HttpService/Frontend improvements (#782)

- zenhttp: added `GetServiceUri()`/`GetExternalHost()`
  - enables code to quickly generate an externally reachable URI for a given service
- frontend: improved Uri handling (better defaults)
  - added support for 404 page (to make it easier to find a good URL)

1 files changed, 41 insertions, 7 deletions

diff --git a/src/zenhttp/servers/httpasio.cpp b/src/zenhttp/servers/httpasio.cpp
index fbc7fe401..0c0238886 100644
--- a/src/zenhttp/servers/httpasio.cpp
+++ b/src/zenhttp/servers/httpasio.cpp
@@ -7,6 +7,7 @@
 #include <zencore/fmtutils.h>
 #include <zencore/logging.h>
 #include <zencore/memory/llm.h>
+#include <zencore/system.h>
 #include <zencore/thread.h>
 #include <zencore/trace.h>
 #include <zencore/windows.h>
@@ -506,6 +507,8 @@ public:
 	HttpService*			   RouteRequest(std::string_view Url);
 	IHttpRequestFilter::Result FilterRequest(HttpServerRequest& Request);
 
+	bool IsLoopbackOnly() const;
+
 	asio::io_service						 m_IoService;
 	asio::io_service::work					 m_Work{m_IoService};
 	std::unique_ptr<asio_http::HttpAcceptor> m_Acceptor;
@@ -1601,7 +1604,8 @@ struct HttpAcceptor
 
 	void StopAccepting() { m_IsStopped = true; }
 
-	int GetAcceptPort() { return m_Acceptor.local_endpoint().port(); }
+	int	 GetAcceptPort() const { return m_Acceptor.local_endpoint().port(); }
+	bool IsLoopbackOnly() const { return m_Acceptor.local_endpoint().address().is_loopback(); }
 
 	bool IsValid() const { return m_IsValid; }
 
@@ -1975,6 +1979,12 @@ HttpAsioServerImpl::FilterRequest(HttpServerRequest& Request)
 	return RequestFilter->FilterRequest(Request);
 }
 
+bool
+HttpAsioServerImpl::IsLoopbackOnly() const
+{
+	return m_Acceptor && m_Acceptor->IsLoopbackOnly();
+}
+
 }  // namespace zen::asio_http
 
 //////////////////////////////////////////////////////////////////////////
@@ -1987,12 +1997,13 @@ public:
 	HttpAsioServer(const AsioConfig& Config);
 	~HttpAsioServer();
 
-	virtual void OnRegisterService(HttpService& Service) override;
-	virtual int	 OnInitialize(int BasePort, std::filesystem::path DataDir) override;
-	virtual void OnSetHttpRequestFilter(IHttpRequestFilter* RequestFilter) override;
-	virtual void OnRun(bool IsInteractiveSession) override;
-	virtual void OnRequestExit() override;
-	virtual void OnClose() override;
+	virtual void		OnRegisterService(HttpService& Service) override;
+	virtual int			OnInitialize(int BasePort, std::filesystem::path DataDir) override;
+	virtual void		OnSetHttpRequestFilter(IHttpRequestFilter* RequestFilter) override;
+	virtual void		OnRun(bool IsInteractiveSession) override;
+	virtual void		OnRequestExit() override;
+	virtual void		OnClose() override;
+	virtual std::string OnGetExternalHost() const override;
 
 private:
 	Event			 m_ShutdownEvent;
@@ -2067,6 +2078,29 @@ HttpAsioServer::OnInitialize(int BasePort, std::filesystem::path DataDir)
 	return m_BasePort;
 }
 
+std::string
+HttpAsioServer::OnGetExternalHost() const
+{
+	if (m_Impl->IsLoopbackOnly())
+	{
+		return "127.0.0.1";
+	}
+
+	// Use the UDP connect trick: connecting a UDP socket to an external address
+	// causes the OS to select the appropriate local interface without sending any data.
+	try
+	{
+		asio::io_service	  IoService;
+		asio::ip::udp::socket Sock(IoService, asio::ip::udp::v4());
+		Sock.connect(asio::ip::udp::endpoint(asio::ip::address::from_string("8.8.8.8"), 80));
+		return Sock.local_endpoint().address().to_string();
+	}
+	catch (const std::exception&)
+	{
+		return GetMachineName();
+	}
+}
+
 void
 HttpAsioServer::OnRun(bool IsInteractive)
 {