Add set_tunnel_hostname_addr_map() and deprecate set_hostname_addr_map() (#2647)

Through a CONNECT proxy it is the proxy that connects to the origin, and the CONNECT target was always the original hostname, so there was no way to send the tunnel to another address. set_tunnel_hostname_addr_map() sets that target on SSLClient, Client and WebSocketClient. The CONNECT request's Host follows it, including the Digest retry, while the Host header, the SNI and the certificate check inside the tunnel keep the original hostname. The map is also copied to a redirect client.

set_hostname_addr_map() is deprecated in favor of set_direct_hostname_addr_map(), which behaves the same and names the connection it applies to. The two maps are independent and correspond to curl's --resolve and --connect-to; neither applies to the proxy's own address.

httplib.h

@@ -2927,7 +2927,12 @@ public:
   size_t is_socket_open() const;
   socket_t socket() const;
 
+  [[deprecated("Use set_direct_hostname_addr_map() instead.")]]
   void set_hostname_addr_map(std::map<std::string, std::string> addr_map);
+  void
+  set_direct_hostname_addr_map(std::map<std::string, std::string> addr_map);
+  void
+  set_tunnel_hostname_addr_map(std::map<std::string, std::string> addr_map);
 
   void set_default_headers(Headers headers);
 
@@ -3059,6 +3064,9 @@ protected:
   // hostname; only the connection target changes, never the identity.
   std::map<std::string, std::string> addr_map_;
 
+  // Hostname to CONNECT target map, used only through a proxy.
+  std::map<std::string, std::string> tunnel_addr_map_;
+
   // Default headers
   Headers default_headers_;
 
@@ -3348,7 +3356,12 @@ public:
   size_t is_socket_open() const;
   socket_t socket() const;
 
+  [[deprecated("Use set_direct_hostname_addr_map() instead.")]]
   void set_hostname_addr_map(std::map<std::string, std::string> addr_map);
+  void
+  set_direct_hostname_addr_map(std::map<std::string, std::string> addr_map);
+  void
+  set_tunnel_hostname_addr_map(std::map<std::string, std::string> addr_map);
 
   void set_default_headers(Headers headers);
 
@@ -4748,7 +4761,12 @@ public:
   set_connection_timeout(const std::chrono::duration<Rep, Period> &duration);
 
   void set_interface(const std::string &intf);
+  [[deprecated("Use set_direct_hostname_addr_map() instead.")]]
   void set_hostname_addr_map(std::map<std::string, std::string> addr_map);
+  void
+  set_direct_hostname_addr_map(std::map<std::string, std::string> addr_map);
+  void
+  set_tunnel_hostname_addr_map(std::map<std::string, std::string> addr_map);
 
   void set_proxy(const std::string &host, int port);
   void set_proxy_basic_auth(const std::string &username,
@@ -4820,6 +4838,9 @@ private:
   // hostname; only the connection target changes, never the identity.
   std::map<std::string, std::string> addr_map_;
 
+  // Hostname to CONNECT target map, used only through a proxy.
+  std::map<std::string, std::string> tunnel_addr_map_;
+
   std::string proxy_host_;
   int proxy_port_ = -1;
   std::string proxy_basic_auth_username_;
@@ -13046,6 +13067,17 @@ make_host_and_port_string_always_port(const std::string &host, int port) {
   return prepare_host_string(host) + ":" + std::to_string(port);
 }
 
+// Request target of a CONNECT for `host`, with `addr_map` applied.
+inline std::string
+make_connect_request_target(const std::map<std::string, std::string> &addr_map,
+                            const std::string &host, int port) {
+  std::string connect_host;
+  std::string ip;
+  apply_addr_map(addr_map, host, connect_host, ip);
+  return make_host_and_port_string_always_port(ip.empty() ? connect_host : ip,
+                                               port);
+}
+
 // Value for the Host header a client sends when the caller supplied none.
 // Only the value: callers decide where in their header list it goes.
 inline std::string make_default_host_header_value(const std::string &host,
@@ -16574,6 +16606,7 @@ inline void ClientImpl::setup_redirect_client(ClientType &client) {
 
   // Copy network and socket settings
   client.addr_map_ = addr_map_;
+  client.tunnel_addr_map_ = tunnel_addr_map_;
   client.set_address_family(address_family_);
   client.set_tcp_nodelay(tcp_nodelay_);
   client.set_ipv6_v6only(ipv6_v6only_);
@@ -18086,9 +18119,19 @@ inline void ClientImpl::set_path_encode(bool on) { path_encode_ = on; }
 
 inline void
 ClientImpl::set_hostname_addr_map(std::map<std::string, std::string> addr_map) {
+  set_direct_hostname_addr_map(std::move(addr_map));
+}
+
+inline void ClientImpl::set_direct_hostname_addr_map(
+    std::map<std::string, std::string> addr_map) {
   addr_map_ = std::move(addr_map);
 }
 
+inline void ClientImpl::set_tunnel_hostname_addr_map(
+    std::map<std::string, std::string> addr_map) {
+  tunnel_addr_map_ = std::move(addr_map);
+}
+
 inline void ClientImpl::set_default_headers(Headers headers) {
   default_headers_ = std::move(headers);
 }
@@ -18797,7 +18840,17 @@ inline socket_t Client::socket() const { return cli_->socket(); }
 
 inline void
 Client::set_hostname_addr_map(std::map<std::string, std::string> addr_map) {
-  cli_->set_hostname_addr_map(std::move(addr_map));
+  cli_->set_direct_hostname_addr_map(std::move(addr_map));
+}
+
+inline void Client::set_direct_hostname_addr_map(
+    std::map<std::string, std::string> addr_map) {
+  cli_->set_direct_hostname_addr_map(std::move(addr_map));
+}
+
+inline void Client::set_tunnel_hostname_addr_map(
+    std::map<std::string, std::string> addr_map) {
+  cli_->set_tunnel_hostname_addr_map(std::move(addr_map));
 }
 
 inline void Client::set_default_headers(Headers headers) {
@@ -19165,6 +19218,10 @@ inline bool SSLClient::connect_with_proxy(
     std::chrono::time_point<std::chrono::steady_clock> start_time,
     Response &res, bool &success, Error &error) {
   success = true;
+  auto connect_target =
+      detail::make_connect_request_target(tunnel_addr_map_, host_, port_);
+  auto retargeted = connect_target !=
+                    detail::make_host_and_port_string_always_port(host_, port_);
   Response proxy_res;
   if (!detail::process_client_socket(
           socket.sock, read_timeout_sec_, read_timeout_usec_,
@@ -19172,8 +19229,8 @@ inline bool SSLClient::connect_with_proxy(
           start_time, [&](Stream &strm) {
             Request req2;
             req2.method = "CONNECT";
-            req2.path =
-                detail::make_host_and_port_string_always_port(host_, port_);
+            req2.path = connect_target;
+            if (retargeted) { req2.set_header("Host", connect_target); }
             if (max_timeout_msec_ > 0) {
               req2.start_time_ = std::chrono::steady_clock::now();
             }
@@ -19212,8 +19269,8 @@ inline bool SSLClient::connect_with_proxy(
                 start_time, [&](Stream &strm) {
                   Request req3;
                   req3.method = "CONNECT";
-                  req3.path = detail::make_host_and_port_string_always_port(
-                      host_, port_);
+                  req3.path = connect_target;
+                  if (retargeted) { req3.set_header("Host", connect_target); }
                   req3.headers.insert(detail::make_digest_authentication_header(
                       req3, make_request_target(req3), auth, 1,
                       detail::random_string(10), proxy_digest_auth_username_,
@@ -24058,9 +24115,19 @@ inline void WebSocketClient::set_interface(const std::string &intf) {
 
 inline void WebSocketClient::set_hostname_addr_map(
     std::map<std::string, std::string> addr_map) {
+  set_direct_hostname_addr_map(std::move(addr_map));
+}
+
+inline void WebSocketClient::set_direct_hostname_addr_map(
+    std::map<std::string, std::string> addr_map) {
   addr_map_ = std::move(addr_map);
 }
 
+inline void WebSocketClient::set_tunnel_hostname_addr_map(
+    std::map<std::string, std::string> addr_map) {
+  tunnel_addr_map_ = std::move(addr_map);
+}
+
 inline bool WebSocketClient::is_proxy_enabled() const {
   if (proxy_host_.empty() || proxy_port_ == -1) { return false; }
   if (no_proxy_entries_.empty()) { return true; }
@@ -24110,7 +24177,8 @@ inline bool WebSocketClient::connect_with_proxy(Response &proxy_res,
                                                 Error &error) {
   Request req;
   req.method = "CONNECT";
-  req.path = detail::make_host_and_port_string_always_port(host_, port_);
+  req.path =
+      detail::make_connect_request_target(tunnel_addr_map_, host_, port_);
   req.headers.emplace("Host", req.path);
   detail::add_default_user_agent_header(req);
   detail::add_authorization_header(req, proxy_basic_auth_username_,