src/vs/workbench/api/common/extHostFileSystem.ts/ExtHostFileSystem/$read
class ExtHostFileSystem:	$read(handle: number, fd: number, pos: number, length: number): Promise<VSBuffer> {
		const provider = this._getFsProvider(handle);
		if (!provider.read) {
			throw new Error('FileSystemProvider does not implement "read"');
		}
		const data = VSBuffer.alloc(length);
		return Promise.resolve(provider.read(fd, pos, data.buffer, 0, length)).then(read => {
			return data.slice(0, read); // don't send zeros
		});
	}