ret = ffurl_alloc(&whip_uc, s->url, AVIO_FLAG_READ_WRITE, &s->interrupt_callback); if (ret < 0) { av_log(s, AV_LOG_ERROR, "Failed to alloc HTTP context: %s\n", s->url); goto end; } if (!rtc->sdp_offer || !strlen(rtc->sdp_offer)) { av_log(s, AV_LOG_ERROR, "No offer to exchange\n"); ret = AVERROR(EINVAL); goto end; } snprintf(buf, sizeof(buf), "Cache-Control: no-cache\r\n" "Content-Type: application/sdp\r\n"); av_opt_set(whip_uc->priv_data, "headers", buf, 0); av_opt_set(whip_uc->priv_data, "chunked_post", "0", 0); av_opt_set_bin(whip_uc->priv_data, "post_data", rtc->sdp_offer, (int)strlen(rtc->sdp_offer), 0);怎么用上述方法改写

上述代码是使用 FFmpeg 库中的 `ffurl_alloc` 函数创建一个 HTTP 连接，并发送一个带有 SDP offer 的 POST 请求。如果你要使用 `libsoup` 库代替 FFmpeg 库，可以按照以下步骤进行修改：

1. 创建 `SoupSession` 对象

首先，需要使用 `soup_session_new` 函数创建一个 `SoupSession` 对象，它将用于发送 HTTP 请求。

SoupSession *session = soup_session_new ();

2. 创建 `SoupMessage` 对象并设置请求头和请求体

然后，需要使用 `soup_message_new` 函数创建一个 `SoupMessage` 对象，并使用 `soup_message_headers_append` 函数设置请求头。最后，使用 `soup_message_set_request` 函数设置请求体。

SoupMessage *msg = soup_message_new ("POST", s->url);
soup_message_headers_append (msg->request_headers, "Cache-Control", "no-cache");
soup_message_headers_append (msg->request_headers, "Content-Type", "application/sdp");
soup_message_set_request (msg, "application/sdp", SOUP_MEMORY_COPY, rtc->sdp_offer, strlen (rtc->sdp_offer));

3. 发送 HTTP 请求

使用 `soup_session_send_message` 函数将该消息发送到服务器，并等待响应。如果需要在发送请求时设置超时时间，可以使用 `soup_session_send_message_async` 函数。

SoupMessage *response = soup_session_send_message (session, msg);

4. 处理响应

在收到服务器的响应后，需要使用 `soup_message_body_flatten` 函数将响应体转换为字符串，并进行相应的处理。

if (SOUP_STATUS_IS_SUCCESSFUL (response->status_code)) {
  gchar *response_body = soup_message_body_flatten (response->response_body, NULL);
  // 处理响应体
  g_free (response_body);
} else {
  // 处理错误
}

最终代码如下：

#include <libsoup/soup.h>

...

int send_post_request(const char *url, const char *sdp_offer) {
    SoupSession *session = soup_session_new ();
    SoupMessage *msg = soup_message_new ("POST", url);
    soup_message_headers_append (msg->request_headers, "Cache-Control", "no-cache");
    soup_message_headers_append (msg->request_headers, "Content-Type", "application/sdp");
    soup_message_set_request (msg, "application/sdp", SOUP_MEMORY_COPY, sdp_offer, strlen (sdp_offer));
    SoupMessage *response = soup_session_send_message (session, msg);
    if (SOUP_STATUS_IS_SUCCESSFUL (response->status_code)) {
      gchar *response_body = soup_message_body_flatten (response->response_body, NULL);
      // 处理响应体
      g_free (response_body);
      return 0;
    } else {
      // 处理错误
      return -1;
    }
}