vfs: Began testing InMemoryVFS

tests/vfs-tests.js

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+const {expect} = require("chai");
+const {InMemoryVFS} = require("../vfs");
+const {MemoryWritable, promisePiped} = require("../streams");
+
+function abstractVFSBehavior( VFS, name ) {
+	describe(name + " acts like a VFS", function () {
+		describe("Given a file which does not exist", function(){
+			it("when queried it does not exist", async function(){
+				const sut = new VFS();
+				expect(await sut.exists("nonexistent-file")).to.eq(false);
+			});
+		});
+
+		describe("When creating a file as bytes", function(){
+			beforeEach(async function(){
+				this.sut = new VFS();
+				this.fileName = "devision";
+				this.fileContents = "where do we go from here, stop and shed a tear";
+				await this.sut.putBytes(this.fileName, this.fileContents, this.fileContents.encoding);
+			});
+
+			it("is readable as a stream", async function(){
+				const istream = await this.sut.createReadableStream(this.fileName);
+				//TODO: The following should really be abstracted into a "promise to read all bytes" thing
+				const sink = new MemoryWritable();
+				await promisePiped(istream,sink);
+				expect(sink.bytes.toString("utf-8")).to.deep.eq(this.fileContents);
+			});
+
+			it("is readable as bytes", async function(){
+				const bytes = await this.sut.asBytes(this.fileName);
+				expect(bytes.toString("utf-8")).to.deep.eq(this.fileContents);
+			});
+			it("can not mutate returned byte buffer", async function(){
+				const bytes1 = await this.sut.asBytes(this.fileName);
+				bytes1.writeUInt32LE(51);
+				const bytes2 = await this.sut.asBytes(this.fileName);
+				expect(bytes2.toString("utf-8")).to.deep.eq(this.fileContents);
+			});
+		});
+	});
+}
+
+abstractVFSBehavior(InMemoryVFS, "InMemoryVFS");

vfs.js

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+/**
+ * @module vfs
+ *
+ * Virtual File System
+ *
+ * Provides a framework to abstract out operating against the local file system or a remote file system.  This is useful
+ * in testing, distributed portability, or vendor independence.
+ */
+const {
+	MemoryReadable,
+	MemoryWritable
+} = require("./streams");
+
+class InMemoryVFS {
+	constructor() {
+		this.files = {};
+	}
+
+	async exists( file ){
+		return !!this.files[file];
+	}
+
+	async unlink( file ){
+		if( this.files[file] ){
+			delete this.files[file];
+		}
+	}
+
+	async createReadableStream( file ){
+		if( !(await this.exists(file)) ){
+			throw new Error("No such file "+ file);
+		}
+		return new MemoryReadable(this.files[file]);
+	}
+
+	async asBytes( file ){
+		return Buffer.from(this.files[file]);
+	}
+
+	async putBytes( file, bytes, encoding ){
+		this.files[file] = Buffer.from(bytes, encoding);
+	}
+
+	async createWritableStream( file ){
+		const writable = new MemoryWritable();
+		writable.on("finish", () => {
+			this.files[file] = writable.bytes;
+		});
+		return writable;
+	}
+}
+
+module.exports = {
+	InMemoryVFS
+}