Make schema reloading more resilient. Closes graphql#940 (graphql#951)

* Make schema reloading more resilient. Closes graphql#940

* Regarding "If there’s an active introspection query, wait for it’s result before sending another one" is default behavior when schema is reloading. The changes I made to account for this are unnecessary and actually cause polling to stop if the endpoint is unreachable.

* getIsPollingSchema catching regex error

* add schema reference equality & printing cache

* improve code readability

* cleanup: remove dead code

* fix build: use lru-cache. less unneeded repaints

* fix lru cache usage

packages/graphql-playground-react/package.json

@@ -105,6 +105,7 @@
     "why-did-you-update": "0.1.1"
   },
   "dependencies": {
+    "@types/lru-cache": "^4.1.1",
     "apollo-link": "^1.0.7",
     "apollo-link-http": "^1.3.2",
     "apollo-link-ws": "1.0.8",

packages/graphql-playground-react/src/components/Playground.tsx

@@ -27,7 +27,7 @@ import {
 } from '../state/sessions/actions'
 import { setConfigString } from '../state/general/actions'
 import { initState } from '../state/workspace/actions'
-import { GraphQLSchema, printSchema } from 'graphql'
+import { GraphQLSchema } from 'graphql'
 import { createStructuredSelector } from 'reselect'
 import {
   getIsConfigTab,
@@ -50,6 +50,7 @@ import { getWorkspaceId } from './Playground/util/getWorkspaceId'
 import { getSettings, getSettingsString } from '../state/workspace/reducers'
 import { Backoff } from './Playground/util/fibonacci-backoff'
 import { debounce } from 'lodash'
+import { cachedPrintSchema } from './util'
 
 export interface Response {
   resultID: string
@@ -173,6 +174,7 @@ export class Playground extends React.PureComponent<Props & ReduxProps, State> {
   private backoff: Backoff
   private initialIndex: number = -1
   private mounted = false
+  private initialSchemaFetch = true
 
   constructor(props: Props & ReduxProps) {
     super(props)
@@ -270,11 +272,14 @@ export class Playground extends React.PureComponent<Props & ReduxProps, State> {
       })
       if (schema) {
         this.updateSchema(currentSchema, schema.schema, props)
-        this.props.schemaFetchingSuccess(
-          data.endpoint,
-          schema.tracingSupported,
-          props.isPollingSchema,
-        )
+        if (this.initialSchemaFetch) {
+          this.props.schemaFetchingSuccess(
+            data.endpoint,
+            schema.tracingSupported,
+            props.isPollingSchema,
+          )
+          this.initialSchemaFetch = false
+        }
         this.backoff.stop()
       }
     } catch (e) {
@@ -367,10 +372,17 @@ export class Playground extends React.PureComponent<Props & ReduxProps, State> {
     props: Readonly<{ children?: React.ReactNode }> &
       Readonly<Props & ReduxProps>,
   ) {
-    const currentSchemaStr = currentSchema ? printSchema(currentSchema) : null
-    const newSchemaStr = printSchema(newSchema)
-    if (newSchemaStr !== currentSchemaStr || !props.isPollingSchema) {
-      this.setState({ schema: newSchema })
+    // first check for reference equality
+    if (currentSchema !== newSchema) {
+      // if references are not equal, do an equality check on the printed schema
+      const currentSchemaStr = currentSchema
+        ? cachedPrintSchema(currentSchema)
+        : null
+      const newSchemaStr = cachedPrintSchema(newSchema)
+
+      if (newSchemaStr !== currentSchemaStr || !props.isPollingSchema) {
+        this.setState({ schema: newSchema })
+      }
     }
   }
 

packages/graphql-playground-react/src/components/Playground/SchemaFetcher.ts

@@ -5,6 +5,7 @@ import { Map, set } from 'immutable'
 import { makeOperation } from './util/makeOperation'
 import { parseHeaders } from './util/parseHeaders'
 import { LinkCreatorProps } from '../../state/sessions/fetchingSagas'
+import * as LRU from 'lru-cache'
 
 export interface TracingSchemaTuple {
   schema: GraphQLSchema
@@ -18,19 +19,53 @@ export interface SchemaFetchProps {
 
 export type LinkGetter = (session: LinkCreatorProps) => { link: ApolloLink }
 
+/**
+ * The SchemaFetcher class servers the purpose of providing the GraphQLSchema.
+ * All sagas and every part of the UI is using this as a singleton to prevent
+ * unnecessary calls to the server. We're not storing this information in Redux,
+ * as it's a good practice to only store serializable data in Redux.
+ * GraphQLSchema objects are serializable, but can easily exceed the localStorage
+ * max. Another reason to keep this in a separate class is, that we have more
+ * advanced requirements like caching.
+ */
 export class SchemaFetcher {
-  cache: Map<string, TracingSchemaTuple>
+  /**
+   * The `sessionCache` property is used for UI components, that need fast access to the current schema.
+   * If the relevant information of the session didn't change (endpoint and headers),
+   * the cached schema will be returned.
+   */
+  sessionCache: LRU.Cache<string, TracingSchemaTuple>
+  /**
+   * The `schemaInstanceCache` property is used to prevent unnecessary buildClientSchema calls.
+   * It's tested by stringifying the introspection result, which is orders of magnitude
+   * faster than rebuilding the schema.
+   */
+  schemaInstanceCache: LRU.Cache<string, GraphQLSchema>
+  /**
+   * The `linkGetter` property is a callback that provides an ApolloLink instance.
+   * This can be overriden by the user.
+   */
   linkGetter: LinkGetter
+  /**
+   * In order to prevent duplicate fetching of the same schema, we keep track
+   * of all subsequent calls to `.fetch` with the `fetching` property.
+   */
   fetching: Map<string, Promise<any>>
+  /**
+   * Other parts of the application can subscribe to change of a schema for a
+   * particular session. These subscribers are being kept track of in the
+   * `subscriptions` property
+   */
   subscriptions: Map<string, (schema: GraphQLSchema) => void> = Map()
   constructor(linkGetter: LinkGetter) {
-    this.cache = Map()
+    this.sessionCache = new LRU<string, TracingSchemaTuple>({ max: 10 })
+    this.schemaInstanceCache = new LRU({ max: 10 })
     this.fetching = Map()
     this.linkGetter = linkGetter
   }
   async fetch(session: SchemaFetchProps) {
     const hash = this.hash(session)
-    const cachedSchema = this.cache.get(hash)
+    const cachedSchema = this.sessionCache.get(hash)
     if (cachedSchema) {
       return cachedSchema
     }
@@ -52,6 +87,19 @@ export class SchemaFetcher {
   hash(session: SchemaFetchProps) {
     return `${session.endpoint}~${session.headers || ''}`
   }
+  private getSchema(data: any) {
+    const schemaString = JSON.stringify(data)
+    const cachedSchema = this.schemaInstanceCache.get(schemaString)
+    if (cachedSchema) {
+      return cachedSchema
+    }
+
+    const schema = buildClientSchema(data as any)
+
+    this.schemaInstanceCache.set(schemaString, schema)
+
+    return schema
+  }
   private fetchSchema(
     session: SchemaFetchProps,
   ): Promise<{ schema: GraphQLSchema; tracingSupported: boolean } | null> {
@@ -83,15 +131,15 @@ export class SchemaFetcher {
             throw new NoSchemaError(endpoint)
           }
 
-          const schema = buildClientSchema(schemaData.data as any)
+          const schema = this.getSchema(schemaData.data as any)
           const tracingSupported =
             (schemaData.extensions && Boolean(schemaData.extensions.tracing)) ||
             false
-          const result = {
+          const result: TracingSchemaTuple = {
             schema,
             tracingSupported,
           }
-          this.cache = this.cache.set(this.hash(session), result)
+          this.sessionCache.set(this.hash(session), result)
           resolve(result)
           this.fetching = this.fetching.remove(hash)
           const subscription = this.subscriptions.get(hash)

packages/graphql-playground-react/src/components/Playground/TopBar/Polling.tsx

@@ -3,7 +3,6 @@ import PollingIcon from './PollingIcon'
 
 export interface Props {
   interval: number
-  isReloadingSchema: boolean
   onReloadSchema: () => void
 }
 
@@ -47,17 +46,15 @@ class SchemaPolling extends React.Component<Props, State> {
     }
   }
   componentWillReceiveProps(nextProps: Props) {
-    if (nextProps.isReloadingSchema !== this.props.isReloadingSchema) {
-      this.updatePolling(nextProps)
-    }
+    this.updatePolling(nextProps)
   }
 
   render() {
     return <PollingIcon animate={this.state.windowVisible} />
   }
   private updatePolling = (props: Props = this.props) => {
     this.clearTimer()
-    if (!props.isReloadingSchema && this.state.windowVisible) {
+    if (this.state.windowVisible) {
       // timer starts only when introspection not in flight
       this.timer = setInterval(() => props.onReloadSchema(), props.interval)
     }

packages/graphql-playground-react/src/components/Playground/TopBar/SchemaReload.tsx

@@ -2,6 +2,9 @@ import * as React from 'react'
 import ReloadIcon from './Reload'
 import Polling from './Polling'
 import { ISettings } from '../../../types'
+import { createStructuredSelector } from 'reselect'
+import { getIsReloadingSchema } from '../../../state/sessions/selectors'
+import { connect } from 'react-redux'
 
 export interface Props {
   isPollingSchema: boolean
@@ -10,12 +13,11 @@ export interface Props {
   settings: ISettings
 }
 
-export default (props: Props) => {
+const SchemaReload = (props: Props) => {
   if (props.isPollingSchema) {
     return (
       <Polling
         interval={props.settings['schema.polling.interval']}
-        isReloadingSchema={props.isReloadingSchema}
         onReloadSchema={props.onReloadSchema}
       />
     )
@@ -27,3 +29,9 @@ export default (props: Props) => {
     />
   )
 }
+
+const mapStateToProps = createStructuredSelector({
+  isReloadingSchema: getIsReloadingSchema,
+})
+
+export default connect(mapStateToProps)(SchemaReload)

packages/graphql-playground-react/src/components/Playground/TopBar/TopBar.tsx

@@ -8,7 +8,6 @@ import { createStructuredSelector } from 'reselect'
 import {
   getEndpoint,
   getSelectedSession,
-  getIsReloadingSchema,
   getEndpointUnreachable,
   getIsPollingSchema,
 } from '../../../state/sessions/selectors'
@@ -29,7 +28,6 @@ export interface Props {
   endpoint: string
   shareEnabled?: boolean
   fixedEndpoint?: boolean
-  isReloadingSchema: boolean
   isPollingSchema: boolean
   endpointUnreachable: boolean
 
@@ -83,7 +81,6 @@ class TopBar extends React.Component<Props, {}> {
               <SchemaReload
                 settings={settings}
                 isPollingSchema={this.props.isPollingSchema}
-                isReloadingSchema={this.props.isReloadingSchema}
                 onReloadSchema={this.props.refetchSchema}
               />
             </div>
@@ -157,7 +154,6 @@ class TopBar extends React.Component<Props, {}> {
 const mapStateToProps = createStructuredSelector({
   endpoint: getEndpoint,
   fixedEndpoint: getFixedEndpoint,
-  isReloadingSchema: getIsReloadingSchema,
   isPollingSchema: getIsPollingSchema,
   endpointUnreachable: getEndpointUnreachable,
   settings: getSettings,

packages/graphql-playground-react/src/components/PlaygroundWrapper.tsx

@@ -427,10 +427,8 @@ class PlaygroundWrapper extends React.Component<
 
   handleSaveConfig = () => {
     /* tslint:disable-next-line */
-    console.log('handleSaveConfig called')
     if (typeof this.props.onSaveConfig === 'function') {
       /* tslint:disable-next-line */
-      console.log('calling this.props.onSaveConfig', this.state.configString)
       this.props.onSaveConfig(this.state.configString!)
     }
   }

packages/graphql-playground-react/src/components/util.ts

@@ -1,4 +1,6 @@
 import { GraphQLConfig, GraphQLConfigEnpointConfig } from '../graphqlConfig'
+import { GraphQLSchema, printSchema } from 'graphql'
+import * as LRU from 'lru-cache'
 
 export function getActiveEndpoints(
   config: GraphQLConfig,
@@ -32,3 +34,20 @@ export function getEndpointFromEndpointConfig(
     }
   }
 }
+
+const printSchemaCache: LRU.Cache<GraphQLSchema, string> = new LRU({ max: 10 })
+/**
+ * A cached version of `printSchema`
+ * @param schema GraphQLSchema instance
+ */
+export function cachedPrintSchema(schema: GraphQLSchema) {
+  const cachedString = printSchemaCache.get(schema)
+  if (cachedString) {
+    return cachedString
+  }
+
+  const schemaString = printSchema(schema)
+  printSchemaCache.set(schema, schemaString)
+
+  return schemaString
+}