extract ax25 frame from usp frame

src/main/java/ru/r2cloud/jradio/usp/UspBeacon.java

@@ -11,34 +11,33 @@
 
 public class UspBeacon extends Beacon {
 
-	private int etherType;
 	private Header header;
-	private Integer ax25Length;
 	private byte[] payload;
 
 	@Override
 	public void readBeacon(byte[] data) throws IOException, UncorrectableException {
-		DataInputStream dis = new DataInputStream(new ByteArrayInputStream(data));
-		etherType = dis.readUnsignedShort();
-		if (etherType == 0x08FF) {
-			int lengthByte1 = dis.readUnsignedByte();
-			int lengthByte2 = dis.readUnsignedByte();
-			// little-endian length
-			ax25Length = (lengthByte2 << 8) + lengthByte1;
-			header = new Header(dis);
+		if (data[0] == (byte) 0x08 && data[1] == (byte) 0xFF) {
+			// discard external USP beacon fields
+			int ax25Length = ((data[3] & 0xFF) << 8) + (data[2] & 0xFF);
+			if (ax25Length <= data.length - 4) {
+				byte[] ax25Frame = new byte[ax25Length];
+				System.arraycopy(data, 4, ax25Frame, 0, ax25Frame.length);
+				data = ax25Frame;
+			}
 		}
-		int available = dis.available();
+		DataInputStream dis = new DataInputStream(new ByteArrayInputStream(data));
+		header = new Header(dis);
 		try {
-			readBeacon(etherType, dis);
+			readBeacon(dis);
 		} catch (EOFException e) {
-			payload = new byte[available];
-			System.arraycopy(data, data.length - available, payload, 0, payload.length);
+			payload = new byte[data.length - Header.LENGTH_BYTES];
+			System.arraycopy(data, Header.LENGTH_BYTES, payload, 0, payload.length);
 		}
 
 	}
 
 	@SuppressWarnings("unused")
-	public void readBeacon(int etherType, DataInputStream dis) throws IOException, UncorrectableException {
+	public void readBeacon(DataInputStream dis) throws IOException, UncorrectableException {
 		payload = new byte[dis.available()];
 		dis.readFully(payload);
 	}
@@ -51,22 +50,6 @@ public void setPayload(byte[] payload) {
 		this.payload = payload;
 	}
 
-	public Integer getAx25Length() {
-		return ax25Length;
-	}
-
-	public void setAx25Length(Integer ax25Length) {
-		this.ax25Length = ax25Length;
-	}
-
-	public int getEtherType() {
-		return etherType;
-	}
-
-	public void setEtherType(int etherType) {
-		this.etherType = etherType;
-	}
-
 	public Header getHeader() {
 		return header;
 	}

src/main/java/ru/r2cloud/jradio/usp/UspDecoder.java

@@ -79,14 +79,25 @@ public byte[] decode(byte[] raw) throws UncorrectableException {
 			decoded = viterbiShort.decode(dataFrame);
 		}
 		Scrambler.shuffle(decoded);
+		byte[] result;
 		if (code == 0) {
-			return ReedSolomon.CCSDS.decodeDualBasis(decoded);
+			result = ReedSolomon.CCSDS.decodeDualBasis(decoded);
 		} else {
 			System.arraycopy(decoded, 0, paddedFrame, paddedFrame.length - decoded.length, decoded.length);
 			byte[] padded = ReedSolomon.CCSDS.decodeDualBasis(paddedFrame);
 			System.arraycopy(padded, padded.length - shortFrame.length, shortFrame, 0, shortFrame.length);
-			return shortFrame;
+			result = shortFrame;
 		}
+		// extract ax25 frame
+		if (result[0] == (byte) 0x08 && result[1] == (byte) 0xFF) {
+			int ax25Length = ((result[3] & 0xFF) << 8) + (result[2] & 0xFF);
+			if (ax25Length <= result.length - 4) {
+				byte[] ax25Frame = new byte[ax25Length];
+				System.arraycopy(result, 4, ax25Frame, 0, ax25Frame.length);
+				result = ax25Frame;
+			}
+		}
+		return result;
 	}
 
 	@Override

src/test/java/ru/r2cloud/jradio/usp/UspBeaconTest.java

@@ -1,31 +1,25 @@
 package ru.r2cloud.jradio.usp;
 
-import java.io.DataInputStream;
-import java.io.EOFException;
-import java.io.IOException;
-
 import org.junit.Test;
 
 import ru.r2cloud.jradio.AssertJson;
-import ru.r2cloud.jradio.fec.ccsds.UncorrectableException;
 
 public class UspBeaconTest {
 
 	@Test
-	public void testEofException() throws Exception {
+	public void testFullUSPFrame() throws Exception {
 		byte[] data = { 8, -1, 27, 0, -92, 100, -126, -100, -116, 64, 96, -92, -90, 96, 96, -90, 64, 111, 0, -16, -31, -1, 2, 0, 1, 0, 3, 0, 0, 38, 6, 61, 86, -113, 23, -116, 104, 84, -30, 119, -60, -1, -65, 0, 0, 0, 0, 0 };
-		TestUspBeacon beacon = new TestUspBeacon();
+		UspBeacon beacon = new UspBeacon();
 		beacon.readBeacon(data);
 		AssertJson.assertObjectsEqual("UspBeaconEof.json", beacon);
 	}
 
-	private static class TestUspBeacon extends UspBeacon {
-
-		@Override
-		public void readBeacon(int etherType, DataInputStream dis) throws IOException, UncorrectableException {
-			throw new EOFException();
-		}
-
+	@Test
+	public void testShortAx25Frame() throws Exception {
+		byte[] data = { -92, 100, -126, -100, -116, 64, 96, -92, -90, 96, 96, -90, 64, 111, 0, -16, -31, -1, 2, 0, 1, 0, 3, 0, 0, 38, 6 };
+		UspBeacon beacon = new UspBeacon();
+		beacon.readBeacon(data);
+		AssertJson.assertObjectsEqual("UspBeaconEof.json", beacon);
 	}
 
 }