在 C/C++ 中制作 libcurl json 发布请求

Question

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

1. https://github.com/nlohmann/json <- 用于 json 序列化/反序列化
2. 库库尔

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

它期待 utf-8 的 Content-Type: application/json 的 POST，具有如下 json 主体：

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

发布请求通过，但响应给出错误。 我试图确定这是我的 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 output ：

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()返回一个 std::string，其范围取决于您是否处于开发构建中。 在开发构建期间，它总是通过 localhost，而在发布构建中，它通过实时 web url。

有谁知道我在这里可能做错了什么？

Answer 1

第一个错误是curl_easy_setopt(curl, CURLOPT_POSTFIELDSIZE, sizeof(json_data.dump().c_str())); . sizeof并没有按照您的设想进行。

另一个错误是curl_easy_setopt(curl, CURLOPT_POSTFIELDS, json_data.dump().c_str()); 存储指向临时数据内部的指针json_data.dump() ，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。

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

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

应该解决这个问题。 可以省略设置CURLOPT_POSTFIELDSIZE ，如果在CURLOPT_COPYPOSTFIELDS之前没有设置大小，则假定数据是一个以空字符结尾的字符串 - 这是你的情况。