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agent.go
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agent.go
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package teleagent
import (
"io"
"net"
"os"
"strings"
"time"
"github.com/gravitational/teleport/lib/utils"
"github.com/gravitational/trace"
log "github.com/sirupsen/logrus"
"golang.org/x/crypto/ssh/agent"
)
// Agent extends the agent.Agent interface.
// APIs which accept this interface promise to
// call `Close()` when they are done using the
// supplied agent.
type Agent interface {
agent.Agent
io.Closer
}
// nopCloser wraps an agent.Agent in the extended
// Agent interface by adding a NOP closer.
type nopCloser struct {
agent.Agent
}
func (n nopCloser) Close() error { return nil }
// NopCloser wraps an agent.Agent with a NOP closer, allowing it
// to be passed to APIs which expect the extended agent interface.
func NopCloser(std agent.Agent) Agent {
return nopCloser{std}
}
// Getter is a function used to get an agent instance.
type Getter func() (Agent, error)
// AgentServer is implementation of SSH agent server
type AgentServer struct {
getAgent Getter
listener net.Listener
path string
}
// NewServer returns new instance of agent server
func NewServer(getter Getter) *AgentServer {
return &AgentServer{getAgent: getter}
}
// ListenUnixSocket starts listening and serving agent assuming that
func (a *AgentServer) ListenUnixSocket(path string, uid, gid int, mode os.FileMode) error {
l, err := net.Listen("unix", path)
if err != nil {
return trace.Wrap(err)
}
if err := os.Chown(path, uid, gid); err != nil {
l.Close()
return trace.ConvertSystemError(err)
}
if err := os.Chmod(path, mode); err != nil {
l.Close()
return trace.ConvertSystemError(err)
}
a.listener = l
a.path = path
return nil
}
// Serve starts serving on the listener, assumes that Listen was called before
func (a *AgentServer) Serve() error {
if a.listener == nil {
return trace.BadParameter("Serve needs a Listen call first")
}
var tempDelay time.Duration // how long to sleep on accept failure
for {
conn, err := a.listener.Accept()
if err != nil {
neterr, ok := err.(net.Error)
if !ok {
return trace.Wrap(err, "unknown error")
}
if !neterr.Temporary() {
if !strings.Contains(neterr.Error(), "use of closed network connection") {
log.Errorf("got permanent error: %v", err)
}
return err
}
if tempDelay == 0 {
tempDelay = 5 * time.Millisecond
} else {
tempDelay *= 2
}
if max := 1 * time.Second; tempDelay > max {
tempDelay = max
}
log.Errorf("got temp error: %v, will sleep %v", err, tempDelay)
time.Sleep(tempDelay)
continue
}
tempDelay = 0
// get an agent instance for serving this conn
instance, err := a.getAgent()
if err != nil {
log.Errorf("Failed to get agent: %v", err)
return trace.Wrap(err)
}
// serve agent protocol against conn in a
// separate goroutine.
go func() {
defer instance.Close()
if err := agent.ServeAgent(instance, conn); err != nil {
if err != io.EOF {
log.Error(err)
}
}
}()
}
}
// ListenAndServe is similar http.ListenAndServe
func (a *AgentServer) ListenAndServe(addr utils.NetAddr) error {
l, err := net.Listen(addr.AddrNetwork, addr.Addr)
if err != nil {
return trace.Wrap(err)
}
a.listener = l
return a.Serve()
}
// Close closes listener and stops serving agent
func (a *AgentServer) Close() error {
var errors []error
if a.listener != nil {
log.Debugf("AgentServer(%v) is closing", a.listener.Addr())
if err := a.listener.Close(); err != nil {
errors = append(errors, trace.ConvertSystemError(err))
}
}
if a.path != "" {
if err := os.Remove(a.path); err != nil {
errors = append(errors, trace.ConvertSystemError(err))
}
}
return trace.NewAggregate(errors...)
}