offsetEncoder

function offsetEncoder<TEncoder>(encoder, config): TEncoder;

Moves the offset of a given encoder before and/or after encoding.

This function allows an encoder to write its encoded value at a different offset than the one originally provided. It supports both pre-offset adjustments (before encoding) and post-offset adjustments (after encoding).

The pre-offset function determines where encoding should start, while the post-offset function adjusts where the next encoder should continue writing.

For more details, see offsetCodec.

Type Parameters

Type Parameter
`TEncoder` extends `AnyEncoder`

Parameters

Parameter	Type	Description
`encoder`	`TEncoder`	The encoder to adjust.
`config`	`OffsetConfig`	An object specifying how the offset should be modified.

Returns

TEncoder

A new encoder with adjusted offsets.

Examples

Moving the pre-offset forward by 2 bytes.

const encoder = offsetEncoder(getU32Encoder(), {
    preOffset: ({ preOffset }) => preOffset + 2,
});
const bytes = new Uint8Array(10);
encoder.write(42, bytes, 0); // Actually written at offset 2

Moving the post-offset forward by 2 bytes.

const encoder = offsetEncoder(getU32Encoder(), {
    postOffset: ({ postOffset }) => postOffset + 2,
});
const bytes = new Uint8Array(10);
const nextOffset = encoder.write(42, bytes, 0); // Next encoder starts at offset 6 instead of 4

Using wrapBytes to ensure an offset wraps around the byte array length.

const encoder = offsetEncoder(getU32Encoder(), {
    preOffset: ({ wrapBytes }) => wrapBytes(-4), // Moves offset to last 4 bytes of the array
});
const bytes = new Uint8Array(10);
encoder.write(42, bytes, 0); // Writes at bytes.length - 4

Remarks

If you need both encoding and decoding offsets to be adjusted, use offsetCodec.