smart-http: Fix recognition of gzip encoding

Some clients coming through proxies may advertise a different
Accept-Encoding, for example "Accept-Encoding: gzip(proxy)".
Matching by substring causes us to identify this as a false positive;
that the client understands gzip encoding and will inflate the
response before reading it.

In this particular case however it doesn't.  Its the reverse proxy
server in front of JGit letting us know the proxy<->JGit link can
be gzip compressed, while the client<->proxy part of the link is not:

  client <-- no gzip --> proxy <-- gzip --> JGit

Use a more standard method of parsing by splitting the value into
tokens, and only using gzip if one of the tokens is exactly the
string "gzip".  Add a unit test to make sure this isn't broken in
the future.

Change-Id: Ib4c40f9db177322c7a2640808a6c10b3c4a73819
Signed-off-by: Shawn O. Pearce <spearce@spearce.org>
Signed-off-by: Matthias Sohn <matthias.sohn@sap.com>

org.eclipse.jgit.http.server/src/org/eclipse/jgit/http/server/ServletUtils.java

@@ -191,8 +191,23 @@ public final class ServletUtils {
 	}
 
 	static boolean acceptsGzipEncoding(final HttpServletRequest req) {
-		final String accepts = req.getHeader(HDR_ACCEPT_ENCODING);
-		return accepts != null && 0 <= accepts.indexOf(ENCODING_GZIP);
+		return acceptsGzipEncoding(req.getHeader(HDR_ACCEPT_ENCODING));
+	}
+
+	static boolean acceptsGzipEncoding(String accepts) {
+		if (accepts == null)
+			return false;
+
+		int b = 0;
+		while (b < accepts.length()) {
+			int comma = accepts.indexOf(',', b);
+			int e = 0 <= comma ? comma : accepts.length();
+			String term = accepts.substring(b, e).trim();
+			if (term.equals(ENCODING_GZIP))
+				return true;
+			b = e + 1;
+		}
+		return false;
 	}
 
 	private static byte[] compress(final byte[] raw) throws IOException {

org.eclipse.jgit.http.test/tst/org/eclipse/jgit/http/server/ServletUtilsTest.java

@@ -0,0 +1,64 @@
+/*
+ * Copyright (C) 2011, Google Inc.
+ * and other copyright owners as documented in the project's IP log.
+ *
+ * This program and the accompanying materials are made available
+ * under the terms of the Eclipse Distribution License v1.0 which
+ * accompanies this distribution, is reproduced below, and is
+ * available at http://www.eclipse.org/org/documents/edl-v10.php
+ *
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or
+ * without modification, are permitted provided that the following
+ * conditions are met:
+ *
+ * - Redistributions of source code must retain the above copyright
+ *   notice, this list of conditions and the following disclaimer.
+ *
+ * - Redistributions in binary form must reproduce the above
+ *   copyright notice, this list of conditions and the following
+ *   disclaimer in the documentation and/or other materials provided
+ *   with the distribution.
+ *
+ * - Neither the name of the Eclipse Foundation, Inc. nor the
+ *   names of its contributors may be used to endorse or promote
+ *   products derived from this software without specific prior
+ *   written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND
+ * CONTRIBUTORS "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES,
+ * INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
+ * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR
+ * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+ * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
+ * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
+ * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+ * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
+ * STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
+ * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF
+ * ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+package org.eclipse.jgit.http.server;
+
+import static org.junit.Assert.assertFalse;
+import static org.junit.Assert.assertTrue;
+
+import org.junit.Test;
+
+public class ServletUtilsTest {
+	@Test
+	public void testAcceptGzip() {
+		assertFalse(ServletUtils.acceptsGzipEncoding((String) null));
+		assertFalse(ServletUtils.acceptsGzipEncoding(""));
+
+		assertTrue(ServletUtils.acceptsGzipEncoding("gzip"));
+		assertTrue(ServletUtils.acceptsGzipEncoding("deflate,gzip"));
+		assertTrue(ServletUtils.acceptsGzipEncoding("gzip,deflate"));
+
+		assertFalse(ServletUtils.acceptsGzipEncoding("gzip(proxy)"));
+		assertFalse(ServletUtils.acceptsGzipEncoding("proxy-gzip"));
+	}
+}