http.server: Use TemporaryBuffer and compress some responses

The HTTP server side code now uses the same approach that the smart
HTTP client code uses when preparing a request body.  The payload
is streamed into a TemporaryBuffer of limited size.  If the entire
data fits, its compressed with gzip if the user agent supports that,
and a Content-Length header is used to transmit the fixed length
body to the peer.  If however the data overflows the limited memory
segment, its streamed uncompressed to the peer.

One might initially think that larger contents which overflow
the buffer should also be compressed, rather than sent raw, since
they were deemed "large".  But usually these larger contents are
actually a pack file which has been already heavily compressed by
Git specific routines.  Trying to deflate that with gzip is probably
going to take up more space, not less, so the compression overhead
isn't worthwhile.

This buffer and compress optimization helps repositories with a
large number of references, as their text based advertisements
compress well. For example jgit's own native repository currently
requires 32,628 bytes for its full advertisement of 489 references.
Most repositories have fewer references, and thus could compress
their entire response in one buffer.

Change-Id: I790609c9f763339e0a1db9172aa570e29af96f42
Signed-off-by: Shawn O. Pearce <spearce@spearce.org>

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

@@ -44,9 +44,9 @@
 package org.eclipse.jgit.http.server;
 
 import static org.eclipse.jgit.http.server.ServletUtils.getRepository;
-import static org.eclipse.jgit.http.server.ServletUtils.send;
 
 import java.io.IOException;
+import java.io.OutputStreamWriter;
 import java.util.Map;
 
 import javax.servlet.http.HttpServlet;
@@ -69,20 +69,18 @@ class InfoRefsServlet extends HttpServlet {
 			final HttpServletResponse rsp) throws IOException {
 		// Assume a dumb client and send back the dumb client
 		// version of the info/refs file.
-		final byte[] raw = dumbHttp(req);
 		rsp.setContentType(HttpSupport.TEXT_PLAIN);
 		rsp.setCharacterEncoding(Constants.CHARACTER_ENCODING);
-		send(raw, req, rsp);
-	}
 
-	private byte[] dumbHttp(final HttpServletRequest req) throws IOException {
 		final Repository db = getRepository(req);
 		final RevWalk walk = new RevWalk(db);
 		final RevFlag ADVERTISED = walk.newFlag("ADVERTISED");
-		final StringBuilder out = new StringBuilder();
+
+		final OutputStreamWriter out = new OutputStreamWriter(
+				new SmartOutputStream(req, rsp), Constants.CHARSET);
 		final RefAdvertiser adv = new RefAdvertiser() {
 			@Override
-			protected void writeOne(final CharSequence line) {
+			protected void writeOne(final CharSequence line) throws IOException {
 				// Whoever decided that info/refs should use a different
 				// delimiter than the native git:// protocol shouldn't
 				// be allowed to design this sort of stuff. :-(
@@ -100,6 +98,6 @@ class InfoRefsServlet extends HttpServlet {
 		Map<String, Ref> refs = db.getAllRefs();
 		refs.remove(Constants.HEAD);
 		adv.send(refs);
-		return out.toString().getBytes(Constants.CHARACTER_ENCODING);
+		out.close();
 	}
 }

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

@@ -50,9 +50,7 @@ import static javax.servlet.http.HttpServletResponse.SC_UNSUPPORTED_MEDIA_TYPE;
 import static org.eclipse.jgit.http.server.ServletUtils.getInputStream;
 import static org.eclipse.jgit.http.server.ServletUtils.getRepository;
 
-import java.io.ByteArrayOutputStream;
 import java.io.IOException;
-import java.io.OutputStream;
 
 import javax.servlet.http.HttpServlet;
 import javax.servlet.http.HttpServletRequest;
@@ -104,11 +102,14 @@ class ReceivePackServlet extends HttpServlet {
 		}
 
 		final Repository db = getRepository(req);
-		final ByteArrayOutputStream out = new ByteArrayOutputStream();
 		try {
 			final ReceivePack rp = receivePackFactory.create(req, db);
 			rp.setBiDirectionalPipe(false);
+			rsp.setContentType(RSP_TYPE);
+
+			final SmartOutputStream out = new SmartOutputStream(req, rsp);
 			rp.receive(getInputStream(req), out, null);
+			out.close();
 
 		} catch (ServiceNotAuthorizedException e) {
 			rsp.sendError(SC_UNAUTHORIZED);
@@ -123,20 +124,5 @@ class ReceivePackServlet extends HttpServlet {
 			rsp.sendError(SC_INTERNAL_SERVER_ERROR);
 			return;
 		}
-
-		reply(rsp, out.toByteArray());
-	}
-
-	private void reply(final HttpServletResponse rsp, final byte[] result)
-			throws IOException {
-		rsp.setContentType(RSP_TYPE);
-		rsp.setContentLength(result.length);
-		final OutputStream os = rsp.getOutputStream();
-		try {
-			os.write(result);
-			os.flush();
-		} finally {
-			os.close();
-		}
 	}
 }

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

@@ -189,7 +189,7 @@ public final class ServletUtils {
 		return content;
 	}
 
-	private static boolean acceptsGzipEncoding(final HttpServletRequest req) {
+	static boolean acceptsGzipEncoding(final HttpServletRequest req) {
 		final String accepts = req.getHeader(HDR_ACCEPT_ENCODING);
 		return accepts != null && 0 <= accepts.indexOf(ENCODING_GZIP);
 	}

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

@@ -0,0 +1,130 @@
+/*
+ * Copyright (C) 2010, 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.eclipse.jgit.http.server.ServletUtils.acceptsGzipEncoding;
+import static org.eclipse.jgit.util.HttpSupport.ENCODING_GZIP;
+import static org.eclipse.jgit.util.HttpSupport.HDR_CONTENT_ENCODING;
+
+import java.io.IOException;
+import java.io.OutputStream;
+import java.util.zip.GZIPOutputStream;
+
+import javax.servlet.http.HttpServletRequest;
+import javax.servlet.http.HttpServletResponse;
+
+import org.eclipse.jgit.util.TemporaryBuffer;
+
+/**
+ * Buffers a response, trying to gzip it if the user agent supports that.
+ * <p>
+ * If the response overflows the buffer, gzip is skipped and the response is
+ * streamed to the client as its produced, most likely using HTTP/1.1 chunked
+ * encoding. This is useful for servlets that produce mixed-mode content, where
+ * smaller payloads are primarily pure text that compresses well, while much
+ * larger payloads are heavily compressed binary data. {@link UploadPackServlet}
+ * is one such servlet.
+ */
+class SmartOutputStream extends TemporaryBuffer {
+	private static final int LIMIT = 32 * 1024;
+
+	private final HttpServletRequest req;
+
+	private final HttpServletResponse rsp;
+
+	private boolean startedOutput;
+
+	SmartOutputStream(final HttpServletRequest req,
+			final HttpServletResponse rsp) {
+		super(LIMIT);
+		this.req = req;
+		this.rsp = rsp;
+	}
+
+	@Override
+	protected OutputStream overflow() throws IOException {
+		startedOutput = true;
+		return rsp.getOutputStream();
+	}
+
+	public void close() throws IOException {
+		super.close();
+
+		if (!startedOutput) {
+			// If output hasn't started yet, the entire thing fit into our
+			// buffer. Try to use a proper Content-Length header, and also
+			// deflate the response with gzip if it will be smaller.
+			TemporaryBuffer out = this;
+
+			if (256 < out.length() && acceptsGzipEncoding(req)) {
+				TemporaryBuffer gzbuf = new TemporaryBuffer.Heap(LIMIT);
+				try {
+					GZIPOutputStream gzip = new GZIPOutputStream(gzbuf);
+					out.writeTo(gzip, null);
+					gzip.close();
+					if (gzbuf.length() < out.length()) {
+						out = gzbuf;
+						rsp.setHeader(HDR_CONTENT_ENCODING, ENCODING_GZIP);
+					}
+				} catch (IOException err) {
+					// Most likely caused by overflowing the buffer, meaning
+					// its larger if it were compressed. Discard compressed
+					// copy and use the original.
+				}
+			}
+
+			// The Content-Length cannot overflow when cast to an int, our
+			// hardcoded LIMIT constant above assures us we wouldn't store
+			// more than 2 GiB of content in memory.
+			rsp.setContentLength((int) out.length());
+			final OutputStream os = rsp.getOutputStream();
+			try {
+				out.writeTo(os, null);
+				os.flush();
+			} finally {
+				os.close();
+			}
+		}
+	}
+}

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

@@ -46,9 +46,7 @@ package org.eclipse.jgit.http.server;
 import static javax.servlet.http.HttpServletResponse.SC_FORBIDDEN;
 import static javax.servlet.http.HttpServletResponse.SC_UNAUTHORIZED;
 import static org.eclipse.jgit.http.server.ServletUtils.getRepository;
-import static org.eclipse.jgit.http.server.ServletUtils.send;
 
-import java.io.ByteArrayOutputStream;
 import java.io.IOException;
 
 import javax.servlet.Filter;
@@ -90,13 +88,14 @@ abstract class SmartServiceInfoRefs implements Filter {
 			final HttpServletResponse rsp = (HttpServletResponse) response;
 			try {
 				final Repository db = getRepository(req);
-				final ByteArrayOutputStream buf = new ByteArrayOutputStream();
+				rsp.setContentType("application/x-" + svc + "-advertisement");
+
+				final SmartOutputStream buf = new SmartOutputStream(req, rsp);
 				final PacketLineOut out = new PacketLineOut(buf);
 				out.writeString("# service=" + svc + "\n");
 				out.end();
 				advertise(req, db, new PacketLineOutRefAdvertiser(out));
-				rsp.setContentType("application/x-" + svc + "-advertisement");
-				send(buf.toByteArray(), req, rsp);
+				buf.close();
 			} catch (ServiceNotAuthorizedException e) {
 				rsp.sendError(SC_UNAUTHORIZED);
 

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

@@ -106,7 +106,10 @@ class UploadPackServlet extends HttpServlet {
 			final UploadPack up = uploadPackFactory.create(req, db);
 			up.setBiDirectionalPipe(false);
 			rsp.setContentType(RSP_TYPE);
-			up.upload(getInputStream(req), rsp.getOutputStream(), null);
+
+			final SmartOutputStream out = new SmartOutputStream(req, rsp);
+			up.upload(getInputStream(req), out, null);
+			out.close();
 
 		} catch (ServiceNotAuthorizedException e) {
 			rsp.reset();

org.eclipse.jgit.http.test/tst/org/eclipse/jgit/http/test/SmartClientSmartServerTest.java

@@ -1,5 +1,5 @@
 /*
- * Copyright (C) 2009-2010, Google Inc.
+ * Copyright (C) 2010, Google Inc.
  * and other copyright owners as documented in the project's IP log.
  *
  * This program and the accompanying materials are made available
@@ -253,8 +253,6 @@ public class SmartClientSmartServerTest extends HttpTestCase {
 		assertEquals(200, service.getStatus());
 		assertEquals("application/x-git-upload-pack-result", service
 				.getResponseHeader(HDR_CONTENT_TYPE));
-		assertNull("no compression (never compressed)", service
-				.getResponseHeader(HDR_CONTENT_ENCODING));
 	}
 
 	public void testFetchUpdateExisting() throws Exception {