feat(NODE-4873): support EJSON stringify from BigInt to $numberLong

src/extended_json.ts

@@ -234,6 +234,13 @@ function serializeValue(value: any, options: EJSONSerializeOptions): any {
     return { $numberDouble: Object.is(value, -0) ? '-0.0' : value.toString() };
   }
 
+  if (typeof value === 'bigint') {
+    if (!options.relaxed) {
+      return { $numberLong: BigInt.asIntN(64, value).toString() };
+    }
+    return Number(BigInt.asIntN(64, value));
+  }
+
   if (value instanceof RegExp || isRegExp(value)) {
     let flags = value.flags;
     if (flags === undefined) {

test/node/extended_json.test.ts

@@ -2,6 +2,7 @@ import * as BSON from '../register-bson';
 const EJSON = BSON.EJSON;
 import * as vm from 'node:vm';
 import { expect } from 'chai';
+import { BSONDataView } from '../../src/utils/byte_utils';
 
 // BSON types
 const Binary = BSON.Binary;
@@ -180,6 +181,62 @@ describe('Extended JSON', function () {
     expect(EJSON.parse(serialized)).to.deep.equal(numbers);
   });
 
+  it('truncates bigint values when they are outside the range [BSON_INT64_MIN, BSON_INT64_MAX] in canonical mode', function () {
+    const numbers = { a: 2n ** 64n + 1n, b: -(2n ** 64n) - 1n };
+    const serialized = EJSON.stringify(numbers, { relaxed: false });
+    expect(serialized).to.equal('{"a":{"$numberLong":"1"},"b":{"$numberLong":"-1"}}');
+  });
+
+  it('truncates bigint values in the same way as BSON.serialize in canonical mode', function () {
+    const number = { a: 0x1234_5678_1234_5678_9999n };
+    const stringified = EJSON.stringify(number, { relaxed: false });
+    const serialized = BSON.serialize(number);
+
+    const VALUE_OFFSET = 7;
+    const dataView = BSONDataView.fromUint8Array(serialized);
+    const serializedValue = dataView.getBigInt64(VALUE_OFFSET, true);
+    const parsed = JSON.parse(stringified);
+
+    expect(parsed).to.have.property('a');
+    expect(parsed['a']).to.have.property('$numberLong');
+    expect(parsed.a.$numberLong).to.equal(0x5678_1234_5678_9999n.toString());
+
+    expect(parsed.a.$numberLong).to.equal(serializedValue.toString());
+  });
+
+  it('truncates bigint values in the same way as BSON.serialize in relaxed mode', function () {
+    const number = { a: 0x1234_0000_1234_5678_9999n }; // Ensure that the serialized number can be exactly represented as a JS number
+    const stringified = EJSON.stringify(number, { relaxed: true });
+    const serializedDoc = BSON.serialize(number);
+
+    const VALUE_OFFSET = 7;
+    const dataView = BSONDataView.fromUint8Array(serializedDoc);
+    const parsed = JSON.parse(stringified);
+
+    expect(parsed).to.have.property('a');
+    expect(parsed.a).to.equal(0x0000_1234_5678_9999);
+
+    expect(parsed.a).to.equal(Number(dataView.getBigInt64(VALUE_OFFSET, true)));
+  });
+
+  it('serializes bigint values to numberLong in canonical mode', function () {
+    const number = { a: 2n };
+    const serialized = EJSON.stringify(number, { relaxed: false });
+    expect(serialized).to.equal('{"a":{"$numberLong":"2"}}');
+  });
+
+  it('serializes bigint values to Number in relaxed mode', function () {
+    const number = { a: 10000n };
+    const serialized = EJSON.stringify(number, { relaxed: true });
+    expect(serialized).to.equal('{"a":10000}');
+  });
+
+  it('loses precision when serializing bigint values outside of range [Number.MIN_SAFE_INTEGER, Number.MAX_SAFE_INTEGER] in relaxed mode', function () {
+    const numbers = { a: -(2n ** 53n) - 1n, b: 2n ** 53n + 2n };
+    const serialized = EJSON.stringify(numbers, { relaxed: true });
+    expect(serialized).to.equal('{"a":-9007199254740992,"b":9007199254740994}');
+  });
+
   it('should correctly parse null values', function () {
     expect(EJSON.parse('null')).to.be.null;
     expect(EJSON.parse('[null]')[0]).to.be.null;