From cf38d96543b2086a863ef4823ee769ec45cc45a4 Mon Sep 17 00:00:00 2001
From: zousar <2936246+zousar@users.noreply.github.com>
Date: Thu, 27 Jan 2022 01:01:05 -0700
Subject: Handle HTTP port collisions when initializing server (#40)

---
 zenhttp/httpsys.cpp | 55 +++++++++++++++++++++++++++++++++++++++--------------
 1 file changed, 41 insertions(+), 14 deletions(-)

(limited to 'zenhttp/httpsys.cpp')

diff --git a/zenhttp/httpsys.cpp b/zenhttp/httpsys.cpp
index b3d109b6a..3c57f7ce3 100644
--- a/zenhttp/httpsys.cpp
+++ b/zenhttp/httpsys.cpp
@@ -746,7 +746,7 @@ HttpSysServer::~HttpSysServer()
 	}
 }
 
-void
+int
 HttpSysServer::InitializeServer(int BasePort)
 {
 	using namespace std::literals;
@@ -762,7 +762,7 @@ HttpSysServer::InitializeServer(int BasePort)
 	{
 		ZEN_ERROR("Failed to create server session for '{}': {:#x}", WideToUtf8(WildcardUrlPath), Result);
 
-		return;
+		return BasePort;
 	}
 
 	Result = HttpCreateUrlGroup(m_HttpSessionId, &m_HttpUrlGroupId, 0);
@@ -771,17 +771,29 @@ HttpSysServer::InitializeServer(int BasePort)
 	{
 		ZEN_ERROR("Failed to create URL group for '{}': {:#x}", WideToUtf8(WildcardUrlPath), Result);
 
-		return;
+		return BasePort;
 	}
 
+	int EffectivePort = BasePort;
+
 	Result = HttpAddUrlToUrlGroup(m_HttpUrlGroupId, WildcardUrlPath.c_str(), HTTP_URL_CONTEXT(0), 0);
 
+	// Sharing violation implies the port is being used by another process
+	for (int PortOffset = 1; (Result == ERROR_SHARING_VIOLATION) && (PortOffset < 10); ++PortOffset)
+	{
+		EffectivePort = BasePort + (PortOffset * 100);
+		WildcardUrlPath.Reset();
+		WildcardUrlPath << u8"http://*:"sv << int64_t(EffectivePort) << u8"/"sv;
+
+		Result = HttpAddUrlToUrlGroup(m_HttpUrlGroupId, WildcardUrlPath.c_str(), HTTP_URL_CONTEXT(0), 0);
+	}
+
 	m_BaseUris.clear();
 	if (Result == NO_ERROR)
 	{
 		m_BaseUris.push_back(WildcardUrlPath.c_str());
 	}
-	else
+	else if (Result == ERROR_ACCESS_DENIED)
 	{
 		// If we can't register the wildcard path, we fall back to local paths
 		// This local paths allow requests originating locally to function, but will not allow
@@ -792,14 +804,26 @@ HttpSysServer::InitializeServer(int BasePort)
 
 		const std::u8string_view Hosts[] = {u8"[::1]"sv, u8"localhost"sv, u8"127.0.0.1"sv};
 
-		for (const std::u8string_view Host : Hosts)
+		ULONG InternalResult = ERROR_SHARING_VIOLATION;
+		for (int PortOffset = 0; (InternalResult == ERROR_SHARING_VIOLATION) && (PortOffset < 10); ++PortOffset)
 		{
-			WideStringBuilder<64> LocalUrlPath;
-			LocalUrlPath << u8"http://"sv << Host << u8":"sv << int64_t(BasePort) << u8"/"sv;
+			EffectivePort = BasePort + (PortOffset * 100);
 
-			if (HttpAddUrlToUrlGroup(m_HttpUrlGroupId, LocalUrlPath.c_str(), HTTP_URL_CONTEXT(0), 0) == NO_ERROR)
+			for (const std::u8string_view Host : Hosts)
 			{
-				m_BaseUris.push_back(LocalUrlPath.c_str());
+				WideStringBuilder<64> LocalUrlPath;
+				LocalUrlPath << u8"http://"sv << Host << u8":"sv << int64_t(EffectivePort) << u8"/"sv;
+
+				InternalResult = HttpAddUrlToUrlGroup(m_HttpUrlGroupId, LocalUrlPath.c_str(), HTTP_URL_CONTEXT(0), 0);
+
+				if (InternalResult == NO_ERROR)
+				{
+					m_BaseUris.push_back(LocalUrlPath.c_str());
+				}
+				else
+				{
+					break;
+				}
 			}
 		}
 	}
@@ -808,7 +832,7 @@ HttpSysServer::InitializeServer(int BasePort)
 	{
 		ZEN_ERROR("Failed to add base URL to URL group for '{}': {:#x}", WideToUtf8(WildcardUrlPath), Result);
 
-		return;
+		return BasePort;
 	}
 
 	HTTP_BINDING_INFO HttpBindingInfo = {{0}, 0};
@@ -823,7 +847,7 @@ HttpSysServer::InitializeServer(int BasePort)
 	{
 		ZEN_ERROR("Failed to create request queue for '{}': {:#x}", WideToUtf8(m_BaseUris.front()), Result);
 
-		return;
+		return EffectivePort;
 	}
 
 	HttpBindingInfo.Flags.Present	   = 1;
@@ -835,7 +859,7 @@ HttpSysServer::InitializeServer(int BasePort)
 	{
 		ZEN_ERROR("Failed to set server binding property for '{}': {:#x}", WideToUtf8(m_BaseUris.front()), Result);
 
-		return;
+		return EffectivePort;
 	}
 
 	// Create I/O completion port
@@ -853,6 +877,8 @@ HttpSysServer::InitializeServer(int BasePort)
 
 		ZEN_INFO("Started http.sys server at '{}'", WideToUtf8(m_BaseUris.front()));
 	}
+
+	return EffectivePort;
 }
 
 void
@@ -1603,11 +1629,12 @@ InitialRequestHandler::HandleCompletion(ULONG IoResult, ULONG_PTR NumberOfBytesT
 // HttpServer interface implementation
 //
 
-void
+int
 HttpSysServer::Initialize(int BasePort)
 {
-	InitializeServer(BasePort);
+	int EffectivePort = InitializeServer(BasePort);
 	StartServer();
+	return EffectivePort;
 }
 
 void
-- 
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