Add the outgoing_bind option

Lets the admin choose a local address to bind each outgoing (IRC) socket.

doc/biboumi.1.md

@@ -120,6 +120,15 @@ The configuration file uses a simple format of the form
   negociating a TLS session. By default this value is unset and biboumi
   tries a list of well-known paths.
 
+`outgoing_bind`
+
+  An address (IPv4 or IPv6) to bind the outgoing sockets to.  If no value is
+  specified, it will use the one assigned by the operating system.  You can
+  for example use outgoing_bind=192.168.1.11 to force biboumi to use the
+  interface with this address.  Note that this is only used for connections
+  to IRC servers, the connection to the XMPP server is always done locally
+  on 127.0.0.1.
+
 The configuration can be re-read at runtime (you can for example change the
 log level without having to restart biboumi) by sending SIGUSR1 or SIGUSR2
 (see kill(1)) to the process.

louloulibs/network/tcp_socket_handler.cpp

@@ -56,6 +56,34 @@ void TCPSocketHandler::init_socket(const struct addrinfo* rp)
     ::close(this->socket);
   if ((this->socket = ::socket(rp->ai_family, rp->ai_socktype, rp->ai_protocol)) == -1)
     throw std::runtime_error("Could not create socket: "s + strerror(errno));
+  // Bind the socket to a specific address, if specified
+  if (!this->bind_addr.empty())
+    {
+      // Convert the address from string format to a sockaddr that can be
+      // used in bind()
+      struct addrinfo* result;
+      int err = ::getaddrinfo(this->bind_addr.data(), nullptr, nullptr, &result);
+      if (err != 0)
+        log_error("Failed to bind socket to " << this->bind_addr << ": "
+                  << gai_strerror(err));
+      else
+        {
+          struct addrinfo* rp;
+          int bind_error;
+          for (rp = result; rp; rp = rp->ai_next)
+            {
+              if ((bind_error = ::bind(this->socket,
+                         reinterpret_cast<const struct sockaddr*>(rp->ai_addr),
+                         rp->ai_addrlen)) == 0)
+                break;
+            }
+          if (!rp)
+            log_error("Failed to bind socket to " << this->bind_addr << ": "
+                      << strerror(bind_error));
+          else
+            log_info("Socket successfully bound to " << this->bind_addr);
+        }
+    }
   int optval = 1;
   if (::setsockopt(this->socket, SOL_SOCKET, SO_KEEPALIVE, &optval, sizeof(optval)) == -1)
     log_warning("Failed to enable TCP keepalive on socket: " << strerror(errno));

louloulibs/network/tcp_socket_handler.hpp

@@ -224,6 +224,12 @@ protected:
 
   bool hostname_resolution_failed;
 
+  /**
+   * Address to bind the socket to, before calling connect().
+   * If empty, it’s equivalent to binding to INADDR_ANY.
+   */
+  std::string bind_addr;
+
 private:
   TCPSocketHandler(const TCPSocketHandler&) = delete;
   TCPSocketHandler(TCPSocketHandler&&) = delete;

src/irc/irc_client.cpp

@@ -86,6 +86,9 @@ void IrcClient::start()
   this->bridge->send_xmpp_message(this->hostname, "", "Connecting to "s +
                                   this->hostname + ":" + port + " (" +
                                   (tls ? "encrypted" : "not encrypted") + ")");
+
+  this->bind_addr = Config::get("outgoing_bind", "");
+
   this->connect(this->hostname, port, tls);
 }