Provide middlewares for content negociation

They will make more sense with #133, but right now they can be used with
'Router.matcher'.

Add minimal tests.

src/valum-negociate.vala

@@ -0,0 +1,74 @@
+/*
+ * This file is part of Valum.
+ *
+ * Valum is free software: you can redistribute it and/or modify it under the
+ * terms of the GNU Lesser General Public License as published by the Free
+ * Software Foundation, either version 3 of the License, or (at your option) any
+ * later version.
+ *
+ * Valum is distributed in the hope that it will be useful, but WITHOUT ANY
+ * WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR
+ * A PARTICULAR PURPOSE.  See the GNU Lesser General Public License for more
+ * details.
+ *
+ * You should have received a copy of the GNU Lesser General Public License
+ * along with Valum.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+using Soup;
+
+namespace Valum {
+
+	/**
+	 * Negociate a HTTP header against a given expectation.
+	 *
+	 * The header is extracted as a quality list and a lookup is performed to
+	 * see if the expected value is accepted by the user agent.
+	 *
+	 * @since 0.3
+	 *
+	 * @param header_name header to negociate
+	 * @param expectation expected value in the quality list
+	 */
+	public MatcherCallback negociate (string header_name, string expectation) {
+		return (req) => {
+			var header = req.headers.get_list (header_name);
+			return header != null && header_parse_quality_list (header, null).find_custom (expectation, strcmp) != null;
+		};
+	}
+
+	/**
+	 * @since 0.3
+	 */
+	public MatcherCallback accept (string content_type) {
+		return negociate ("Accept", content_type);
+	}
+
+	/**
+	 * @since 0.3
+	 */
+	public MatcherCallback accept_charset (string charset) {
+		return negociate ("Accept-Charset", charset);
+	}
+
+	/**
+	 * @since 0.3
+	 */
+	public MatcherCallback accept_encoding (string encoding) {
+		return negociate ("Accept-Encoding", encoding);
+	}
+
+	/**
+	 * @since 0.3
+	 */
+	public MatcherCallback accept_language (string language) {
+		return negociate ("Accept-Language", language);
+	}
+
+	/**
+	 * @since 0.3
+	 */
+	public MatcherCallback accept_ranges (string ranges) {
+		return negociate ("Accept-Ranges", ranges);
+	}
+}

tests/negociate-test.vala

@@ -0,0 +1,17 @@
+using Valum;
+using VSGI.Test;
+
+/**
+ * @since 0.3
+ */
+public void test_negociate () {
+	var req = new Request (new Connection (), "GET", new Soup.URI ("http://localhost/"));
+
+	req.headers.append ("Accept", "text/html; q=0.9, text/xml; q=0");
+
+	assert (negociate ("Accept", "text/html") (req, null));
+	assert (!negociate ("Accept", "text/xml") (req, null));
+	assert (!negociate ("Accept-Encoding", "utf-8") (req, null));
+}
+
+

tests/tests.vala

@@ -24,6 +24,8 @@ public int main (string[] args) {
 	Test.init (ref args);
 	Test.bug_base ("https://github.com/valum-framework/valum/issues/%s");
 
+	Test.add_func ("/negociate", test_negociate);
+
 	Test.add_func ("/router", test_router);
 	Test.add_func ("/router/handle", test_router_handle);
 	Test.add_func ("/router/custom_method", test_router_custom_method);