使用libcurl调用Baichuan API时model参数已设置仍提示缺失

我按照建议使用cJSON库生成请求消息的数据段，通过curl构造请求头和数据部分，以POST方式发送请求，但系统提示未设置model参数，可实际上我已经配置了该参数。以下是我的代码及运行结果：

int main(int argc, char **argv){

    CURL *curl;
    char *url = NULL;
    CURLcode res = CURLE_OK;
    url = "https://api.baichuan-ai.com/v1/chat/completions";

    // 初始化用于存储响应数据的结构体
    struct MemoryStruct chunk;
    chunk.memory = malloc(1);
    chunk.size = 0;          

    char *auth_header = "Authorization: Bearer " KIMI_API;
    char *content_header = "Content-Type: application/json";

    struct curl_slist *headers = NULL;
    headers = curl_slist_append(headers, auth_header);
    headers = curl_slist_append(headers, content_header);

    cJSON *data = cJSON_CreateObject();

    char *messages = "巴黎奥运会中国体育代表团共获多少金牌?";
    
    cJSON_AddStringToObject(data, "model", "Baichuan4");
    cJSON_AddStringToObject(data, "messages", messages);
    cJSON_AddNumberToObject(data, "max_tokens", 1024);
    cJSON_AddNumberToObject(data, "temperature", 0.5);

    char *json_string = cJSON_Print(data);
    curl_global_init(CURL_GLOBAL_DEFAULT);
    curl = curl_easy_init();
    printf("%s \n", json_string);

    if (curl)
    {
        curl_easy_setopt(curl, CURLOPT_HTTPHEADER, headers);
        curl_easy_setopt(curl, CURLOPT_POSTFIELDS, data);
        curl_easy_setopt(curl, CURLOPT_URL, url);
        curl_easy_setopt(curl, CURLOPT_WRITEFUNCTION, WriteMemoryCallback);
        curl_easy_setopt(curl, CURLOPT_WRITEDATA, (void *)&chunk);

        res = curl_easy_perform(curl);

        if (res == CURLE_OK){
            printf("Response:\n%s\n", chunk.memory);
        } else {
            printf("failed");
        }
        curl_easy_cleanup(curl);
    }
    free(chunk.memory);

    return 0;
}

运行结果：

{
        "model":        "Baichuan4",
        "messages":     "巴黎奥运会中国体育代表团共获多少金牌?",
        "max_tokens":   1024,
        "temperature":  0.5
} 
Response:
{"error":{"code":"model_is_empty","param":null,"type":"invalid_request_error","message":"you must provide a model parameter"}}

问题分析与修复 #

1. 核心错误：POST数据传递错误 #

你设置CURLOPT_POSTFIELDS时，传递的是cJSON对象指针data，但curl需要的是序列化后的JSON字符串（即你生成的json_string）。cJSON对象是内存中的结构体，直接传递给curl会导致发送的数据不是合法JSON，服务端无法解析到model参数。

2. 次要错误：messages参数格式不符合接口要求 #

百川AI的chat completions接口中，messages要求是数组格式，每个元素是包含role和content的对象，而非直接传字符串。即使修复第一个问题，这个错误也会导致接口调用失败。

修正后的代码 #

int main(int argc, char **argv){

    CURL *curl;
    char *url = NULL;
    CURLcode res = CURLE_OK;
    url = "https://api.baichuan-ai.com/v1/chat/completions";

    // 初始化用于存储响应数据的结构体
    struct MemoryStruct chunk;
    chunk.memory = malloc(1);
    chunk.size = 0;          

    char *auth_header = "Authorization: Bearer " KIMI_API;
    char *content_header = "Content-Type: application/json";

    struct curl_slist *headers = NULL;
    headers = curl_slist_append(headers, auth_header);
    headers = curl_slist_append(headers, content_header);

    cJSON *data = cJSON_CreateObject();

    // 修正messages参数格式：数组+role+content结构
    cJSON *messages = cJSON_CreateArray();
    cJSON *user_msg = cJSON_CreateObject();
    cJSON_AddStringToObject(user_msg, "role", "user");
    cJSON_AddStringToObject(user_msg, "content", "巴黎奥运会中国体育代表团共获多少金牌?");
    cJSON_AddItemToArray(messages, user_msg);
    
    cJSON_AddStringToObject(data, "model", "Baichuan4");
    cJSON_AddItemToObject(data, "messages", messages); // 添加数组到对象
    cJSON_AddNumberToObject(data, "max_tokens", 1024);
    cJSON_AddNumberToObject(data, "temperature", 0.5);

    char *json_string = cJSON_Print(data);
    curl_global_init(CURL_GLOBAL_DEFAULT);
    curl = curl_easy_init();
    printf("%s \n", json_string);

    if (curl)
    {
        curl_easy_setopt(curl, CURLOPT_HTTPHEADER, headers);
        curl_easy_setopt(curl, CURLOPT_POSTFIELDS, json_string); // 传递序列化后的JSON字符串
        curl_easy_setopt(curl, CURLOPT_URL, url);
        curl_easy_setopt(curl, CURLOPT_WRITEFUNCTION, WriteMemoryCallback);
        curl_easy_setopt(curl, CURLOPT_WRITEDATA, (void *)&chunk);

        res = curl_easy_perform(curl);

        if (res == CURLE_OK){
            printf("Response:\n%s\n", chunk.memory);
        } else {
            printf("failed");
        }
        curl_easy_cleanup(curl);
    }
    free(chunk.memory);
    cJSON_Delete(data); // 释放cJSON对象内存
    free(json_string); // 释放序列化后的字符串内存

    return 0;
}

关键修正点 #

• 将CURLOPT_POSTFIELDS的参数从data改为json_string，确保发送合法JSON文本。
• 重构messages为接口要求的数组结构，每个消息包含role和content字段。
• 添加cJSON对象和字符串的内存释放，避免内存泄漏。

内容的提问来源于stack exchange，提问作者L JF