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package connectors
import (
"context"
"fmt"
"io"
"strconv"
"strings"
"time"
"github.com/mimecast/dtail/internal/clients/handlers"
"github.com/mimecast/dtail/internal/config"
"github.com/mimecast/dtail/internal/io/dlog"
"github.com/mimecast/dtail/internal/ssh/client"
"golang.org/x/crypto/ssh"
)
// ServerConnection represents a connection to a single remote dtail server via
// SSH protocol.
type ServerConnection struct {
// The full server string as received from the server discovery (can be with port number)
server string
// Only the hostname or FQDN (without the port number)
hostname string
// Only the port number.
port int
config *ssh.ClientConfig
handler handlers.Handler
commands []string
hostKeyCallback client.HostKeyCallback
throttlingDone bool
}
// NewServerConnection returns a new DTail SSH server connection.
func NewServerConnection(server string, userName string,
authMethods []ssh.AuthMethod, hostKeyCallback client.HostKeyCallback,
handler handlers.Handler, commands []string) *ServerConnection {
dlog.Client.Debug(server, "Creating new connection", server, handler, commands)
c := ServerConnection{
hostKeyCallback: hostKeyCallback,
server: server,
handler: handler,
commands: commands,
config: &ssh.ClientConfig{
User: userName,
Auth: authMethods,
HostKeyCallback: hostKeyCallback.Wrap(),
Timeout: time.Second * 2,
},
}
c.initServerPort()
return &c
}
// Server returns the server hostname connected to.
func (c *ServerConnection) Server() string { return c.server }
// Handler returns the handler used for the connection.
func (c *ServerConnection) Handler() handlers.Handler { return c.handler }
// Attempt to parse the server port address from the provided server FQDN.
func (c *ServerConnection) initServerPort() {
parts := strings.Split(c.server, ":")
if len(parts) == 1 {
c.hostname = c.server
c.port = config.Common.SSHPort
return
}
dlog.Client.Debug("Parsing port from hostname", parts)
port, err := strconv.Atoi(parts[1])
if err != nil {
dlog.Client.FatalPanic("Unable to parse client port", c.server, parts, err)
}
c.hostname = parts[0]
c.port = port
}
// Start the connection to the server.
func (c *ServerConnection) Start(ctx context.Context, cancel context.CancelFunc,
throttleCh, statsCh chan struct{}) {
// Throttle how many connections can be established concurrently (based on ch length)
dlog.Client.Debug(c.server, "Throttling connection", len(throttleCh), cap(throttleCh))
select {
case throttleCh <- struct{}{}:
case <-ctx.Done():
dlog.Client.Debug(c.server, "Not establishing connection as context is done",
len(throttleCh), cap(throttleCh))
return
}
dlog.Client.Debug(c.server, "Throttling says that the connection can be established",
len(throttleCh), cap(throttleCh))
go func() {
defer func() {
if !c.throttlingDone {
dlog.Client.Debug(c.server, "Unthrottling connection (1)",
len(throttleCh), cap(throttleCh))
c.throttlingDone = true
<-throttleCh
}
cancel()
}()
if err := c.dial(ctx, cancel, throttleCh, statsCh); err != nil {
dlog.Client.Warn(c.server, err)
if c.hostKeyCallback.Untrusted(c.server) {
dlog.Client.Debug(c.server, "Not trusting host")
}
}
}()
<-ctx.Done()
}
// Dail into a new SSH connection. Close connection in case of an error.
func (c *ServerConnection) dial(ctx context.Context, cancel context.CancelFunc,
throttleCh, statsCh chan struct{}) error {
dlog.Client.Debug(c.server, "Incrementing connection stats")
statsCh <- struct{}{}
defer func() {
dlog.Client.Debug(c.server, "Decrementing connection stats")
<-statsCh
}()
address := fmt.Sprintf("%s:%d", c.hostname, c.port)
dlog.Client.Debug(c.server, "Dialing into the connection", address)
client, err := ssh.Dial("tcp", address, c.config)
if err != nil {
return err
}
defer client.Close()
return c.session(ctx, cancel, client, throttleCh)
}
// Create the SSH session. Close the session in case of an error.
func (c *ServerConnection) session(ctx context.Context, cancel context.CancelFunc,
client *ssh.Client, throttleCh chan struct{}) error {
dlog.Client.Debug(c.server, "Creating SSH session")
session, err := client.NewSession()
if err != nil {
return err
}
defer session.Close()
return c.handle(ctx, cancel, session, throttleCh)
}
func (c *ServerConnection) handle(ctx context.Context, cancel context.CancelFunc,
session *ssh.Session, throttleCh chan struct{}) error {
dlog.Client.Debug(c.server, "Creating handler for SSH session")
stdinPipe, err := session.StdinPipe()
if err != nil {
return err
}
stdoutPipe, err := session.StdoutPipe()
if err != nil {
return err
}
if err := session.Shell(); err != nil {
return err
}
go func() {
io.Copy(stdinPipe, c.handler)
cancel()
}()
go func() {
io.Copy(c.handler, stdoutPipe)
cancel()
}()
go func() {
select {
case <-c.handler.Done():
case <-ctx.Done():
}
cancel()
}()
// Send all commands to client.
for _, command := range c.commands {
dlog.Client.Debug(command)
c.handler.SendMessage(command)
}
if !c.throttlingDone {
dlog.Client.Debug(c.server, "Unthrottling connection (2)",
len(throttleCh), cap(throttleCh))
c.throttlingDone = true
<-throttleCh
}
<-ctx.Done()
c.handler.Shutdown()
return nil
}
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