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/**
* @file
* libavformat multi-client network API usage example.
*
* @example http_multiclient.c
* This example will serve a file without decoding or demuxing it over http.
* Multiple clients can connect and will receive the same file.
*/
//out_url是服务器  in_url是文件
av_format_network_init();//初始化网络库 只在线程安全时或者GnuTLS或者OpenSSL
av_dict_set();//设置AVDictionary
avio_open2();//打开io上下文
avio_accept();//从s服务端读取上下文到c
fork();//分成两个同样的进程 父进程pid为正数 子进程pid为0
//pid==0 	
//	process_client();单独进程
//	avio_close();关闭s上下文
//pid>0
//	avio_close();关闭c上下文

avio_close();//s
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static void process_client(AVIOContext *client, const char *in_uri)
{
    while ((ret = avio_handshake(client)) > 0) {//通过握手协议获取一个新连接
		av_opt_get(client, "resource", AV_OPT_SEARCH_CHILDREN, &resource);//获取resource属性
		if (resource && strlen(resource))//不是 ""和null
			break;
		av_freep(&resource);//释放掉
	}
    if (ret < 0)
		goto end;
	av_log(client, AV_LOG_TRACE, "resource=%p\n", resource);
	if (resource && resource[0] == '/' && !strcmp((resource + 1), in_uri)) {//检查链接合法性
		reply_code = 200;
	}
	else {
		reply_code = AVERROR_HTTP_NOT_FOUND;
	}
	if ((ret = av_opt_set_int(client, "reply_code", reply_code, AV_OPT_SEARCH_CHILDREN)) < 0) {//设置到一个子对象上的reply_code
		av_log(client, AV_LOG_ERROR, "Failed to set reply_code: %s.\n", av_err2str(ret));
		goto end;
	}
	av_log(client, AV_LOG_TRACE, "Set reply code to %d\n", reply_code);

	while ((ret = avio_handshake(client)) > 0);//正在握手 在这里等待

	if (ret < 0)
		goto end;

	fprintf(stderr, "Handshake performed.\n");
	if (reply_code != 200)
		goto end;
	fprintf(stderr, "Opening input file.\n");
	if ((ret = avio_open2(&input, in_uri, AVIO_FLAG_READ, NULL, NULL)) < 0) {//通过url创建一个io上下文
		av_log(input, AV_LOG_ERROR, "Failed to open input: %s: %s.\n", in_uri,
			av_err2str(ret));
		goto end;
	}
	for (;;) {
		n = avio_read(input, buf, sizeof(buf));//读
		if (n < 0) {
			if (n == AVERROR_EOF)
				break;
			av_log(input, AV_LOG_ERROR, "Error reading from input: %s.\n",
				av_err2str(n));
			break;
		}
		avio_write(client, buf, n);//写
		avio_flush(client);//刷新
	}
end:
	avio_flush();
	avio_close();
	avio_close();
	av_freep();
}