在 C/C++ 中发出 libcurl json post 请求

Question

我正在编写一个 Qt 应用程序，并且我有一个用于注册用户的按钮。我正在使用以下库：

https://github.com/nlohmann/json <- json serialization/deserialization
libcurl

我的目标是能够向以下端点发出 post 请求： http://localhost:8000/api/register

它需要 POST 的内容类型：application/json，utf-8，json 正文如下：

{
    "username": "test", 
    "password": "test"
}

post 请求通过，但响应出错。我正在尝试确定这是我的 libcurl 代码的问题，还是我的 python django 应用程序的错误。

这是 libcurl 代码的详细输出：

E0125 08:52:00.886679  5816 API.h:43] {"password":"test2","username":"test"}
* STATE: INIT => CONNECT handle 0x2489d6b0bf8; line 1835 (connection #-5000)
* Added connection 0. The cache now contains 1 members
* family0 == v4, family1 == v6
*   Trying 127.0.0.1:8000...
* STATE: CONNECT => CONNECTING handle 0x2489d6b0bf8; line 1896 (connection #0)
* Connected to 127.0.0.1 (127.0.0.1) port 8000 (#0)
* STATE: CONNECTING => PROTOCONNECT handle 0x2489d6b0bf8; line 2030 (connection #0)
* STATE: PROTOCONNECT => DO handle 0x2489d6b0bf8; line 2051 (connection #0)
> POST /api/register HTTP/1.1
Host: 127.0.0.1:8000
User-Agent: Jellybean-Launcher
Content-Type: application/json; charset: utf-8
Accept: application/json
Content-Length: 8

* STATE: DO => DID handle 0x2489d6b0bf8; line 2147 (connection #0)
* STATE: DID => PERFORMING handle 0x2489d6b0bf8; line 2266 (connection #0)
* Mark bundle as not supporting multiuse
* HTTP 1.1 or later with persistent connection
< HTTP/1.1 400 Bad Request
< Date: Tue, 25 Jan 2022 16:52:00 GMT
< Server: WSGIServer/0.2 CPython/3.9.7
< Content-Type: application/json
< Vary: Accept, Cookie
< Allow: POST, OPTIONS
< X-Frame-Options: DENY
< Content-Length: 109
< X-Content-Type-Options: nosniff
< Referrer-Policy: same-origin
<
{"detail":"JSON parse error - 'utf-8' codec can't decode byte 0xdd in position 0: invalid continuation byte"}* STATE: PERFORMING => DONE handle 0x2489d6b0bf8; line 2465 (connection #0)
* multi_done: status: 0 prem: 0 done: 0
* Connection #0 to host 127.0.0.1 left intact
* Expire cleared (transfer 0x2489d6b0bf8)

这是 libcurl 代码本身：

void RegisterUser(std::string username, std::string password)
{
    curl_global_init(CURL_GLOBAL_ALL);

    nlohmann::json json_data;
    json_data["username"] = "test";
    json_data["password"] = "test2";
    CURL* curl = curl_easy_init();
    CURLcode res;

    if (curl)
    {
        curl_easy_setopt(curl, CURLOPT_URL, GetRegistrationURL().c_str());
        curl_easy_setopt(curl, CURLOPT_VERBOSE, 1L);
        
        struct curl_slist* chunk = NULL;
        chunk = curl_slist_append(chunk, "Content-Type: application/json; charset: utf-8");
        chunk = curl_slist_append(chunk, "Accept: application/json");

        curl_easy_setopt(curl, CURLOPT_HTTPHEADER, chunk);
        curl_easy_setopt(curl, CURLOPT_POST, 1L);

        /* Set the expected POST size. */
        curl_easy_setopt(curl, CURLOPT_POSTFIELDSIZE, sizeof(json_data.dump().c_str()));
        LOG(ERROR) << json_data.dump().c_str();
        curl_easy_setopt(curl, CURLOPT_POSTFIELDS, json_data.dump().c_str());
        curl_easy_setopt(curl, CURLOPT_USERAGENT, "Jellybean-Launcher");


        res = curl_easy_perform(curl);
        if (res == CURLE_OK)
        {
            //res = curl_easy_getinfo(curl, CURLINFO_CONTENT_TYPE, &ct);
        }
        curl_easy_cleanup(curl);
        curl_slist_free_all(chunk);
    }

    curl_global_cleanup();

}

GetRegistrationURL() Returns 一个 std::string 的范围取决于您是否在开发构建中。在开发构建期间，它始终通过 localhost，在发布构建中，它通过实时网络 url.

有人知道我这里可能做错了什么吗？

Answer 1

第一个错误在行 curl_easy_setopt(curl, CURLOPT_POSTFIELDSIZE, sizeof(json_data.dump().c_str())); 中。 sizeof 并没有按照您的预期去做。

还有一个错误是 curl_easy_setopt(curl, CURLOPT_POSTFIELDS, json_data.dump().c_str()); 行存储了一个指向临时数据 json_data.dump() 内部的指针，它会导致未定义的行为，可能会发送垃圾。错误 'utf-8' codec can't decode byte 0xdd 提示有关已删除内存区域的 Microsoft C 运行时标记 0xdddddddd。

curl_easy_setopt(curl, CURLOPT_POSTFIELDSIZE, (long)json_data.dump().size()));

curl_easy_setopt(curl, CURLOPT_COPYPOSTFIELDS, json_data.dump().c_str());

应该可以解决这个问题。设置 CURLOPT_POSTFIELDSIZE 可以省略，如果在 CURLOPT_COPYPOSTFIELDS 之前未设置大小，则数据被假定为 null-terminated 字符串 - 这是您的情况。

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