Merge pull request msgpack#437 from msgpack/unpacker-try-nil

xerial · web-flow · commit 53a24d7a3414 · 2017-10-20T18:40:31.000-07:00
Add MessageUnpacker.tryUnpackNil() method
diff --git a/msgpack-core/src/main/java/org/msgpack/core/MessageUnpacker.java b/msgpack-core/src/main/java/org/msgpack/core/MessageUnpacker.java
@@ -389,7 +389,7 @@ private boolean ensureBuffer()
     public MessageFormat getNextFormat()
             throws IOException
     {
-        // makes sure that buffer has at leat 1 byte
+        // makes sure that buffer has at least 1 byte
         if (!ensureBuffer()) {
             throw new MessageInsufficientBufferException();
         }
@@ -731,6 +731,31 @@ public void unpackNil()
         throw unexpected("Nil", b);
     }
 
+    /**
+     * Peeks a Nil byte and reads it if next byte is a nil value.
+     *
+     * The difference from {@link unpackNil} is that unpackNil throws an exception if the next byte is not nil value
+     * while this tryUnpackNil method returns false without changing position.
+     *
+     * @return true if a nil value is read
+     * @throws MessageInsufficientBufferException when the end of file reached
+     * @throws IOException when underlying input throws IOException
+     */
+    public boolean tryUnpackNil()
+            throws IOException
+    {
+        // makes sure that buffer has at least 1 byte
+        if (!ensureBuffer()) {
+            throw new MessageInsufficientBufferException();
+        }
+        byte b = buffer.getByte(position);
+        if (b == Code.NIL) {
+            readByte();
+            return true;
+        }
+        return false;
+    }
+
     /**
      * Reads true or false.
      *
diff --git a/msgpack-core/src/test/scala/org/msgpack/core/MessagePackTest.scala b/msgpack-core/src/test/scala/org/msgpack/core/MessagePackTest.scala
@@ -240,6 +240,19 @@ class MessagePackTest extends MessagePackSpec {
       check(null, _.packNil, { unpacker => unpacker.unpackNil(); null })
     }
 
+    "skipping a nil value" taggedAs ("try") in {
+      check(true, _.packNil, _.tryUnpackNil)
+      check(false, { packer => packer.packString("val") }, { unpacker => unpacker.tryUnpackNil() })
+      check("val", { packer => packer.packString("val") }, { unpacker => unpacker.tryUnpackNil(); unpacker.unpackString() })
+      check("val", { packer => packer.packNil(); packer.packString("val") }, { unpacker => unpacker.tryUnpackNil(); unpacker.unpackString() })
+      try {
+        checkException(null, { _ => }, _.tryUnpackNil)
+      }
+      catch {
+        case e: MessageInsufficientBufferException => // OK
+      }
+    }
+
     "pack/unpack integer values" taggedAs ("int") in {
       val sampleData = Seq[Long](Int.MinValue.toLong -
         10, -65535, -8191, -1024, -255, -127, -63, -31, -15, -7, -3, -1, 0, 2, 4, 8, 16, 32, 64, 128, 256, 1024, 8192, 65536,
