Map HTTPS server variable to X-Forwarded-Proto header

In express.js, "trust proxy" mode allows is to properly handle the
scenario of being behind a proxy server, while still properly exposing
the client IP/protocol from the request object.

The enableXFF configuration option for iisnode propagates the
X-Forwarded-For header, but not X-Forwarded-Proto. This commit adds the
X-Forwarded-Proto header as well, in scenarios where enableXFF is true.

For details, see:
https://github.com/tjanczuk/iisnode/issues/265

src/iisnode/chttpprotocol.cpp

@@ -46,6 +46,9 @@ PCSTR CHttpProtocol::httpRequestHeaders[] = {
 	"User-Agent"
 };
 
+static const PCSTR schemeHttp = "http";
+static const PCSTR schemeHttps = "https";
+
 HRESULT CHttpProtocol::Append(IHttpContext* context, const char* content, DWORD contentLength, void** buffer, DWORD* bufferLength, DWORD* offset)
 {
 	HRESULT hr;
@@ -165,6 +168,22 @@ HRESULT CHttpProtocol::SerializeRequestHeaders(CNodeHttpStoredContext* ctx, void
 		PSOCKADDR addr = request->GetRemoteAddress();
 		DWORD addrSize = addr->sa_family == AF_INET ? sizeof SOCKADDR_IN : sizeof SOCKADDR_IN6;
 		ErrorIf(0 != WSAAddressToString(addr, addrSize, NULL, remoteHost, &remoteHostSize), GetLastError());
+
+		// Determine the incoming request protocol scheme
+		PCSTR varValue, varScheme = schemeHttp;
+		DWORD varValueLength;
+		if (S_OK == context->GetServerVariable("HTTPS", &varValue, &varValueLength))
+		{
+			if (0 == strcmpi("on", varValue))
+			{
+				varScheme = schemeHttps;
+			}
+		}
+
+		// Add the X-Forwarded-Proto header (default is http)
+		CheckError(CHttpProtocol::Append(context, "X-Forwarded-Proto: ", 19, result, &bufferLength, &offset));
+		CheckError(CHttpProtocol::Append(context, varScheme, 0, result, &bufferLength, &offset));
+		CheckError(CHttpProtocol::Append(context, "\r\n", 2, result, &bufferLength, &offset));	
 	}
 
 	for (int i = 0; i < raw->Headers.UnknownHeaderCount; i++)

test/functional/tests/118_xff.js

@@ -5,5 +5,5 @@ iisnode adds X-Forwarded-For header to HTTP requests when issnode\@enableXFF is
 var iisnodeassert = require("iisnodeassert");
 
 iisnodeassert.sequence([
-    iisnodeassert.get(10000, "/118_xff/hello.js", 200, "Request contains X-Forwarded-For header")
+    iisnodeassert.get(10000, "/118_xff/hello.js", 200, "Request contains X-Forwarded-For and X-Forwarded-Proto headers")
 ]);

test/functional/www/118_xff/hello.js

@@ -2,13 +2,14 @@ var http = require('http');
 
 http.createServer(function (req, res) {
     res.setHeader('Content-Type', 'text/html');
-    if (req.headers.hasOwnProperty('x-forwarded-for')) {
+    if (req.headers.hasOwnProperty('x-forwarded-for') && req.headers.hasOwnProperty('x-forwarded-proto')) {
         res.setHeader('x-echo-x-forwarded-for', req.headers['x-forwarded-for']);
+        res.setHeader('x-echo-x-forwarded-proto', req.headers['x-forwarded-proto']);
         res.writeHead(200);
-        res.end('Request contains X-Forwarded-For header');
+        res.end('Request contains X-Forwarded-For and X-Forwarded-Proto headers');
     }
     else {
         res.writeHead(200);
         res.end('Request does not contain X-Forwarded-For header');
     }
-}).listen(process.env.PORT);  
+}).listen(process.env.PORT);