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: I30cda8a6d11ad235b56457adf54a2d27095d964e
Signed-off-by: Shawn O. Pearce <spearce@spearce.org>

1 files changed, 17 insertions, 2 deletions

diff --git a/org.eclipse.jgit.http.server/src/org/eclipse/jgit/http/server/ServletUtils.java b/org.eclipse.jgit.http.server/src/org/eclipse/jgit/http/server/ServletUtils.java
index 28dabe4cc7..4e47c95ad0 100644
--- a/org.eclipse.jgit.http.server/src/org/eclipse/jgit/http/server/ServletUtils.java
+++ b/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 {