Struct Header 

pub struct Header<E = ()> {
    pub version: Version,
    pub verifying_key: VerifyingKey,
    pub signature: Signature,
    pub payload_size: PayloadSize,
    pub payload_hash: Option<Hash>,
    pub seq_num: SeqNum,
    pub backlink: Option<Hash>,
    pub extensions: E,
    /* private fields */
}

Header of a p2panda operation with known extensions type.

The header holds all metadata required to cryptographically secure and authenticate a message Body and it’s custom extensions.

See AnyHeader for dealing with headers when you don’t care about the concrete extensions type (E).

Example

use p2panda_core::{Header, SigningKey};

let signing_key = SigningKey::generate();

let header = Header::builder()
    .body(b"Hello, Icebear!")
     // Sign the header with the author's private key.
    .build(&signing_key, ());

Fields

version: Version

Operation format version, allowing backwards compatibility when specification changes.

verifying_key: VerifyingKey

Author of this operation.

signature: Signature

Signature by author over all fields in header, providing authenticity.

payload_size: PayloadSize

Number of bytes of the body of this operation, must be zero if no body is given.

payload_hash: Option<Hash>

Hash of the body of this operation, must be included if payload_size is non-zero and omitted otherwise.

Keeping the hash here allows us to delete the payload (off-chain data) while retaining the ability to check the signature of the header.

seq_num: SeqNum

Number of operations this author has published to this log, begins with 0 and is always incremented by 1 with each new operation by the same author.

backlink: Option<Hash>

Hash of the previous operation of the same author and log. Can be omitted if first operation in log.

extensions: E

Custom additional data.

Implementations

impl<E> Header<E>

where E: Extensions,

pub fn builder() -> Builder<E>

Returns builder to create & sign new header.

pub fn encode(&self) -> Vec<u8>

Encodes header to byte-representation (CBOR).

pub fn decode(bytes: &[u8]) -> Result<Self, HeaderError>

Attempts decoding header from bytes.

This might fail if integrity checks failed or header formatting is invalid.

pub fn hash(&self) -> Hash

BLAKE3 hash digest of the header bytes.

This hash is used as the unique identifier of an operation, aka the Operation Id.

pub fn size(&self) -> u32

Size of header when encoded as CBOR bytes.

impl<E> Header<E>

where E: Extensions,

pub fn to_hex(&self) -> String

Available on crate features test_utils only.

pub fn sign(&mut self, signer: &SigningKey)

Available on crate features test_utils only.

pub fn verify(&self) -> bool

Available on crate features test_utils only.

Trait Implementations

impl<'a, E> Arbitrary<'a> for Header<E>

where E: Default + Extensions,

Available on crate feature arbitrary only.

fn arbitrary(u: &mut Unstructured<'a>) -> Result<Self>

Generate an arbitrary value of Self from the given unstructured data.

fn arbitrary_take_rest(u: Unstructured<'a>) -> Result<Self, Error>

Generate an arbitrary value of Self from the entirety of the given unstructured data.

fn size_hint(depth: usize) -> (usize, Option<usize>)

Get a size hint for how many bytes out of an Unstructured this type needs to construct itself.

fn try_size_hint( depth: usize, ) -> Result<(usize, Option<usize>), MaxRecursionReached>

Get a size hint for how many bytes out of an Unstructured this type needs to construct itself.

impl<E> Borrow<Header<E>> for Operation<E>

fn borrow(&self) -> &Header<E>

Immutably borrows from an owned value.

impl<E> Chain<Hash> for Header<E>

where E: Extensions,

fn backlink(&self) -> Option<Hash>

Pointer at previous entry in log which gives us the integrity guarantee of the “hash chain”. The first entry in a log returns None.

fn seq_num(&self) -> SeqNum

Sequence numbers are helpful to fastly detect forks and use the much faster and optimized diffing strategy when the local log is not forked.

impl<E: Clone> Clone for Header<E>

fn clone(&self) -> Header<E>

Returns a duplicate of the value.

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

Performs copy-assignment from source.

impl<E: Debug> Debug for Header<E>

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

Formats the value using the given formatter.

impl<E> Default for Header<E>

where E: Default,

Available on crate features test_utils only.

fn default() -> Self

This is for hacky low-level access to this type, don’t use this in production.

Size and digest get re-computed whenever called in test environments. Note that we can’t re-encode extensions_cbor if E was changed in a test. Ideally you don’t want to test extensions-related code here anyway.

impl<E> Digest<Hash> for Header<E>

where E: Extensions,

fn hash(&self) -> Hash

Hash digest of peer-to-peer data-type which can be used as the identifier.

impl<E: Eq> Eq for Header<E>

impl<E> Offchain<Hash> for Header<E>

where E: Extensions,

fn payload(&self) -> Option<&Body>

Authenticated payload.

fn payload_hash(&self) -> Option<Hash>

Hash digest of the payload.

fn payload_size(&self) -> PayloadSize

Size in bytes of the payload.

impl<E: PartialEq> PartialEq for Header<E>

fn eq(&self, other: &Header<E>) -> bool

Equality operator ==.

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

Inequality operator !=.

impl<E> Provenance<VerifyingKey> for Header<E>

where E: Extensions,

fn author(&self) -> VerifyingKey

Identity of the author of data-type.

fn verify(&self) -> bool

Checks if data-type and given author is authentic.

impl<E: PartialEq> StructuralPartialEq for Header<E>

impl<E> TryFrom<AnyHeader> for Header<E>

where E: Extensions,

type Error = HeaderError

The type returned in the event of a conversion error.

fn try_from(value: AnyHeader) -> Result<Self, Self::Error>

Performs the conversion.

impl<E> TryFrom<Header<E>> for AnyHeader

where E: Extensions,

type Error = HeaderError

The type returned in the event of a conversion error.

fn try_from(value: Header<E>) -> Result<Self, Self::Error>

Performs the conversion.