Cleanup use of java.util.Inflater, fixing rare infinite loops

The native implementation of inflate() can set finished to return
true at the same time as it copies the last bytes into the buffer.

Check for finished on each iteration, terminating as soon as libz
knows the stream was completely inflated.

If not finished, it is likely input is required before the next
native call could do any useful work. Most invocations are passing
in a buffer large enough to store the entire result. A partial return
from inflate() will need more input before it can continue. Checking
right away that needsInput() is true saves a native call to determine
no bytes can be inflated without more input.

This should fix a rare infinite loop condition inside of inflation
when an object ends exactly at the end of a block boundary, and
the next block contains only the 20 byte trailing SHA-1.

When the stream is finished each new attempt to inflate() returns
n == 0, as no additional bytes were output. The needsInput() test
tries to add the length of the footer block to itself, but then loops
back around an reloads the same block as the block is smaller than
a full block size. A zero length input is set to the inflater,
which triggers needsInput() condition again.

Change-Id: I95d02bfeab4bf995a254d49166b4ae62d1f21346

org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/dfs/DfsBlock.java

@@ -74,11 +74,6 @@ final class DfsBlock {
 		return block.length;
 	}
 
-	int remaining(long pos) {
-		int ptr = (int) (pos - start);
-		return block.length - ptr;
-	}
-
 	boolean contains(DfsPackKey want, long pos) {
 		return pack == want && start <= pos && pos < end;
 	}
@@ -94,9 +89,11 @@ final class DfsBlock {
 		return n;
 	}
 
-	void setInput(Inflater inf, long pos) {
+	int setInput(long pos, Inflater inf) {
 		int ptr = (int) (pos - start);
-		inf.setInput(block, ptr, block.length - ptr);
+		int cnt = block.length - ptr;
+		inf.setInput(block, ptr, cnt);
+		return cnt;
 	}
 
 	void crc32(CRC32 out, long pos, int cnt) {

org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/dfs/DfsInserter.java

@@ -460,31 +460,29 @@ public class DfsInserter extends ObjectInserter {
 			}
 
 			Inflater inf = ctx.inflater();
-			DfsBlock b = setInput(inf, pos);
+			pos += setInput(pos, inf);
 			for (int dstoff = 0;;) {
 				int n = inf.inflate(dstbuf, dstoff, dstbuf.length - dstoff);
-				if (n > 0)
 				dstoff += n;
-				else if (inf.needsInput() && b != null) {
-					pos += b.remaining(pos);
-					b = setInput(inf, pos);
-				} else if (inf.needsInput())
-					throw new EOFException(DfsText.get().unexpectedEofInPack);
-				else if (inf.finished())
+				if (inf.finished())
 					return dstbuf;
-				else
+				if (inf.needsInput())
+					pos += setInput(pos, inf);
+				else if (n == 0)
 					throw new DataFormatException();
 			}
 		}
 
-		private DfsBlock setInput(Inflater inf, long pos) throws IOException {
-			if (pos < currPos) {
-				DfsBlock b = getOrLoadBlock(pos);
-				b.setInput(inf, pos);
-				return b;
+		private int setInput(long pos, Inflater inf) throws IOException {
+			if (pos < currPos)
+				return getOrLoadBlock(pos).setInput(pos, inf);
+			if (pos < currPos + currPtr) {
+				int s = (int) (pos - currPos);
+				int n = currPtr - s;
+				inf.setInput(currBuf, s, n);
+				return n;
 			}
-			inf.setInput(currBuf, (int) (pos - currPos), currPtr);
-			return null;
+			throw new EOFException(DfsText.get().unexpectedEofInPack);
 		}
 
 		private DfsBlock getOrLoadBlock(long pos) throws IOException {

org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/dfs/DfsReader.java

@@ -600,11 +600,11 @@ public final class DfsReader extends ObjectReader implements ObjectReuseAsIs {
 	 *            position within the file to read from.
 	 * @param dstbuf
 	 *            destination buffer the inflater should output decompressed
-	 *            data to.
+	 *            data to. Must be large enough to store the entire stream,
+	 *            unless headerOnly is true.
 	 * @param headerOnly
 	 *            if true the caller wants only {@code dstbuf.length} bytes.
-	 * @return updated <code>dstoff</code> based on the number of bytes
-	 *         successfully inflated into <code>dstbuf</code>.
+	 * @return number of bytes inflated into <code>dstbuf</code>.
 	 * @throws IOException
 	 *             this cursor does not match the provider or id and the proper
 	 *             window could not be acquired through the provider's cache.
@@ -616,25 +616,18 @@ public final class DfsReader extends ObjectReader implements ObjectReuseAsIs {
 			boolean headerOnly) throws IOException, DataFormatException {
 		prepareInflater();
 		pin(pack, position);
-		block.setInput(inf, position);
-		int dstoff = 0;
-		for (;;) {
+		position += block.setInput(position, inf);
+		for (int dstoff = 0;;) {
 			int n = inf.inflate(dstbuf, dstoff, dstbuf.length - dstoff);
-			if (n == 0) {
-				if (headerOnly && dstoff == dstbuf.length)
+			dstoff += n;
+			if (inf.finished() || (headerOnly && dstoff == dstbuf.length))
 				return dstoff;
 			if (inf.needsInput()) {
-					position += block.remaining(position);
 				pin(pack, position);
-					block.setInput(inf, position);
-					continue;
-				}
-				if (inf.finished())
-					return dstoff;
+				position += block.setInput(position, inf);
+			} else if (n == 0)
 				throw new DataFormatException();
 		}
-			dstoff += n;
-		}
 	}
 
 	DfsBlock quickCopy(DfsPackFile p, long pos, long cnt)

org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/file/PackFile.java

@@ -335,7 +335,7 @@ public class PackFile implements Iterable<PackIndex.MutableEntry> {
 			return null;
 		}
 
-		if (curs.inflate(this, position, dstbuf, 0) != sz)
+		if (curs.inflate(this, position, dstbuf, false) != sz)
 			throw new EOFException(MessageFormat.format(
 					JGitText.get().shortCompressedStreamAt,
 					Long.valueOf(position)));
@@ -886,7 +886,7 @@ public class PackFile implements Iterable<PackIndex.MutableEntry> {
 		// the longest delta instruction header.
 		//
 		final byte[] hdr = new byte[18];
-		wc.inflate(this, pos, hdr, 0);
+		wc.inflate(this, pos, hdr, true /* headerOnly */);
 		return hdr;
 	}
 

org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/file/WindowCursor.java

@@ -290,11 +290,11 @@ final class WindowCursor extends ObjectReader implements ObjectReuseAsIs {
 	 *            position within the file to read from.
 	 * @param dstbuf
 	 *            destination buffer the inflater should output decompressed
-	 *            data to.
-	 * @param dstoff
-	 *            current offset within <code>dstbuf</code> to inflate into.
-	 * @return updated <code>dstoff</code> based on the number of bytes
-	 *         successfully inflated into <code>dstbuf</code>.
+	 *            data to. Must be large enough to store the entire stream,
+	 *            unless headerOnly is true.
+	 * @param headerOnly
+	 *            if true the caller wants only {@code dstbuf.length} bytes.
+	 * @return number of bytes inflated into <code>dstbuf</code>.
 	 * @throws IOException
 	 *             this cursor does not match the provider or id and the proper
 	 *             window could not be acquired through the provider's cache.
@@ -303,24 +303,21 @@ final class WindowCursor extends ObjectReader implements ObjectReuseAsIs {
 	 *             stream corruption is likely.
 	 */
 	int inflate(final PackFile pack, long position, final byte[] dstbuf,
-			int dstoff) throws IOException, DataFormatException {
+			boolean headerOnly) throws IOException, DataFormatException {
 		prepareInflater();
 		pin(pack, position);
 		position += window.setInput(position, inf);
-		do {
+		for (int dstoff = 0;;) {
 			int n = inf.inflate(dstbuf, dstoff, dstbuf.length - dstoff);
-			if (n == 0) {
+			dstoff += n;
+			if (inf.finished() || (headerOnly && dstoff == dstbuf.length))
+				return dstoff;
 			if (inf.needsInput()) {
 				pin(pack, position);
 				position += window.setInput(position, inf);
-				} else if (inf.finished())
-					return dstoff;
-				else
+			} else if (n == 0)
 				throw new DataFormatException();
 		}
-			dstoff += n;
-		} while (dstoff < dstbuf.length);
-		return dstoff;
 	}
 
 	ByteArrayWindow quickCopy(PackFile p, long pos, long cnt)

org.eclipse.jgit/src/org/eclipse/jgit/transport/PackParser.java

@@ -1653,7 +1653,7 @@ public abstract class PackParser {
 				int n = 0;
 				while (n < cnt) {
 					int r = inf.inflate(dst, pos + n, cnt - n);
-					if (r == 0) {
+					n += r;
 					if (inf.finished())
 						break;
 					if (inf.needsInput()) {
@@ -1662,16 +1662,11 @@ public abstract class PackParser {
 
 						p = fill(src, 1);
 						inf.setInput(buf, p, bAvail);
-						} else {
-							throw new CorruptObjectException(
-									MessageFormat
-											.format(
+					} else if (r == 0) {
+						throw new CorruptObjectException(MessageFormat.format(
 								JGitText.get().packfileCorruptionDetected,
 								JGitText.get().unknownZlibError));
 					}
-					} else {
-						n += r;
-					}
 				}
 				actualSize += n;
 				return 0 < n ? n : -1;