curl/docs/examples/pop3-tls.c

/***************************************************************************
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 *
 * Copyright (C) 1998 - 2020, Daniel Stenberg, <daniel@haxx.se>, et al.
 *
 * This software is licensed as described in the file COPYING, which
 * you should have received as part of this distribution. The terms
 * are also available at https://curl.se/docs/copyright.html.
 *
 * You may opt to use, copy, modify, merge, publish, distribute and/or sell
 * copies of the Software, and permit persons to whom the Software is
 * furnished to do so, under the terms of the COPYING file.
 *
 * This software is distributed on an "AS IS" basis, WITHOUT WARRANTY OF ANY
 * KIND, either express or implied.
 *
 ***************************************************************************/

/* <DESC>
 * POP3 example using TLS
 * </DESC>
 */

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

/* This is a simple example showing how to retrieve mail using libcurl's POP3
 * capabilities. It builds on the pop3-retr.c example adding transport
 * security to protect the authentication details from being snooped.
 *
 * Note that this example requires libcurl 7.20.0 or above.
 */

int main(void)
{
  CURL *curl;
  CURLcode res = CURLE_OK;

  curl = curl_easy_init();
  if(curl) {
    /* Set username and password */
    curl_easy_setopt(curl, CURLOPT_USERNAME, "user");
    curl_easy_setopt(curl, CURLOPT_PASSWORD, "secret");

    /* This will retrieve message 1 from the user's mailbox */
    curl_easy_setopt(curl, CURLOPT_URL, "pop3://pop.example.com/1");

    /* In this example, we'll start with a plain text connection, and upgrade
     * to Transport Layer Security (TLS) using the STLS 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");

    /* 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);

    /* Perform the retr */
    res = curl_easy_perform(curl);

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

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

  return (int)res;
}