add Webserver constructor that probes a port range. Necessary if multiple instances are running.

webserver.cc

@@ -18,10 +18,39 @@ namespace pEp {
     , _acceptor{_ioc, {addr, port}}
     , _doc_root{doc_root}
     , _generic_handler{}
+    , _port{port}
     , _running{false}
     { }
 
 
+Webserver::Webserver(net::ip::address addr, unsigned short start_port, unsigned short end_port)
+: _ioc{1}
+, _acceptor{_ioc}
+, _doc_root{} // no doc_root
+, _generic_handler{}
+, _port{-1}
+, _running{false}
+{
+    boost::system::error_code ec{};
+
+    for(unsigned short port = start_port; port<=end_port; ++port)
+    {
+        _acceptor.bind( {addr, port }, ec );
+        if(!ec)
+        {
+            _port = port;
+            break;
+        }
+    }
+    
+    if(_port<0)
+    {
+        throw boost::system::system_error(ec, "Cannot bind to any port from "
+            + std::to_string(start_port) + " to " + std::to_string(end_port) + ".");
+    }
+}
+
+
 beast::string_view Webserver::mime_type(beast::string_view path)
 {
     using beast::iequals;

webserver.hh

@@ -43,6 +43,7 @@ namespace pEp {
             std::string _doc_root;
             std::unordered_map< std::string, Handling > _urls;
             handler_t _generic_handler;
+            int  _port;
             bool _running;
             std::mutex _mtx;
 
@@ -51,9 +52,15 @@ namespace pEp {
             // if doc_root is empty, don't deliver arbitrary files.
             Webserver(net::ip::address addr, unsigned short port, const std::string& doc_root = "");
 
+            // probes all ports from start_port ... end_port, inclusive.
+            Webserver(net::ip::address addr, unsigned short start_port, unsigned short end_port);
+
             Webserver(const Webserver&) = delete;
             Webserver& operator=(const Webserver&) = delete;
             virtual ~Webserver() = default;
+            
+            constexpr
+            int port() const noexcept { return _port; }
 
             void add_url_handler   (const std::string& url_regex, handler_t handler);
             void remove_url_handler(const std::string& url_regex);