[FIX] Resource#getSize: Retrieve Resource's size (#256)

Stats.size was not set for a stream.
To ensure Resource's size can be retrieved for:
* stream
* string
* buffer
async method is introduced which uses #getBuffer to
ensure that size retrieval works for all content types.

followup of #253

lib/Resource.js

@@ -120,7 +120,6 @@ class Resource {
 		this._buffer = buffer;
 		this._contentDrained = false;
 		this._streamDrained = false;
-		this._setSize(this._buffer.byteLength);
 	}
 
 	/**
@@ -211,17 +210,6 @@ class Resource {
 		this._streamDrained = false;
 	}
 
-	/**
-	 * Set the size in bytes
-	 *
-	 * @param {number} size byte size
-	 * @private
-	 * @see https://nodejs.org/api/fs.html#fs_stats_size
-	 */
-	_setSize(size) {
-		this._statInfo.size = size;
-	}
-
 	/**
 	 * Gets the resources path
 	 *
@@ -254,6 +242,21 @@ class Resource {
 		return this._statInfo;
 	}
 
+	/**
+	 * Size in bytes allocated by the underlying buffer.
+	 *
+	 * @see {TypedArray#byteLength}
+	 * @returns {Promise<number>} size in bytes, <code>0</code> if there is no content yet
+	 */
+	async getSize() {
+		// if resource does not have any content it should have 0 bytes
+		if (!this._buffer && !this._createStream && !this._stream) {
+			return 0;
+		}
+		const buffer = await this.getBuffer();
+		return buffer.byteLength;
+	}
+
 	_getNameFromPath(virPath) {
 		return path.posix.basename(virPath);
 	}

test/lib/Resource.js

@@ -148,52 +148,60 @@ test("Resource: size modification", async (t) => {
 	const resource = new Resource({
 		path: "my/path/to/resource"
 	});
-	t.falsy(resource.getStatInfo().size, "initial size is not defined");
+	t.is(await resource.getSize(), 0, "initial size without content");
 
 	// string
 	resource.setString("Content");
 
-	t.is(resource.getStatInfo().size, 7, "size after manually setting the string");
-	t.is(new Resource({
+	t.is(await resource.getSize(), 7, "size after manually setting the string");
+	t.is(await new Resource({
 		path: "my/path/to/resource",
 		string: "Content"
-	}).getStatInfo().size, 7, "size when passing string to constructor");
+	}).getSize(), 7, "size when passing string to constructor");
 
 
 	// buffer
 	resource.setBuffer(Buffer.from("Super"));
 
-	t.is(resource.getStatInfo().size, 5, "size after manually setting the string");
+	t.is(await resource.getSize(), 5, "size after manually setting the string");
 
 	const clonedResource1 = await resource.clone();
-	t.is(clonedResource1.getStatInfo().size, 5, "size after cloning the resource");
+	t.is(await clonedResource1.getSize(), 5, "size after cloning the resource");
 
 
 	// buffer with alloc
 	const buf = Buffer.alloc(1234);
 	buf.write("some string", 0, "utf8");
 	resource.setBuffer(buf);
 
-	t.is(resource.getStatInfo().size, 1234, "buffer with alloc after setting the buffer");
-	t.is(new Resource({
+	t.is(await resource.getSize(), 1234, "buffer with alloc after setting the buffer");
+	t.is(await new Resource({
 		path: "my/path/to/resource",
 		buffer: buf
-	}).getStatInfo().size, 1234, "buffer with alloc when passing buffer to constructor");
+	}).getSize(), 1234, "buffer with alloc when passing buffer to constructor");
 
 	const clonedResource2 = await resource.clone();
-	t.is(clonedResource2.getStatInfo().size, 1234, "buffer with alloc atfer clone");
-});
-
-test("Resource: _setSize", (t) => {
-	t.plan(1);
+	t.is(await clonedResource2.getSize(), 1234, "buffer with alloc after clone");
 
-	const resource = new Resource({
-		path: "my/path/to/resource"
+	// stream
+	const streamResource = new Resource({
+		path: "my/path/to/resource",
 	});
+	const stream = new Stream.Readable();
+	stream._read = function() {};
+	stream.push("I am a ");
+	stream.push("readable ");
+	stream.push("stream!");
+	stream.push(null);
 
-	resource._setSize(1337);
+	streamResource.setStream(stream);
 
-	t.is(resource.getStatInfo().size, 1337);
+	// stream is read and stored in buffer
+	// test parallel size retrieval
+	const [size1, size2] = await Promise.all([streamResource.getSize(), streamResource.getSize()]);
+	t.is(size1, 23, "size for streamResource, parallel 1");
+	t.is(size2, 23, "size for streamResource, parallel 2");
+	t.is(await streamResource.getSize(), 23, "size for streamResource read again");
 });
 
 test("Resource: setStream", (t) => {
@@ -333,12 +341,12 @@ test("integration stat - resource size", async (t) => {
 			return fs.createReadStream(fsPath);
 		}
 	});
-	t.is(resource.getStatInfo().size, 91);
+	t.is(await resource.getSize(), 91);
 
 	// Setting the same content again should end up with the same size
 	resource.setString(await resource.getString());
-	t.is(resource.getStatInfo().size, 91);
+	t.is(await resource.getSize(), 91);
 
 	resource.setString("myvalue");
-	t.is(resource.getStatInfo().size, 7);
+	t.is(await resource.getSize(), 7);
 });