FuelLabs/fuels-ts · error · FuelError

DECODE_ERROR

DECODE_ERROR

Error message

Invalid std string data size.

What it means

Thrown by StdStringCoder.decode() when the data buffer is shorter than WORD_SIZE (8 bytes). A Sway std::string::String is encoded as a u64 character-count prefix followed by UTF-8 bytes, so at least 8 bytes are required to read the length prefix alone.

Source

Thrown at packages/abi-coder/src/encoding/coders/StdStringCoder.ts:25

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

export class StdStringCoder extends Coder<string, string> {
  static memorySize = 1;
  constructor() {
    super('struct', 'struct String', WORD_SIZE);
  }

  encode(value: string): Uint8Array {
    const bytes = toUtf8Bytes(value);
    const lengthBytes = new BigNumberCoder('u64').encode(value.length);

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

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

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

    return [toUtf8String(dataBytes), offsetAndLength + length];
  }
}

View on GitHub (pinned to b3f37c91ac)

Solutions

1. Verify data.length >= 8 before calling decode().
2. Confirm you are using StdStringCoder (variable-length struct String) and not StringCoder (fixed-length str[N]).
3. Ensure the data originates from a compatible Sway ABI encoding.

Example fix

// before
stdStringCoder.decode(new Uint8Array([0, 0, 0]), 0); // throws DECODE_ERROR

// after
if (data.length < 8) {
  throw new Error('Data too short for std String decode');
}
stdStringCoder.decode(data, 0);

function canDecodeStdString(data: Uint8Array): boolean {
  return data.length >= 8; // WORD_SIZE
}

When it happens

Trigger: Passing fewer than 8 bytes to decode(). Decoding data that was not produced by StdStringCoder.encode(). Receiving a truncated ABI payload from an RPC response.

Common situations: Using the wrong coder for the data (e.g., StringCoder fixed-length vs StdStringCoder variable-length). Malformed data from chain. Buffer allocation or slicing errors upstream.

Related errors

• DECODE_ERROR
• DECODE_ERROR
• DECODE_ERROR
• DECODE_ERROR
• DECODE_ERROR

AI-assisted analysis of FuelLabs/fuels-ts@b3f37c91ac (2026-08-12). Data as JSON: /api/errors/33ad57ddff7265da. Report an issue: GitHub.