server: Populate Request.Host field

request.go

@@ -23,7 +23,9 @@ type Request struct {
 	// For international domain names, Host may be in Punycode or
 	// Unicode form. Use golang.org/x/net/idna to convert it to
 	// either format if needed.
-	// This field is ignored by the Gemini server.
+	//
+	// For server requests, Host specifies the host on which the URL
+	// is sought.
 	Host string
 
 	// For client requests, Certificate optionally specifies the

server.go

@@ -291,6 +291,7 @@ func (srv *Server) respond(conn net.Conn) {
 	if tlsConn, ok := conn.(*tls.Conn); ok {
 		state := tlsConn.ConnectionState()
 		req.TLS = &state
+		req.Host = state.ServerName
 	}
 
 	// Store remote address