How to upload picture to mattermost server by using libcurl? - c++

Question

Trying to build a C++ application to upload images to mattermost server(version 5.14.0).And I have get access token,channel id by using my C++ code.But I can't upload image by using libcurl.
This is my CPP code(using libcurl right now):
void uploadPicture(string url,string channelId, string path,string fileName,string token)
{
url += "/api/v4/files";
CURL *curl;
struct curl_httppost *formpost = NULL;
struct curl_httppost *lastptr = NULL;
curl_formadd(&formpost, &lastptr,
CURLFORM_COPYNAME, "files",
CURLFORM_FILE, path.c_str(),
CURLFORM_FILENAME,"test.jpg",
CURLFORM_CONTENTTYPE, "image/jpeg",
CURLFORM_END);
curl_formadd(&formpost, &lastptr,
CURLFORM_COPYNAME, "client_ids",
CURLFORM_COPYCONTENTS, "test.jpg",
CURLFORM_END);
curl_formadd(&formpost, &lastptr,
CURLFORM_COPYNAME, "channel_id",
CURLFORM_COPYCONTENTS, channelId.c_str(),
CURLFORM_END);
struct curl_slist *headers = NULL;
string auth = "Authorization:Bearer ";
auth += token;
headers = curl_slist_append(headers, "Content-Type:multipart/form-data");
headers = curl_slist_append(headers, auth.c_str());
CURLcode res;
curl = curl_easy_init();
if (curl)
{
res = curl_easy_setopt(curl, CURLOPT_URL, url.c_str());
res = curl_easy_setopt(curl, CURLOPT_HTTPHEADER, headers);
res = curl_easy_setopt(curl, CURLOPT_HTTPPOST,formpost);
res = curl_easy_setopt(curl, CURLOPT_WRITEFUNCTION, getFileInfo);
res = curl_easy_setopt(curl, CURLOPT_POST, 1);
res = curl_easy_perform(curl);
if (res != 0)
{
curl_slist_free_all(headers);
curl_easy_cleanup(curl);
}
}
}
But it won't work...Please tell me where the problem is.

Answer 1

At last.I find a solution:
void uploadByMimeApi(string url, string channelId, string path, string fileName, string token)
{
url += "/api/v4/files";
CURL *curl = curl_easy_init();
curl_mime *mime;
curl_mimepart *part;
curl_mimepart *part2;
curl_mimepart *part3;
/* Build an HTTP form */
mime = curl_mime_init(curl);
part = curl_mime_addpart(mime);
curl_mime_name(part, "files");
curl_mime_filedata(part, path.c_str());
curl_mime_type(part, "image/jpeg");
part2 = curl_mime_addpart(mime);
curl_mime_data(part2, channelId.c_str(), CURL_ZERO_TERMINATED);
curl_mime_name(part2, "channel_id");
part3 = curl_mime_addpart(mime);
curl_mime_data(part3, "test", CURL_ZERO_TERMINATED);
curl_mime_name(part3, "client_ids");
//header issue
struct curl_slist *headers = NULL;
static const char buf[] = "Expect:";
string auth = "Authorization:Bearer ";
auth += token;
headers = curl_slist_append(headers, auth.c_str());
headers = curl_slist_append(headers, buf);
/* Post and send it. */
curl_easy_setopt(curl, CURLOPT_VERBOSE, 1L);
curl_easy_setopt(curl, CURLOPT_HTTPHEADER, headers);
curl_easy_setopt(curl, CURLOPT_MIMEPOST, mime);
curl_easy_setopt(curl, CURLOPT_URL, url.c_str());
curl_easy_setopt(curl, CURLOPT_WRITEFUNCTION, getFileInfo);
curl_easy_perform(curl);
/* Clean-up. */
curl_easy_cleanup(curl);
curl_mime_free(mime);
}