::Future>,
client: Arc,
}
impl CollationFetch {
/// Create a new collation fetcher for the given chain.
pub fn new(parachain: ParaId, relay_parent: BlockId, relay_parent_hash: Hash, collators: C, client: Arc) -> Self {
CollationFetch {
relay_parent_hash,
relay_parent,
collators,
client,
parachain,
live_fetch: None,
}
}
/// Access the underlying relay parent hash.
pub fn relay_parent(&self) -> Hash {
self.relay_parent_hash
}
}
impl Future for CollationFetch {
type Item = (Collation, Extrinsic);
type Error = C::Error;
fn poll(&mut self) -> Poll<(Collation, Extrinsic), C::Error> {
loop {
let x = {
let parachain = self.parachain.clone();
let (r, c) = (self.relay_parent_hash, &self.collators);
let poll = self.live_fetch
.get_or_insert_with(move || c.collate(parachain, r).into_future())
.poll();
try_ready!(poll)
};
match validate_collation(&*self.client, &self.relay_parent, &x) {
Ok(()) => {
// TODO: generate extrinsic while verifying.
return Ok(Async::Ready((x, Extrinsic)));
}
Err(e) => {
debug!("Failed to validate parachain due to API error: {}", e);
// just continue if we got a bad collation or failed to validate
self.live_fetch = None;
self.collators.note_bad_collator(x.receipt.collator)
}
}
}
}
}
// Errors that can occur when validating a parachain.
error_chain! {
types { Error, ErrorKind, ResultExt; }
errors {
InactiveParachain(id: ParaId) {
description("Collated for inactive parachain"),
display("Collated for inactive parachain: {:?}", id),
}
ValidationFailure {
description("Parachain candidate failed validation."),
display("Parachain candidate failed validation."),
}
WrongHeadData(expected: Vec, got: Vec) {
description("Parachain validation produced wrong head data."),
display("Parachain validation produced wrong head data (expected: {:?}, got {:?}", expected, got),
}
}
links {
PolkadotApi(::polkadot_api::Error, ::polkadot_api::ErrorKind);
}
}
/// Check whether a given collation is valid. Returns `Ok` on success, error otherwise.
pub fn validate_collation(client: &P, relay_parent: &BlockId, collation: &Collation) -> Result<(), Error> {
use parachain::{self, ValidationParams};
let para_id = collation.receipt.parachain_index;
let validation_code = client.parachain_code(relay_parent, para_id)?
.ok_or_else(|| ErrorKind::InactiveParachain(para_id))?;
let chain_head = client.parachain_head(relay_parent, para_id)?
.ok_or_else(|| ErrorKind::InactiveParachain(para_id))?;
let params = ValidationParams {
parent_head: chain_head,
block_data: collation.block_data.0.clone(),
};
match parachain::wasm::validate_candidate(&validation_code, params) {
Ok(result) => {
if result.head_data == collation.receipt.head_data.0 {
Ok(())
} else {
Err(ErrorKind::WrongHeadData(
collation.receipt.head_data.0.clone(),
result.head_data
).into())
}
}
Err(_) => Err(ErrorKind::ValidationFailure.into())
}
}