Problems using libcurl to send email (C++ and Win32)
<p>I'm currently experiencing some problems and was hoping I could gain some insight as to what is going on by posting it here. I want to write a simple C++ application (or C) to send an email to a gmail account. I am in a win32 (xp sp2) environment and I am using dev C++ as my compiler. I've included the curl libraries and the application seems to compile fine, however it does not send the email nor does it display errors. Here is the code that I found that I am using to do this:</p>

<pre><code>#include &lt;stdio.h&gt;
#include &lt;string.h&gt;
#include &lt;curl/curl.h&gt;
#include &lt;conio.h&gt;
#include &lt;iostream&gt;

/* This is a simple example showing how to send mail using libcurl's SMTP 
 * capabilities. It builds on the simplesmtp.c example, adding some
 * authentication and transport security.
 */ 

#define FROM    "&lt;email@email.com&gt;"
#define TO      "&lt;email@gmail.com&gt;"
#define CC      "&lt;email@gmail.com&gt;"

using namespace std; 

static const char *payload_text[]={
  "Date: Mon, 29 Nov 2010 21:54:29 +1100\n",
  "To: " TO "\n",
  "From: " FROM "(Example User)\n",
  "Cc: " CC "(Another example User)\n",
  "Message-ID: &lt;dcd7cb36-11db-487a-9f3a-e652a9458efd@rfcpedant.example.org&gt;\n",
  "Subject: SMTP TLS example message\n",
  "\n", /* empty line to divide headers from body, see RFC5322 */ 
  "The body of the message starts here.\n",
  "\n",
  "It could be a lot of lines, could be MIME encoded, whatever.\n",
  "Check RFC5322.\n",
  NULL
};

struct upload_status {
  int lines_read;
};

static size_t payload_source(void *ptr, size_t size, size_t nmemb, void *userp)
{
struct upload_status *upload_ctx = (struct upload_status *)userp;
const char *data;

if ((size == 0) || (nmemb == 0) || ((size*nmemb) &lt; 1)) {
return 0;
}

data = payload_text[upload_ctx-&gt;lines_read];

if (data) {
size_t len = strlen(data);
memcpy(ptr, data, len);
upload_ctx-&gt;lines_read ++;
return len;
}
return 0;
}





int main(void)
{
  //cout &lt;&lt; "starting";
  //_getch();
  CURL *curl;
  CURLcode res;
  struct curl_slist *recipients = NULL;
  struct upload_status upload_ctx;

  upload_ctx.lines_read = 0;

  curl = curl_easy_init();
  if (curl) {

    curl_easy_setopt(curl, CURLOPT_VERBOSE, 1);
    /* This is the URL for your mailserver. Note the use of port 587 here,
     * instead of the normal SMTP port (25). Port 587 is commonly used for
     * secure mail submission (see RFC4403), but you should use whatever
     * matches your server configuration. */ 
    curl_easy_setopt(curl, CURLOPT_URL, "smtp://smtp.gmail.com:587");


/* In this example, we'll start with a plain text connection, and upgrade
 * to Transport Layer Security (TLS) using the STARTTLS command. Be careful
 * of using CURLUSESSL_TRY here, because if TLS upgrade fails, the transfer
 * will continue anyway - see the security discussion in the libcurl
 * tutorial for more details. */ 
curl_easy_setopt(curl, CURLOPT_USE_SSL, (long)CURLUSESSL_ALL);

/* If your server doesn't have a valid certificate, then you can disable
 * part of the Transport Layer Security protection by setting the
 * CURLOPT_SSL_VERIFYPEER and CURLOPT_SSL_VERIFYHOST options to 0 (false).
 *   curl_easy_setopt(curl, CURLOPT_SSL_VERIFYPEER, 0L);
 *   curl_easy_setopt(curl, CURLOPT_SSL_VERIFYHOST, 0L);
 * That is, in general, a bad idea. It is still better than sending your
 * authentication details in plain text though.
 * Instead, you should get the issuer certificate (or the host certificate
 * if the certificate is self-signed) and add it to the set of certificates
 * that are known to libcurl using CURLOPT_CAINFO and/or CURLOPT_CAPATH. See
 * docs/SSLCERTS for more information.
 */ 
//curl_easy_setopt(curl, CURLOPT_CAINFO, "/path/to/certificate.pem");

/* A common reason for requiring transport security is to protect
 * authentication details (user names and passwords) from being "snooped"
 * on the network. Here is how the user name and password are provided: */ 
curl_easy_setopt(curl, CURLOPT_USERNAME, "username");
curl_easy_setopt(curl, CURLOPT_PASSWORD, "password");

/* value for envelope reverse-path */ 
curl_easy_setopt(curl, CURLOPT_MAIL_FROM, FROM);
/* Add two recipients, in this particular case they correspond to the
 * To: and Cc: addressees in the header, but they could be any kind of
 * recipient. */ 
recipients = curl_slist_append(recipients, TO);
recipients = curl_slist_append(recipients, CC);
curl_easy_setopt(curl, CURLOPT_MAIL_RCPT, recipients);

/* In this case, we're using a callback function to specify the data. You
 * could just use the CURLOPT_READDATA option to specify a FILE pointer to
 * read from.
 */ 
curl_easy_setopt(curl, CURLOPT_READFUNCTION, payload_source);
curl_easy_setopt(curl, CURLOPT_READDATA, &amp;upload_ctx);

/* Since the traffic will be encrypted, it is very useful to turn on debug
 * information within libcurl to see what is happening during the transfer.
 */ 
curl_easy_setopt(curl, CURLOPT_VERBOSE, 1L);

/* send the message (including headers) */ 
res = curl_easy_perform(curl);
/* Check for errors */ 
if(res != CURLE_OK)
  fprintf(stderr, "curl_easy_perform() failed: %s\n",
          curl_easy_strerror(res));

/* free the list of recipients and clean up */ 
curl_slist_free_all(recipients);
curl_easy_cleanup(curl);
_getch();


}

return 0;
}
</code></pre>

<p>When I compile and run this, I see a black screen for a milisecond or so, then nothing, no email sent, no errors, etc. I thought by adding the 'curl_easy_setopt(curl, CURLOPT_VERBOSE, 1);' (as reccomended per libcurl's website) would display output, but nothing. So I added the '_getch()' line at the end before the return, and still the window is dissappearing.</p>

<p>I also tried using 'system("pause")' before the final return to no avail either. Currently is appears I need to get the readable output to further debug the problem so I can continue on and get this code to send emails.</p>

<p>I have also tried changing the port to 465 to no avail either. </p>

<p>Anyone have any idea what's going on here? Thank you for your time. </p>
