如何使用libcurl发布JSON缓冲区? [英] How do I POST a buffer of JSON using libcurl?
问题描述
我的C ++程序当前通过管道(popen("curl ..."))调用curl，以将JSON数据文件发布到Web服务器.由于需要将JSON保存到文件并在子shell中调用curl，因此这具有明显的性能限制.我想重写它以使用libcurl，但是我不清楚如何做到这一点.我传递给popen()的命令行是:
My C++ program currently invokes curl through a pipe (popen("curl ...")) to POST a file of JSON data to a web server. This has obvious performance limitations due to the need to save the JSON to a file and invoke curl in a subshell. I'd like to rewrite it to use libcurl, but it is not clear to me how to do this. The command line I pass to popen() is:
curl -s -S -D /dev/null -H "Content-Type: application/json" -X POST -d file-of-json http://server/handler.php
在需要发布JSON数据(约3K)之前，它位于RAM的缓冲区中.我原本希望使用libcurl的CURLOPT_READFUNCTION将缓冲区假脱机到libcurl(但是我可以使用其他方法)，并且使用CURLOPT_WRITEFUNCTION来捕获服务器的答复，就像我从popen的管道中读取答复一样.
The JSON data (about 3K) is sitting in a buffer in RAM before I need to post it. I was expecting to use libcurl's CURLOPT_READFUNCTION to spool the buffer to libcurl (but I am open to alternatives), and CURLOPT_WRITEFUNCTION to capture the server's reply, similar to how I read the reply from popen's pipe.
所有这些似乎很简单.令人困惑的是我需要CURLOPT_POST，CURLOPT_HTTPPOST，CURLOPT_POSTFIELDS，CURLOPT_HTTPHEADER的哪种组合.我已经读过很多关于该主题的文章(无双关语)，但都没有完全符合我的情况.有什么建议吗?
All that seems straightforward. What is confusing is which combination of CURLOPT_POST, CURLOPT_HTTPPOST, CURLOPT_POSTFIELDS, CURLOPT_HTTPHEADER I need. I have read many posts on this subject (no pun intended), and none exactly match my scenario. Any suggestions?
[请注意，我通常没有任何URL编码的表单字段，例如:http://server/handler.php?I=do¬=use&these=in&my=query]
[Note that I normally do not have any URL-encoded form fields, like this: http://server/handler.php?I=do¬=use&these=in&my=query]
推荐答案
此处提供了示例代码: http://curl.haxx.se/libcurl/c/post-callback.html
There is example code for this here: http://curl.haxx.se/libcurl/c/post-callback.html
/***************************************************************************
* _ _ ____ _
* Project ___| | | | _ \| |
* / __| | | | |_) | |
* | (__| |_| | _ <| |___
* \___|\___/|_| \_\_____|
*
* Copyright (C) 1998 - 2011, 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.
*
***************************************************************************/
/* An example source code that issues a HTTP POST and we provide the actual
* data through a read callback.
*/
#include
#include
#include
const char data[]="this is what we post to the silly web server";
struct WriteThis {
const char *readptr;
int sizeleft;
};
static size_t read_callback(void *ptr, size_t size, size_t nmemb, void *userp)
{
struct WriteThis *pooh = (struct WriteThis *)userp;
if(size*nmemb sizeleft) {
*(char *)ptr = pooh->readptr[0]; /* copy one single byte */
pooh->readptr++; /* advance pointer */
pooh->sizeleft--; /* less data left */
return 1; /* we return 1 byte at a time! */
}
return 0; /* no more data left to deliver */
}
int main(void)
{
CURL *curl;
CURLcode res;
struct WriteThis pooh;
pooh.readptr = data;
pooh.sizeleft = strlen(data);
curl = curl_easy_init();
if(curl) {
/* First set the URL that is about to receive our POST. */
curl_easy_setopt(curl, CURLOPT_URL, "http://example.com/index.cgi");
/* Now specify we want to POST data */
curl_easy_setopt(curl, CURLOPT_POST, 1L);
/* we want to use our own read function */
curl_easy_setopt(curl, CURLOPT_READFUNCTION, read_callback);
/* pointer to pass to our read function */
curl_easy_setopt(curl, CURLOPT_READDATA, &pooh);
/* get verbose debug output please */
curl_easy_setopt(curl, CURLOPT_VERBOSE, 1L);
/*
If you use POST to a HTTP 1.1 server, you can send data without knowing
the size before starting the POST if you use chunked encoding. You
enable this by adding a header like "Transfer-Encoding: chunked" with
CURLOPT_HTTPHEADER. With HTTP 1.0 or without chunked transfer, you must
specify the size in the request.
*/
#ifdef USE_CHUNKED
{
struct curl_slist *chunk = NULL;
chunk = curl_slist_append(chunk, "Transfer-Encoding: chunked");
res = curl_easy_setopt(curl, CURLOPT_HTTPHEADER, chunk);
/* use curl_slist_free_all() after the *perform() call to free this
list again */
}
#else
/* Set the expected POST size. If you want to POST large amounts of data,
consider CURLOPT_POSTFIELDSIZE_LARGE */
curl_easy_setopt(curl, CURLOPT_POSTFIELDSIZE, (curl_off_t)pooh.sizeleft);
#endif
#ifdef DISABLE_EXPECT
/*
Using POST with HTTP 1.1 implies the use of a "Expect: 100-continue"
header. You can disable this header with CURLOPT_HTTPHEADER as usual.
NOTE: if you want chunked transfer too, you need to combine these two
since you can only set one list of headers with CURLOPT_HTTPHEADER. */
/* A less good option would be to enforce HTTP 1.0, but that might also
have other implications. */
{
struct curl_slist *chunk = NULL;
chunk = curl_slist_append(chunk, "Expect:");
res = curl_easy_setopt(curl, CURLOPT_HTTPHEADER, chunk);
/* use curl_slist_free_all() after the *perform() call to free this
list again */
}
#endif
/* Perform the request, res will get the return code */
res = curl_easy_perform(curl);
/* always cleanup */
curl_easy_cleanup(curl);
}
return 0;
}
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