如何使用 libcurl POST JSON 缓冲区？
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How do I POST a buffer of JSON using libcurl?
提问by Randall Cook
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:
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，这具有明显的性能限制。我想重写它以使用 libcurl，但我不清楚如何做到这一点。我传递给的命令行popen()是：
curl -s -S -D /dev/null -H "Content-Type: application/json" -X POST -d file-of-json http://server/handler.php
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_READFUNCTIONto spool the buffer to libcurl (but I am open to alternatives), and CURLOPT_WRITEFUNCTIONto capture the server's reply, similar to how I read the reply from popen's pipe.
在我需要发布它之前，JSON 数据（大约 3K）位于 RAM 中的缓冲区中。我期待使用 libcurlCURLOPT_READFUNCTION将缓冲区假脱机到 libcurl（但我愿意接受替代方案），并CURLOPT_WRITEFUNCTION捕获服务器的回复，类似于我从 popen 的管道中读取回复的方式。
All that seems straightforward. What is confusing is which combination of CURLOPT_POST, CURLOPT_HTTPPOST, CURLOPT_POSTFIELDS, CURLOPT_HTTPHEADERI need. I have read many posts on this subject (no pun intended), and none exactly match my scenario. Any suggestions?
所有这一切看起来都很简单。令人困惑的是我需要CURLOPT_POST, CURLOPT_HTTPPOST, CURLOPT_POSTFIELDS, 的哪种组合CURLOPT_HTTPHEADER。我已经阅读了很多关于这个主题的帖子（没有双关语），但没有一个完全符合我的情况。有什么建议？
[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]
[请注意，我通常没有任何 URL 编码的表单字段，如下所示：http://server/handler.php?I=do¬=use&these=in&my=query]
采纳答案by Alastair Maw
There is example code for this here: http://curl.haxx.se/libcurl/c/post-callback.html
这里有示例代码：http: //curl.haxx.se/libcurl/c/post-callback.html
/***************************************************************************
* _ _ ____ _
* Project ___| | | | _ \| |
* / __| | | | |_) | |
* | (__| |_| | _ <| |___
* \___|\___/|_| \_\_____|
*
* Copyright (C) 1998 - 2011, Daniel Stenberg, <[email protected]>, 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;
}
回答by Greg Prisament
You can use CURLOPT_POSTFIELDS:
您可以使用CURLOPT_POSTFIELDS：
CURL *curl = curl_easy_init();
curl_easy_setopt(curl, CURLOPT_URL, "http://example.com/api/endpoint");
curl_easy_setopt(curl, CURLOPT_POSTFIELDS, "{\"hi\" : \"there\"}");
curl_easy_perform(curl);
Since CURLOPT_POSTFIELDSdoes not modify the payload in any way, it is very convenient for POSTing JSON data. Also note that, when CURLOPT_POSTFIELDSis supplied, it automatically enables CURLOPT_POSTso there is no need to provide CURLOPT_POSTin the request.
由于CURLOPT_POSTFIELDS不会以任何方式修改有效负载，因此非常方便 POSTing JSON 数据。另请注意，当CURLOPT_POSTFIELDS提供时，它会自动启用，CURLOPT_POST因此无需CURLOPT_POST在请求中提供。
回答by Stephan Scheller
What about the required Content-Typeheader to match application/jsonjust like the op is asking?
就像操作所要求的那样Content-Type匹配所需的标头application/json呢？
Using the CURLOPT_POSTFIELDSfrom two answers above as well as CURLOPT_POST, the Content-Typeautomatically gets set to application/x-www-form-urlencoded.
使用CURLOPT_POSTFIELDS上面的两个答案以及CURLOPT_POST，Content-Type自动设置为application/x-www-form-urlencoded.
The only way for me to get the headers set correctly was to add what is outlined in this answer: JSON requests in C using libcurl
我正确设置标头的唯一方法是添加此答案中概述的内容：JSON requests in C using libcurl
回答by F10PPY
Also, you may use RAW input instead of adding extra backslashes:
此外，您可以使用 RAW 输入而不是添加额外的反斜杠：
curl_easy_setopt(curl, CURLOPT_POSTFIELDS, R"anydelim( {"hi" : "there"} )anydelim");
with delimiter or without it.
带分隔符或不带分隔符。
