fix: Unknown encoding when undefined is used

[mcandeia]

The behavior of buffer.toString(encoding) is not compliant with nodejs API. it throws an error UNKNOWN_ENCODING: null (or undefined) because it's being passed as a string "undefined" or "null"

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[mcandeia]

I have read the CLA Document and I hereby sign the CLA

[mcandeia]

@anonrig fixed a test that was failing due to this expected behavior: https://github.com/cloudflare/workerd/blob/main/src/workerd/api/node/tests/buffer-nodejs-test.js#L5803

[mcandeia]

@anonrig can you help me to decide one thing?

The NodeJs implementation does not fallback for null encoding - leading into a TypeError as this test covers (https://github.com/cloudflare/workerd/blob/main/src/workerd/api/node/tests/buffer-nodejs-test.js#L5823)

This test was failing before because of the wrong conversion to null (as a string) but now it isn't failing anymore because it is well-covered by the encoding?.toString().

The nodejs implementation on the other hand does the following:

1. Buffer.prototype.toString implementation uses getEncodingOpts when encoding is null
2. https://github.com/nodejs/node/blob/a73c41c51e7711086b9801afd5e91ae2f96a7694/lib/buffer.js#L722C10-L722C24
3. it concats null with '' https://github.com/nodejs/node/blob/a73c41c51e7711086b9801afd5e91ae2f96a7694/lib/buffer.js#L723
4. which results into a null as a string value with length of 4

5. The switch case will not match with any option https://github.com/nodejs/node/blob/a73c41c51e7711086b9801afd5e91ae2f96a7694/lib/buffer.js#L725
6. then it returns undefined and only then throws an error: https://github.com/nodejs/node/blob/a73c41c51e7711086b9801afd5e91ae2f96a7694/lib/buffer.js#L863

The options we have:

1. Remove the test case and let undefined and null have the same behavior
2. make sure null encoding is not allowed and explicitly throw an error

[anonrig]

Hi @mcandeia,

Thank you for the awesome comment. I love it! Here's a suggestion to fix the issue:

diff --git a/src/node/internal/internal_buffer.ts b/src/node/internal/internal_buffer.ts
index cfde61ea..f57ba153 100644
--- a/src/node/internal/internal_buffer.ts
+++ b/src/node/internal/internal_buffer.ts
@@ -28,7 +28,10 @@ import {
   isUint8Array,
 } from 'node-internal:internal_types';
 
-import { normalizeEncoding } from 'node-internal:internal_utils';
+import {
+  normalizeEncoding,
+  getEncodingOps,
+} from 'node-internal:internal_utils';
 
 import { validateString } from 'node-internal:validators';
 
@@ -648,7 +651,7 @@ Buffer.prototype.toString = function toString(
     return '';
   }
 
-  const normalizedEncoding = normalizeEncoding(encoding?.toString());
+  const normalizedEncoding = getEncodingOps(encoding);
   if (normalizedEncoding === undefined) {
     throw new ERR_UNKNOWN_ENCODING(`${encoding}`);
   }
diff --git a/src/node/internal/internal_utils.ts b/src/node/internal/internal_utils.ts
index 7290f4f5..3a80b921 100644
--- a/src/node/internal/internal_utils.ts
+++ b/src/node/internal/internal_utils.ts
@@ -42,10 +42,12 @@ export function normalizeEncoding(enc?: string): Encoding | undefined {
     enc === 'UTF-8'
   )
     return UTF8;
-  return slowCases(enc);
+  return getEncodingOps(enc);
 }
 
-export function slowCases(enc: unknown): Encoding | undefined {
+export function getEncodingOps(enc: unknown): Encoding | undefined {
+  // eslint-disable-next-line @typescript-eslint/restrict-plus-operands
+  enc += '';
   // @ts-expect-error TS18046 TS complains about unknown can not have length.
   switch (enc.length) {
     case 4:
diff --git a/src/workerd/api/node/tests/buffer-nodejs-test.js b/src/workerd/api/node/tests/buffer-nodejs-test.js
index 3dc88c3a..09c56f80 100644
--- a/src/workerd/api/node/tests/buffer-nodejs-test.js
+++ b/src/workerd/api/node/tests/buffer-nodejs-test.js
@@ -5815,7 +5815,8 @@ export const toStringRange = {
       },
       {
         name: 'TypeError',
-      }
+      },
+      'toString() with 0 and null as the encoding should have thrown'
     );
 
     throws(
@@ -5824,7 +5825,8 @@ export const toStringRange = {
       },
       {
         name: 'TypeError',
-      }
+      },
+      'toString() with null encoding should have thrown'
     );
   },
 };

[anonrig]

By the way, I forgot. Can you add a test so we don't regress in the future? Thank you.