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Added signalLevel and isMlat.
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Added two test cases to check for proper detection of the magic MLAT
timestamp.
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@wiseman
wiseman committed May 24, 2016
1 parent d0f77e0 commit 107a6f2
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Showing 5 changed files with 168 additions and 30 deletions.
75 changes: 53 additions & 22 deletions src/main/java/com/lemondronor/modesbeast/BeastMessageParser.java
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Original file line number Diff line number Diff line change
Expand Up @@ -9,20 +9,40 @@
* This is a Java implementation of the parser from Virtual Radar Server.
*/
public class BeastMessageParser {
static final int ESCAPE = 0x1A;

static final int BEAST_ESCAPE = 0x1A;
static final byte[] mlatGeneratedMessageTimestamp = new byte[] { (byte) 0xFF, 0x00, 0x4D, 0x4C, 0x41, 0x54 };

private class ExtractResult {
int endOfPacket;
int startOfPacket;
int dataLength;
int signalLevel;

ExtractResult(int endOfPacket, int startOfPacket, int dataLength,
int signalLevel) {
this.endOfPacket = endOfPacket;
this.startOfPacket = startOfPacket;
this.dataLength = dataLength;
this.signalLevel = signalLevel;
}
}

private byte[] readBuffer;
private int readBufferLength;
private byte[] payload;
private byte[] timestampBytes;
private boolean sawFirstPacket;
private boolean isBinaryFormat;
private boolean hasParity;
private boolean hasMlatPrefix;
private boolean isMlat;
private byte avrMessageStartIndicator;
private boolean streamFormatIsEstablished;
private ByteBuffer extractedBytes;

public BeastMessageParser() {
this.timestampBytes = new byte[6];
}

/**
Expand Down Expand Up @@ -51,16 +71,18 @@ public Collection<ExtractedBytes> parse(byte[] bytes, int offset, int bytesRead)
while (startOfPacket != -1 && startOfPacket < readBufferLength) {
int endOfPacket;
int dataLength = 0;
int signalLevel = -1;
if (!isBinaryFormat) {
endOfPacket = ArrayUtils.indexOf(readBuffer, (byte) ';', startOfPacket);
if (endOfPacket >= (readBufferLength - startOfPacket)) {
endOfPacket = ArrayUtils.INDEX_NOT_FOUND;
}
} else {
int[] extractResult = extractBinaryPayload(startOfPacket, dataLength);
endOfPacket = extractResult[0];
startOfPacket = extractResult[1];
dataLength = extractResult[2];
ExtractResult extractResult = extractBinaryPayload(startOfPacket, dataLength);
endOfPacket = extractResult.endOfPacket;
startOfPacket = extractResult.startOfPacket;
dataLength = extractResult.dataLength;
signalLevel = extractResult.signalLevel;
}
if (endOfPacket == -1) {
break;
Expand All @@ -73,9 +95,11 @@ public Collection<ExtractedBytes> parse(byte[] bytes, int offset, int bytesRead)
}

if (dataLength == 7 || dataLength == 14) {
ExtractedBytes extractedBytes = new ExtractedBytes(
Arrays.copyOf(payload, dataLength),
hasParity || isBinaryFormat);
ExtractedBytes extractedBytes = new ExtractedBytes()
.bytes(Arrays.copyOf(payload, dataLength))
.hasParity(hasParity || isBinaryFormat)
.signalLevel(signalLevel)
.isMlat(isMlat);
result.add(extractedBytes);
}
startOfPacket = findStartIndex(firstByteAfterLastValidPacket);
Expand Down Expand Up @@ -154,22 +178,22 @@ private int extractHexDigitValue(byte by) {
private boolean establishStreamFormat() {
if (!streamFormatIsEstablished) {
isBinaryFormat = ArrayUtils.indexOf(
readBuffer, (byte) ESCAPE, 0, readBufferLength) != ArrayUtils.INDEX_NOT_FOUND;
readBuffer, (byte) BEAST_ESCAPE, 0, readBufferLength) != ArrayUtils.INDEX_NOT_FOUND;
if (isBinaryFormat) {
streamFormatIsEstablished = true;
} else if (readBufferLength > 22) {
for (byte ch : readBuffer) {
switch (ch) {
case 0x2a:
case 0x2a: // '*'
streamFormatIsEstablished = true;
hasParity = true;
avrMessageStartIndicator = ch;
break;
case 0x3a:
case 0x3a: // ':'
streamFormatIsEstablished = true;
avrMessageStartIndicator = ch;
break;
case 0x40:
case 0x40: // '@'
streamFormatIsEstablished = true;
hasParity = true;
hasMlatPrefix = true;
Expand Down Expand Up @@ -201,9 +225,9 @@ private int findStartIndex(int start) {
} else {
for (int i = start; i < readBufferLength; ++i) {
byte ch = readBuffer[i];
if (ch == ESCAPE) {
if (ch == BEAST_ESCAPE) {
if (++i < readBufferLength) {
if (readBuffer[i] != ESCAPE) {
if (readBuffer[i] != BEAST_ESCAPE) {
result = i;
break;
}
Expand All @@ -214,7 +238,7 @@ private int findStartIndex(int start) {
return result;
}

private int[] extractBinaryPayload(int startOfPacket, int dataLength) {
private ExtractResult extractBinaryPayload(int startOfPacket, int dataLength) {
dataLength = 0;
switch (readBuffer[startOfPacket++]) {
case 0x31:
Expand All @@ -233,15 +257,26 @@ private int[] extractBinaryPayload(int startOfPacket, int dataLength) {
}
int si = startOfPacket;
int di = 0;
int signalLevel = -1;
isMlat = true;
for (; si < readBufferLength && di < 7; ++si, ++di) {
byte ch = readBuffer[si];
if (ch == ESCAPE && ++si > readBufferLength) {
if (ch == BEAST_ESCAPE && ++si > readBufferLength) {
break;
}
if (di == 6) {
// Make sure, e.g., 0xFF gets converted into 255.
signalLevel = ch & 0xFF;
} else {
timestampBytes[di] = ch;
if (isMlat && ch != mlatGeneratedMessageTimestamp[di]) {
isMlat = false;
}
}
}
for (di = 0; si < readBufferLength && di < dataLength; ++si) {
byte ch = readBuffer[si];
if (ch == ESCAPE) {
if (ch == BEAST_ESCAPE) {
if (++si >= readBufferLength) {
break;
}
Expand All @@ -250,11 +285,7 @@ private int[] extractBinaryPayload(int startOfPacket, int dataLength) {
payload[di++] = ch;
}
int endOfPacket = di != dataLength ? ArrayUtils.INDEX_NOT_FOUND : si;
int[] result = new int[3];
result[0] = endOfPacket;
result[1] = startOfPacket;
result[2] = dataLength;
return result;
return new ExtractResult(endOfPacket, startOfPacket, dataLength, signalLevel);
}

/**
Expand Down
29 changes: 28 additions & 1 deletion src/main/java/com/lemondronor/modesbeast/ExtractedBytes.java
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Original file line number Diff line number Diff line change
Expand Up @@ -6,10 +6,37 @@
public class ExtractedBytes {
public byte[] bytes;
public boolean hasParity;
public boolean badChecksum;
public int signalLevel;
public boolean isMlat;

public ExtractedBytes(byte[] bytes, boolean hasParity) {
public ExtractedBytes() {
signalLevel = -1;
}

public ExtractedBytes bytes(byte[] bytes) {
this.bytes = bytes;
return this;
}

public ExtractedBytes badChecksum(boolean badChecksum) {
this.badChecksum = badChecksum;
return this;
}

public ExtractedBytes hasParity(boolean hasParity) {
this.hasParity = hasParity;
return this;
}

public ExtractedBytes signalLevel(int signalLevel) {
this.signalLevel = signalLevel;
return this;
}

public ExtractedBytes isMlat(boolean isMlat) {
this.isMlat = isMlat;
return this;
}

public byte[] getByteArray() {
Expand Down
18 changes: 16 additions & 2 deletions src/test/java/com/lemondronor/modesbeast/BeastMessageParserTest.java
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Original file line number Diff line number Diff line change
Expand Up @@ -50,11 +50,18 @@ public void checkTestSpec() {
e1 = extracteds.get(0);
}
if (spec.extracted1 != null) {
assertNotNull(e1);
assertNotNull(spec.comment, e1);
assertArrayEquals(
desc(spec.comment, spec.extracted1, e1.getByteArray()),
spec.extracted1, e1.getByteArray());
assertEquals(spec.hasParity1, e1.hasParity);
assertEquals(spec.comment, spec.hasParity1, e1.hasParity);
assertEquals(spec.comment, spec.badChecksum1, e1.badChecksum);
if (spec.signalLevel1 != null) {
assertEquals(spec.comment, spec.signalLevel1.intValue(), e1.signalLevel);
} else {
assertEquals(spec.comment, -1, e1.signalLevel);
}
assertEquals(spec.comment, spec.isMlat1, e1.isMlat);
}
ExtractedBytes e2 = null;
if (extracteds.size() > 1) {
Expand All @@ -66,6 +73,13 @@ public void checkTestSpec() {
desc(spec.comment, spec.extracted2, e2.getByteArray()),
spec.extracted2, e2.getByteArray());
assertEquals(spec.hasParity2, e2.hasParity);
assertEquals(spec.badChecksum2, e2.badChecksum);
if (spec.signalLevel2 != null) {
assertEquals(spec.signalLevel2.intValue(), e2.signalLevel);
} else {
assertEquals(-1, e2.signalLevel);
}
assertEquals(spec.isMlat2, e2.isMlat);
} else {
assertNull(e2);
}
Expand Down
8 changes: 8 additions & 0 deletions src/test/java/com/lemondronor/modesbeast/TestSpec.java
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Original file line number Diff line number Diff line change
Expand Up @@ -12,9 +12,13 @@ public class TestSpec {
public byte[] extracted1;
public Boolean hasParity1;
public Boolean badChecksum1;
public Integer signalLevel1;
public Boolean isMlat1;
public byte[] extracted2;
public Boolean hasParity2;
public Boolean badChecksum2;
public Integer signalLevel2;
public Boolean isMlat2;
public String comment;

/**
Expand All @@ -33,9 +37,13 @@ public static Collection<TestSpec> readFromFile(String path) {
spec.extracted1 = parsePacket((String)desc.get("Extracted1"));
spec.hasParity1 = (Boolean)desc.get("HasParity1");
spec.badChecksum1 = (Boolean)desc.get("BadChecksum1");
spec.signalLevel1 = (Integer)desc.get("SignalLevel1");
spec.isMlat1 = (Boolean)desc.get("IsMlat1");
spec.extracted2 = parsePacket((String)desc.get("Extracted2"));
spec.hasParity2 = (Boolean)desc.get("HasParity2");
spec.badChecksum2 = (Boolean)desc.get("BadChecksum2");
spec.signalLevel2 = (Integer)desc.get("SignalLevel2");
spec.isMlat2 = (Boolean)desc.get("IsMlat2");
spec.comment = (String) desc.get("Comment");
specs.add(spec);
}
Expand Down
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