利用libcurl进行图片上传和下载

前言

通过使用libcur可以快捷地对图片进行上传和下载，下载和ftp流程类似，上传需要注意图片格式和服务器表单等配置要求

上传

根据libcur官方描述：

curl_mime_init creates a handle to a new empty mime structure intended to be used with easy_handle. This mime structure can be subsequently filled using the mime API, then attached to easy_handle using option CURLOPT_MIMEPOST within a curl_easy_setopt call.
Using a mime handle is the recommended way to post an HTTP form, format and send a multi-part email with SMTP or upload such an email to an IMAP server.

http头参考如下：

Content-Type: multipart/form-data; boundary=----WebKitFormBoundaryHGUYvaM49N5Bm27p

mine内容参考如下：

Content-Disposition: form-data; name=“files”; filename=“test.jpg”
Content-Type: image/jpeg

参考libcurl示例代码，结合以上要求，实际上不同服务器参数可能有差异，需要根据自身配置来调整

int file_upload(const char* url, const char* filename)
{
    
    
    int ret = -1;
    CURL* easy_handle;
    CURLcode res;

    CURLcode code;
    code = curl_global_init(CURL_GLOBAL_ALL);

    if (CURLE_OK != code) {
    
    
        fprintf(stderr, "init libcurl failed\n");
        return ret;
    }

    curl_mime *mime;
    curl_mimepart *part;
    easy_handle = curl_easy_init();

    /* Build an HTTP form with a single field named "data", */
    mime = curl_mime_init(easy_handle);
    part = curl_mime_addpart(mime);
    curl_mime_name(part, "files");
    curl_mime_filedata(part, filename);
    curl_mime_type(part, "image/jpeg");

    curl_easy_setopt(easy_handle, CURLOPT_URL, url);
    curl_easy_setopt(easy_handle, CURLOPT_MIMEPOST, mime);
    curl_easy_setopt(easy_handle, CURLOPT_VERBOSE, 1);

    res = curl_easy_perform(easy_handle);
    /* Now run off and do what you've been told! */
    if (res != CURLE_OK) {
    
    
        /* we failed */
        printf("curl_easy_perform() failed: %s\n", curl_easy_strerror(res));
    } else {
    
    
        long httpStatus;
        curl_easy_getinfo(easy_handle, CURLINFO_RESPONSE_CODE, &httpStatus);
        printf("httpStatus = %ld\n", httpStatus);
        ret = 0;
    }

    curl_easy_cleanup(easy_handle);
    curl_mime_free(mime);
    curl_global_cleanup();

    return ret;
}

下载

参考libcur中的ftpget，只需要一个简单的GET方法，把接收到的数据保存成图片文件即可

struct FtpFile {
    
    
    const char *filename;
    FILE *stream;
};

static size_t my_fwrite(void *buffer, size_t size, size_t nmemb, void *stream)
{
    
    
    struct FtpFile *out = (struct FtpFile *)stream;
    if (!out->stream) {
    
    
        /* open file for writing */
        out->stream = fopen(out->filename, "wb");
        if (!out->stream) {
    
    
            return -1; /* failure, can't open file to write */
        }
    }
    return fwrite(buffer, size, nmemb, out->stream);
}

int file_download(const char* url, const char* filename)
{
    
    
    int ret = -1;
    CURL *curl;
    CURLcode res;
    struct FtpFile ftpfile = {
    
    
        filename, /* name to store the file as if successful */
        NULL
    };

    curl_global_init(CURL_GLOBAL_DEFAULT);

    curl = curl_easy_init();
    if (curl) {
    
    
        /*
        * You better replace the URL with one that works!
        */
        // url: "ftp://ftp.example.com/curl/curl-7.9.2.tar.gz"
        curl_easy_setopt(curl, CURLOPT_URL, url);
        /* Define our callback to get called when there's data to be written */
        curl_easy_setopt(curl, CURLOPT_WRITEFUNCTION, my_fwrite);
        /* Set a pointer to our struct to pass to the callback */
        curl_easy_setopt(curl, CURLOPT_WRITEDATA, &ftpfile);

        curl_easy_setopt(curl, CURLOPT_CONNECTTIMEOUT, 10L);
        curl_easy_setopt(curl, CURLOPT_TIMEOUT, 100L);

        /* Switch on full protocol/debug output */
        curl_easy_setopt(curl, CURLOPT_VERBOSE, 1L);

        res = curl_easy_perform(curl);
        if (res != CURLE_OK) {
    
    
            /* we failed */
            printf("curl_easy_perform() failed: %s\n", curl_easy_strerror(res));
        } else {
    
    
            unsigned int httpStatus;
            curl_easy_getinfo(curl, CURLINFO_RESPONSE_CODE, &httpStatus);
            printf("httpStatus = %u\n", httpStatus);
            if (httpStatus == 200) {
    
    
                ret = 0;
            }
        }

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

    if (ftpfile.stream) {
    
    
        fclose(ftpfile.stream); /* close the local file */
    }

    curl_global_cleanup();

    return ret;
}