tapDecoderBytes

function tapDecoderBytes<TDecoder>(decoder, tap): TDecoder;

Observes the raw bytes of a decoder before it decodes them, without modifying them.

This function takes an existing decoder and returns a new decoder of the exact same type that calls the provided tap function with the byte array before each value is read. The bytes are provided as a ReadonlyUint8Array and are passed through unchanged, making this useful for adding validation guards, logging, or other read-only side effects on the raw bytes.

If the tap function throws, the decoding is aborted and the error propagates to the caller.

Type Parameters

Type Parameter	Description
`TDecoder` extends `AnyDecoder`	The type of the decoder being tapped. The returned decoder has the same type.

Parameters

Parameter	Type	Description
`decoder`	`TDecoder`	The decoder whose raw bytes should be observed.
`tap`	(`bytes`, `offset`) => `void`	A function called with the byte array and offset before reading. It may throw to abort decoding.

Returns

TDecoder

A new decoder of the same type that observes its raw bytes.

Throws

Whatever error the tap function throws, aborting the decoding.

Example

Guarding the raw bytes of a boolean decoder.

const decoder = tapDecoderBytes(getBooleanDecoder(), (bytes, offset) => {
    if (bytes[offset] > 1) throw new Error('Expected a 0 or a 1 for booleans');
});
decoder.decode(new Uint8Array([1])); // true
decoder.decode(new Uint8Array([2])); // Throws 'Expected a 0 or a 1 for booleans'

Remarks

To observe the decoded value instead of the raw bytes, use tapDecoder.