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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 (
"errors"
"github.com/mongodb/mongo-go-driver/bson"
"github.com/mongodb/mongo-go-driver/core/readconcern"
"github.com/mongodb/mongo-go-driver/core/readpref"
"github.com/mongodb/mongo-go-driver/core/uuid"
"github.com/mongodb/mongo-go-driver/core/writeconcern"
)
// 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 transaciton.
var ErrUnackWCUnsupported = errors.New("transactions do not support unacknowledged write concerns")
// Type describes the type of the session
type Type uint8
// These constants are the valid types for a client session.
const (
Explicit Type = iota
Implicit
)
// State indicates the state of the FSM.
type state uint8
// Client Session states
const (
None state = iota
Starting
InProgress
Committed
Aborted
)
// Client is a session for clients to run commands.
type Client struct {
*Server
ClientID uuid.UUID
ClusterTime *bson.Document
Consistent bool // causal consistency
OperationTime *bson.Timestamp
SessionType Type
Terminated bool
RetryingCommit bool
Committing bool
Aborting bool
RetryWrite bool
// options for the current transaction
// most recently set by transactionopt
CurrentRc *readconcern.ReadConcern
CurrentRp *readpref.ReadPref
CurrentWc *writeconcern.WriteConcern
// default transaction options
transactionRc *readconcern.ReadConcern
transactionRp *readpref.ReadPref
transactionWc *writeconcern.WriteConcern
pool *Pool
state state
}
func getClusterTime(clusterTime *bson.Document) (uint32, uint32) {
if clusterTime == nil {
return 0, 0
}
clusterTimeVal, err := clusterTime.LookupErr("$clusterTime")
if err != nil {
return 0, 0
}
timestampVal, err := clusterTimeVal.MutableDocument().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 *bson.Document, ct2 *bson.Document) *bson.Document {
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
}
// NewClientSession creates a Client.
func NewClientSession(pool *Pool, clientID uuid.UUID, sessionType Type, opts ...ClientOptioner) (*Client, error) {
c := &Client{
Consistent: true, // causal consistency defaults to true
ClientID: clientID,
SessionType: sessionType,
pool: pool,
}
var err error
for _, opt := range opts {
err = opt.Option(c)
if err != nil {
return nil, err
}
}
servSess, err := pool.GetSession()
if err != nil {
return nil, err
}
c.Server = servSess
return c, nil
}
// AdvanceClusterTime updates the session's cluster time.
func (c *Client) AdvanceClusterTime(clusterTime *bson.Document) 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 *bson.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 updates the session's last used time.
// Must be called whenver this session is used to send a command to the server.
func (c *Client) UpdateUseTime() error {
if c.Terminated {
return ErrSessionEnded
}
c.updateUseTime()
return nil
}
// EndSession ends the session.
func (c *Client) EndSession() {
if c.Terminated {
return
}
c.Terminated = true
c.pool.ReturnSession(c.Server)
return
}
// TransactionInProgress returns true if the client session is in an active transaction.
func (c *Client) TransactionInProgress() bool {
return c.state == InProgress
}
// TransactionStarting returns true if the client session is starting a transaction.
func (c *Client) TransactionStarting() bool {
return c.state == 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.state == Starting || c.state == InProgress
}
// TransactionCommitted returns true of the client session just committed a transaciton.
func (c *Client) TransactionCommitted() bool {
return c.state == Committed
}
// CheckStartTransaction checks to see if allowed to start transaction and returns
// an error if not allowed
func (c *Client) CheckStartTransaction() error {
if c.state == InProgress || c.state == Starting {
return ErrTransactInProgress
}
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 ...ClientOptioner) error {
err := c.CheckStartTransaction()
if err != nil {
return err
}
c.IncrementTxnNumber()
c.RetryingCommit = false
for _, opt := range opts {
err := opt.Option(c)
if err != nil {
return err
}
}
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 !writeconcern.AckWrite(c.CurrentWc) {
c.clearTransactionOpts()
return ErrUnackWCUnsupported
}
c.state = Starting
return nil
}
// CheckCommitTransaction checks to see if allowed to commit transaction and returns
// an error if not allowed.
func (c *Client) CheckCommitTransaction() error {
if c.state == None {
return ErrNoTransactStarted
} else if c.state == 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.state = Committed
return nil
}
// CheckAbortTransaction checks to see if allowed to abort transaction and returns
// an error if not allowed.
func (c *Client) CheckAbortTransaction() error {
if c.state == None {
return ErrNoTransactStarted
} else if c.state == Committed {
return ErrAbortAfterCommit
} else if c.state == Aborted {
return ErrAbortTwice
}
return nil
}
// AbortTransaction updates the state for a successfully committed 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.state = Aborted
c.clearTransactionOpts()
return nil
}
// ApplyCommand advances the state machine upon command execution.
func (c *Client) ApplyCommand() {
if c.Committing {
// Do not change state if committing after already committed
return
}
if c.state == Starting {
c.state = InProgress
} else if c.state == Committed || c.state == Aborted {
c.clearTransactionOpts()
c.state = None
}
}
func (c *Client) clearTransactionOpts() {
c.RetryingCommit = false
c.Aborting = false
c.Committing = false
c.CurrentWc = nil
c.CurrentRp = nil
c.CurrentRc = nil
}