Added BsonReader.peekBinarySubType as a more efficient alternative to BsonReader.mark/reset, to avoid

a double copy of the byte array.

Author: jyemin

bson/src/main/org/bson/AbstractBsonReader.java

@@ -112,6 +112,12 @@ protected boolean isClosed() {
      */
     protected abstract BsonBinary doReadBinaryData();
 
+    /**
+     * Handles the logic to peek at the binary subtype.
+     *
+     * @return the binary subtype
+     */
+    protected abstract byte doPeekBinarySubType();
 
     /**
      * Handles the logic to read booleans
@@ -261,6 +267,12 @@ public BsonBinary readBinaryData() {
         return doReadBinaryData();
     }
 
+    @Override
+    public byte peekBinarySubType() {
+        checkPreconditions("readBinaryData", BsonType.BINARY);
+        return doPeekBinarySubType();
+    }
+
     @Override
     public boolean readBoolean() {
         checkPreconditions("readBoolean", BsonType.BOOLEAN);

bson/src/main/org/bson/BsonBinaryReader.java

@@ -130,6 +130,15 @@ protected BsonBinary doReadBinaryData() {
         return new BsonBinary(type, bytes);
     }
 
+    @Override
+    protected byte doPeekBinarySubType() {
+        mark();
+        bsonInput.readInt32();
+        byte type = bsonInput.readByte();
+        reset();
+        return type;
+    }
+
     @Override
     protected boolean doReadBoolean() {
         return bsonInput.readByte() == 0x1;

bson/src/main/org/bson/BsonDocumentReader.java

@@ -36,6 +36,11 @@ protected BsonBinary doReadBinaryData() {
         return currentValue.asBinary();
     }
 
+    @Override
+    protected byte doPeekBinarySubType() {
+        return currentValue.asBinary().getType();
+    }
+
     @Override
     protected boolean doReadBoolean() {
         return currentValue.asBoolean().getValue();

bson/src/main/org/bson/BsonReader.java

@@ -43,6 +43,14 @@ public interface BsonReader {
      */
     BsonBinary readBinaryData();
 
+    /**
+     * Peeks the subtype of the binary data that the reader is positioned at.  This operation is not permitted if the mark is already set.
+     *
+     * @return the subtype
+     * @see #mark()
+     */
+    byte peekBinarySubType();
+
     /**
      * Reads a BSON Binary data element from the reader.
      *
@@ -358,5 +366,4 @@ public interface BsonReader {
      * @throws org.bson.BSONException if no mark has been set
      */
     void reset();
-
 }

bson/src/main/org/bson/json/JsonReader.java

@@ -80,6 +80,11 @@ protected BsonBinary doReadBinaryData() {
         return (BsonBinary) currentValue;
     }
 
+    @Override
+    protected byte doPeekBinarySubType() {
+       return doReadBinaryData().getType();
+    }
+
     @Override
     protected boolean doReadBoolean() {
         return (Boolean) currentValue;

bson/src/test/org/bson/LimitedLookaheadMarkSpecification.groovy

@@ -241,4 +241,44 @@ class LimitedLookaheadMarkSpecification extends Specification {
                 new JsonWriter(new StringWriter())
         ]
     }
+
+    def 'should peek binary subtype'(BsonWriter writer) {
+        given:
+        writer.with {
+            writeStartDocument()
+            writeBinaryData('binary', new BsonBinary(BsonBinarySubType.UUID_LEGACY, new byte[16]))
+            writeInt64('int64', 52L)
+            writeEndDocument()
+        }
+
+        when:
+        BsonReader reader
+        if (writer instanceof BsonDocumentWriter) {
+            reader = new BsonDocumentReader(writer.document)
+        } else if (writer instanceof BsonBinaryWriter) {
+            BasicOutputBuffer buffer = (BasicOutputBuffer) writer.getBsonOutput();
+            reader = new BsonBinaryReader(new ByteBufferBsonInput(buffer.getByteBuffers().get(0)), true)
+        } else if (writer instanceof JsonWriter) {
+            reader = new JsonReader(writer.writer.toString())
+        }
+
+        reader.readStartDocument()
+        reader.readName()
+        def subType = reader.peekBinarySubType()
+        def binary = reader.readBinaryData()
+        def longValue = reader.readInt64('int64')
+        reader.readEndDocument()
+
+        then:
+        subType == BsonBinarySubType.UUID_LEGACY.value
+        binary == new BsonBinary(BsonBinarySubType.UUID_LEGACY, new byte[16])
+        longValue == 52L
+
+        where:
+        writer << [
+                new BsonDocumentWriter(new BsonDocument()),
+                new BsonBinaryWriter(new BasicOutputBuffer(), false),
+                new JsonWriter(new StringWriter())
+        ]
+    }
 }

driver-core/src/main/com/mongodb/codecs/DocumentCodec.java

@@ -178,11 +178,8 @@ private Object readValue(final BsonReader reader, final DecoderContext decoderCo
             reader.readNull();
             return null;
         } else if (bsonType == BsonType.BINARY) {
-            reader.mark();
-            byte bsonSubType = reader.readBinaryData().getType();
-            reader.reset();
-            if (bsonSubType == BsonBinarySubType.UUID_STANDARD.getValue()
-                    || bsonSubType == BsonBinarySubType.UUID_LEGACY.getValue()) {
+            byte bsonSubType = reader.peekBinarySubType();
+            if (bsonSubType == BsonBinarySubType.UUID_STANDARD.getValue() || bsonSubType == BsonBinarySubType.UUID_LEGACY.getValue()) {
                 return registry.get(UUID.class).decode(reader, decoderContext);
             }
         }