Using Easy Curl to do an FTP Upload with SSL on Linux - c

Question

I have developed a ‘C’ application on a Linux box using the libcurl example http://curl.askapache.com/c/ftpupload.html I work fine. I have been asked to use SSL for both “data encryption for both the control channel and data channel.” I am not been able to find an example of adding SSL to the example I followed. Here is the core of the FTP program:
// get a FILE * of the same file
hd_src = fopen(local_file, "rb");
// curl init
curl_global_init(CURL_GLOBAL_ALL);
// get a curl handle
curl = curl_easy_init();
if (curl) { // build a list of commands to pass to libcurl
headerlist = curl_slist_append(headerlist, buf_1);
#ifdef DEBUG
// we want to use our own read function
curl_easy_setopt(curl, CURLOPT_READFUNCTION, read_callback);
#endif
// enable uploading
curl_easy_setopt(curl, CURLOPT_UPLOAD, 1L);
// specify target
curl_easy_setopt(curl, CURLOPT_URL, ftp_url);
curl_easy_setopt(curl, CURLOPT_USERPWD, user_password);
curl_easy_setopt(curl, CURLOPT_PORT, 21);
// 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
curl_easy_setopt(curl, CURLOPT_READDATA, hd_src);
// Set the size of the file to upload
curl_easy_setopt(curl, CURLOPT_INFILESIZE_LARGE, (curl_off_t) fsize);
// Now run off and do what you've been told!
res = curl_easy_perform(curl);
// Check for errors
if (res != CURLE_OK) {
char *s;
s = malloc((sizeof(char) * 100) + 1);
sprintf(s, "curl_easy_perform() failed: %s - Error Number: %d\n",
curl_easy_strerror(res), res);
returnResults->error = true;
returnResults->errorMessage = s;
return returnResults;
}
// clean up the FTP commands list
curl_slist_free_all(headerlist);
// always cleanup
curl_easy_cleanup(curl);
}
fclose(hd_src); // close the local file
curl_global_cleanup();

Answer 1

There's however an existing example code on the libcurl site showing how you do FTP-SSL to download a file: ftpsget.c - it shows the very little SSL magic you need to add. That magic is the same for uploads:
/* We activate SSL and we require it for both control and data */
curl_easy_setopt(curl, CURLOPT_USE_SSL, CURLUSESSL_ALL);
In fact, you can add this single line into the FTP upload example. and it'll do FTPS uploads for you.