From dd6f534ad71711e8bca219c391101f0d601c040f Mon Sep 17 00:00:00 2001
From: Neal Beeken <neal.beeken@mongodb.com>
Date: Thu, 22 Feb 2024 18:30:57 -0500
Subject: [PATCH] perf(NODE-5910): optimize small byte copies

---
 src/objectid.ts             | 17 ++++++++++++++++
 src/parser/serializer.ts    | 26 ++++++++++++-------------
 test/node/object_id.test.ts | 39 +++++++++++++++++++++++++++++++++++++
 3 files changed, 68 insertions(+), 14 deletions(-)

diff --git a/src/objectid.ts b/src/objectid.ts
index b448f61b2..69c2a24f0 100644
--- a/src/objectid.ts
+++ b/src/objectid.ts
@@ -269,6 +269,23 @@ export class ObjectId extends BSONValue {
     return new ObjectId();
   }
 
+  /** @internal */
+  serializeInto(uint8array: Uint8Array, index: number): 12 {
+    uint8array[index] = this.buffer[0];
+    uint8array[index + 1] = this.buffer[1];
+    uint8array[index + 2] = this.buffer[2];
+    uint8array[index + 3] = this.buffer[3];
+    uint8array[index + 4] = this.buffer[4];
+    uint8array[index + 5] = this.buffer[5];
+    uint8array[index + 6] = this.buffer[6];
+    uint8array[index + 7] = this.buffer[7];
+    uint8array[index + 8] = this.buffer[8];
+    uint8array[index + 9] = this.buffer[9];
+    uint8array[index + 10] = this.buffer[10];
+    uint8array[index + 11] = this.buffer[11];
+    return 12;
+  }
+
   /**
    * Creates an ObjectId from a second based number, with the rest of the ObjectId zeroed out. Used for comparisons or sorting the ObjectId.
    *
diff --git a/src/parser/serializer.ts b/src/parser/serializer.ts
index f5f562266..0c6ddcea6 100644
--- a/src/parser/serializer.ts
+++ b/src/parser/serializer.ts
@@ -256,16 +256,7 @@ function serializeObjectId(buffer: Uint8Array, key: string, value: ObjectId, ind
   index = index + numberOfWrittenBytes;
   buffer[index++] = 0;
 
-  // Write the objectId into the shared buffer
-  const idValue = value.id;
-
-  if (isUint8Array(idValue)) {
-    for (let i = 0; i < 12; i++) {
-      buffer[index++] = idValue[i];
-    }
-  } else {
-    throw new BSONError('object [' + JSON.stringify(value) + '] is not a valid ObjectId');
-  }
+  index += value.serializeInto(buffer, index);
 
   // Adjust index
   return index;
@@ -289,7 +280,11 @@ function serializeBuffer(buffer: Uint8Array, key: string, value: Uint8Array, ind
   // Write the default subtype
   buffer[index++] = constants.BSON_BINARY_SUBTYPE_DEFAULT;
   // Copy the content form the binary field to the buffer
-  buffer.set(value, index);
+  if (size <= 16) {
+    for (let i = 0; i < size; i++) buffer[index + i] = value[i];
+  } else {
+    buffer.set(value, index);
+  }
   // Adjust the index
   index = index + size;
   return index;
@@ -343,7 +338,7 @@ function serializeDecimal128(buffer: Uint8Array, key: string, value: Decimal128,
   index = index + numberOfWrittenBytes;
   buffer[index++] = 0;
   // Write the data from the value
-  buffer.set(value.bytes.subarray(0, 16), index);
+  for (let i = 0; i < 16; i++) buffer[index + i] = value.bytes[i];
   return index + 16;
 }
 
@@ -552,8 +547,11 @@ function serializeBinary(buffer: Uint8Array, key: string, value: Binary, index:
     buffer[index++] = (size >> 24) & 0xff;
   }
 
-  // Write the data to the object
-  buffer.set(data, index);
+  if (size <= 16) {
+    for (let i = 0; i < size; i++) buffer[index + i] = data[i];
+  } else {
+    buffer.set(data, index);
+  }
   // Adjust the index
   index = index + value.position;
   return index;
diff --git a/test/node/object_id.test.ts b/test/node/object_id.test.ts
index 2af8b1326..62344c3a6 100644
--- a/test/node/object_id.test.ts
+++ b/test/node/object_id.test.ts
@@ -485,4 +485,43 @@ describe('ObjectId', function () {
       });
     });
   });
+
+  context('serializeInto()', () => {
+    it('writes oid bytes to input buffer', () => {
+      const oid = new ObjectId('61'.repeat(12));
+      const buffer = new Uint8Array(20);
+      // @ts-expect-error: internal method
+      oid.serializeInto(buffer, 0);
+      expect(buffer.subarray(0, 12)).to.deep.equal(Buffer.from('61'.repeat(12), 'hex'));
+    });
+
+    it('writes oid bytes to input buffer at offset', () => {
+      const oid = new ObjectId('61'.repeat(12));
+      const buffer = new Uint8Array(20);
+      // @ts-expect-error: internal method
+      oid.serializeInto(buffer, 5);
+      expect(buffer.subarray(5, 5 + 12)).to.deep.equal(Buffer.from('61'.repeat(12), 'hex'));
+    });
+
+    it('does not validate input types', () => {
+      const oid = new ObjectId('61'.repeat(12));
+      const object = {};
+      // @ts-expect-error: internal method
+      oid.serializeInto(object, 'b');
+      expect(object).to.deep.equal({
+        b: 0x61,
+        b1: 0x61,
+        b2: 0x61,
+        b3: 0x61,
+        b4: 0x61,
+        b5: 0x61,
+        b6: 0x61,
+        b7: 0x61,
+        b8: 0x61,
+        b9: 0x61,
+        b10: 0x61,
+        b11: 0x61
+      });
+    });
+  });
 });