utility to write unsigned shorts

core/src/main/groovy/com/muwire/core/util/DataUtil.groovy

@@ -0,0 +1,17 @@
+package com.muwire.core.util
+
+class DataUtil {
+	
+	private static int MAX_SHORT = (0x1 << 16) - 1
+
+	static writeUnsignedShort(int value, OutputStream os) {
+		if (value > MAX_SHORT || value < 0)
+			throw new IllegalArgumentException("$value invalid")
+		
+		byte lsb = (byte) (value & 0xFF)
+		byte msb = (byte) (value >> 8)
+		
+		os.write(msb)
+		os.write(lsb)	
+	}
+}

core/src/test/groovy/com/muwire/core/util/DataUtilTest.groovy

@@ -0,0 +1,29 @@
+package com.muwire.core.util
+
+import static org.junit.Assert.fail
+
+import org.junit.Test
+
+class DataUtilTest {
+
+	
+	private static void usVal(int value) {
+		ByteArrayOutputStream baos = new ByteArrayOutputStream()
+		DataUtil.writeUnsignedShort(value, baos)
+		def is = new DataInputStream(new ByteArrayInputStream(baos.toByteArray()))
+		assert is.readUnsignedShort() == value
+	}
+	@Test
+	void testUnsignedShort() {
+		usVal(0)
+		usVal(20)
+		usVal(Short.MAX_VALUE)
+		usVal(Short.MAX_VALUE + 1)
+		usVal(0xFFFF)
+		
+		try {
+			usVal(0xFFFF + 1)
+			fail()
+		} catch (IllegalArgumentException expected) {}
+	}
+}