Libcurl C++使用multi接口获取HTTP响应码返回0的排查求助

问题根因 #

CURLINFO_RESPONSE_CODE是请求执行完成后才会被填充的属性，你将读取响应码的逻辑放在了setup函数中——此时刚初始化easy handle，还没发送请求、也没有收到服务端响应，拿到的自然是默认初始化值0。

修复方案 #

调整curl_easy_getinfo的调用时机到所有请求执行完成之后、easy handle清理之前即可。

修改后完整代码 #

#include <iostream>
#include <stdlib.h>
#include <string.h>
#include <errno.h>

#include <sys/time.h>
#include <unistd.h>
#include <curl/curl.h>
#include <curl/mprintf.h>

#ifndef CURLPIPE_MULTIPLEX
#define CURLPIPE_MULTIPLEX 0
#endif

struct transfer {
        CURL *easy;
        unsigned int num;
        FILE *out;
};

#define NUM_HANDLES 1000

size_t write_data(void *buffer, size_t size, size_t nmemb, void *userp)
{
        return size * nmemb;
}

static void setup(struct transfer *t, int num)
{
        CURL *hnd;
        hnd = t->easy = curl_easy_init();

        /* set the same URL */
        curl_easy_setopt(hnd, CURLOPT_URL, "https://httpstat.us/200");


        curl_easy_setopt(hnd, CURLOPT_WRITEFUNCTION, write_data);

        /* HTTP/2 please */
        curl_easy_setopt(hnd, CURLOPT_HTTP_VERSION, CURL_HTTP_VERSION_2_0);

        /* we use a self-signed test server, skip verification during debugging */
        curl_easy_setopt(hnd, CURLOPT_SSL_VERIFYPEER, 0L);
        curl_easy_setopt(hnd, CURLOPT_SSL_VERIFYHOST, 0L);

        #if (CURLPIPE_MULTIPLEX > 0)
        /* wait for pipe connection to confirm */
        curl_easy_setopt(hnd, CURLOPT_PIPEWAIT, 1L);
        #endif
}

int main(int argc, char **argv)
{
        struct transfer trans[NUM_HANDLES];
        CURLM *multi_handle;
        int i;
        int still_running = 0; /* keep number of running handles */
        int num_transfers;

        if(argc > 1) {
        /* if given a number, do that many transfers */
        num_transfers = atoi(argv[1]);
        if((num_transfers < 1) || (num_transfers > NUM_HANDLES))
                num_transfers = 3; /* a suitable low default */
        }
        else
                num_transfers = 3; /* suitable default */

        /* init a multi stack */
        multi_handle = curl_multi_init();
        for(i = 0; i < num_transfers; i++) {
                setup(&trans[i], i);

                /* add the individual transfer */
                curl_multi_add_handle(multi_handle, trans[i].easy);
        }
        curl_multi_setopt(multi_handle, CURLMOPT_PIPELINING, CURLPIPE_MULTIPLEX);

        do {
                CURLMcode mc = curl_multi_perform(multi_handle, &still_running);

                if(still_running)
                        /* wait for activity, timeout or "nothing" */
                        mc = curl_multi_poll(multi_handle, NULL, 0, 1000, NULL);

                if(mc)
                        break;
        } while(still_running);

        // 所有请求执行完成后读取响应码
        for(i = 0; i < num_transfers; i++) {
                long response_code;
                curl_easy_getinfo(trans[i].easy, CURLINFO_RESPONSE_CODE, &response_code);
                std::cout << "请求" << i+1 << " RESPONSE CODE: " << response_code << std::endl;
        }

        for(i = 0; i < num_transfers; i++) {
                curl_multi_remove_handle(multi_handle, trans[i].easy);
                curl_easy_cleanup(trans[i].easy);
        }

        curl_multi_cleanup(multi_handle);

        return 0;
}

运行验证 #

用原编译命令g++ test.cpp -lcurl -o test编译后运行，即可看到每个请求都打印出200响应码。

内容的提问来源于stack exchange，提问作者p.luck