packages/api-derive/src/chain/subscribeFinalizedHeads.ts
// Copyright 2017-2024 @polkadot/api-derive authors & contributors
// SPDX-License-Identifier: Apache-2.0
import type { Observable } from 'rxjs';
import type { Hash, Header } from '@polkadot/types/interfaces';
import type { DeriveApi } from '../types.js';
import { from, of, switchMap } from 'rxjs';
import { memo } from '../util/index.js';
/**
* Returns a header range from startHash to to (not including) endHash, i.e. lastBlock.parentHash === endHash
*/
export function _getHeaderRange (instanceId: string, api: DeriveApi): (startHash: Hash, endHash: Hash, prev?: Header[]) => Observable<Header[]> {
return memo(instanceId, (startHash: Hash, endHash: Hash, prev: Header[] = []): Observable<Header[]> =>
api.rpc.chain.getHeader(startHash).pipe(
switchMap((header) =>
header.parentHash.eq(endHash)
? of([header, ...prev])
: api.derive.chain._getHeaderRange(header.parentHash, endHash, [header, ...prev])
)
)
);
}
/**
* @name subscribeFinalizedHeads
* @description An observable of the finalized block headers. Unlike the base
* chain.subscribeFinalizedHeads this does not skip any headers. Since finalization
* may skip specific blocks (finalization happens in terms of chains), this version
* of the derive tracks missing headers (since last retrieved) and provides them
* to the caller
*/
export function subscribeFinalizedHeads (instanceId: string, api: DeriveApi): () => Observable<Header> {
return memo(instanceId, (): Observable<Header> => {
let prevHash: Hash | null = null;
return api.rpc.chain.subscribeFinalizedHeads().pipe(
switchMap((header) => {
const endHash = prevHash;
const startHash = header.parentHash;
prevHash = header.createdAtHash = header.hash;
return endHash === null || startHash.eq(endHash)
? of(header)
: api.derive.chain._getHeaderRange(startHash, endHash, [header]).pipe(
switchMap((headers) =>
from(headers)
)
);
})
);
});
}