example/connect-to: show CURLOPT_CONNECT_TO

Closes #11340

docs/examples/Makefile.inc

@@ -29,6 +29,7 @@ check_PROGRAMS = \
   anyauthput \
   certinfo \
   chkspeed \
+  connect-to \
   cookie_interface \
   debug \
   default-scheme \

docs/examples/connect-to.c

@@ -0,0 +1,70 @@
+/***************************************************************************
+ *                                  _   _ ____  _
+ *  Project                     ___| | | |  _ \| |
+ *                             / __| | | | |_) | |
+ *                            | (__| |_| |  _ <| |___
+ *                             \___|\___/|_| \_\_____|
+ *
+ * Copyright (C) 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.
+ *
+ * SPDX-License-Identifier: curl
+ *
+ ***************************************************************************/
+/* <DESC>
+ * Use CURLOPT_CONNECT_TO to connect to "wrong" host name
+ * </DESC>
+ */
+#include <stdio.h>
+#include <curl/curl.h>
+
+int main(void)
+{
+  CURL *curl;
+  CURLcode res = CURLE_OK;
+
+  /*
+    Each single string should be written using the format
+    HOST:PORT:CONNECT-TO-HOST:CONNECT-TO-PORT where HOST is the host of the
+    request, PORT is the port of the request, CONNECT-TO-HOST is the host name
+    to connect to, and CONNECT-TO-PORT is the port to connect to.
+   */
+  /* instead of curl.se:443, it will resolve and use example.com:443 but in
+     other aspects work as if it still is curl.se */
+  struct curl_slist *host = curl_slist_append(NULL,
+                                              "curl.se:443:example.com:443");
+
+  curl = curl_easy_init();
+  if(curl) {
+    curl_easy_setopt(curl, CURLOPT_CONNECT_TO, host);
+    curl_easy_setopt(curl, CURLOPT_VERBOSE, 1L);
+    curl_easy_setopt(curl, CURLOPT_URL, "https://curl.se/");
+
+    /* since this connects to the wrong host, checking the host name in the
+       server certificate will fail, so unless we disable the check libcurl
+       returns CURLE_PEER_FAILED_VERIFICATION */
+    curl_easy_setopt(curl, CURLOPT_SSL_VERIFYHOST, 0L);
+
+    /* Letting the wrong host name in the certficate be okay, the transfer
+       goes through but will (most likely) cause a 404 or similar because it
+       sends an unknown name in the Host: header field */
+    res = curl_easy_perform(curl);
+
+    /* always cleanup */
+    curl_easy_cleanup(curl);
+  }
+
+  curl_slist_free_all(host);
+
+  return (int)res;
+}