c - 使用 C 的原始 libcurl JSON PUT 请求

Question

我目前正在编写一个类似 REST 的客户端，只需要执行 PUT 请求。

问题:
运行该程序并没有在 URL 的 API 上给出正确的结果，我不知道为什么。

使用curl_easy_perform(curl)在调用时不会抛出错误。但 URL 的 API 上并未生成预期结果。

使用curl_easy_send(curl,..,..,..)抛出一个:不支持的协议(protocol)错误

假设:
我假设我使用curl_easy_opts的顺序有问题？我什至错过了几行关键行？

我一直在这里阅读其他人如何执行 PUT 请求并一直在使用他们的方法。

计划摘要:

我的程序提示用户输入一些字符串/字符数据，然后我自己构建字符串，例如 header 和有效负载。 header 和有效负载均为 JSON 格式，但有效负载只是一个字符串(在本例中为 char *str = (char *)mallo.. 等)。 header 的构造方式如下所示。

我的 header 正在使用

构建

struct curl_slist *headers = NULL;
headers = curl_slist_append(headers, "Accept: application/json");
//there is more content being appended to the header

CURL 函数调用:

    //init winsock stuff
    curl_global_init(CURL_GLOBAL_ALL);

    //get a curl handle
    curl = curl_easy_init();

if(curl){
    //append the headers
    curl_easy_setopt(curl, CURLOPT_HTTPHEADER, headers);

    //specify the target URL
    curl_easy_setopt(curl, CURLOPT_URL, url);

    //connect ( //i added this here since curl_easy_send() says it requires it. )
    curl_easy_setopt(curl, CURLOPT_CONNECT_ONLY,1L); 

    //specify the request (PUT in our case)
    curl_easy_setopt(curl, CURLOPT_CUSTOMREQUEST, "PUT");

    //append the payload
    curl_easy_setopt(curl, CURLOPT_POSTFIELDS, payload);

    res = curl_easy_perform(curl);
    //res = curl_easy_send(curl, payload, strlen(payload),&iolen);

    //check for errors
    if(res != CURLE_OK)
        fprintf(stderr, "curl_easy_perform() failed: %s\n", curl_easy_strerror(res));

    curl_easy_cleanup(curl);
}

Answer 1

您不应使用 CURLOPT_CONNECT_ONLY 选项或 curl_easy_send() 函数，这些函数旨在用于自定义的非 HTTP 协议(protocol)。

参见this page有关如何使用 libcurl 执行 PUT 请求的示例。基本上，您希望启用 CURLOPT_UPLOAD 和 CURLOPT_PUT 选项来表示您正在执行 PUT 请求并启用随请求上传正文，然后设置CURLOPT_READDATA 和 CURLOPT_INFILESIZE_LARGE 选项告诉 libcurl 如何读取您正在上传的数据以及数据有多大。

就您而言，如果内存中已有数据，则无需从文件中读取数据，只需在读取回调中使用 memcpy() 即可。

复制的示例代码如下:

/***************************************************************************
 *                                  _   _ ____  _
 *  Project                     ___| | | |  _ \| |
 *                             / __| | | | |_) | |
 *                            | (__| |_| |  _ <| |___
 *                             \___|\___/|_| \_\_____|
 *
 * Copyright (C) 1998 - 2012, Daniel Stenberg, <daniel@haxx.se>, et al.
 *
 * This software is licensed as described in the file COPYING, which
 * you should have received as part of this distribution. The terms
 * are also available at http://curl.haxx.se/docs/copyright.html.
 *
 * You may opt to use, copy, modify, merge, publish, distribute and/or sell
 * copies of the Software, and permit persons to whom the Software is
 * furnished to do so, under the terms of the COPYING file.
 *
 * This software is distributed on an "AS IS" basis, WITHOUT WARRANTY OF ANY
 * KIND, either express or implied.
 *
 ***************************************************************************/ 
#include <stdio.h>
#include <fcntl.h>
#include <sys/stat.h>
#include <curl/curl.h>

/*
 * This example shows a HTTP PUT operation. PUTs a file given as a command
 * line argument to the URL also given on the command line.
 *
 * This example also uses its own read callback.
 *
 * Here's an article on how to setup a PUT handler for Apache:
 * http://www.apacheweek.com/features/put
 */ 

static size_t read_callback(void *ptr, size_t size, size_t nmemb, void *stream)
{
  size_t retcode;
  curl_off_t nread;

  /* in real-world cases, this would probably get this data differently
     as this fread() stuff is exactly what the library already would do
     by default internally */ 
  retcode = fread(ptr, size, nmemb, stream);

  nread = (curl_off_t)retcode;

  fprintf(stderr, "*** We read %" CURL_FORMAT_CURL_OFF_T
          " bytes from file\n", nread);

  return retcode;
}

int main(int argc, char **argv)
{
  CURL *curl;
  CURLcode res;
  FILE * hd_src ;
  struct stat file_info;

  char *file;
  char *url;

  if(argc < 3)
    return 1;

  file= argv[1];
  url = argv[2];

  /* get the file size of the local file */ 
  stat(file, &file_info);

  /* get a FILE * of the same file, could also be made with
     fdopen() from the previous descriptor, but hey this is just
     an example! */ 
  hd_src = fopen(file, "rb");

  /* In windows, this will init the winsock stuff */ 
  curl_global_init(CURL_GLOBAL_ALL);

  /* get a curl handle */ 
  curl = curl_easy_init();
  if(curl) {
    /* we want to use our own read function */ 
    curl_easy_setopt(curl, CURLOPT_READFUNCTION, read_callback);

    /* enable uploading */ 
    curl_easy_setopt(curl, CURLOPT_UPLOAD, 1L);

    /* HTTP PUT please */ 
    curl_easy_setopt(curl, CURLOPT_PUT, 1L);

    /* specify target URL, and note that this URL should include a file
       name, not only a directory */ 
    curl_easy_setopt(curl, CURLOPT_URL, url);

    /* now specify which file to upload */ 
    curl_easy_setopt(curl, CURLOPT_READDATA, hd_src);

    /* provide the size of the upload, we specicially typecast the value
       to curl_off_t since we must be sure to use the correct data size */ 
    curl_easy_setopt(curl, CURLOPT_INFILESIZE_LARGE,
                     (curl_off_t)file_info.st_size);

    /* Now run off and do what you've been told! */ 
    res = curl_easy_perform(curl);
    /* Check for errors */ 
    if(res != CURLE_OK)
      fprintf(stderr, "curl_easy_perform() failed: %s\n",
              curl_easy_strerror(res));

    /* always cleanup */ 
    curl_easy_cleanup(curl);
  }
  fclose(hd_src); /* close the local file */ 

  curl_global_cleanup();
  return 0;
}