# gizlang:cbor

CBOR (RFC 8949) as a value, for the binary structures of WebAuthn and COSE keys. It reads any definite length and writes the shortest one: integers within i64, byte and text strings, arrays, maps, false, true and null. Tags, floats, other simple values, indefinite lengths and integers past i64 are errors: no protocol this module serves needs them, and a reader that refuses them cannot misread them.

```gizlang
import * as Cbor from "gizlang:cbor";
```

## Types

### `Value`

```gizlang
type Value = | { kind: "int"; value: i64; } | { kind: "bytes"; value: bytes; } | { kind: "text"; value: string; } | { kind: "array"; items: Vec<Value>; } | { kind: "map"; keys: Vec<Value>; values: Vec<Value>; } | { kind: "bool"; value: bool; } | { kind: "null"; }
```

A CBOR item. A map keeps its keys and values in order, as two Vecs of equal length; a repeated key keeps both.

- `int`
- `bytes`
- `text`
- `array`
- `map`
- `bool`
- `null`

### `CborError`

```gizlang
type CborError = { offset: i64; message: string; }
```

Where the bytes stop being CBOR, in bytes, and why.

- `offset`: `i64`
- `message`: `string`

### `Read`

```gizlang
type Read = { value: Value; next: i64; }
```

An item read, and the position after it.

- `value`: `gizlang_cbor.Value`
- `next`: `i64`

## Functions

### `read`

```gizlang
function read(data: bytes, at: i64): Result<Read, CborError>
```

The item at AT in DATA and the position after it: for items that sit back to back, as the key in authenticator data.

Effects: fail.

### `decode`

```gizlang
function decode(data: bytes): Value throws CborError
```

The one item that DATA holds, and nothing after it.

Effects: fail.

### `encode`

```gizlang
function encode(value: Value): bytes
```

The CBOR bytes of VALUE: definite lengths, each in its shortest form.

Effects: fail.

### `lookup`

```gizlang
function lookup(container: Value, key: Value): Option<Value>
```

The item of MAP at KEY (an int, bytes or text item), or undefined. A repeated key gives its first value.

Effects: fail.

### `bytesOf`

```gizlang
function bytesOf(v: Value): Option<bytes>
```

The bytes of a byte string item, or undefined.

### `textOf`

```gizlang
function textOf(v: Value): Option<string>
```

The text of a text string item, or undefined.

### `intOf`

```gizlang
function intOf(v: Value): Option<i64>
```

The integer of an integer item, or undefined.