/
client_session.go
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/
client_session.go
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// Copyright (C) MongoDB, Inc. 2017-present.
//
// Licensed under the Apache License, Version 2.0 (the "License"); you may
// not use this file except in compliance with the License. You may obtain
// a copy of the License at http://www.apache.org/licenses/LICENSE-2.0
package session // import "go.mongodb.org/mongo-driver/x/mongo/driver/session"
import (
"context"
"errors"
"time"
"go.mongodb.org/mongo-driver/bson"
"go.mongodb.org/mongo-driver/bson/primitive"
"go.mongodb.org/mongo-driver/internal/uuid"
"go.mongodb.org/mongo-driver/mongo/address"
"go.mongodb.org/mongo-driver/mongo/description"
"go.mongodb.org/mongo-driver/mongo/readconcern"
"go.mongodb.org/mongo-driver/mongo/readpref"
"go.mongodb.org/mongo-driver/mongo/writeconcern"
"go.mongodb.org/mongo-driver/x/bsonx/bsoncore"
)
// ErrSessionEnded is returned when a client session is used after a call to endSession().
var ErrSessionEnded = errors.New("ended session was used")
// ErrNoTransactStarted is returned if a transaction operation is called when no transaction has started.
var ErrNoTransactStarted = errors.New("no transaction started")
// ErrTransactInProgress is returned if startTransaction() is called when a transaction is in progress.
var ErrTransactInProgress = errors.New("transaction already in progress")
// ErrAbortAfterCommit is returned when abort is called after a commit.
var ErrAbortAfterCommit = errors.New("cannot call abortTransaction after calling commitTransaction")
// ErrAbortTwice is returned if abort is called after transaction is already aborted.
var ErrAbortTwice = errors.New("cannot call abortTransaction twice")
// ErrCommitAfterAbort is returned if commit is called after an abort.
var ErrCommitAfterAbort = errors.New("cannot call commitTransaction after calling abortTransaction")
// ErrUnackWCUnsupported is returned if an unacknowledged write concern is supported for a transaction.
var ErrUnackWCUnsupported = errors.New("transactions do not support unacknowledged write concerns")
// ErrSnapshotTransaction is returned if an transaction is started on a snapshot session.
var ErrSnapshotTransaction = errors.New("transactions are not supported in snapshot sessions")
// TransactionState indicates the state of the transactions FSM.
type TransactionState uint8
// Client Session states
const (
None TransactionState = iota
Starting
InProgress
Committed
Aborted
)
// String implements the fmt.Stringer interface.
func (s TransactionState) String() string {
switch s {
case None:
return "none"
case Starting:
return "starting"
case InProgress:
return "in progress"
case Committed:
return "committed"
case Aborted:
return "aborted"
default:
return "unknown"
}
}
// LoadBalancedTransactionConnection represents a connection that's pinned by a ClientSession because it's being used
// to execute a transaction when running against a load balancer. This interface is a copy of driver.PinnedConnection
// and exists to be able to pin transactions to a connection without causing an import cycle.
type LoadBalancedTransactionConnection interface {
// Functions copied over from driver.Connection.
WriteWireMessage(context.Context, []byte) error
ReadWireMessage(ctx context.Context) ([]byte, error)
Description() description.Server
Close() error
ID() string
ServerConnectionID() *int64
DriverConnectionID() uint64 // TODO(GODRIVER-2824): change type to int64.
Address() address.Address
Stale() bool
// Functions copied over from driver.PinnedConnection that are not part of Connection or Expirable.
PinToCursor() error
PinToTransaction() error
UnpinFromCursor() error
UnpinFromTransaction() error
}
// Client is a session for clients to run commands.
type Client struct {
*Server
ClientID uuid.UUID
ClusterTime bson.Raw
Consistent bool // causal consistency
OperationTime *primitive.Timestamp
IsImplicit bool
Terminated bool
RetryingCommit bool
Committing bool
Aborting bool
RetryWrite bool
RetryRead bool
Snapshot bool
// options for the current transaction
// most recently set by transactionopt
CurrentRc *readconcern.ReadConcern
CurrentRp *readpref.ReadPref
CurrentWc *writeconcern.WriteConcern
CurrentMct *time.Duration
// default transaction options
transactionRc *readconcern.ReadConcern
transactionRp *readpref.ReadPref
transactionWc *writeconcern.WriteConcern
transactionMaxCommitTime *time.Duration
pool *Pool
TransactionState TransactionState
PinnedServer *description.Server
RecoveryToken bson.Raw
PinnedConnection LoadBalancedTransactionConnection
SnapshotTime *primitive.Timestamp
}
func getClusterTime(clusterTime bson.Raw) (uint32, uint32) {
if clusterTime == nil {
return 0, 0
}
clusterTimeVal, err := clusterTime.LookupErr("$clusterTime")
if err != nil {
return 0, 0
}
timestampVal, err := bson.Raw(clusterTimeVal.Value).LookupErr("clusterTime")
if err != nil {
return 0, 0
}
return timestampVal.Timestamp()
}
// MaxClusterTime compares 2 clusterTime documents and returns the document representing the highest cluster time.
func MaxClusterTime(ct1, ct2 bson.Raw) bson.Raw {
epoch1, ord1 := getClusterTime(ct1)
epoch2, ord2 := getClusterTime(ct2)
if epoch1 > epoch2 {
return ct1
} else if epoch1 < epoch2 {
return ct2
} else if ord1 > ord2 {
return ct1
} else if ord1 < ord2 {
return ct2
}
return ct1
}
// NewImplicitClientSession creates a new implicit client-side session.
func NewImplicitClientSession(pool *Pool, clientID uuid.UUID) *Client {
// Server-side session checkout for implicit sessions is deferred until after checking out a
// connection, so don't check out a server-side session right now. This will limit the number of
// implicit sessions to no greater than an application's maxPoolSize.
return &Client{
pool: pool,
ClientID: clientID,
IsImplicit: true,
}
}
// NewClientSession creates a new explicit client-side session.
func NewClientSession(pool *Pool, clientID uuid.UUID, opts ...*ClientOptions) (*Client, error) {
c := &Client{
pool: pool,
ClientID: clientID,
}
mergedOpts := mergeClientOptions(opts...)
if mergedOpts.DefaultReadPreference != nil {
c.transactionRp = mergedOpts.DefaultReadPreference
}
if mergedOpts.DefaultReadConcern != nil {
c.transactionRc = mergedOpts.DefaultReadConcern
}
if mergedOpts.DefaultWriteConcern != nil {
c.transactionWc = mergedOpts.DefaultWriteConcern
}
if mergedOpts.DefaultMaxCommitTime != nil {
c.transactionMaxCommitTime = mergedOpts.DefaultMaxCommitTime
}
if mergedOpts.Snapshot != nil {
c.Snapshot = *mergedOpts.Snapshot
}
// For explicit sessions, the default for causalConsistency is true, unless Snapshot is
// enabled, then it's false. Set the default and then allow any explicit causalConsistency
// setting to override it.
c.Consistent = !c.Snapshot
if mergedOpts.CausalConsistency != nil {
c.Consistent = *mergedOpts.CausalConsistency
}
if c.Consistent && c.Snapshot {
return nil, errors.New("causal consistency and snapshot cannot both be set for a session")
}
if err := c.SetServer(); err != nil {
return nil, err
}
return c, nil
}
// SetServer will check out a session from the client session pool.
func (c *Client) SetServer() error {
var err error
c.Server, err = c.pool.GetSession()
return err
}
// AdvanceClusterTime updates the session's cluster time.
func (c *Client) AdvanceClusterTime(clusterTime bson.Raw) error {
if c.Terminated {
return ErrSessionEnded
}
c.ClusterTime = MaxClusterTime(c.ClusterTime, clusterTime)
return nil
}
// AdvanceOperationTime updates the session's operation time.
func (c *Client) AdvanceOperationTime(opTime *primitive.Timestamp) error {
if c.Terminated {
return ErrSessionEnded
}
if c.OperationTime == nil {
c.OperationTime = opTime
return nil
}
if opTime.T > c.OperationTime.T {
c.OperationTime = opTime
} else if (opTime.T == c.OperationTime.T) && (opTime.I > c.OperationTime.I) {
c.OperationTime = opTime
}
return nil
}
// UpdateUseTime sets the session's last used time to the current time. This must be called whenever the session is
// used to send a command to the server to ensure that the session is not prematurely marked expired in the driver's
// session pool. If the session has already been ended, this method will return ErrSessionEnded.
func (c *Client) UpdateUseTime() error {
if c.Terminated {
return ErrSessionEnded
}
c.updateUseTime()
return nil
}
// UpdateRecoveryToken updates the session's recovery token from the server response.
func (c *Client) UpdateRecoveryToken(response bson.Raw) {
if c == nil {
return
}
token, err := response.LookupErr("recoveryToken")
if err != nil {
return
}
c.RecoveryToken = token.Document()
}
// UpdateSnapshotTime updates the session's value for the atClusterTime field of ReadConcern.
func (c *Client) UpdateSnapshotTime(response bsoncore.Document) {
if c == nil {
return
}
subDoc := response
if cur, ok := response.Lookup("cursor").DocumentOK(); ok {
subDoc = cur
}
ssTimeElem, err := subDoc.LookupErr("atClusterTime")
if err != nil {
// atClusterTime not included by the server
return
}
t, i := ssTimeElem.Timestamp()
c.SnapshotTime = &primitive.Timestamp{
T: t,
I: i,
}
}
// ClearPinnedResources clears the pinned server and/or connection associated with the session.
func (c *Client) ClearPinnedResources() error {
if c == nil {
return nil
}
c.PinnedServer = nil
if c.PinnedConnection != nil {
if err := c.PinnedConnection.UnpinFromTransaction(); err != nil {
return err
}
if err := c.PinnedConnection.Close(); err != nil {
return err
}
}
c.PinnedConnection = nil
return nil
}
// unpinConnection gracefully unpins the connection associated with the session
// if there is one. This is done via the pinned connection's
// UnpinFromTransaction function.
func (c *Client) unpinConnection() error {
if c == nil || c.PinnedConnection == nil {
return nil
}
err := c.PinnedConnection.UnpinFromTransaction()
closeErr := c.PinnedConnection.Close()
if err == nil && closeErr != nil {
err = closeErr
}
c.PinnedConnection = nil
return err
}
// EndSession ends the session.
func (c *Client) EndSession() {
if c.Terminated {
return
}
c.Terminated = true
// Ignore the error when unpinning the connection because we can't do
// anything about it if it doesn't work. Typically the only errors that can
// happen here indicate that something went wrong with the connection state,
// like it wasn't marked as pinned or attempted to return to the wrong pool.
_ = c.unpinConnection()
c.pool.ReturnSession(c.Server)
}
// TransactionInProgress returns true if the client session is in an active transaction.
func (c *Client) TransactionInProgress() bool {
return c.TransactionState == InProgress
}
// TransactionStarting returns true if the client session is starting a transaction.
func (c *Client) TransactionStarting() bool {
return c.TransactionState == Starting
}
// TransactionRunning returns true if the client session has started the transaction
// and it hasn't been committed or aborted
func (c *Client) TransactionRunning() bool {
return c != nil && (c.TransactionState == Starting || c.TransactionState == InProgress)
}
// TransactionCommitted returns true of the client session just committed a transaction.
func (c *Client) TransactionCommitted() bool {
return c.TransactionState == Committed
}
// CheckStartTransaction checks to see if allowed to start transaction and returns
// an error if not allowed
func (c *Client) CheckStartTransaction() error {
if c.TransactionState == InProgress || c.TransactionState == Starting {
return ErrTransactInProgress
}
if c.Snapshot {
return ErrSnapshotTransaction
}
return nil
}
// StartTransaction initializes the transaction options and advances the state machine.
// It does not contact the server to start the transaction.
func (c *Client) StartTransaction(opts *TransactionOptions) error {
err := c.CheckStartTransaction()
if err != nil {
return err
}
c.IncrementTxnNumber()
c.RetryingCommit = false
if opts != nil {
c.CurrentRc = opts.ReadConcern
c.CurrentRp = opts.ReadPreference
c.CurrentWc = opts.WriteConcern
c.CurrentMct = opts.MaxCommitTime
}
if c.CurrentRc == nil {
c.CurrentRc = c.transactionRc
}
if c.CurrentRp == nil {
c.CurrentRp = c.transactionRp
}
if c.CurrentWc == nil {
c.CurrentWc = c.transactionWc
}
if c.CurrentMct == nil {
c.CurrentMct = c.transactionMaxCommitTime
}
if !writeconcern.AckWrite(c.CurrentWc) {
_ = c.clearTransactionOpts()
return ErrUnackWCUnsupported
}
c.TransactionState = Starting
return c.ClearPinnedResources()
}
// CheckCommitTransaction checks to see if allowed to commit transaction and returns
// an error if not allowed.
func (c *Client) CheckCommitTransaction() error {
if c.TransactionState == None {
return ErrNoTransactStarted
} else if c.TransactionState == Aborted {
return ErrCommitAfterAbort
}
return nil
}
// CommitTransaction updates the state for a successfully committed transaction and returns
// an error if not permissible. It does not actually perform the commit.
func (c *Client) CommitTransaction() error {
err := c.CheckCommitTransaction()
if err != nil {
return err
}
c.TransactionState = Committed
return nil
}
// UpdateCommitTransactionWriteConcern will set the write concern to majority and potentially set a
// w timeout of 10 seconds. This should be called after a commit transaction operation fails with a
// retryable error or after a successful commit transaction operation.
func (c *Client) UpdateCommitTransactionWriteConcern() {
wc := c.CurrentWc
timeout := 10 * time.Second
if wc != nil && wc.GetWTimeout() != 0 {
timeout = wc.GetWTimeout()
}
c.CurrentWc = wc.WithOptions(writeconcern.WMajority(), writeconcern.WTimeout(timeout))
}
// CheckAbortTransaction checks to see if allowed to abort transaction and returns
// an error if not allowed.
func (c *Client) CheckAbortTransaction() error {
if c.TransactionState == None {
return ErrNoTransactStarted
} else if c.TransactionState == Committed {
return ErrAbortAfterCommit
} else if c.TransactionState == Aborted {
return ErrAbortTwice
}
return nil
}
// AbortTransaction updates the state for a successfully aborted transaction and returns
// an error if not permissible. It does not actually perform the abort.
func (c *Client) AbortTransaction() error {
err := c.CheckAbortTransaction()
if err != nil {
return err
}
c.TransactionState = Aborted
return c.clearTransactionOpts()
}
// StartCommand updates the session's internal state at the beginning of an operation. This must be called before
// server selection is done for the operation as the session's state can impact the result of that process.
func (c *Client) StartCommand() error {
if c == nil {
return nil
}
// If we're executing the first operation using this session after a transaction, we must ensure that the session
// is not pinned to any resources.
if !c.TransactionRunning() && !c.Committing && !c.Aborting {
return c.ClearPinnedResources()
}
return nil
}
// ApplyCommand advances the state machine upon command execution. This must be called after server selection is
// complete.
func (c *Client) ApplyCommand(desc description.Server) error {
if c.Committing {
// Do not change state if committing after already committed
return nil
}
if c.TransactionState == Starting {
c.TransactionState = InProgress
// If this is in a transaction and the server is a mongos, pin it
if desc.Kind == description.Mongos {
c.PinnedServer = &desc
}
} else if c.TransactionState == Committed || c.TransactionState == Aborted {
c.TransactionState = None
return c.clearTransactionOpts()
}
return nil
}
func (c *Client) clearTransactionOpts() error {
c.RetryingCommit = false
c.Aborting = false
c.Committing = false
c.CurrentWc = nil
c.CurrentRp = nil
c.CurrentRc = nil
c.RecoveryToken = nil
return c.ClearPinnedResources()
}