BinaryFormat.Length

Binary

Returns a binary format that limits the amount of data that can be read.

Syntax

BinaryFormat.Length(binaryFormat as function, length as any) as function

Parameters

Name	Type	Required	Description
`binaryFormat`	`function`	Yes	The binary format to limit.
`length`	`any`	Yes	The number of bytes to read, or a binary format value that reads the length from the stream before the data.

Return Value

function — A binary format function that reads data up to the specified byte limit.

Remarks

BinaryFormat.Length returns a binary format that restricts how many bytes a given binary format can consume. This is useful when a binary format like BinaryFormat.List or BinaryFormat.Binary would otherwise read to the end of the stream.

The length parameter can be:

A number -- Limits the read to exactly that many bytes.
A binary format -- Reads the length value from the stream first (using the specified format), then limits the subsequent read to that many bytes.

This is particularly useful for parsing binary structures where a length field precedes a variable-length payload, or when you need to read only a fixed portion of a stream with a format that would normally consume all remaining data.

Examples

Example 1: Limit the number of bytes read

let
    binaryData = #binary({1, 2, 3}),
    listFormat = BinaryFormat.Length(
        BinaryFormat.List(BinaryFormat.Byte),
        2
    )
in
    listFormat(binaryData)

Example 2: Use a length prefix from the stream

let
    binaryData = #binary({1, 2, 3}),
    listFormat = BinaryFormat.Length(
        BinaryFormat.List(BinaryFormat.Byte),
        BinaryFormat.Byte
    )
in
    listFormat(binaryData)

Compatibility

✓ Power BI Desktop✓ Power BI Service✓ Excel Desktop✓ Excel Online✓ Dataflows✓ Fabric Notebooks