| // Copyright 2019 The Fuchsia Authors. All rights reserved. |
| // Use of this source code is governed by a BSD-style license that can be |
| // found in the LICENSE file. |
| |
| package sshclient |
| |
| import ( |
| "bytes" |
| "fmt" |
| "io" |
| "log" |
| "net" |
| "strings" |
| "sync" |
| "time" |
| |
| "golang.org/x/crypto/ssh" |
| ) |
| |
| // Client is a wrapper around ssh that supports keepalive and auto-reconnection. |
| type Client struct { |
| addr string |
| config *ssh.ClientConfig |
| shuttingDown bool |
| done chan struct{} |
| keepaliveDuration time.Duration |
| |
| // This mutex protects the following fields |
| mu sync.Mutex |
| client *ssh.Client |
| conn net.Conn |
| connectionListeners []*sync.WaitGroup |
| disconnectionListeners []*sync.WaitGroup |
| } |
| |
| // NewClient creates a new ssh client to the address. |
| func NewClient(addr string, config *ssh.ClientConfig) *Client { |
| c := &Client{ |
| addr: addr, |
| config: config, |
| client: nil, |
| conn: nil, |
| shuttingDown: false, |
| done: make(chan struct{}), |
| keepaliveDuration: 10 * time.Second, |
| } |
| go c.keepalive() |
| |
| // Wait for the initial connection, so we don't return a client that's |
| // in a "just created but not connected" state. |
| c.WaitToBeConnected() |
| |
| return c |
| } |
| |
| // Helper to create an ssh client and connection to the address. |
| func connect(addr string, config *ssh.ClientConfig) (*ssh.Client, net.Conn, error) { |
| conn, err := net.DialTimeout("tcp", addr, config.Timeout) |
| if err != nil { |
| return nil, nil, err |
| } |
| clientConn, chans, reqs, err := ssh.NewClientConn(conn, addr, config) |
| if err != nil { |
| conn.Close() |
| return nil, nil, err |
| } |
| client := ssh.NewClient(clientConn, chans, reqs) |
| |
| return client, conn, nil |
| } |
| |
| func (c *Client) makeSession(stdout io.Writer, stderr io.Writer) (*ssh.Session, error) { |
| // Temporarily grab the lock and make a copy of the client. This |
| // prevents a long running `Run` command from blocking the keep-alive |
| // goroutine. |
| c.mu.Lock() |
| client := c.client |
| c.mu.Unlock() |
| |
| if client == nil { |
| return nil, fmt.Errorf("ssh is disconnected") |
| } |
| |
| session, err := client.NewSession() |
| if err != nil { |
| return nil, err |
| } |
| |
| session.Stdout = stdout |
| session.Stderr = stderr |
| return session, nil |
| } |
| |
| // Start a command on the remote device and write STDOUT and STDERR to the |
| // passed in io.Writers. |
| func (c *Client) Start(command string, stdout io.Writer, stderr io.Writer) (*ssh.Session, error) { |
| session, err := c.makeSession(stdout, stderr) |
| if err != nil { |
| return nil, err |
| } |
| |
| log.Printf("spawning: %s", command) |
| |
| if err := session.Start(command); err != nil { |
| session.Close() |
| return nil, err |
| } |
| return session, nil |
| } |
| |
| // Run a command to completion on the remote device and write STDOUT and STDERR |
| // to the passed in io.Writers. |
| func (c *Client) Run(command string, stdout io.Writer, stderr io.Writer) error { |
| session, err := c.makeSession(stdout, stderr) |
| if err != nil { |
| return err |
| } |
| defer session.Close() |
| |
| log.Printf("running: %s", command) |
| |
| return session.Run(command) |
| } |
| |
| // Close the ssh client connections. |
| func (c *Client) Close() { |
| c.shuttingDown = true |
| close(c.done) |
| c.disconnect() |
| } |
| |
| // GetSshConnection returns the first field in the remote SSH_CONNECTION |
| // environment variable. |
| func (c *Client) GetSshConnection() (string, error) { |
| var stdout bytes.Buffer |
| var stderr bytes.Buffer |
| err := c.Run("PATH= echo $SSH_CONNECTION", &stdout, &stderr) |
| if err != nil { |
| return "", fmt.Errorf("failed to read SSH_CONNECTION: %s: %s", err, string(stderr.Bytes())) |
| } |
| return strings.Split(string(stdout.Bytes()), " ")[0], nil |
| } |
| |
| // WaitToBeConnected blocks until the ssh connection is available for use. |
| func (c *Client) WaitToBeConnected() { |
| log.Printf("waiting for %s to to connect", c.addr) |
| |
| var wg sync.WaitGroup |
| c.RegisterConnectListener(&wg) |
| wg.Wait() |
| |
| log.Printf("connected to %s", c.addr) |
| } |
| |
| // RegisterConnectListener adds a waiter that gets notified when the ssh |
| // client is connected. |
| func (c *Client) RegisterConnectListener(wg *sync.WaitGroup) { |
| wg.Add(1) |
| |
| c.mu.Lock() |
| if c.client == nil { |
| c.connectionListeners = append(c.connectionListeners, wg) |
| } else { |
| wg.Done() |
| } |
| c.mu.Unlock() |
| } |
| |
| // RegisterDisconnectListener adds a waiter that gets notified when the ssh |
| // client is disconnected. |
| func (c *Client) RegisterDisconnectListener(wg *sync.WaitGroup) { |
| wg.Add(1) |
| |
| c.mu.Lock() |
| if c.client == nil { |
| wg.Done() |
| } else { |
| c.disconnectionListeners = append(c.disconnectionListeners, wg) |
| } |
| c.mu.Unlock() |
| } |
| |
| // IsConnected checks if we are currently connected to the server. |
| func (c *Client) IsConnected() bool { |
| c.mu.Lock() |
| defer c.mu.Unlock() |
| |
| return c.client != nil |
| } |
| |
| // disconnect from ssh, and notify anyone waiting for disconnection. |
| func (c *Client) disconnect() { |
| c.mu.Lock() |
| defer c.mu.Unlock() |
| |
| c.disconnectLocked() |
| } |
| |
| func (c *Client) disconnectLocked() { |
| log.Printf("disconnected from %s", c.addr) |
| |
| if c.client != nil { |
| c.client.Close() |
| c.client = nil |
| } |
| |
| for _, listener := range c.disconnectionListeners { |
| listener.Done() |
| } |
| c.disconnectionListeners = []*sync.WaitGroup{} |
| } |
| |
| // Make a single attempt to reconnect to the ssh server. |
| func (c *Client) reconnectLocked() { |
| // We can exit early if we are shutting down, or we already have a client. |
| if c.shuttingDown || c.client != nil { |
| return |
| } |
| |
| log.Printf("attempting to reconnect to %s...", c.addr) |
| |
| client, conn, err := connect(c.addr, c.config) |
| if err == nil { |
| c.client = client |
| c.conn = conn |
| |
| for _, listener := range c.connectionListeners { |
| listener.Done() |
| } |
| c.connectionListeners = []*sync.WaitGroup{} |
| |
| log.Printf("reconnected to %s", c.addr) |
| } else { |
| log.Printf("reconnection failed: %s", err) |
| } |
| } |
| |
| // Send periodic keep-alives. If we don't do this, then we might not observe |
| // the server side disconnecting from us. |
| func (c *Client) keepalive() { |
| c.emitKeepalive() |
| |
| for { |
| select { |
| case <-time.After(c.keepaliveDuration): |
| c.emitKeepalive() |
| case <-c.done: |
| return |
| } |
| } |
| } |
| |
| // Emit a heartbeat to the ssh server. |
| func (c *Client) emitKeepalive() { |
| // If the client is disconnected from the server, attempt to reconnect. |
| // Otherwise, emit a heartbeat. |
| c.mu.Lock() |
| defer c.mu.Unlock() |
| |
| if c.client == nil { |
| c.reconnectLocked() |
| return |
| } |
| |
| // ssh keepalive is not completely reliable. So in addition to emitting |
| // it, we'll also set a tcp deadline to timeout if we don't get a |
| // keepalive response within some period of time. |
| c.conn.SetDeadline(time.Now().Add(c.keepaliveDuration * 2)) |
| |
| _, _, err := c.client.SendRequest("keepalive@openssh.com", true, nil) |
| if err != nil { |
| if !c.shuttingDown { |
| log.Printf("disconnected from %s: %s", c.addr, err) |
| } |
| c.disconnectLocked() |
| } |
| } |