Add stringifyJsonWithBigInts helper

packages/rpc-transport-http/src/__tests__/stringify-json-with-bigints-test.ts

@@ -0,0 +1,73 @@
+import { stringifyJsonWithBigints } from '../stringify-json-with-bigints';
+
+const MAX_SAFE_INTEGER = BigInt(Number.MAX_SAFE_INTEGER);
+const MAX_SAFE_INTEGER_PLUS_ONE = BigInt(Number.MAX_SAFE_INTEGER) + 1n;
+
+describe('stringifyJsonWithBigints', () => {
+    it.each`
+        input                        | expectedString
+        ${0n}                        | ${'0'}
+        ${-0n}                       | ${'0'}
+        ${1n}                        | ${'1'}
+        ${-1n}                       | ${'-1'}
+        ${42n}                       | ${'42'}
+        ${-42n}                      | ${'-42'}
+        ${100000n}                   | ${'100000'}
+        ${-100000n}                  | ${'-100000'}
+        ${123n * 10n ** 32n}         | ${'12300000000000000000000000000000000'}
+        ${-123n * 10n ** 32n}        | ${'-12300000000000000000000000000000000'}
+        ${MAX_SAFE_INTEGER}          | ${MAX_SAFE_INTEGER.toString()}
+        ${MAX_SAFE_INTEGER_PLUS_ONE} | ${MAX_SAFE_INTEGER_PLUS_ONE.toString()}
+    `('strigifies bigint $input as a numerical value', ({ expectedString, input }) => {
+        expect(stringifyJsonWithBigints(input)).toBe(expectedString);
+    });
+    it('strigifies BigInts within nested structures', () => {
+        const input = {
+            alice: 42n,
+            bob: [3.14, BigInt(3e8), { baz: 1234567890123456789012345678901234567890n }],
+        };
+        expect(stringifyJsonWithBigints(input)).toBe(
+            '{"alice":42,"bob":[3.14,300000000,{"baz":1234567890123456789012345678901234567890}]}',
+        );
+    });
+    it.each`
+        input          | expectedString
+        ${0.5}         | ${'0.5'}
+        ${-0.5}        | ${'-0.5'}
+        ${3.14159265}  | ${'3.14159265'}
+        ${-3.14159265} | ${'-3.14159265'}
+        ${1e-5}        | ${'0.00001'}
+        ${-1e-5}       | ${'-0.00001'}
+        ${1e-32}       | ${'1e-32'}
+        ${-1189e-32}   | ${'-1.189e-29'}
+    `('strigifies number $input as a numerical value', ({ expectedString, input }) => {
+        expect(stringifyJsonWithBigints(input)).toBe(expectedString);
+    });
+    it.each([
+        null,
+        false,
+        true,
+        [],
+        [null, true, false],
+        {},
+        { foo: 'bar' },
+        '',
+        'Hello World',
+        '42 apples',
+        'base64',
+        '"base64',
+        '""base64',
+        '\\base64',
+        '\\"base64',
+        '\\""base64',
+        '\\\\base64',
+        '\\\\"base64',
+        '\\\\""base64',
+        'He said: "I will eat 3 bananas"',
+        { message_100: 'Hello to the 1st World' },
+        { message_200: 'Hello to the "2nd World"' },
+        { data: ['', 'base64'] },
+    ])('does not alter the value of %s', input => {
+        expect(stringifyJsonWithBigints(input)).toBe(JSON.stringify(input));
+    });
+});

packages/rpc-transport-http/src/stringify-json-with-bigints.ts

@@ -0,0 +1,22 @@
+/**
+ * Transforms a value into a JSON string, whilst rendering bigints as large unsafe integers.
+ */
+export function stringifyJsonWithBigints(value: unknown, space?: number | string): string {
+    return unwrapBigIntValueObject(
+        JSON.stringify(value, (_, v) => (typeof v === 'bigint' ? wrapBigIntValueObject(v) : v), space),
+    );
+}
+
+type BigIntValueObject = {
+    // `$` implies 'this is a value object'.
+    // `n` implies 'interpret the value as a bigint'.
+    $n: string;
+};
+
+function wrapBigIntValueObject(value: bigint): BigIntValueObject {
+    return { $n: `${value}` };
+}
+
+function unwrapBigIntValueObject(value: string): string {
+    return value.replace(/\{\s*"\$n"\s*:\s*"(-?\d+)"\s*\}/g, '$1');
+}