addCodecSentinel

Call Signature

function addCodecSentinel<TFrom, TTo>(
    codec,
    sentinel,
): FixedSizeCodec<TFrom, TTo>;

Creates a Codec that writes a given Uint8Array sentinel after the encoded value and, when decoding, continues reading until the sentinel is found.

This sets a limit on variable-size codecs and tells us when to stop decoding.

Type Parameters

Type Parameter	Description
`TFrom`	The type of the value to encode.
`TTo`	The type of the decoded value.

Parameters

Parameter	Type
`codec`	`FixedSizeCodec`<`TFrom`, `TTo`>
`sentinel`	`ReadonlyUint8Array`

Returns

FixedSizeCodec<TFrom, TTo>

Example

const codec = addCodecSentinel(getUtf8Codec(), new Uint8Array([255, 255]));
codec.encode('hello');
// 0x68656c6c6fffff
//   |        └-- Our sentinel.
//   └-- Our encoded string.

Remarks

Note that the sentinel must not be present in the encoded data and must be present in the decoded data for this to work. If this is not the case, dedicated errors will be thrown.

const sentinel = new Uint8Array([108, 108]); // 'll'
const codec = addCodecSentinel(getUtf8Codec(), sentinel);
 
codec.encode('hello'); // Throws: sentinel is in encoded data.
codec.decode(new Uint8Array([1, 2, 3])); // Throws: sentinel missing in decoded data.

Separate addEncoderSentinel and addDecoderSentinel functions are also available.

const bytes = addEncoderSentinel(getUtf8Encoder(), sentinel).encode('hello');
const value = addDecoderSentinel(getUtf8Decoder(), sentinel).decode(bytes);

See