feat!(NODE-4850): serialize negative zero to double (#529)

Author: nbbeeken

docs/upgrade-to-v5.md

@@ -100,3 +100,21 @@ The following deprecated methods have been removed:
 - `ObjectId.prototype.get_inc`
 - `ObjectId.get_inc`
   - The `static getInc()` is private since invoking it increments the next `ObjectId` index, so invoking would impact the creation of subsequent ObjectIds.
+
+### Negative Zero is now serialized to Double
+
+BSON serialize will now preserve negative zero values as a floating point number.
+
+Previously it was required to use the `Double` type class to preserve `-0`:
+```ts
+BSON.deserialize(BSON.serialize({ d: -0 }))
+// no type preservation, returns { d: 0 }
+BSON.deserialize(BSON.serialize({ d: new Double(-0) }))
+// type preservation, returns { d: -0 }
+```
+
+Now `-0` can be used directly
+```ts
+BSON.deserialize(BSON.serialize({ d: -0 }))
+// type preservation, returns { d: -0 }
+```

src/parser/serializer.ts

@@ -68,48 +68,39 @@ function serializeString(buffer: Uint8Array, key: string, value: string, index:
   return index;
 }
 
-const SPACE_FOR_FLOAT64 = new Uint8Array(8);
-const DV_FOR_FLOAT64 = new DataView(
-  SPACE_FOR_FLOAT64.buffer,
-  SPACE_FOR_FLOAT64.byteOffset,
-  SPACE_FOR_FLOAT64.byteLength
-);
+const NUMBER_SPACE = new DataView(new ArrayBuffer(8), 0, 8);
+const FOUR_BYTE_VIEW_ON_NUMBER = new Uint8Array(NUMBER_SPACE.buffer, 0, 4);
+const EIGHT_BYTE_VIEW_ON_NUMBER = new Uint8Array(NUMBER_SPACE.buffer, 0, 8);
+
 function serializeNumber(buffer: Uint8Array, key: string, value: number, index: number) {
-  // We have an integer value
-  // TODO(NODE-2529): Add support for big int
-  if (
-    Number.isInteger(value) &&
-    value >= constants.BSON_INT32_MIN &&
-    value <= constants.BSON_INT32_MAX
-  ) {
-    // If the value fits in 32 bits encode as int32
-    // Set int type 32 bits or less
-    buffer[index++] = constants.BSON_DATA_INT;
-    // Number of written bytes
-    const numberOfWrittenBytes = ByteUtils.encodeUTF8Into(buffer, key, index);
-    // Encode the name
-    index = index + numberOfWrittenBytes;
-    buffer[index++] = 0;
-    // Write the int value
-    buffer[index++] = value & 0xff;
-    buffer[index++] = (value >> 8) & 0xff;
-    buffer[index++] = (value >> 16) & 0xff;
-    buffer[index++] = (value >> 24) & 0xff;
+  const isNegativeZero = Object.is(value, -0);
+
+  const type =
+    !isNegativeZero &&
+    Number.isSafeInteger(value) &&
+    value <= constants.BSON_INT32_MAX &&
+    value >= constants.BSON_INT32_MIN
+      ? constants.BSON_DATA_INT
+      : constants.BSON_DATA_NUMBER;
+
+  if (type === constants.BSON_DATA_INT) {
+    NUMBER_SPACE.setInt32(0, value, true);
   } else {
-    // Encode as double
-    buffer[index++] = constants.BSON_DATA_NUMBER;
-    // Number of written bytes
-    const numberOfWrittenBytes = ByteUtils.encodeUTF8Into(buffer, key, index);
-    // Encode the name
-    index = index + numberOfWrittenBytes;
-    buffer[index++] = 0;
-    // Write float
-    DV_FOR_FLOAT64.setFloat64(0, value, true);
-    buffer.set(SPACE_FOR_FLOAT64, index);
-    // Adjust index
-    index = index + 8;
+    NUMBER_SPACE.setFloat64(0, value, true);
   }
 
+  const bytes =
+    type === constants.BSON_DATA_INT ? FOUR_BYTE_VIEW_ON_NUMBER : EIGHT_BYTE_VIEW_ON_NUMBER;
+
+  buffer[index++] = type;
+
+  const numberOfWrittenBytes = ByteUtils.encodeUTF8Into(buffer, key, index);
+  index = index + numberOfWrittenBytes;
+  buffer[index++] = 0x00;
+
+  buffer.set(bytes, index);
+  index += bytes.byteLength;
+
   return index;
 }
 
@@ -387,8 +378,8 @@ function serializeDouble(buffer: Uint8Array, key: string, value: Double, index:
   buffer[index++] = 0;
 
   // Write float
-  DV_FOR_FLOAT64.setFloat64(0, value.value, true);
-  buffer.set(SPACE_FOR_FLOAT64, index);
+  NUMBER_SPACE.setFloat64(0, value.value, true);
+  buffer.set(EIGHT_BYTE_VIEW_ON_NUMBER, index);
 
   // Adjust index
   index = index + 8;

test/node/double.test.ts

@@ -1,6 +1,9 @@
 import * as BSON from '../register-bson';
 const Double = BSON.Double;
 
+const BSON_DOUBLE_TYPE_INDICATOR = 0x01;
+const BSON_INT_TYPE_INDICATOR = 0x10;
+
 describe('BSON Double Precision', function () {
   context('class Double', function () {
     describe('constructor()', function () {
@@ -78,14 +81,15 @@ describe('BSON Double Precision', function () {
     });
   });
 
-  it('NODE-4335: does not preserve -0 in serialize-deserialize roundtrip if JS number is used', function () {
-    // TODO (NODE-4335): -0 should be serialized as double
-    // This test is demonstrating the behavior of -0 being serialized as an int32 something we do NOT want to unintentionally change, but may want to change in the future, which the above ticket serves to track.
+  it('does preserve -0 in serialize as a double', function () {
     const value = -0;
     const serializedDouble = BSON.serialize({ d: value });
     const type = serializedDouble[4];
-    expect(type).to.not.equal(BSON.BSON_DATA_NUMBER);
-    expect(type).to.equal(BSON.BSON_DATA_INT);
+    expect(type).to.equal(BSON_DOUBLE_TYPE_INDICATOR);
+    expect(type).to.not.equal(BSON_INT_TYPE_INDICATOR);
+    expect(serializedDouble.subarray(7, 15)).to.deep.equal(
+      new Uint8Array(new Float64Array([-0]).buffer)
+    );
   });
 
   describe('extended JSON', () => {