed to create tcp socket\n");
return -1;
}
ret = bindSocketAddr(serverSockfd, "0.0.0.0", SERVER_PORT);
if(ret < 0)
{
printf("failed to bind addr\n");
return -1;
}
ret = listen(serverSockfd, 10);
if(ret < 0)
{
printf("failed to listen\n");
return -1;
}
serverRtpSockfd = createUdpSocket();
serverRtcpSockfd = createUdpSocket();
if(serverRtpSockfd < 0 || serverRtcpSockfd < 0)
{
printf("failed to create udp socket\n");
return -1;
}
if(bindSocketAddr(serverRtpSockfd, "0.0.0.0", SERVER_RTP_PORT) < 0 ||
bindSocketAddr(serverRtcpSockfd, "0.0.0.0", SERVER_RTCP_PORT) < 0)
{
printf("failed to bind addr\n");
return -1;
}
printf("rtsp://127.0.0.1:%d\n", SERVER_PORT);
while(1)
{
int clientSockfd;
char clientIp[40];
int clientPort;
clientSockfd = acceptClient(serverSockfd, clientIp, &clientPort);
if(clientSockfd < 0)
{
printf("failed to accept client\n");
return -1;
}
printf("accept client;client ip:%s,client port:%d\n", clientIp, clientPort);
doClient(clientSockfd, clientIp, clientPort, serverRtpSockfd, serverRtcpSockfd);
}
return 0;
}
八、测试
编译运行源码，打开vlc，输入rtsp://127.0.0.1:8554，点击开始播放，可以看到控制台会打印出交互过程，或是用wireshak抓包
本篇文章到这里结束，至此完成了RTSP协议的交互部分，在PLAY之后并没有开始发送RTP包，所以暂时还看不到视频，究竟如何发送RTP包，请看下一篇文章
