feat(VsockFirecrackerClient): Add client to talk to FC microVMs

src/base/Transports.ts

@@ -1,6 +1,7 @@
 export enum Transport {
   direct = 'direct',
   stdio = 'stdio',
+  uds = 'uds',
   vsock = 'vsock',
   tcp = 'tcp',
   http = 'http',
@@ -19,13 +20,49 @@ export interface StdioAddress {
   cwd?: string
 }
 
+/**
+ * An address in the Unix Domain Socket (UDS) address family
+ *
+ * @see https://en.wikipedia.org/wiki/Unix_domain_socket
+ */
+export class UdsAddress {
+  public readonly type: Transport.uds = Transport.uds
+
+  /**
+   * The file system path to the socket
+   */
+  public readonly path: string
+
+  public constructor (path: string) {
+    this.path = path
+  }
+}
+
+/**
+ * An address int the Linux VSOCK address family
+ *
+ * @see http://man7.org/linux/man-pages/man7/vsock.7.html
+ */
 export class VsockAddress {
   public readonly type: Transport.vsock = Transport.vsock
 
+  /**
+   * The port number
+   */
   public readonly port: number
 
-  public constructor (port: number = 6000) {
+  /**
+   * The file system path to the socket
+   *
+   * Although VSOCK addresses do not include a path,
+   * Firecracker uses a UDS on the host. This allows
+   * for that use case.
+   */
+  public readonly path?: string
+
+  public constructor (port: number = 6000, path?: string) {
     this.port = port
+    this.path = path
   }
 }
 

src/vsock/VsockFirecrackerClient.ts

@@ -0,0 +1,35 @@
+import { getLogger } from '@stencila/logga';
+import net from 'net';
+import { VsockAddress } from '../base/Transports';
+import StreamClient from '../stream/StreamClient';
+
+const log = getLogger('executa:vsock:client')
+
+export default class VsockFirecrackerClient extends StreamClient {
+  private socket: net.Socket
+
+  public constructor(address: VsockAddress = new VsockAddress()) {
+    const { path, port} = address
+    if (path === undefined) throw (`Path is required`)
+
+    const socket = net.connect(path)
+    socket.on('connect', () => {
+      log.debug(`${path}:${port}: connecting`)
+      socket.write(`CONNECT ${port}\n`)
+    })
+    socket.on('error', error => {
+      log.error(`${path}:${port}: ${error}`)
+    })
+    socket.on('close', () => {
+      // If there is no server listening in the VM then the connection will be closed.
+      log.debug(`${path}:${port}: connection-closed`)
+    })
+
+    super(socket, socket)
+    this.socket = socket
+  }
+
+  public stop() {
+    this.socket.destroy()
+  }
+}