FuelLabs/fuels-ts · error · FuelError

ENCODE_ERROR

ENCODE_ERROR

Error message

Expected array value.

What it means

Thrown by RawSliceCoder.encode() when the input is not a JavaScript array. RawSliceCoder encodes Sway raw untyped slices and expects a number[] (array of byte values 0-255). Passing any non-array value, including a string, number, object, or even a Uint8Array, triggers this error because Uint8Array fails Array.isArray().

Source

Thrown at packages/abi-coder/src/encoding/coders/RawSliceCoder.ts:18

import { ErrorCode, FuelError } from '@fuel-ts/errors';
import { bn } from '@fuel-ts/math';

import { WORD_SIZE } from '../../utils/constants';

import { Coder } from './AbstractCoder';
import { ArrayCoder } from './ArrayCoder';
import { BigNumberCoder } from './BigNumberCoder';
import { NumberCoder } from './NumberCoder';

export class RawSliceCoder extends Coder<number[], number[]> {
  constructor() {
    super('raw untyped slice', 'raw untyped slice', WORD_SIZE);
  }

  encode(value: number[]): Uint8Array {
    if (!Array.isArray(value)) {
      throw new FuelError(ErrorCode.ENCODE_ERROR, `Expected array value.`);
    }

    const internalCoder = new ArrayCoder(new NumberCoder('u8'), value.length);
    const bytes = internalCoder.encode(value);
    const lengthBytes = new BigNumberCoder('u64').encode(bytes.length);

    return new Uint8Array([...lengthBytes, ...bytes]);
  }

  decode(data: Uint8Array, offset: number): [number[], number] {
    if (data.length < this.encodedLength) {
      throw new FuelError(ErrorCode.DECODE_ERROR, `Invalid raw slice data size.`);
    }

    const offsetAndLength = offset + WORD_SIZE;
    const lengthBytes = data.slice(offset, offsetAndLength);
    const length = bn(new BigNumberCoder('u64').decode(lengthBytes, 0)[0]).toNumber();
    const dataBytes = data.slice(offsetAndLength, offsetAndLength + length);

View on GitHub (pinned to b3f37c91ac)

Solutions

1. Convert the value to number[] before encoding: Array.from(uint8Array) or split a string into char codes.
2. If you have a Uint8Array, use Array.from() to convert, or use VecCoder/BytesCoder which accepts Uint8Array directly.
3. Ensure each element is an integer in the 0-255 range.

Example fix

// before
rawSliceCoder.encode('abc');               // throws ENCODE_ERROR
rawSliceCoder.encode(new Uint8Array([97]));  // throws ENCODE_ERROR

// after
rawSliceCoder.encode([97, 98, 99]);
rawSliceCoder.encode(Array.from(uint8Array));

function isRawSliceValue(value: unknown): boolean {
  return Array.isArray(value) && value.every(v => typeof v === 'number' && v >= 0 && v <= 255 && Number.isInteger(v));
}

function isRawSliceInput(value: unknown): value is number[] {
  return Array.isArray(value) && value.every(v => typeof v === 'number' && Number.isInteger(v) && v >= 0 && v <= 255);
}

When it happens

Trigger: Calling encode('hello') (string instead of char codes), encode(42), or encode(new Uint8Array([...])). Note that Uint8Array is not accepted by RawSliceCoder even though it looks array-like. Passing a BN or object also fails.

Common situations: Confusing RawSliceCoder (number[]) with VecCoder (which does accept Uint8Array). Passing a hex string instead of a byte array. Deserializing data from JSON as an object rather than an array.

Related errors

• ENCODE_ERROR
• ABI_TYPES_AND_VALUES_MISMATCH
• ENCODE_ERROR
• ENCODE_ERROR
• ENCODE_ERROR

AI-assisted analysis of FuelLabs/fuels-ts@b3f37c91ac (2026-08-12). Data as JSON: /api/errors/b51a4b9bd9b22363. Report an issue: GitHub.