smtp-tls: new example

This example shows how to send SMTP with TLS

docs/examples/Makefile.inc

@@ -4,7 +4,7 @@ check_PROGRAMS = 10-at-a-time anyauthput cookie_interface debug fileupload \
   https multi-app multi-debugcallback multi-double multi-post multi-single \
   persistant post-callback postit2 sepheaders simple simplepost simplessl  \
   sendrecv httpcustomheader certinfo chkspeed ftpgetinfo ftp-wildcard \
-  smtp-multi simplesmtp
+  smtp-multi simplesmtp smtp-tls
 
 # These examples require external dependencies that may not be commonly
 # available on POSIX systems, so don't bother attempting to compile them here.

docs/examples/smtp-tls.c

@@ -0,0 +1,135 @@
+/*****************************************************************************
+ *                                  _   _ ____  _
+ *  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"
+  "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;
+}