Add storage subscription API endpoints (#126)

* Add storage subscriptions

* StorageResult formatting

* Decoding WIP

* Storage subsciptions in place

* Allow null decodes, ref https://github.com/polkadot-js/apps/issues/215

* e2e tests for subscribeStorage

* Cache subscription results, return with changeset

packages/api-format/src/format.ts

@@ -2,18 +2,29 @@
 // This software may be modified and distributed under the terms
 // of the ISC license. See the LICENSE file for details.
 
-import { Param$Types, Param$Type$Array } from '@polkadot/params/types';
+import { Storages } from '@polkadot/storage/types';
+import { SectionItem, Param$Types, Param$Type$Array } from '@polkadot/params/types';
 import { FormattersFunctionMap } from './types';
 
 import typeToString from '@polkadot/params/typeToString';
 import isUndefined from '@polkadot/util/is/undefined';
 import logger from '@polkadot/util/logger';
+import u8aToHex from '@polkadot/util/u8a/toHex';
+import createStorageKey from '@polkadot/storage/key';
 
 import echo from './echo';
 
 const l = logger('api-format');
 
 function formatSingleType (formatters: FormattersFunctionMap, type: Param$Types, value: any): any {
+  if (type === 'StorageKey') {
+    const [key, ...params]: [SectionItem<Storages>, Array<any>] = value;
+
+    return u8aToHex(
+      createStorageKey(key).apply(null, params)
+    );
+  }
+
   const formatter = formatters.get(type);
 
   if (isUndefined(formatter)) {

packages/api-format/src/input.ts

@@ -5,6 +5,7 @@
 import { Params, Param$Types } from '@polkadot/params/types';
 import { FormatterFunction } from './types';
 
+import assert from '@polkadot/util/assert';
 import addressDecode from '@polkadot/util-keyring/address/decode';
 import bytesEncode from '@polkadot/primitives/json/bytes/encode';
 import hashEncode from '@polkadot/primitives/json/hash/encode';
@@ -19,6 +20,13 @@ const formatters = new Map<Param$Types, FormatterFunction>([
 ]);
 
 export default function formatInputs (params: Params, values: Array<any>): Array<any> {
+  const required = params.filter(({ isOptional }) => !isOptional);
+  const optionalText = params.length
+    ? ` (${(params.length - required.length) || 'none'} optional)`
+    : '';
+
+  assert(values.length >= required.length && values.length <= params.length, `${params.length || 'no'} params expected${optionalText}, found ${values.length} instead`);
+
   const types = params.map(({ type }) => type);
 
   return format(formatters, types, values);