FuelLabs/fuels-ts · error · FuelError

ENCODE_ERROR

ENCODE_ERROR

Error message

Value length mismatch during encode.

What it means

Thrown by StringCoder.encode() when the input string's character length does not exactly match the coder's declared fixed length N (from str[N] in the ABI). StringCoder represents Sway's fixed-size string type; the character count must be exactly N. This uses JavaScript string .length (UTF-16 code units), so strings with surrogate pairs may behave unexpectedly.

Source

Thrown at packages/abi-coder/src/encoding/coders/StringCoder.ts:13

import { ErrorCode, FuelError } from '@fuel-ts/errors';
import { toUtf8Bytes, toUtf8String } from '@fuel-ts/utils';

import { Coder } from './AbstractCoder';

export class StringCoder<TLength extends number = number> extends Coder<string, string> {
  constructor(length: TLength) {
    super('string', `str[${length}]`, length);
  }

  encode(value: string): Uint8Array {
    if (value.length !== this.encodedLength) {
      throw new FuelError(ErrorCode.ENCODE_ERROR, `Value length mismatch during encode.`);
    }

    return toUtf8Bytes(value);
  }

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

    const bytes = data.slice(offset, offset + this.encodedLength);

    if (bytes.length !== this.encodedLength) {
      throw new FuelError(ErrorCode.DECODE_ERROR, `Invalid string byte data size.`);
    }

    return [toUtf8String(bytes), offset + this.encodedLength];
  }

View on GitHub (pinned to b3f37c91ac)

Solutions

1. Pad or truncate the string to exactly N characters before encoding.
2. Update the ABI type to match the actual string length, or use a variable-length type.
3. Use a variable-length type (StdString/StrSlice) if the length is dynamic.

Example fix

// before
const coder = new StringCoder(5);
coder.encode('hi'); // throws ENCODE_ERROR

// after
const coder = new StringCoder(5);
const padded = 'hi'.padEnd(5, '\0');
coder.encode(padded);

function fitsFixedString(value: string, length: number): boolean {
  return value.length === length;
}

function isFixedStringLength(value: unknown, length: number): value is string {
  return typeof value === 'string' && value.length === length;
}

When it happens

Trigger: ABI declares str[5] but you pass 'hi' (2 chars) or 'hello world' (11 chars). Passing an empty string to str[10]. Passing user input of a different length than the fixed field expects.

Common situations: ABI mismatch: the Sway contract declares a different str length than the client assumes. User input that is shorter or longer than the fixed field. Forgetting to pad fixed-length strings to their declared size.

Related errors

• ABI_TYPES_AND_VALUES_MISMATCH
• ENCODE_ERROR
• ENCODE_ERROR
• ENCODE_ERROR
• ENCODE_ERROR

AI-assisted analysis of FuelLabs/fuels-ts@b3f37c91ac (2026-08-12). Data as JSON: /api/errors/1ee3b9b8dcd086a5. Report an issue: GitHub.