由浅入深C系列五：使用libcurl进行基于http get/post模式的C语言交互应用开发

简介

大多数在linux下的开发者，都会用到curl这个命令行工具。对于进行restful api的测试等，非常方便。其实，这个工具还提供了一个C的开发库，可以很方便的在C语言开发环境下完成基于http的请求和响应交互，高效的开发基于http/smtp等的网络应用程序

/* 2023-08-14 更新宏定义 
    1. 使用可变参数，支持多项输出; 
    2. 去除Z中默认加上的双引号; 
*/
#define X_LOG_DEBUG(Z, X...) \
    printf("[%s %s] [%s.%d] [%s] [DEBUG] " Z "\n", __DATE__, __TIME__, __FILE__, __LINE__, __FUNCTION__, ##X)

环境准备

下载并安装curl的开发包

yum install libcurl-devel.x86_64

在线资源

开发过程中主要参考CURL官方介绍及API参考文档 | link

示例代码

多余的话就不多说了，直接上示例代码，通过代码中的注释来说明开发过程。

#include 
#include 
#include 
#include "../include/xhttp.h"

/*
-  这个是一个回调函数，主要用于curl在执行过程中，当有被请求的数据到达时，被调用来向-curl_easy_setopt设置的chunk中写入数据。
  这个回调函数在curl_easy_perform执行完成前会被调用多次。当执行完成后，从chunk中取出这次交互返回的数据。
*/
static size_t cb_write_data(void *data, size_t size, size_t nmemb, void *clientp)
{
    size_t realsize = size * nmemb;
    http_response *mem = (http_response *)clientp;

    char *ptr = realloc(mem->response, mem->size + realsize + 1);
    if(ptr == NULL)
        return 0;  /* out of response_st! */
 
    mem->response = ptr;
    memcpy(&(mem->response[mem->size]), data, realsize);
    mem->size += realsize;
    mem->response[mem->size] = 0;
    
    return realsize;
}

/*
  这个是向外发布的一个函数，调用的方式示例如下：
  char* payload = "{\"code\":\"\",\"codeUuid\":\"\",\"loginName\":\"user@domain\",\"loginPwd\":\"xxxxxxxx\"}";
  http_response *resp = http_post("https://local.domain/admin-api/session/login", NULL, payload);
  使用完返回数据后，记得释放resp->reesponse，避免内存漏。
*/
http_response* http_post(char* url, char* token, char* payload) 
{
    http_response chunk = {0};
    /* 设置curl上下文，对curl实例进行初始化 */
    curl_global_init(CURL_GLOBAL_ALL);
    CURL *curl = curl_easy_init();
    CURLcode res;
    if(curl) 
    {
        X_LOG_DEBUG("%s", "libcurl curl_easy_setopt start ...");
        /* 设置curl各个参数： 请求地址 */
        curl_easy_setopt(curl, CURLOPT_URL, url);
        /* 设置curl各个参数： 请求方式为post */
        curl_easy_setopt(curl, CURLOPT_POST, 1L);

		/* 设置curl各个参数： http中的请求头部分的内容 */
        X_LOG_DEBUG("%s", "libcurl curl_easy_setopt CURLOPT_HTTPHEADER start ...");
        struct curl_slist *list = {0};
        list = curl_slist_append(NULL, "Content-Type: application/json;charset=utf8");
        list = curl_slist_append(list, "routeurl: /project/project-list");
        /* 设置curl各个参数： 可选部分，如果请求中要求token，可以设置上 */
        if (token != NULL)
        {
            char* x_access_token_str = (char*)malloc( MAX_UTMP_TOKEN_SIZE );
            sprintf(x_access_token_str, "x-access-token: %s", token);
            X_LOG_DEBUG("%s", x_access_token_str);
            list = curl_slist_append(list, x_access_token_str);
        }
        curl_easy_setopt(curl, CURLOPT_HTTPHEADER, list);

        X_LOG_DEBUG("%s", "libcurl curl_easy_setopt CURLOPT_USERAGENT start ...");
        /* some servers do not like requests that are made without a user-agent 
            field, so we provide one */
        curl_easy_setopt(curl, CURLOPT_USERAGENT, "Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:82.0) Gecko/20100101 Firefox/82.0");

		/* 设置curl各个参数： http的请求体部分，主要是请求中携带的数据 */
        /* POST data */
        X_LOG_DEBUG("%s", "libcurl curl_easy_setopt CURLOPT_POSTFIELDSIZE/CURLOPT_POSTFIELDS start ...");
        X_LOG_DEBUG("request body data is:%s", payload);
        X_LOG_DEBUG("request body len is:%d", strlen(payload));
        /* size of the POST data */
        curl_easy_setopt(curl, CURLOPT_POSTFIELDSIZE, strlen(payload));
        /* pass in a pointer to the data - libcurl will not copy */
        curl_easy_setopt(curl, CURLOPT_POSTFIELDS, payload);

		/* 设置curl各个参数： 重要部分，设置了返回值的回调函数和返回值的内存放置区域 */
        /* RECEIVE DATA */
        X_LOG_DEBUG("%s", "libcurl curl_easy_setopt CURLOPT_WRITEFUNCTION/CURLOPT_WRITEDATA start ...");
        /* send all data to this function  */
        curl_easy_setopt(curl, CURLOPT_WRITEFUNCTION, cb_write_data);
        /* we pass our 'chunk' struct to the callback function */
        curl_easy_setopt(curl, CURLOPT_WRITEDATA, (void *)&chunk);

        X_LOG_DEBUG("%s", "libcurl curl_easy_setopt successfully complete ...");

		/* 执行curl请求，并获取返回值：CURLE_OK，表示执行成功 */
        X_LOG_DEBUG("%s", "libcurl curl_easy_perform start ...");
        res = curl_easy_perform(curl);
        X_LOG_DEBUG("%s", "libcurl curl_easy_perform successfully complete ...");
    
        if(res != CURLE_OK) {
            fprintf(stderr, "curl_easy_perform() is failed: %s", curl_easy_strerror(res));
            curl_slist_free_all(list); /* free the list again */
            curl_easy_cleanup(curl);
        } else {
        	/* 处理curl返回的数据 */
            X_LOG_DEBUG("chunk size %d", chunk.size);

            http_response response = {0};
            response.response = (char*)malloc(1048576*5);
            memset(response.response, 0, chunk.size+1);
            memcpy(response.response, chunk.response, chunk.size+1);
            response.size = chunk.size;

            /* remember to free the buffer */
            free(chunk.response);
            curl_slist_free_all(list); /* free the list again */ 
            curl_global_cleanup();
            
            return &response;
        }
    } 
}

引用的头文件如下：

#ifndef __X_HTTP_H__
#define __X_HTTP_H__

#include 
#include 
/* 更新宏定义 1. 使用可变参数，支持多项输出; 2. 去除Z中默认加上的双引号; */
#define X_LOG_DEBUG(Z, X...) \
    printf("[%s %s] [%s.%d] [%s] [DEBUG] " Z "\n", __DATE__, __TIME__, __FILE__, __LINE__, __FUNCTION__, ##X)

#define MAX_UTMP_TOKEN_SIZE 8192

typedef struct http_response_s {
  char *response;
  size_t size;
} http_response;

typedef struct http_request_s {
    char *request;
    size_t size;
} http_request;

http_response* http_post(char* url, char* token, char* payload);

#endif

测试调用

int main(int argc, char** argv) {
	char* payload = "{\"code\":\"\",\"codeUuid\":\"\",\"loginName\":\"user@domain\",\"loginPwd\":\"xxxxxxxx\"}";
	http_response *resp = http_post("https://local.domain/admin-api/session/login", NULL, payload);
	printf("http_response [%d] is: %s\n", resp->size, resp->response);
	char *tokenVal = strstr(resp->response, "xaccessToken");
	int end = strlen(tokenVal);
	*(tokenVal + end-2) = 0;
	char** token_arr;
	__strtok_r(tokenVal, ":", token_arr);
	char* replacementKey = strtrim(token_arr[0], '\"');
	exit(0)
}

运行结果

[Aug 11 2023 10:20:02] [src/xhttp.c.37] [http_post] [DEBUG] "libcurl curl_easy_setopt start ..."
[Aug 11 2023 10:20:02] [src/xhttp.c.42] [http_post] [DEBUG] "libcurl curl_easy_setopt CURLOPT_HTTPHEADER start ..."
[Aug 11 2023 10:20:02] [src/xhttp.c.55] [http_post] [DEBUG] "libcurl curl_easy_setopt CURLOPT_USERAGENT start ..."
[Aug 11 2023 10:20:02] [src/xhttp.c.61] [http_post] [DEBUG] "libcurl curl_easy_setopt CURLOPT_POSTFIELDSIZE/CURLOPT_POSTFIELDS start ..."
[Aug 11 2023 10:20:02] [src/xhttp.c.62] [http_post] [DEBUG] "request body data is:{"code":"","codeUuid":"","loginName":"user@domain","loginPwd":"xxxxxxxx"}"
[Aug 11 2023 10:20:02] [src/xhttp.c.63] [http_post] [DEBUG] "request body len is:75"
[Aug 11 2023 10:20:02] [src/xhttp.c.70] [http_post] [DEBUG] "libcurl curl_easy_setopt CURLOPT_WRITEFUNCTION/CURLOPT_WRITEDATA start ..."
[Aug 11 2023 10:20:02] [src/xhttp.c.76] [http_post] [DEBUG] "libcurl curl_easy_setopt successfully complete ..."
[Aug 11 2023 10:20:02] [src/xhttp.c.79] [http_post] [DEBUG] "libcurl curl_easy_perform start ..."
[Aug 11 2023 10:20:02] [src/xhttp.c.81] [http_post] [DEBUG] "libcurl curl_easy_perform successfully complete ..."
[Aug 11 2023 10:20:02] [src/xhttp.c.90] [http_post] [DEBUG] "chunk size 6693"