Strange behavior when using TextDecoder #9941

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1. abdallahkadour

   added

   bug-pending-triageReported bug, pending triage to confirm.Reported bug, pending triage to confirm.

   on Jun 21, 2022
2. CatchABus

   added

   bug

   on Jul 27, 2022
3. CatchABus commented on Jul 27, 2022

   

   CatchABus

   on Jul 27, 2022

   Contributor

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   Thanks a lot for reporting this. I have also taken a look in cbor repo discussion about it and I can confirm NS polyfill for these 2 classes is incomplete or outdated. There is already been a small discussion with another member and I believe we'll look into this.
   Until then, I suggest that you use a 3rd-party polyfill for those if possible.
4. rigor789

   removed

   bug-pending-triageReported bug, pending triage to confirm.Reported bug, pending triage to confirm.

   on Jul 27, 2022
5. triniwiz

   self-assigned this

   on Jul 27, 2022
6. abdallahkadour commented on Dec 9, 2022

   

   abdallahkadour

   on Dec 9, 2022

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   As a workaround, the library cbor-sync could be used.
7. kjeib commented on Oct 14, 2026

   

   kjeib

   on Oct 14, 2026

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   I believe the root cause of this (and of a failure we hit with libp2p) is that TextDecoder.decode() ignores a view's byteOffset and byteLength.

   packages/core/text/text-common.ts, still the case on main:

   public decode(input: BufferSource): string {
   	const buffer = ArrayBuffer.isView(input) ? input.buffer : input;
   	...
   	const inputAs8 = new Uint8Array(buffer);

   For a typed-array view, input.buffer is the whole underlying ArrayBuffer, so the decoder decodes bytes outside the view.

   Minimal reproduction

   const bytes = new Uint8Array([0x78, 0x78, 0x68, 0x69]); // "xxhi"
   new TextDecoder().decode(bytes.subarray(2));             // expected "hi"; decodes the whole buffer instead

   Libraries that decode from sub-arrays of a larger buffer — CBOR parsers, protobuf, length-prefixed protocols — break silently. In our case, libp2p's multistream-select decodes protocol names from sub-arrays, so every stream negotiation on NativeScript failed ("did not read multistream-select header", and the remote's protocol read as an empty string): no identify and no circuit-relay reservation, while the same code works in Node, browsers and React Native.

   Suggested fix

   const bytes = ArrayBuffer.isView(input)
   	? new Uint8Array(input.buffer, input.byteOffset, input.byteLength)
   	: new Uint8Array(input);

   Environment: @nativescript/core 8.9.9 (the same code is in 9.1.3 / main), NativeScript Android runtime 8.9.2, V8 10.3, Galaxy S7 (Android 8).

   Workaround until it is fixed — wrap decode so views are copied first:

   const original = TextDecoder.prototype.decode;
   TextDecoder.prototype.decode = function (input, options) {
     if (input && ArrayBuffer.isView(input) && (input.byteOffset !== 0 || input.byteLength !== input.buffer.byteLength)) {
       input = new Uint8Array(input.buffer.slice(input.byteOffset, input.byteOffset + input.byteLength));
     }
     return original.call(this, input, options);
   };