Tests and bugfixes for XorErasureDecoder.

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

@@ -23,7 +23,7 @@ class XorErasureDecoder implements ErasureDecoder {
 		// All the pieces must have the same length - take the minimum
 		int length = MAX_FRAME_LENGTH;
 		for(int i = 0; i < n; i++) {
-			if(set[i] == null) {
+			if(set[i] != null) {
 				int len = set[i].getLength();
 				if(len < length) length = len;
 			}

test/build.xml

@@ -61,6 +61,7 @@
 			<test name='net.sf.briar.transport.IncomingSegmentedEncryptionLayerTest'/>
 			<test name='net.sf.briar.transport.OutgoingEncryptionLayerImplTest'/>
 			<test name='net.sf.briar.transport.OutgoingSegmentedEncryptionLayerTest'/>
+			<test name='net.sf.briar.transport.XorErasureDecoderTest'/>
 			<test name='net.sf.briar.transport.XorErasureEncoderTest'/>
 			<test name='net.sf.briar.util.ByteUtilsTest'/>
 			<test name='net.sf.briar.util.FileUtilsTest'/>

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

+package net.sf.briar.transport;
+
+import static net.sf.briar.api.transport.TransportConstants.FRAME_HEADER_LENGTH;
+import static net.sf.briar.api.transport.TransportConstants.MAC_LENGTH;
+import static net.sf.briar.api.transport.TransportConstants.MAX_FRAME_LENGTH;
+import net.sf.briar.BriarTestCase;
+import net.sf.briar.api.FormatException;
+import net.sf.briar.api.transport.Segment;
+
+import static org.junit.Assert.assertArrayEquals;
+import org.junit.Test;
+
+public class XorErasureDecoderTest extends BriarTestCase {
+
+	@Test
+	public void testMaximumLength() throws Exception {
+		// A frame of the maximum length should be decoded successfully
+		Segment[] set = encodeEmptyFrame(MAX_FRAME_LENGTH / 4, 5);
+		XorErasureDecoder d = new XorErasureDecoder(5);
+		Frame f = new Frame();
+		assertTrue(d.decodeFrame(f, set));
+		// Check the header
+		byte[] b = f.getBuffer();
+		assertEquals(0L, HeaderEncoder.getFrameNumber(b));
+		int payload = MAX_FRAME_LENGTH - FRAME_HEADER_LENGTH - MAC_LENGTH;
+		assertEquals(payload, HeaderEncoder.getPayloadLength(b));
+		assertEquals(0, HeaderEncoder.getPaddingLength(b));
+		// Check the body
+		assertEquals(MAX_FRAME_LENGTH, f.getLength());
+		for(int i = FRAME_HEADER_LENGTH; i < MAX_FRAME_LENGTH; i++) {
+			assertEquals(0, b[i]);
+		}
+		// A frame larger than the maximum length should not be decoded
+		set = encodeEmptyFrame(MAX_FRAME_LENGTH / 4 + 1, 5);
+		try {
+			d.decodeFrame(f, set);
+		} catch(FormatException expected) {}
+	}
+
+	@Test
+	public void testMinimumLengthIsUsed() throws Exception {
+		Segment[] set = encodeEmptyFrame(250, 4);
+		// Replace one of the pieces with a longer piece
+		byte[] b = set[1].getBuffer();
+		assertArrayEquals(new byte[250], b);
+		set[1] = new SegmentImpl(251);
+		set[1].setLength(251);
+		// The frame should be decoded successfully
+		XorErasureDecoder d = new XorErasureDecoder(4);
+		Frame f = new Frame();
+		assertTrue(d.decodeFrame(f, set));
+		// The minimum of the segments' lengths should have been used
+		assertEquals(750, f.getLength());
+	}
+
+	private Segment[] encodeEmptyFrame(int length, int n) {
+		Segment[] set = new Segment[n];
+		for(int i = 0; i < n; i++) {
+			set[i] = new SegmentImpl(length);
+			set[i].setLength(length);
+		}
+		int payload = length * (n - 1) - FRAME_HEADER_LENGTH - MAC_LENGTH;
+		HeaderEncoder.encodeHeader(set[0].getBuffer(), 0L, payload, 0);
+		HeaderEncoder.encodeHeader(set[n - 1].getBuffer(), 0L, payload, 0);
+		return set;
+	}
+}