Struct AnyHeader 

pub struct AnyHeader {
    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>,
    /* private fields */
}

Header of a p2panda operation.

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

Extensions

AnyHeader does not know the concrete extensions type. On this level it is only concerned with the validity and integrity of the append-only log type itself which is enough for most low-level protocols, such as the sync protocol.

Applications usually want to attach custom extensions to the header, if you need to know the type you can easily convert from AnyHeader to Header with an explicit E extensions type.

use p2panda_core::{AnyHeader, Hash, Header, SigningKey};
use serde::{Deserialize, Serialize};

#[derive(Clone, Debug, PartialEq, Eq, Serialize, Deserialize)]
struct MyExtensions {
    dependencies: Vec<Hash>,
}

let signing_key = SigningKey::generate();

// Create a Header with concrete extension type `MyExtensions`.
let header = Header::builder()
    .build(&signing_key, MyExtensions {
        dependencies: vec![Hash::from([0; 32])],
    });

// Encode it to CBOR bytes, this is how we transmit operations over the network.
let bytes = header.encode();

// Convert it to `AnyHeader` which doesn't know the extensions type.
let any_header = AnyHeader::decode(&bytes)?;

// Bring it back to a concrete Header type with `MyExtensions`.
let header_again = Header::try_from(any_header)?;
assert_eq!(header, header_again);

Please note that at this stage we can only verify the integrity and authenticity of the attached extensions, we don’t know if the extensions themselves are valid. We can only find out if this is correct if we know the concrete E type.

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.

Implementations

impl AnyHeader

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

Attempts decoding header from bytes.

This fails if integrity checks failed or header formatting is invalid.

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

Encodes header to byte-representation (CBOR).

pub fn hash(&self) -> Hash

BLAKE3 hash 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.

Trait Implementations

impl Chain<Hash> for AnyHeader

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 Clone for AnyHeader

fn clone(&self) -> AnyHeader

Returns a duplicate of the value.

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

Performs copy-assignment from source.

impl Debug for AnyHeader

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

Formats the value using the given formatter.

impl Digest<Hash> for AnyHeader

fn hash(&self) -> Hash

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

impl Eq for AnyHeader

impl Offchain<Hash> for AnyHeader

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 PartialEq for AnyHeader

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

Equality operator ==.

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

Inequality operator !=.

impl Provenance<VerifyingKey> for AnyHeader

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 StructuralPartialEq for AnyHeader

impl TryFrom<&[u8]> for AnyHeader

type Error = HeaderError

The type returned in the event of a conversion error.

fn try_from(value: &[u8]) -> Result<Self, Self::Error>

Performs the conversion.

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.

impl TryFrom<Vec<u8>> for AnyHeader

type Error = HeaderError

The type returned in the event of a conversion error.

fn try_from(value: Vec<u8>) -> Result<Self, Self::Error>

Performs the conversion.