Allow empty frames.

components/net/sf/briar/transport/ConnectionReaderImpl.java

@@ -54,7 +54,7 @@ implements ConnectionReader {
 
 	@Override
 	public int read() throws IOException {
-		if(betweenFrames && !readFrame()) return -1;
+		if(betweenFrames && !readNonEmptyFrame()) return -1;
 		int i = payload[payloadOff];
 		payloadOff++;
 		payloadLen--;
@@ -69,7 +69,7 @@ implements ConnectionReader {
 
 	@Override
 	public int read(byte[] b, int off, int len) throws IOException {
-		if(betweenFrames && !readFrame()) return -1;
+		if(betweenFrames && !readNonEmptyFrame()) return -1;
 		len = Math.min(len, payloadLen);
 		System.arraycopy(payload, payloadOff, b, off, len);
 		payloadOff += len;
@@ -78,7 +78,15 @@ implements ConnectionReader {
 		return len;
 	}
 
-	private boolean readFrame() throws IOException {
+	private boolean readNonEmptyFrame() throws IOException {
+		int payload = 0;
+		do {
+			payload = readFrame();
+		} while(payload == 0);
+		return payload > 0;
+	}
+
+	private int readFrame() throws IOException {
 		assert betweenFrames;
 		// Don't allow more than 2^32 frames to be read
 		if(frame > MAX_32_BIT_UNSIGNED) throw new IllegalStateException();
@@ -89,7 +97,7 @@ implements ConnectionReader {
 			if(read == -1) break;
 			offset += read;
 		}
-		if(offset == 0) return false; // EOF between frames
+		if(offset == 0) return -1; // EOF between frames
 		if(offset < header.length) throw new EOFException(); // Unexpected EOF
 		// Check that the frame number is correct and the length is legal
 		if(!HeaderEncoder.validateHeader(header, frame, maxPayloadLength))
@@ -122,8 +130,8 @@ implements ConnectionReader {
 		byte[] expectedMac = mac.doFinal();
 		decrypter.readMac(footer);
 		if(!Arrays.equals(expectedMac, footer)) throw new FormatException();
-		betweenFrames = false;
 		frame++;
-		return true;
+		if(payloadLen > 0) betweenFrames = false;
+		return payloadLen;
 	}
 }

components/net/sf/briar/transport/HeaderEncoder.java

@@ -1,13 +1,13 @@
 package net.sf.briar.transport;
 
-import net.sf.briar.api.transport.TransportConstants;
+import static net.sf.briar.api.transport.TransportConstants.FRAME_HEADER_LENGTH;
 import net.sf.briar.util.ByteUtils;
 
 class HeaderEncoder {
 
 	static void encodeHeader(byte[] header, long frame, int payload,
 			int padding) {
-		if(header.length < TransportConstants.FRAME_HEADER_LENGTH)
+		if(header.length < FRAME_HEADER_LENGTH)
 			throw new IllegalArgumentException();
 		if(frame < 0 || frame > ByteUtils.MAX_32_BIT_UNSIGNED)
 			throw new IllegalArgumentException();
@@ -21,24 +21,22 @@ class HeaderEncoder {
 	}
 
 	static boolean validateHeader(byte[] header, long frame, int max) {
-		if(header.length < TransportConstants.FRAME_HEADER_LENGTH)
-			return false;
+		if(header.length < FRAME_HEADER_LENGTH) return false;
 		if(ByteUtils.readUint32(header, 0) != frame) return false;
 		int payload = ByteUtils.readUint16(header, 4);
 		int padding = ByteUtils.readUint16(header, 6);
-		if(payload + padding == 0) return false;
 		if(payload + padding > max) return false;
 		return true;
 	}
 
 	static int getPayloadLength(byte[] header) {
-		if(header.length < TransportConstants.FRAME_HEADER_LENGTH)
+		if(header.length < FRAME_HEADER_LENGTH)
 			throw new IllegalArgumentException();
 		return ByteUtils.readUint16(header, 4);
 	}
 
 	static int getPaddingLength(byte[] header) {
-		if(header.length < TransportConstants.FRAME_HEADER_LENGTH)
+		if(header.length < FRAME_HEADER_LENGTH)
 			throw new IllegalArgumentException();
 		return ByteUtils.readUint16(header, 6);
 	}

test/net/sf/briar/transport/ConnectionReaderImplTest.java

@@ -33,10 +33,8 @@ public class ConnectionReaderImplTest extends TransportTest {
 		ByteArrayInputStream in = new ByteArrayInputStream(frame);
 		ConnectionDecrypter d = new NullConnectionDecrypter(in);
 		ConnectionReader r = new ConnectionReaderImpl(d, mac, macKey);
-		try {
-			r.getInputStream().read();
-			fail();
-		} catch(FormatException expected) {}
+		// There should be no bytes available before EOF
+		assertEquals(-1, r.getInputStream().read());
 	}
 
 	@Test