feat: prefetch frequently used contexts in OA v4

package.json

@@ -40,6 +40,7 @@
     "test:vc": "scripts/runVcTest.sh",
     "lint": "eslint . --ext .ts,.json --max-warnings 0",
     "lint:fix": "npm run lint -- --fix",
+    "fetch-v4-contexts": "npx ts-node scripts/fetchV4Contexts.ts",
     "generate-v4-fixtures": "npx ts-node scripts/generateV4JsonFixtures.ts",
     "generate-v4-json-schemas": "npx ts-node scripts/generateV4JsonSchemas.ts",
     "publish:schema": "./scripts/publishSchema.sh",

scripts/fetchV4Contexts.ts

@@ -0,0 +1,25 @@
+import fs from "fs";
+import path from "path";
+import { ContextUrl, urlToSafeFilename } from "../src/4.0/context";
+
+const OUTPUT_DIR = path.resolve("./src/4.0/contexts/__generated__");
+
+// make sure the output directory exists
+if (fs.existsSync(OUTPUT_DIR)) {
+  fs.rmSync(OUTPUT_DIR, { recursive: true });
+}
+fs.mkdirSync(OUTPUT_DIR, { recursive: true });
+
+const CONTEXTS_TO_FETCH = Object.values(ContextUrl);
+
+for (const url of CONTEXTS_TO_FETCH) {
+  fetch(url)
+    .then((res) => res.json())
+    .then((context) => {
+      const filename = urlToSafeFilename(url);
+      fs.writeFileSync(path.join(OUTPUT_DIR, filename), JSON.stringify(context, null, 2));
+    })
+    .catch((err) => {
+      console.error(`Unable to fetch OA v4.0 context`, err);
+    });
+}

src/4.0/context.ts

@@ -1,5 +1,6 @@
-import { expand, Options, JsonLdDocument } from "jsonld";
 import { fetch } from "cross-fetch";
+import { readFile } from "fs/promises";
+import { expand, Options, JsonLdDocument } from "jsonld";
 
 export const ContextUrl = {
   w3c_vc_v2: "https://www.w3.org/ns/credentials/v2",
@@ -11,25 +12,31 @@ export const ContextType = {
   OAV4Context: "OpenAttestationCredential",
 } as const;
 
-const preloadedContextList = [ContextUrl.w3c_vc_v2, ContextUrl.oa_vc_v4];
-const contexts: Map<string, any> = new Map();
+const PREFETECHED_CONTEXT_LIST = Object.values(ContextUrl);
+const contextCache: Map<string, any> = new Map();
 
-// Preload frequently used contexts
-// https://github.com/digitalbazaar/jsonld.js?tab=readme-ov-file#custom-document-loader
 let isFirstLoad = true;
+// https://github.com/digitalbazaar/jsonld.js?tab=readme-ov-file#custom-document-loader
 // FIXME: @types/json-ld seems to be outdated as callback is supposed to be options
 const documentLoader: Options.DocLoader["documentLoader"] = async (url, _) => {
+  // On first load: Preload frequently used contexts from "src/4.0/contexts/__generated__/*"
   if (isFirstLoad) {
     isFirstLoad = false;
-    for (const url of preloadedContextList) {
-      const document = await fetch(url).then((res) => res.json());
-      contexts.set(url, document);
+    for (const url of PREFETECHED_CONTEXT_LIST) {
+      try {
+        const filename = urlToSafeFilename(url);
+        const document = await readFile(`../4.0/contexts/__generated__/${filename}`, "utf-8");
+        const parsed = JSON.parse(document);
+        contextCache.set(url, parsed);
+      } catch (e) {
+        console.warn(`Unable to prefetch context from ${url}`, e);
+      }
     }
   }
-  if (contexts.get(url)) {
+  if (contextCache.get(url)) {
     return {
       contextUrl: undefined, // this is for a context via a link header
-      document: contexts.get(url), // this is the actual document that was loaded
+      document: contextCache.get(url), // this is the actual document that was loaded
       documentUrl: url, // this is the actual context URL after redirects
     };
   } else {
@@ -57,3 +64,12 @@ export class UnableToInterpretContextError extends Error {
     Object.setPrototypeOf(this, UnableToInterpretContextError.prototype);
   }
 }
+
+/**
+ * Convert URL to a filename-safe string
+ * @param url string
+ * @returns string
+ */
+export function urlToSafeFilename(url: string) {
+  return url.replace(/[/\\?%*:|"<>]/g, "-");
+}