memoize reading lib/graphql/static/schema*.json files (github#28443)

Author: peterbe

lib/read-json-file.js

@@ -31,6 +31,10 @@ export function readCompressedJsonFileFallback(xpath) {
   }
 }
 
+// This is used to make sure the `readCompressedJsonFileFallbackLazily()`
+// function isn't used with the same exact first argument more than once.
+const globalCacheCounter = {}
+
 // Wrapper on readCompressedJsonFileFallback that initially only checks
 // if the file exists but doesn't read the content till you call it.
 export function readCompressedJsonFileFallbackLazily(xpath) {
@@ -57,7 +61,18 @@ export function readCompressedJsonFileFallbackLazily(xpath) {
     }
   }
   return () => {
-    if (!cache.has(xpath)) cache.set(xpath, readCompressedJsonFileFallback(xpath))
+    if (!cache.has(xpath)) {
+      cache.set(xpath, readCompressedJsonFileFallback(xpath))
+      if (globalCacheCounter[xpath]) {
+        console.warn(
+          "If this happens it's because the readCompressedJsonFileFallbackLazily " +
+            'function has been called non-globally. Only use ' +
+            'readCompressedJsonFileFallback once at module-level.'
+        )
+        throw new Error(`Globally reading the same file more than once (${xpath})`)
+      }
+      globalCacheCounter[xpath] = 1
+    }
     return cache.get(xpath)
   }
 }

middleware/contextualizers/graphql.js

@@ -1,4 +1,7 @@
-import { readCompressedJsonFileFallbackLazily } from '../../lib/read-json-file.js'
+import {
+  readCompressedJsonFileFallbackLazily,
+  readCompressedJsonFileFallback,
+} from '../../lib/read-json-file.js'
 import { allVersions } from '../../lib/all-versions.js'
 const previews = readCompressedJsonFileFallbackLazily('./lib/graphql/static/previews.json')
 const upcomingChanges = readCompressedJsonFileFallbackLazily(
@@ -20,6 +23,17 @@ const explorerUrl =
     ? 'https://graphql.github.com/explorer'
     : 'http://localhost:3000'
 
+const graphQLVersionSchemaCache = new Map()
+function readGraphQLVersionSchema(graphqlVersion) {
+  if (!graphQLVersionSchemaCache.has(graphqlVersion)) {
+    graphQLVersionSchemaCache.set(
+      graphqlVersion,
+      readCompressedJsonFileFallback(`lib/graphql/static/schema-${graphqlVersion}.json`)
+    )
+  }
+  return graphQLVersionSchemaCache.get(graphqlVersion)
+}
+
 export default function graphqlContext(req, res, next) {
   const currentVersionObj = allVersions[req.context.currentVersion]
   // ignore requests to non-GraphQL reference paths
@@ -34,9 +48,7 @@ export default function graphqlContext(req, res, next) {
   const graphqlVersion = currentVersionObj.miscVersionName
 
   req.context.graphql = {
-    schemaForCurrentVersion: readCompressedJsonFileFallbackLazily(
-      `lib/graphql/static/schema-${graphqlVersion}.json`
-    )(),
+    schemaForCurrentVersion: readGraphQLVersionSchema(graphqlVersion),
     previewsForCurrentVersion: previews()[graphqlVersion],
     upcomingChangesForCurrentVersion: upcomingChanges()[graphqlVersion],
     prerenderedObjectsForCurrentVersion: prerenderedObjects()[graphqlVersion],