Add fast path for writing BdfDictionaries.

bramble-core/src/main/java/org/briarproject/bramble/data/BdfWriterImpl.java

@@ -2,6 +2,7 @@ package org.briarproject.bramble.data;
 
 import org.briarproject.bramble.api.Bytes;
 import org.briarproject.bramble.api.FormatException;
+import org.briarproject.bramble.api.data.BdfDictionary;
 import org.briarproject.bramble.api.data.BdfWriter;
 import org.briarproject.nullsafety.NotNullByDefault;
 
@@ -11,6 +12,7 @@ import java.util.ArrayList;
 import java.util.Collection;
 import java.util.List;
 import java.util.Map;
+import java.util.Map.Entry;
 
 import javax.annotation.Nullable;
 import javax.annotation.concurrent.NotThreadSafe;
@@ -171,16 +173,24 @@ final class BdfWriterImpl implements BdfWriter {
 	@Override
 	public void writeDictionary(Map<?, ?> m) throws IOException {
 		out.write(DICTIONARY);
-		// Write entries in canonical order
+		if (m instanceof BdfDictionary) {
-		List<String> keys = new ArrayList<>(m.size());
+			// Entries are already sorted and keys are known to be strings
-		for (Object k : m.keySet()) {
+			for (Entry<String, Object> e : ((BdfDictionary) m).entrySet()) {
-			if (!(k instanceof String)) throw new FormatException();
+				writeString(e.getKey());
-			keys.add((String) k);
+				writeObject(e.getValue());
-		}
+			}
-		sort(keys);
+		} else {
-		for (String key : keys) {
+			// Check that keys are strings, write entries in canonical order
-			writeString(key);
+			List<String> keys = new ArrayList<>(m.size());
-			writeObject(m.get(key));
+			for (Object k : m.keySet()) {
+				if (!(k instanceof String)) throw new FormatException();
+				keys.add((String) k);
+			}
+			sort(keys);
+			for (String key : keys) {
+				writeString(key);
+				writeObject(m.get(key));
+			}
 		}
 		out.write(END);
 	}

bramble-core/src/test/java/org/briarproject/bramble/data/BdfWriterImplTest.java

@@ -1,5 +1,6 @@
 package org.briarproject.bramble.data;
 
+import org.briarproject.bramble.api.data.BdfDictionary;
 import org.briarproject.bramble.test.BrambleTestCase;
 import org.briarproject.bramble.util.StringUtils;
 import org.junit.Test;
@@ -168,9 +169,11 @@ public class BdfWriterImplTest extends BrambleTestCase {
 
 	@Test
 	public void testWriteDictionary() throws IOException {
-		// Use LinkedHashMap to get predictable iteration order
+		// Add entries to dictionary in descending order - they should be
+		// output in ascending order. Use LinkedHashMap to get predictable
+		// iteration order
 		Map<String, Object> m = new LinkedHashMap<>();
-		for (int i = 0; i < 4; i++) m.put(String.valueOf(i), i);
+		for (int i = 3; i >= 0; i--) m.put(String.valueOf(i), i);
 		w.writeDictionary(m);
 		// DICTIONARY tag, keys as strings and values as integers, END tag
 		checkContents("70" + "41" + "01" + "30" + "21" + "00" +
@@ -179,6 +182,20 @@ public class BdfWriterImplTest extends BrambleTestCase {
 				"41" + "01" + "33" + "21" + "03" + "80");
 	}
 
+	@Test
+	public void testWriteBdfDictionary() throws IOException {
+		// Add entries to dictionary in descending order - they should be
+		// output in ascending order
+		BdfDictionary d = new BdfDictionary();
+		for (int i = 3; i >= 0; i--) d.put(String.valueOf(i), i);
+		w.writeDictionary(d);
+		// DICTIONARY tag, keys as strings and values as integers, END tag
+		checkContents("70" + "41" + "01" + "30" + "21" + "00" +
+				"41" + "01" + "31" + "21" + "01" +
+				"41" + "01" + "32" + "21" + "02" +
+				"41" + "01" + "33" + "21" + "03" + "80");
+	}
+
 	@Test
 	public void testWriteNestedDictionariesAndLists() throws IOException {
 		Map<String, Object> inner = new LinkedHashMap<>();