libcurl在上传数据之前延迟1秒，命令行curl不会 [英] libcurl delays for 1 second before uploading data, command-line curl does not

问题描述

我使用libcurl向本地服务发送一个API命令（即在127.0.0.1上）。

I am using libcurl to send an API command to a local service (i.e. on 127.0.0.1).

程序用于替换shell脚本使用 curl 程序。）

The program is intended to replace a shell script (that uses the curl program.)

一切正常，除了在某处有1秒延迟，从调用 curl_easy_perform（）到我第一次调用读回调函数的时间过去了1秒。

Everything is working, except that there is a 1-second delay somewhere, i.e 1 second elapses from the time I call curl_easy_perform() to when my read callback function is first called.

C程序使用这些选项（错误检查和回调代码省略）：

The C program is using these options (error checking & callback code omitted):

curl_easy_setopt(curl, CURLOPT_URL, "http://127.0.0.1:12345/x");
curl_easy_setopt(curl, CURLOPT_UPLOAD, 1);
curl_easy_setopt(curl, CURLOPT_INFILESIZE, (long)getLengthOfCommandObject());
curl_easy_setopt(curl, CURLOPT_READFUNCTION, &myReadFunction);
curl_easy_setopt(curl, CURLOPT_WRITEFUNCTION, &myWriteFunction);

但是如果我从shell中运行 curl 像这样：

But if I run curl from the shell like this:

$ curl --data-binary '<command>' http://127.0.0.1:12345/x

它会立即发送请求，而不会受到1秒的延迟。

it sends the request immediately, without suffering from the 1-second delay.

可能导致延迟的原因是什么，是否有可以设置的选项来阻止它？

What might be causing the delay, and is there an option I can set to prevent it?

修改服务器基于 mongoose

推荐答案

延迟的原因是：

• libcurl是发送预期：100-继续 header


• 服务器（基于 mongoose ）为未配置为发送 100继续响应自动。


• libcurl等待此响应最多1秒。

• libcurl was sending an Expect: 100-Continue header
• The server (which is based on mongoose) is not configured to send 100 Continue responses automatically.
• libcurl waits up to 1 second for this response. If it does not receive it after this time then it proceeds to send the request body anyway.

客户端的解决方案是：禁用 Expect 头，如下所示：

A solution on the client side is to disable the Expect header like so:

headers = curl_slist_append(NULL, "Expect:");
curl_easy_setopt(curl, CURLOPT_HTTPHEADER, headers);
// ...
result = curl_easy_perform(curl);
curl_slist_free_all(headers);

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