Add proxy client example

examples/http-proxy-client/main.c

@@ -0,0 +1,64 @@
+// Copyright (c) 2020 Cesanta Software Limited
+// All rights reserved
+//
+// Example HTTP client that uses a proxy server. Usage:
+//    make
+//    ./example PROXY:PORT http://www.ladyada.net
+//
+// To enable SSL/TLS for this client, build it like this:
+//    make MBEDTLS_DIR=/path/to/your/mbedtls/installation
+
+#include "mongoose.h"
+
+// Print HTTP response and signal that we're done
+static void fn(struct mg_connection *c, int ev, void *ev_data, void *fn_data) {
+  const char *url = fn_data;
+  static bool connected;
+  if (ev == MG_EV_HTTP_MSG) {
+    struct mg_http_message *hm = (struct mg_http_message *) ev_data;
+    printf("%.*s", (int) hm->message.len, hm->message.ptr);
+    exit(EXIT_SUCCESS);
+  } else if (ev == MG_EV_CONNECT) {
+    // Proxy TCP connection established. Send CONNECT request
+    struct mg_str host = mg_url_host(url);
+    // c->is_hexdumping = 1;
+    mg_printf(c, "CONNECT %.*s:%hu HTTP/1.1\r\nHost: %.*s:%hu\r\n\r\n",
+              (int) host.len, host.ptr, mg_url_port(url), (int) host.len,
+              host.ptr, mg_url_port(url));
+    // If target URL is SSL/TLS, command client connection to use TLS
+    if (mg_url_is_ssl(url)) {
+      struct mg_tls_opts opts = {.ca = "ca.pem"};
+      mg_tls_init(c, &opts);
+    }
+  } else if (!connected && ev == MG_EV_READ) {
+    struct mg_http_message hm;
+    int n = mg_http_parse((char *) c->recv.buf, c->recv.len, &hm);
+    if (n > 0) {
+      struct mg_str host = mg_url_host(url);
+      // CONNECT response - tunnel is established
+      connected = true;
+      LOG(LL_DEBUG,
+          ("Connected to proxy, status: %.*s", (int) hm.uri.len, hm.uri.ptr));
+      mg_iobuf_delete(&c->recv, n);
+      // Send request to the target server
+      mg_printf(c, "GET / HTTP/1.0\r\nHost: %.*s\r\n\r\n", (int) host.len,
+                host.ptr);
+    }
+  }
+}
+
+int main(int argc, char *argv[]) {
+  struct mg_mgr mgr;
+
+  if (argc != 3) {
+    fprintf(stderr, "Usage: %s PROXY_URL URL\n", argv[0]);
+    return EXIT_FAILURE;
+  }
+
+  mg_mgr_init(&mgr);                            // Initialise event manager
+  mg_http_connect(&mgr, argv[1], fn, argv[2]);  // Connect to the proxy
+  for (;;) mg_mgr_poll(&mgr, 1000);             // Event loop
+  mg_mgr_free(&mgr);
+
+  return 0;
+}