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)

2 files changed, 42 insertions, 15 deletions

diff --git a/src/zenserver/frontend/frontend.cpp b/src/zenserver/frontend/frontend.cpp
index 1cf451e91..579a65c5a 100644
--- a/src/zenserver/frontend/frontend.cpp
+++ b/src/zenserver/frontend/frontend.cpp
@@ -114,6 +114,8 @@ HttpFrontendService::HandleRequest(zen::HttpServerRequest& Request)
 {
 	using namespace std::literals;
 
+	ExtendableStringBuilder<256> UriBuilder;
+
 	std::string_view Uri = Request.RelativeUriWithExtension();
 	for (; Uri.length() > 0 && Uri[0] == '/'; Uri = Uri.substr(1))
 		;
@@ -121,6 +123,11 @@ HttpFrontendService::HandleRequest(zen::HttpServerRequest& Request)
 	{
 		Uri = "index.html"sv;
 	}
+	else if (Uri.back() == '/')
+	{
+		UriBuilder << Uri << "index.html"sv;
+		Uri = UriBuilder;
+	}
 
 	// Dismiss if the URI contains .. anywhere to prevent arbitrary file reads
 	if (Uri.find("..") != Uri.npos)
@@ -145,27 +152,47 @@ HttpFrontendService::HandleRequest(zen::HttpServerRequest& Request)
 		return Request.WriteResponse(HttpResponseCode::Forbidden);
 	}
 
-	// The given content directory overrides any zip-fs discovered in the binary
-	if (!m_Directory.empty())
-	{
-		auto		 FullPath = m_Directory / std::filesystem::path(Uri).make_preferred();
-		FileContents File	  = ReadFile(FullPath);
-
-		if (!File.ErrorCode)
+	auto WriteResponseForUri = [this,
+								&Request](std::string_view InUri, HttpResponseCode ResponseCode, HttpContentType ContentType) -> bool {
+		// The given content directory overrides any zip-fs discovered in the binary
+		if (!m_Directory.empty())
 		{
-			return Request.WriteResponse(HttpResponseCode::OK, ContentType, File.Data[0]);
+			auto		 FullPath = m_Directory / std::filesystem::path(InUri).make_preferred();
+			FileContents File	  = ReadFile(FullPath);
+
+			if (!File.ErrorCode)
+			{
+				Request.WriteResponse(ResponseCode, ContentType, File.Data[0]);
+
+				return true;
+			}
 		}
-	}
 
-	if (m_ZipFs)
-	{
-		if (IoBuffer FileBuffer = m_ZipFs->GetFile(Uri))
+		if (m_ZipFs)
 		{
-			return Request.WriteResponse(HttpResponseCode::OK, ContentType, FileBuffer);
+			if (IoBuffer FileBuffer = m_ZipFs->GetFile(InUri))
+			{
+				Request.WriteResponse(HttpResponseCode::OK, ContentType, FileBuffer);
+
+				return true;
+			}
 		}
-	}
 
-	Request.WriteResponse(HttpResponseCode::NotFound, HttpContentType::kText, "Not found"sv);
+		return false;
+	};
+
+	if (WriteResponseForUri(Uri, HttpResponseCode::OK, ContentType))
+	{
+		return;
+	}
+	else if (WriteResponseForUri("404.html"sv, HttpResponseCode::NotFound, HttpContentType::kHTML))
+	{
+		return;
+	}
+	else
+	{
+		Request.WriteResponse(HttpResponseCode::NotFound, HttpContentType::kText, "Not found"sv);
+	}
 }
 
 }  // namespace zen
diff --git a/src/zenserver/frontend/html.zip b/src/zenserver/frontend/html.zip
index d70a5a62b..3d90c18a8 100644
--- a/src/zenserver/frontend/html.zip
+++ b/src/zenserver/frontend/html.zip