Generate minimal headers on 304 Not Modified

Favour 'ETag' over 'Last-Modified' when they are both enabled. It's
redundant to produce both, especially since 'ETag' is a much stronger
validator.

Avoid producing 'ETag', 'Last-Modified' or 'Cache-Control' or any
content-related headers when raising a '304 Not Modified' in static
resources.

Set the encoding to 'Soup.Encoding.NONE' to produce response headers
consistent with no content.

src/valum-router.vala

@@ -334,6 +334,9 @@ namespace Valum {
 			} catch (Success.PARTIAL_CONTENT s) {
 				res.status = s.code;
 				res.headers.append ("Range", s.message);
+			} catch (Redirection.NOT_MODIFIED r) {
+				res.status = r.code;
+				res.headers.set_encoding (global::Soup.Encoding.NONE);
 			} catch (Redirection r) {
 				res.status = r.code;
 				res.headers.append ("Location", r.message);

src/valum-static.vala

@@ -90,37 +90,32 @@ namespace Valum.Static {
 		return (req, res, next, stack) => {
 			var file = root.resolve_relative_path (stack.pop_tail ().get_string ());
 
-			if (ServeFlags.PUBLIC in serve_flags)
-				res.headers.append ("Cache-Control", "public");
-
 			try {
-				var cached = false;
-
 				if (ServeFlags.ETAG in serve_flags) {
 					var etag = "\"%s\"".printf (file.query_info (FileAttribute.ETAG_VALUE,
 					                                             FileQueryInfoFlags.NONE).get_etag ());
 
-					res.headers.replace ("ETag", etag);
+					if (etag == req.headers.get_one ("If-None-Match"))
+						throw new Redirection.NOT_MODIFIED ("");
 
-					cached |= (etag == req.headers.get_one ("If-None-Match"));
+					res.headers.replace ("ETag", etag);
 				}
 
-				if (ServeFlags.LAST_MODIFIED in serve_flags) {
+				else if (ServeFlags.LAST_MODIFIED in serve_flags) {
 					var last_modified = file.query_info (FileAttribute.TIME_MODIFIED,
 					                                     FileQueryInfoFlags.NONE).get_modification_time ();
 
-					res.headers.replace ("Last-Modified",
-					                     new Soup.Date.from_time_t (last_modified.tv_sec).to_string (Soup.DateFormat.HTTP));
-
 					var if_modified_since = req.headers.get_one ("If-Modified-Since");
 
-					cached |=
-						if_modified_since != null &&
-						new Soup.Date.from_string (if_modified_since).to_timeval ().tv_sec >= last_modified.tv_sec;
+					if (if_modified_since != null && new Soup.Date.from_string (if_modified_since).to_timeval ().tv_sec >= last_modified.tv_sec)
+						throw new Redirection.NOT_MODIFIED ("");
+
+					res.headers.replace ("Last-Modified",
+					                     new Soup.Date.from_time_t (last_modified.tv_sec).to_string (Soup.DateFormat.HTTP));
 				}
 
-				if (cached)
-					throw new Redirection.NOT_MODIFIED ("");
+				if (ServeFlags.PUBLIC in serve_flags)
+					res.headers.append ("Cache-Control", "public");
 
 				var file_read_stream = file.read ();
 
@@ -200,22 +195,22 @@ namespace Valum.Static {
 				return;
 			}
 
-			if (ServeFlags.PUBLIC in serve_flags)
-				res.headers.append ("Cache-Control", "public");
-
 			if (ServeFlags.ETAG in serve_flags) {
 				var etag = path in etag_cache ?
 					etag_cache[path] :
 					"\"%s\"".printf (Checksum.compute_for_bytes (ChecksumType.SHA1, lookup));
 
 				etag_cache[path] = etag;
 
-				res.headers.replace ("ETag", etag);
-
 				if (etag == req.headers.get_one ("If-None-Match"))
 					throw new Redirection.NOT_MODIFIED ("");
+
+				res.headers.replace ("ETag", etag);
 			}
 
+			if (ServeFlags.PUBLIC in serve_flags)
+				res.headers.append ("Cache-Control", "public");
+
 			// set the content-type based on a good guess
 			bool uncertain;
 			res.headers.set_content_type (ContentType.guess (path, lookup.get_data (), out uncertain), null);