examples: add a couple of simple pop3s examples

These examples show how to fetch a single message (RETR command) and how to
list all the messages in a given mailbox (LIST command), with authentication
via SSL.

They were both based on the https.c example.

docs/examples/pop3s.c

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+/***************************************************************************
+ *                                  _   _ ____  _
+ *  Project                     ___| | | |  _ \| |
+ *                             / __| | | | |_) | |
+ *                            | (__| |_| |  _ <| |___
+ *                             \___|\___/|_| \_\_____|
+ *
+ * Copyright (C) 1998 - 2011, 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 http://curl.haxx.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.
+ *
+ ***************************************************************************/
+#include <stdio.h>
+#include <curl/curl.h>
+
+int main(void)
+{
+  CURL *curl;
+  CURLcode res;
+
+  curl = curl_easy_init();
+  if(curl) {
+    /* Set username and password */
+    curl_easy_setopt(curl, CURLOPT_USERPWD, "user:password");
+
+    /* This will only fetch the message with ID "1" of the given mailbox */
+    curl_easy_setopt(curl, CURLOPT_URL, "pop3s://user@pop.example.com/1");
+
+#ifdef SKIP_PEER_VERIFICATION
+    /*
+     * If you want to connect to a site who isn't using a certificate that is
+     * signed by one of the certs in the CA bundle you have, you can skip the
+     * verification of the server's certificate. This makes the connection
+     * A LOT LESS SECURE.
+     *
+     * If you have a CA cert for the server stored someplace else than in the
+     * default bundle, then the CURLOPT_CAPATH option might come handy for
+     * you.
+     */
+    curl_easy_setopt(curl, CURLOPT_SSL_VERIFYPEER, 0L);
+#endif
+
+#ifdef SKIP_HOSTNAME_VERFICATION
+    /*
+     * If the site you're connecting to uses a different host name that what
+     * they have mentioned in their server certificate's commonName (or
+     * subjectAltName) fields, libcurl will refuse to connect. You can skip
+     * this check, but this will make the connection less secure.
+     */
+    curl_easy_setopt(curl, CURLOPT_SSL_VERIFYHOST, 0L);
+#endif
+
+    res = curl_easy_perform(curl);
+
+    /* always cleanup */
+    curl_easy_cleanup(curl);
+  }
+  return 0;
+}

docs/examples/pop3slist.c

@@ -0,0 +1,68 @@
+/***************************************************************************
+ *                                  _   _ ____  _
+ *  Project                     ___| | | |  _ \| |
+ *                             / __| | | | |_) | |
+ *                            | (__| |_| |  _ <| |___
+ *                             \___|\___/|_| \_\_____|
+ *
+ * Copyright (C) 1998 - 2011, 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 http://curl.haxx.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.
+ *
+ ***************************************************************************/
+#include <stdio.h>
+#include <curl/curl.h>
+
+int main(void)
+{
+  CURL *curl;
+  CURLcode res;
+
+  curl = curl_easy_init();
+  if(curl) {
+    /* Set username and password */
+    curl_easy_setopt(curl, CURLOPT_USERPWD, "user:password");
+
+    /* This will list every message of the given mailbox */
+    curl_easy_setopt(curl, CURLOPT_URL, "pop3s://user@pop.example.com/");
+
+#ifdef SKIP_PEER_VERIFICATION
+    /*
+     * If you want to connect to a site who isn't using a certificate that is
+     * signed by one of the certs in the CA bundle you have, you can skip the
+     * verification of the server's certificate. This makes the connection
+     * A LOT LESS SECURE.
+     *
+     * If you have a CA cert for the server stored someplace else than in the
+     * default bundle, then the CURLOPT_CAPATH option might come handy for
+     * you.
+     */
+    curl_easy_setopt(curl, CURLOPT_SSL_VERIFYPEER, 0L);
+#endif
+
+#ifdef SKIP_HOSTNAME_VERFICATION
+    /*
+     * If the site you're connecting to uses a different host name that what
+     * they have mentioned in their server certificate's commonName (or
+     * subjectAltName) fields, libcurl will refuse to connect. You can skip
+     * this check, but this will make the connection less secure.
+     */
+    curl_easy_setopt(curl, CURLOPT_SSL_VERIFYHOST, 0L);
+#endif
+
+    res = curl_easy_perform(curl);
+
+    /* always cleanup */
+    curl_easy_cleanup(curl);
+  }
+  return 0;
+}