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|
package connectors
import (
"errors"
"fmt"
"sync"
"time"
"github.com/mimecast/dtail/internal/clients/handlers"
"github.com/mimecast/dtail/internal/io/dlog"
"github.com/mimecast/dtail/internal/omode"
sessionspec "github.com/mimecast/dtail/internal/session"
)
var (
// ErrSessionUnsupported indicates that the remote side did not advertise
// runtime query update support.
ErrSessionUnsupported = errors.New("runtime query updates unsupported by server")
// ErrSessionAckTimeout indicates that no hidden SESSION acknowledgement arrived in time.
ErrSessionAckTimeout = errors.New("timed out waiting for session acknowledgement")
// ErrSessionRejected indicates that the server explicitly rejected a SESSION request.
ErrSessionRejected = errors.New("session request rejected")
// ErrUnexpectedSessionAck indicates that the client received a malformed or mismatched acknowledgement.
ErrUnexpectedSessionAck = errors.New("unexpected session acknowledgement")
)
const defaultSessionAckTimeout = 2 * time.Second
type committedSessionState struct {
mu sync.RWMutex
committed bool
generation uint64
spec sessionspec.Spec
}
func (s *committedSessionState) commit(spec sessionspec.Spec, generation uint64) {
s.mu.Lock()
defer s.mu.Unlock()
s.committed = true
s.generation = generation
s.spec = spec
}
func (s *committedSessionState) clear() {
s.mu.Lock()
defer s.mu.Unlock()
s.committed = false
s.generation = 0
s.spec = sessionspec.Spec{}
}
func (s *committedSessionState) snapshot() (sessionspec.Spec, uint64, bool) {
s.mu.RLock()
defer s.mu.RUnlock()
return s.spec, s.generation, s.committed
}
func dispatchInitialCommands(server string, handler handlers.Handler, commands []string,
interactiveQuery bool, initialSpec sessionspec.Spec, state *committedSessionState) error {
if !interactiveQuery || initialSpec.Mode == omode.Unknown {
return sendLegacyCommands(handler, commands)
}
if err := applySessionSpec(server, handler, state, initialSpec, defaultSessionAckTimeout); err != nil {
if !errors.Is(err, ErrSessionUnsupported) {
dlog.Client.Warn(server, "Interactive session bootstrap failed, falling back to legacy commands", err)
}
state.clear()
return sendLegacyCommands(handler, commands)
}
return nil
}
func applySessionSpec(server string, handler handlers.Handler,
state *committedSessionState, spec sessionspec.Spec, timeout time.Duration) error {
if handler == nil {
return ErrSessionUnsupported
}
if !supportsQueryUpdates(handler, defaultCapabilityWait) {
return ErrSessionUnsupported
}
action := "start"
nextGeneration := uint64(0)
command, err := spec.StartCommand()
if err != nil {
return err
}
if _, generation, ok := state.snapshot(); ok {
action = "update"
nextGeneration = generation + 1
command, err = spec.UpdateCommand(nextGeneration)
if err != nil {
return err
}
}
drainSessionAcks(handler)
if err := handler.SendMessage(command); err != nil {
return err
}
ack, ok := handler.WaitForSessionAck(resolveSessionAckTimeout(timeout))
if !ok {
return ErrSessionAckTimeout
}
if ack.Error != "" {
return fmt.Errorf("%w: %s", ErrSessionRejected, ack.Error)
}
if ack.Action != action {
return fmt.Errorf("%w: got action %q want %q", ErrUnexpectedSessionAck, ack.Action, action)
}
if ack.Generation == 0 {
return fmt.Errorf("%w: missing generation", ErrUnexpectedSessionAck)
}
if action == "update" && ack.Generation != nextGeneration {
return fmt.Errorf("%w: got generation %d want %d", ErrUnexpectedSessionAck, ack.Generation, nextGeneration)
}
state.commit(spec, ack.Generation)
dlog.Client.Debug(server, "Committed session spec", "action", action, "generation", ack.Generation)
return nil
}
func sendLegacyCommands(handler handlers.Handler, commands []string) error {
for _, command := range commands {
if err := handler.SendMessage(command); err != nil {
return err
}
}
return nil
}
func drainSessionAcks(handler handlers.Handler) {
for {
if _, ok := handler.WaitForSessionAck(0); !ok {
return
}
}
}
func resolveSessionAckTimeout(timeout time.Duration) time.Duration {
if timeout <= 0 {
return defaultSessionAckTimeout
}
return timeout
}
|
