Simplify/harden session derives (#3401)

packages/api-derive/src/session/info.ts

@@ -2,71 +2,31 @@
 // SPDX-License-Identifier: Apache-2.0
 
 import type { ApiInterfaceRx } from '@polkadot/api/types';
-import type { u64 } from '@polkadot/types';
-import type { SessionIndex } from '@polkadot/types/interfaces';
 import type { Observable } from '@polkadot/x-rxjs';
-import type { DeriveSessionIndexes, DeriveSessionInfo } from '../types';
+import type { DeriveSessionInfo } from '../types';
 
 import { map } from '@polkadot/x-rxjs/operators';
 
 import { memo } from '../util';
 
-type ResultType = [boolean, u64, SessionIndex];
-type Result = [ResultType, DeriveSessionIndexes];
-
-function createDerive (api: ApiInterfaceRx, [[hasBabe, epochDuration, sessionsPerEra], { activeEra, activeEraStart, currentEra, currentIndex, validatorCount }]: Result): DeriveSessionInfo {
-  return {
-    activeEra,
-    activeEraStart,
-    currentEra,
-    currentIndex,
-    eraLength: api.registry.createType('BlockNumber', sessionsPerEra.mul(epochDuration)),
-    isEpoch: hasBabe,
-    sessionLength: epochDuration,
-    sessionsPerEra,
-    validatorCount
-  };
-}
-
-function queryAura (api: ApiInterfaceRx): Observable<DeriveSessionInfo> {
-  return api.derive.session.indexes().pipe(
-    map((indexes): DeriveSessionInfo =>
-      createDerive(api, [
-        [
-          false,
-          api.registry.createType('u64', 1),
-          // we may have aura without staking (permissioned)
-          api.consts.staking?.sessionsPerEra || api.registry.createType('SessionIndex', 1)
-        ],
-        indexes
-      ])
-    )
-  );
-}
-
-function queryBabe (api: ApiInterfaceRx): Observable<DeriveSessionInfo> {
-  return api.derive.session.indexes().pipe(
-    map((indexes) =>
-      createDerive(api, [
-        [
-          true,
-          api.consts.babe.epochDuration,
-          // we may have babe without staking (permissioned)
-          api.consts.staking?.sessionsPerEra || api.registry.createType('SessionIndex', 1)
-        ],
-        indexes
-      ])
-    )
-  );
-}
-
 /**
  * @description Retrieves all the session and era query and calculates specific values on it as the length of the session and eras
  */
 export function info (instanceId: string, api: ApiInterfaceRx): () => Observable<DeriveSessionInfo> {
   return memo(instanceId, (): Observable<DeriveSessionInfo> =>
-    api.consts.babe
-      ? queryBabe(api)
-      : queryAura(api)
+    api.derive.session.indexes().pipe(
+      map((indexes) => {
+        const sessionLength = api.consts?.babe?.epochDuration || api.registry.createType('u64', 1);
+        const sessionsPerEra = api.consts?.staking?.sessionsPerEra || api.registry.createType('SessionIndex', 1);
+
+        return {
+          ...indexes,
+          eraLength: api.registry.createType('BlockNumber', sessionsPerEra.mul(sessionLength)),
+          isEpoch: !!api.query.babe,
+          sessionLength,
+          sessionsPerEra
+        };
+      })
+    )
   );
 }

packages/api-derive/src/session/progress.ts

@@ -44,7 +44,7 @@ function queryBabe (api: ApiInterfaceRx): Observable<[DeriveSessionInfo, ResultS
       combineLatest([
         of(info),
         // we may have no staking, but have babe (permissioned)
-        api.query.staking
+        api.query.staking?.erasStartSessionIndex
           ? api.queryMulti<ResultSlots>([
             api.query.babe.currentSlot,
             api.query.babe.epochIndex,
@@ -69,7 +69,7 @@ function queryBabe (api: ApiInterfaceRx): Observable<[DeriveSessionInfo, ResultS
  */
 export function progress (instanceId: string, api: ApiInterfaceRx): () => Observable<DeriveSessionProgress> {
   return memo(instanceId, (): Observable<DeriveSessionProgress> =>
-    api.consts.babe
+    api.query.babe
       ? queryBabe(api).pipe(
         map(([info, slots]: [DeriveSessionInfo, ResultSlotsFlat]): DeriveSessionProgress =>
           createDerive(api, info, slots)