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, 43 insertions, 6 deletions

diff --git a/src/zenhttp/servers/httpsys.cpp b/src/zenhttp/servers/httpsys.cpp
index 6995ffca9..e93ae4853 100644
--- a/src/zenhttp/servers/httpsys.cpp
+++ b/src/zenhttp/servers/httpsys.cpp
@@ -12,6 +12,7 @@
 #include <zencore/memory/llm.h>
 #include <zencore/scopeguard.h>
 #include <zencore/string.h>
+#include <zencore/system.h>
 #include <zencore/timer.h>
 #include <zencore/trace.h>
 #include <zenhttp/packageformat.h>
@@ -27,6 +28,7 @@
 
 #	include <atomic>
 #	include <http.h>
+#	include <asio.hpp>	 // for resolving addresses for GetExternalHost
 
 namespace zen {
 
@@ -93,12 +95,13 @@ public:
 
 	// HttpServer interface implementation
 
-	virtual int	 OnInitialize(int BasePort, std::filesystem::path DataDir) override;
-	virtual void OnRun(bool TestMode) override;
-	virtual void OnRequestExit() override;
-	virtual void OnRegisterService(HttpService& Service) override;
-	virtual void OnSetHttpRequestFilter(IHttpRequestFilter* RequestFilter) override;
-	virtual void OnClose() override;
+	virtual int			OnInitialize(int BasePort, std::filesystem::path DataDir) override;
+	virtual void		OnRun(bool TestMode) override;
+	virtual void		OnRequestExit() override;
+	virtual void		OnRegisterService(HttpService& Service) override;
+	virtual void		OnSetHttpRequestFilter(IHttpRequestFilter* RequestFilter) override;
+	virtual void		OnClose() override;
+	virtual std::string OnGetExternalHost() const override;
 
 	WorkerThreadPool& WorkPool();
 
@@ -2290,6 +2293,40 @@ HttpSysServer::OnRequestExit()
 	m_ShutdownEvent.Set();
 }
 
+std::string
+HttpSysServer::OnGetExternalHost() const
+{
+	// Check whether we registered a public wildcard URL (http://*:port/) or fell back to loopback
+	bool IsPublic = false;
+	for (const auto& Uri : m_BaseUris)
+	{
+		if (Uri.find(L'*') != std::wstring::npos)
+		{
+			IsPublic = true;
+			break;
+		}
+	}
+
+	if (!IsPublic)
+	{
+		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
 HttpSysServer::OnRegisterService(HttpService& Service)
 {