Struct DecodeOptions 

pub struct DecodeOptions { /* private fields */ }

Configuration for CBOR decoding.

DecodeOptions controls the input format (Binary, Hex, or Diagnostic) and the limits the decoder enforces against hostile or malformed input. Construct it with DecodeOptions::new (or Default), adjust settings with the builder methods, and call decode or read_from for a single item, or sequence_decoder / sequence_reader for a CBOR sequence.

The convenience methods on Value (decode, decode_hex, read_from, read_hex_from) all forward to a default DecodeOptions. Use this type directly when you need to decode diagnostic notation, iterate a sequence, relax a limit for a known input, or tighten one for untrusted input.

Options

Option	Default	Purpose
format	Binary	Input syntax: binary, hex text, or diagnostic notation.
recursion_limit	200	Maximum nesting depth of arrays, maps, and tags.
length_limit	1,000,000,000	Maximum declared element count of a single array, map, byte string, or text string.
oom_mitigation	100,000,000	Byte budget for speculative pre-allocation.

recursion_limit

Each array, map, or tag consumes one unit of recursion budget for its contents. Exceeding the limit returns Error::NestingTooDeep. The limit protects against stack overflow on adversarial input and should be well below the stack a thread has available.

length_limit

Applies to the length field in the CBOR head of arrays, maps, byte strings, and text strings. It caps the declared size before any bytes are read, so a malicious header claiming a petabyte-long string is rejected immediately with Error::LengthTooLarge. The limit does not restrict total input size; a valid document may contain many items each up to the limit.

oom_mitigation

CBOR encodes lengths in the head, so a decoder is tempted to pre-allocate a Vec of the declared capacity. On hostile input that is a trivial amplification attack: a few bytes on the wire reserve gigabytes of memory. oom_mitigation is a byte budget, shared across the current decode, that caps the total amount of speculative capacity the decoder may reserve for array backing storage. Once the budget is exhausted, further arrays start empty and grow on demand. Decoding still succeeds if the input is well-formed; only the up-front reservation is bounded.

The budget is consumed, not refilled: a deeply nested structure with many small arrays can drain it early and decode the tail with zero pre-allocation. That is the intended behavior.

Examples

Decode binary CBOR with default limits:

use cbor_core::DecodeOptions;

let v = DecodeOptions::new().decode([0x18, 42]).unwrap();
assert_eq!(v.to_u32().unwrap(), 42);

Switch the input format to hex text or diagnostic notation:

use cbor_core::{DecodeOptions, Format};

let v = DecodeOptions::new().format(Format::Hex).decode("182a").unwrap();
assert_eq!(v.to_u32().unwrap(), 42);

let v = DecodeOptions::new().format(Format::Diagnostic).decode("42").unwrap();
assert_eq!(v.to_u32().unwrap(), 42);

Tighten limits for input from an untrusted source:

use cbor_core::DecodeOptions;

let strict = DecodeOptions::new()
    .recursion_limit(16)
    .length_limit(4096)
    .oom_mitigation(64 * 1024);

assert!(strict.decode([0x18, 42]).is_ok());

Implementations

impl DecodeOptions

pub const fn new() -> Self

Create a new set of options with the crate defaults.

use cbor_core::DecodeOptions;

let opts = DecodeOptions::new();
let v = opts.decode([0x18, 42]).unwrap();
assert_eq!(v.to_u32().unwrap(), 42);

pub const fn format(self, format: Format) -> Self

Select the input format: Binary, Hex, or Diagnostic.

Default: Format::Binary.

use cbor_core::{DecodeOptions, Format};

let hex = DecodeOptions::new().format(Format::Hex).decode("182a").unwrap();
let bin = DecodeOptions::new().decode([0x18, 0x2a]).unwrap();
assert_eq!(hex, bin);

let v = DecodeOptions::new().format(Format::Diagnostic).decode("42").unwrap();
assert_eq!(v.to_u32().unwrap(), 42);

pub const fn recursion_limit(self, limit: u16) -> Self

Set the maximum nesting depth of arrays, maps, and tags.

Default: 200. Input that exceeds the limit returns Error::NestingTooDeep.

use cbor_core::{DecodeOptions, Error};

// Two nested one-element arrays: 0x81 0x81 0x00
let err = DecodeOptions::new()
    .recursion_limit(1)
    .decode([0x81, 0x81, 0x00])
    .unwrap_err();
assert_eq!(err, Error::NestingTooDeep);

pub const fn length_limit(self, limit: u64) -> Self

Set the maximum declared length for byte strings, text strings, arrays, and maps.

Default: 1,000,000,000. Checked against the length field in the CBOR head before any bytes are consumed; an oversized declaration returns Error::LengthTooLarge.

use cbor_core::{DecodeOptions, Error};

// A five-byte text string: 0x65 'h' 'e' 'l' 'l' 'o'
let err = DecodeOptions::new()
    .length_limit(4)
    .decode(b"\x65hello")
    .unwrap_err();
assert_eq!(err, Error::LengthTooLarge);

pub const fn oom_mitigation(self, bytes: usize) -> Self

Set the byte budget for speculative pre-allocation of array backing storage.

Default: 100,000,000. Lower values trade a small amount of decoding throughput for stronger resistance to memory-amplification attacks. Valid input decodes regardless; only the up-front reservation is bounded.

use cbor_core::DecodeOptions;

// A two-element array: 0x82 0x01 0x02
let v = DecodeOptions::new()
    .oom_mitigation(0)
    .decode([0x82, 0x01, 0x02])
    .unwrap();
assert_eq!(v.len(), Some(2));

pub fn decode(&self, bytes: impl AsRef<[u8]>) -> Result<Value>

Decode exactly one CBOR data item from an in-memory buffer.

Accepts any AsRef<[u8]>: &[u8], Vec<u8>, &str, String, and so on. The input must contain exactly one value: any bytes remaining after a successful decode cause Error::InvalidFormat. In Format::Diagnostic mode trailing whitespace and comments are accepted, but nothing else. Use sequence_decoder when the input is a CBOR sequence.

An empty buffer (and, for diagnostic notation, one containing only whitespace and comments) returns Error::UnexpectedEof. A partial value returns Error::UnexpectedEof too.

use cbor_core::{DecodeOptions, Format};

let v = DecodeOptions::new().decode([0x18, 42]).unwrap();
assert_eq!(v.to_u32().unwrap(), 42);

let v = DecodeOptions::new().format(Format::Hex).decode("182a").unwrap();
assert_eq!(v.to_u32().unwrap(), 42);

let v = DecodeOptions::new()
    .format(Format::Diagnostic)
    .decode("42  / trailing comment is fine /")
    .unwrap();
assert_eq!(v.to_u32().unwrap(), 42);

pub fn read_from(&self, reader: impl Read) -> IoResult<Value>

Read a single CBOR data item from a stream.

Designed to be called repeatedly to pull successive elements of a CBOR sequence:

• In Format::Binary and Format::Hex the reader is consumed only up to the end of the item; any bytes after remain in the stream.
• In Format::Diagnostic trailing whitespace and comments are consumed up to either end of stream or a top-level separator comma (the comma is also consumed). Anything else after the value fails with Error::InvalidFormat.

I/O failures are returned as IoError::Io; malformed or oversized input as IoError::Data.

use cbor_core::{DecodeOptions, Format};

let mut bytes: &[u8] = &[0x18, 42];
let v = DecodeOptions::new().read_from(&mut bytes).unwrap();
assert_eq!(v.to_u32().unwrap(), 42);

let mut hex: &[u8] = b"182a";
let v = DecodeOptions::new().format(Format::Hex).read_from(&mut hex).unwrap();
assert_eq!(v.to_u32().unwrap(), 42);

// Diagnostic: repeated read_from pulls successive sequence items.
let mut diag: &[u8] = b"1, 2, 3";
let opts = DecodeOptions::new().format(Format::Diagnostic);
let a = opts.read_from(&mut diag).unwrap();
let b = opts.read_from(&mut diag).unwrap();
let c = opts.read_from(&mut diag).unwrap();
assert_eq!(a.to_u32().unwrap(), 1);
assert_eq!(b.to_u32().unwrap(), 2);
assert_eq!(c.to_u32().unwrap(), 3);

pub fn sequence_decoder<'a, B: AsRef<[u8]> + ?Sized>( &self, input: &'a B, ) -> SequenceDecoder<'a>

Create an iterator over a CBOR sequence stored in memory.

The returned SequenceDecoder yields each successive item of the sequence as Result<Value>. The iterator captures a snapshot of these options; subsequent changes to self do not affect it.

use cbor_core::{DecodeOptions, Format};

let opts = DecodeOptions::new().format(Format::Diagnostic);

let items: Vec<_> = opts
    .sequence_decoder(b"1, 2, 3,")
    .collect::<Result<_, _>>()
    .unwrap();
assert_eq!(items.len(), 3);

pub fn sequence_reader<R: Read>(&self, reader: R) -> SequenceReader<R>

Create an iterator over a CBOR sequence read from a stream.

The returned SequenceReader yields each successive item as IoResult<Value>. None indicates a clean end between items; a truncated item produces Some(Err(_)).

use cbor_core::DecodeOptions;

// Binary CBOR sequence: three one-byte items 0x01 0x02 0x03.
let bytes: &[u8] = &[0x01, 0x02, 0x03];
let items: Vec<_> = DecodeOptions::new()
    .sequence_reader(bytes)
    .collect::<Result<_, _>>()
    .unwrap();
assert_eq!(items.len(), 3);

Trait Implementations

impl Clone for DecodeOptions

fn clone(&self) -> DecodeOptions

Returns a duplicate of the value.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl Debug for DecodeOptions

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.

impl Default for DecodeOptions

fn default() -> Self

Returns the “default value” for a type.