Struct CompactSizeMessage

pub struct CompactSizeMessage(/* private fields */);

A CompactSize-encoded field that is limited to MAX_PROTOCOL_MESSAGE_LEN. Used for sizes or counts of objects that are sent in network messages.

Security

Deserialized sizes must be validated before being used to allocate memory.

Preallocating vectors using untrusted CompactSizes allows memory denial of service attacks. Valid sizes must be less than MAX_PROTOCOL_MESSAGE_LEN / min_serialized_item_bytes (or a lower limit specified by the Zcash consensus rules or Bitcoin network protocol).

As a defence-in-depth for memory preallocation attacks, Zebra rejects sizes greater than the protocol message length limit. (These sizes should be impossible, because each array items takes at least one byte.)

Serialization Examples

use zebra_chain::serialization::{CompactSizeMessage, ZcashSerialize, MAX_PROTOCOL_MESSAGE_LEN};
use std::convert::{TryFrom, TryInto};

let size = CompactSizeMessage::try_from(0x12).unwrap();
let buf = size.zcash_serialize_to_vec().unwrap();
assert_eq!(buf, b"\x12");

let size = CompactSizeMessage::try_from(0xfd).unwrap();
let buf = size.zcash_serialize_to_vec().unwrap();
assert_eq!(buf, b"\xfd\xfd\x00");

let size = CompactSizeMessage::try_from(0xaafd).unwrap();
let buf = size.zcash_serialize_to_vec().unwrap();
assert_eq!(buf, b"\xfd\xfd\xaa");

let max_size: usize = MAX_PROTOCOL_MESSAGE_LEN.try_into().unwrap();
let size = CompactSizeMessage::try_from(max_size).unwrap();
let buf = size.zcash_serialize_to_vec().unwrap();
assert_eq!(buf, b"\xfe\x00\x00\x20\x00");

CompactSizeMessages greater than the maximum network message length can not be constructed:

assert!(CompactSizeMessage::try_from(max_size + 1).is_err());

assert!(CompactSizeMessage::try_from(0xbbaafd).is_err());

assert!(CompactSizeMessage::try_from(0x22ccbbaafd).is_err());

Deserialization Examples

use zebra_chain::serialization::{CompactSizeMessage, ZcashDeserializeInto, MAX_PROTOCOL_MESSAGE_LEN};
use std::{convert::{TryFrom, TryInto}, io::Cursor};

assert_eq!(
    CompactSizeMessage::try_from(0x12).unwrap(),
    Cursor::new(b"\x12").zcash_deserialize_into().unwrap(),
);

assert_eq!(
    CompactSizeMessage::try_from(0xfd).unwrap(),
    Cursor::new(b"\xfd\xfd\x00").zcash_deserialize_into().unwrap(),
);

assert_eq!(
    CompactSizeMessage::try_from(0xaafd).unwrap(),
    Cursor::new(b"\xfd\xfd\xaa").zcash_deserialize_into().unwrap(),
);

let max_size: usize = MAX_PROTOCOL_MESSAGE_LEN.try_into().unwrap();
assert_eq!(
    CompactSizeMessage::try_from(max_size).unwrap(),
    Cursor::new(b"\xfe\x00\x00\x20\x00").zcash_deserialize_into().unwrap(),
);

CompactSizeMessages greater than the maximum network message length are invalid. They return a SerializationError::Parse:

let max_size_plus_one = Cursor::new(b"\xfe\x01\x00\x20\x00");
assert!(CompactSizeMessage::zcash_deserialize(max_size_plus_one).is_err());

let bytes = Cursor::new(b"\xfe\xfd\xaa\xbb\x00");
assert!(CompactSizeMessage::zcash_deserialize(bytes).is_err());

let bytes = Cursor::new(b"\xff\xfd\xaa\xbb\xcc\x22\x00\x00\x00");
assert!(CompactSizeMessage::zcash_deserialize(bytes).is_err());

Trait Implementations

impl Clone for CompactSizeMessage

fn clone(&self) -> CompactSizeMessage

Returns a duplicate of the value.

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

Performs copy-assignment from source.

impl Debug for CompactSizeMessage

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

Formats the value using the given formatter.

impl From<CompactSizeMessage> for usize

fn from(size: CompactSizeMessage) -> Self

Converts to this type from the input type.

impl Hash for CompactSizeMessage

fn hash<__H: Hasher>(&self, state: &mut __H)

Feeds this value into the given Hasher.

fn hash_slice<H>(data: &[Self], state: &mut H)

where H: Hasher, Self: Sized,

Feeds a slice of this type into the given Hasher.

impl Ord for CompactSizeMessage

fn cmp(&self, other: &CompactSizeMessage) -> Ordering

This method returns an Ordering between self and other.

fn max(self, other: Self) -> Self

where Self: Sized,

Compares and returns the maximum of two values.

fn min(self, other: Self) -> Self

where Self: Sized,

Compares and returns the minimum of two values.

fn clamp(self, min: Self, max: Self) -> Self

where Self: Sized,

Restrict a value to a certain interval.

impl PartialEq for CompactSizeMessage

fn eq(&self, other: &CompactSizeMessage) -> bool

Tests for self and other values to be equal, and is used by ==.

fn ne(&self, other: &Rhs) -> bool

Tests for !=. The default implementation is almost always sufficient, and should not be overridden without very good reason.

impl PartialOrd for CompactSizeMessage

fn partial_cmp(&self, other: &CompactSizeMessage) -> Option<Ordering>

This method returns an ordering between self and other values if one exists.

fn lt(&self, other: &Rhs) -> bool

Tests less than (for self and other) and is used by the < operator.

fn le(&self, other: &Rhs) -> bool

Tests less than or equal to (for self and other) and is used by the <= operator.

fn gt(&self, other: &Rhs) -> bool

Tests greater than (for self and other) and is used by the > operator.

fn ge(&self, other: &Rhs) -> bool

Tests greater than or equal to (for self and other) and is used by the >= operator.

impl TryFrom<usize> for CompactSizeMessage

type Error = SerializationError

The type returned in the event of a conversion error.

fn try_from(size: usize) -> Result<Self, Self::Error>

Performs the conversion.

impl ZcashDeserialize for CompactSizeMessage

fn zcash_deserialize<R: Read>(reader: R) -> Result<Self, SerializationError>

Try to read self from the given reader.

impl ZcashSerialize for CompactSizeMessage

fn zcash_serialize<W: Write>(&self, writer: W) -> Result<(), Error>

Serialize a CompactSizeMessage into the Zcash consensus-critical format.

Panics

If the value exceeds MAX_PROTOCOL_MESSAGE_LEN.

fn zcash_serialize_to_vec(&self) -> Result<Vec<u8>, Error>

Helper function to construct a vec to serialize the current struct into

fn zcash_serialized_size(&self) -> usize

Get the size of self by using a fake writer.

impl Copy for CompactSizeMessage

impl Eq for CompactSizeMessage

impl StructuralPartialEq for CompactSizeMessage