[json] when downloading JSON Schema files, do Conditional GETs. Fixes #101050

extensions/json-language-features/client/src/node/schemaCache.ts

@@ -0,0 +1,108 @@
+/*---------------------------------------------------------------------------------------------
+ *  Copyright (c) Microsoft Corporation. All rights reserved.
+ *  Licensed under the MIT License. See License.txt in the project root for license information.
+ *--------------------------------------------------------------------------------------------*/
+
+import { promises as fs } from 'fs';
+import * as path from 'path';
+import { createHash } from 'crypto';
+import { Memento } from 'vscode';
+
+interface CacheEntry {
+	etag: string;
+	fileName: string;
+	accessTime: number;
+}
+
+interface CacheInfo {
+	[schemaUri: string]: CacheEntry;
+}
+
+const MEMENTO_KEY = 'json-schema-cache';
+
+export class JSONSchemaCache {
+	private readonly cacheInfo: CacheInfo;
+
+	constructor(private readonly schemaCacheLocation: string, private readonly globalState: Memento) {
+		this.cacheInfo = globalState.get<CacheInfo>(MEMENTO_KEY, {});
+	}
+
+	getETag(schemaUri: string): string | undefined {
+		return this.cacheInfo[schemaUri]?.etag;
+	}
+
+	async putSchema(schemaUri: string, etag: string, schemaContent: string): Promise<void> {
+		try {
+			const fileName = getCacheFileName(schemaUri);
+			await fs.writeFile(path.join(this.schemaCacheLocation, fileName), schemaContent);
+			const entry: CacheEntry = { etag, fileName, accessTime: new Date().getTime() };
+			this.cacheInfo[schemaUri] = entry;
+		} catch (e) {
+			delete this.cacheInfo[schemaUri];
+		} finally {
+			await this.updateMemento();
+		}
+	}
+
+	async getSchemaIfAccessedSince(schemaUri: string, expirationDuration: number): Promise<string | undefined> {
+		const cacheEntry = this.cacheInfo[schemaUri];
+		if (cacheEntry && cacheEntry.accessTime + expirationDuration >= new Date().getTime()) {
+			return this.loadSchemaFile(schemaUri, cacheEntry);
+		}
+		return undefined;
+	}
+
+	async getSchema(schemaUri: string, etag: string): Promise<string | undefined> {
+		const cacheEntry = this.cacheInfo[schemaUri];
+		if (cacheEntry) {
+			if (cacheEntry.etag === etag) {
+				return this.loadSchemaFile(schemaUri, cacheEntry);
+			} else {
+				this.deleteSchemaFile(schemaUri, cacheEntry);
+			}
+		}
+		return undefined;
+	}
+
+	private async loadSchemaFile(schemaUri: string, cacheEntry: CacheEntry): Promise<string | undefined> {
+		const cacheLocation = path.join(this.schemaCacheLocation, cacheEntry.fileName);
+		try {
+			const content = (await fs.readFile(cacheLocation)).toString();
+			cacheEntry.accessTime = new Date().getTime();
+			return content;
+		} catch (e) {
+			delete this.cacheInfo[schemaUri];
+			return undefined;
+		} finally {
+			await this.updateMemento();
+		}
+	}
+
+	private async deleteSchemaFile(schemaUri: string, cacheEntry: CacheEntry): Promise<void> {
+		const cacheLocation = path.join(this.schemaCacheLocation, cacheEntry.fileName);
+		delete this.cacheInfo[schemaUri];
+		await this.updateMemento();
+		try {
+			await fs.rm(cacheLocation);
+		} catch (e) {
+			// ignore
+		}
+	}
+
+
+	// for debugging
+	public getCacheInfo() {
+		return this.cacheInfo;
+	}
+
+	private async updateMemento() {
+		try {
+			await this.globalState.update(MEMENTO_KEY, this.cacheInfo);
+		} catch (e) {
+			// ignore
+		}
+	}
+}
+function getCacheFileName(uri: string): string {
+	return `${createHash('MD5').update(uri).digest('hex')}.schema.json`;
+}