Add derive.chain.{getHeader,subscribeNewHead} with author (#602)

* Add derive.chain.{getHeader,subscribeNewHead} with author

* tslint cast, ignore

package.json

@@ -24,7 +24,7 @@
   },
   "devDependencies": {
     "@babel/core": "^7.2.2",
-    "@polkadot/dev": "^0.23.12",
+    "@polkadot/dev": "^0.23.13",
     "@polkadot/ts": "^0.1.51"
   }
 }

packages/api-derive/src/chain/getHeader.ts

@@ -0,0 +1,35 @@
+// Copyright 2017-2019 @polkadot/api-derive authors & contributors
+// This software may be modified and distributed under the terms
+// of the Apache-2.0 license. See the LICENSE file for details.
+
+import { Observable, combineLatest, of } from 'rxjs';
+import { catchError, map } from 'rxjs/operators';
+import { ApiInterface$Rx } from '@polkadot/api/types';
+import { AccountId, Header } from '@polkadot/types/index';
+import { HeaderExtended } from '@polkadot/types/Header';
+
+import { drr } from '../util/drr';
+import { HeaderAndValidators } from './subscribeNewHead';
+
+/**
+ * Get the a specific block header and extend it with the author
+ */
+export function getHeader (api: ApiInterface$Rx) {
+  return (hash: Uint8Array | string): Observable<HeaderExtended | undefined> =>
+    combineLatest(
+      api.rpc.chain.getHeader(hash) as Observable<Header>,
+      api.query.session.validators.at(hash) as any as Observable<Array<AccountId>>
+    ).pipe(
+      map(([header, validators]: HeaderAndValidators) =>
+        new HeaderExtended(header, validators)
+      ),
+      catchError(() =>
+        // where rpc.chain.getHeader throws, we will land here - it can happen that
+        // we supplied an invalid hash. (Due to defaults, storeage will have an
+        // empty value, so only the RPC is affected). So return undefined
+        // tslint:disable-next-line
+        of() as Observable<undefined>
+      ),
+      drr()
+    );
+}

packages/api-derive/src/chain/index.ts

@@ -4,3 +4,5 @@
 
 export * from './bestNumber';
 export * from './bestNumberFinalised';
+export * from './getHeader';
+export * from './subscribeNewHead';

packages/api-derive/src/chain/subscribeNewHead.ts

@@ -0,0 +1,39 @@
+// Copyright 2017-2019 @polkadot/api-derive authors & contributors
+// This software may be modified and distributed under the terms
+// of the Apache-2.0 license. See the LICENSE file for details.
+
+import { Observable, combineLatest, of } from 'rxjs';
+import { filter, map, switchMap } from 'rxjs/operators';
+import { ApiInterface$Rx } from '@polkadot/api/types';
+import { AccountId, Header } from '@polkadot/types/index';
+import { HeaderExtended } from '@polkadot/types/Header';
+
+import { drr } from '../util/drr';
+
+export type HeaderAndValidators = [Header, Array<AccountId>];
+
+/**
+ * Subscribe to block headers and extend it with the author
+ */
+export function subscribeNewHead (api: ApiInterface$Rx) {
+  return (): Observable<HeaderExtended> =>
+    (api.rpc.chain.subscribeNewHead() as Observable<Header>)
+      .pipe(
+        filter((header: Header) =>
+          header && !!header.blockNumber
+        ),
+        switchMap((header: Header): Observable<HeaderAndValidators> =>
+          combineLatest(
+            of(header),
+            // theoretically we could combine at the first call with session.validators(), however
+            // we make 100% sure we actually get the validators at a specific block so when these
+            // change at an era boundary, we have the previous values to ensure our indexes are correct
+            api.query.session.validators.at(header.hash) as any as Observable<Array<AccountId>>
+          )
+        ),
+        map(([header, validators]: HeaderAndValidators) =>
+          new HeaderExtended(header, validators)
+        ),
+        drr()
+      );
+}

packages/api/src/types.ts

@@ -29,7 +29,7 @@ export interface DecoratedRpc<OnCall> {
 
 export interface QueryableStorageFunction<OnCall> extends StorageFunction {
   (arg?: any): OnCall;
-  at: (hash: Hash, arg?: any) => OnCall;
+  at: (hash: Uint8Array | string, arg?: any) => OnCall;
 }
 
 export interface QueryableModuleStorage<OnCall> {

packages/types/src/Header.ts

@@ -9,6 +9,7 @@ import { blake2AsU8a } from '@polkadot/util-crypto';
 import Compact from './codec/Compact';
 import Struct from './codec/Struct';
 
+import AccountId from './AccountId';
 import BlockNumber from './BlockNumber';
 import Digest, { DigestItem } from './Digest';
 import Hash from './Hash';
@@ -81,3 +82,30 @@ export default class Header extends Struct {
     return this.get('stateRoot') as Hash;
   }
 }
+
+/**
+ * @name HeaderExtended
+ * @description
+ * A [[Block]] header with an additional `author` field that indicates the block author
+ */
+export class HeaderExtended extends Header {
+  private _author?: AccountId;
+
+  constructor (header: Header, sessionValidators: Array<AccountId>) {
+    super(header);
+
+    const { digest: { logs } } = header;
+    const digestItem = logs.find(({ type }) => type === 'Seal');
+
+    this._author = digestItem && sessionValidators.length
+      ? sessionValidators[digestItem.asSeal.slot.toNumber() % sessionValidators.length]
+      : undefined;
+  }
+
+  /**
+   * @description Convenience method, returns the author for the block
+   */
+  get author (): AccountId | undefined {
+    return this._author;
+  }
+}

yarn.lock

@@ -1293,10 +1293,10 @@
   resolved "https://registry.yarnpkg.com/@nodelib/fs.stat/-/fs.stat-1.1.3.tgz#2b5a3ab3f918cca48a8c754c08168e3f03eba61b"
   integrity sha512-shAmDyaQC4H92APFoIaVDHCx5bStIocgvbwQyxPRrbUY20V1EYTbSDchWbuwlMG3V17cprZhA6+78JfB+3DTPw==
 
-"@polkadot/dev@^0.23.12":
-  version "0.23.12"
-  resolved "https://registry.yarnpkg.com/@polkadot/dev/-/dev-0.23.12.tgz#327c9d326b7a13604f917ce2b6df2686c6e0a73e"
-  integrity sha512-rXLkaYTWqBl3+60grGeyIJFRjl69U7SJfdLrVY+R8hy4/ki4OjOurXnf13sX+gWtVNNNKMmRn+gg6fQ11E59Ow==
+"@polkadot/dev@^0.23.13":
+  version "0.23.13"
+  resolved "https://registry.yarnpkg.com/@polkadot/dev/-/dev-0.23.13.tgz#a1933eb029bc2d6221ab55c89d47abfe22f013d6"
+  integrity sha512-g/WsW8VakLwwKpIoJ2vv7QTp1NOUHbXrHNu4F3soeCFV66MjeTYCKRaH5ipsc6sEK0S/rBZFdAmQcEbi3KJbRg==
   dependencies:
     "@babel/cli" "^7.2.3"
     "@babel/core" "^7.2.2"