curl/docs/examples/smtp-tls.c

/*****************************************************************************
 *                                  _   _ ____  _
 *  Project                     ___| | | |  _ \| |
 *                             / __| | | | |_) | |
 *                            | (__| |_| |  _ <| |___
 *                             \___|\___/|_| \_\_____|
 *
 */

#include <stdio.h>
#include <string.h>
#include <curl/curl.h>

/* 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    "<sender@example.org>"
#define TO      "<addressee@example.net>"
#define CC      "<info@example.org>"

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: <dcd7cb36-11db-487a-9f3a-e652a9458efd@rfcpedant.example.org>\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) < 1)) {
    return 0;
  }

  data = payload_text[upload_ctx->lines_read];

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


int main(void)
{
  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) {
    /* 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://mainserver.example.net: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, 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, 0);
     *   curl_easy_setopt(curl, CURLOPT_SSL_VERIFYHOST, 0);
     * 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, "user@example.net");
    curl_easy_setopt(curl, CURLOPT_PASSWORD, "P@ssw0rd");

    /* 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, &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, 1);

    /* send the message (including headers) */
    res = curl_easy_perform(curl);

    /* free the list of recipients and clean up */
    curl_slist_free_all(recipients);
    curl_easy_cleanup(curl);
  }
  return 0;
}