使用libcurl将Opencv Mat的图像上传到文件服务器，基于post请求和ftp协议两种方法

基于post请求的

基于post请求的方法主要是上传到比如装了nginx-upload-module的nginx服务器上，url参数传文件所在目录，底下的curl_formadd里添加文件名。
不过nginx-upload-module不会把文件文件名，而是保存成名字为00000000xx这样的文件10位数字命名的文件，防止上传文件冲突，需要你自己写php或python脚本把文件搬运到正确的位置或者重命名。
设计的好像挺有道理的（倒是给蓝狗提供个脚本呗）。

size_t writer(char *data, size_t size, size_t nmemb, string *writerData) {
    
    if (writerData == nullptr)
        return 0;
    size_t len = size * nmemb;
    writerData->append(data, len);
    return len;
}

void postUpLoad(const cv::Mat &img, const char *url) {
    
    vector<uchar> vec_Img;

    vector<int> vecCompression_params;

    vecCompression_params.push_back(cv::IMWRITE_JPEG_QUALITY);
    vecCompression_params.push_back(90);
    imencode(".jpg", img, vec_Img, vecCompression_params);

    CURL *curl;
    CURLcode res;

    string buffer;

    struct curl_httppost *post = nullptr;
    struct curl_httppost *last = nullptr;

    curl = curl_easy_init();
    if (curl) {
    
        curl_easy_setopt(curl, CURLOPT_URL, url);
        curl_easy_setopt(curl, CURLOPT_POST, 1);
        struct curl_slist *chunk = nullptr;
        chunk = curl_slist_append(chunk, "Accept:");

        chunk = curl_slist_append(chunk, "Authorization: Token ");

        curl_easy_setopt(curl, CURLOPT_HTTPHEADER, chunk);
        curl_easy_setopt(curl, CURLOPT_WRITEFUNCTION, writer);
        curl_easy_setopt(curl, CURLOPT_WRITEDATA, &buffer);


        curl_formadd(&post, &last,
                     CURLFORM_COPYNAME, "photo",
                     CURLFORM_BUFFER, "photo.jpg",
                     CURLFORM_BUFFERPTR, vec_Img.data(),
                     CURLFORM_BUFFERLENGTH, vec_Img.size(),
                     CURLFORM_CONTENTTYPE, "image/jpg",
                     CURLFORM_END);

        curl_easy_setopt(curl, CURLOPT_HTTPPOST, post);

        // curl_easy_setopt(curl, CURLOPT_DEBUGFUNCTION, my_trace);

        curl_easy_setopt(curl, CURLOPT_VERBOSE, 1L);
        //
        curl_easy_setopt(curl, CURLOPT_FOLLOWLOCATION, 1L);

        res = curl_easy_perform(curl);

        if (res != CURLE_OK)
            fprintf(stderr, "curl_easy_perform() failed: %s\n", curl_easy_strerror(res));

        curl_easy_cleanup(curl);
    }
}

基于ftp协议的

url直接传文件路径，比如ftp://server.name/subdir/image.jpg

struct TmpStream {
    
    void *ptr;
    size_t last_num;
};

static size_t read_callback(void *ptr, size_t size, size_t nmemb, TmpStream *stream) {
    
    if (stream->last_num <= 0)
        return 0;
    size_t retcode = size * nmemb;
    retcode = MIN(retcode, stream->last_num);
    memcpy(ptr, stream->ptr, retcode);
    stream->last_num -= retcode;
// curl_off_t nread = (curl_off_t) retcode;
// fprintf(stderr, " We read %" CURL_FORMAT_CURL_OFF_T
// " bytes from file\n", nread);
    return retcode;
}

void ftpUpload(const cv::Mat &img, const char *url) {
    
    vector<uchar> vec_Img;

    vector<int> vecCompression_params;

    vecCompression_params.push_back(cv::IMWRITE_JPEG_QUALITY);
    vecCompression_params.push_back(90);
    imencode(".jpg", img, vec_Img, vecCompression_params);

    // struct curl_slist *headerlist = nullptr;

    CURL *curl;
    CURLcode res;

    curl = curl_easy_init();

    if (curl) {
    
        curl_easy_setopt(curl, CURLOPT_USERPWD, "smc:123456");
        /* we want to use our own write function */
        // curl_easy_setopt(curl, CURLOPT_WRITEFUNCTION, writer);
        /* we want to use our own read function */
        curl_easy_setopt(curl, CURLOPT_READFUNCTION, read_callback);

        /**create missing dir**/
        curl_easy_setopt(curl, CURLOPT_FTP_CREATE_MISSING_DIRS, 1L);

        /* enable uploading */
        curl_easy_setopt(curl, CURLOPT_UPLOAD, 1L);

        /* specify target */
        curl_easy_setopt(curl, CURLOPT_URL, url);

        // /* pass in that last of FTP commands to run after the transfer */
        // curl_easy_setopt(curl, CURLOPT_POSTQUOTE, headerlist);

        /* now specify which file to upload */
        TmpStream stream = {
    vec_Img.data(), vec_Img.size()};
        curl_easy_setopt(curl, CURLOPT_READDATA, &stream);

        /* Set the size of the file to upload (optional). If you give a *_LARGE option you MUST make sure that the type of the passed-in argument is a curl_off_t. If you use CURLOPT_INFILESIZE (without _LARGE) you must make sure that to pass in a type 'long' argument. */
        curl_easy_setopt(curl, CURLOPT_INFILESIZE_LARGE,
                         (curl_off_t) vec_Img.size());
        /* Now run off and do what you have been told! */
        res = curl_easy_perform(curl);
        /* Check for errors */
        if (res != CURLE_OK)
            fprintf(stderr, "curl_easy_perform() failed: %s\n",
                    curl_easy_strerror(res));

        /* clean up the FTP commands list */
        // curl_slist_free_all(headerlist);

        /* always cleanup */
        curl_easy_cleanup(curl);
    }
}