// Copyright 2011 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
// Package sql provides a generic interface around SQL (or SQL-like)
// databases.
//
// The sql package must be used in conjunction with a database driver.
// See https://golang.org/s/sqldrivers for a list of drivers.
//
// Drivers that do not support context cancellation will not return until
// after the query is completed.
//
// For usage examples, see the wiki page at
// https://golang.org/s/sqlwiki.
package sql
import (
"context"
"database/sql/driver"
"errors"
"fmt"
"io"
"reflect"
"runtime"
"sort"
"strconv"
"sync"
"sync/atomic"
"time"
)
var (
driversMu sync.RWMutex
drivers = make(map[string]driver.Driver)
)
// nowFunc returns the current time; it's overridden in tests.
var nowFunc = time.Now
// Register makes a database driver available by the provided name.
// If Register is called twice with the same name or if driver is nil,
// it panics.
func Register(name string, driver driver.Driver) {
driversMu.Lock()
defer driversMu.Unlock()
if driver == nil {
panic("sql: Register driver is nil")
}
if _, dup := drivers[name]; dup {
panic("sql: Register called twice for driver " + name)
}
drivers[name] = driver
}
func unregisterAllDrivers() {
driversMu.Lock()
defer driversMu.Unlock()
// For tests.
drivers = make(map[string]driver.Driver)
}
// Drivers returns a sorted list of the names of the registered drivers.
func Drivers() []string {
driversMu.RLock()
defer driversMu.RUnlock()
var list []string
for name := range drivers {
list = append(list, name)
}
sort.Strings(list)
return list
}
// A NamedArg is a named argument. NamedArg values may be used as
// arguments to Query or Exec and bind to the corresponding named
// parameter in the SQL statement.
//
// For a more concise way to create NamedArg values, see
// the Named function.
type NamedArg struct {
_Named_Fields_Required struct{}
// Name is the name of the parameter placeholder.
//
// If empty, the ordinal position in the argument list will be
// used.
//
// Name must omit any symbol prefix.
Name string
// Value is the value of the parameter.
// It may be assigned the same value types as the query
// arguments.
Value interface{}
}
// Named provides a more concise way to create NamedArg values.
//
// Example usage:
//
// db.ExecContext(ctx, `
// delete from Invoice
// where
// TimeCreated < @end
// and TimeCreated >= @start;`,
// sql.Named("start", startTime),
// sql.Named("end", endTime),
// )
func Named(name string, value interface{}) NamedArg {
// This method exists because the go1compat promise
// doesn't guarantee that structs don't grow more fields,
// so unkeyed struct literals are a vet error. Thus, we don't
// want to allow sql.NamedArg{name, value}.
return NamedArg{Name: name, Value: value}
}
// IsolationLevel is the transaction isolation level used in TxOptions.
type IsolationLevel int
// Various isolation levels that drivers may support in BeginTx.
// If a driver does not support a given isolation level an error may be returned.
//
// See https://en.wikipedia.org/wiki/Isolation_(database_systems)#Isolation_levels.
const (
LevelDefault IsolationLevel = iota
LevelReadUncommitted
LevelReadCommitted
LevelWriteCommitted
LevelRepeatableRead
LevelSnapshot
LevelSerializable
LevelLinearizable
)
// String returns the name of the transaction isolation level.
func (i IsolationLevel) String() string {
switch i {
case LevelDefault:
return "Default"
case LevelReadUncommitted:
return "Read Uncommitted"
case LevelReadCommitted:
return "Read Committed"
case LevelWriteCommitted:
return "Write Committed"
case LevelRepeatableRead:
return "Repeatable Read"
case LevelSnapshot:
return "Snapshot"
case LevelSerializable:
return "Serializable"
case LevelLinearizable:
return "Linearizable"
default:
return "IsolationLevel(" + strconv.Itoa(int(i)) + ")"
}
}
var _ fmt.Stringer = LevelDefault
// TxOptions holds the transaction options to be used in DB.BeginTx.
type TxOptions struct {
// Isolation is the transaction isolation level.
// If zero, the driver or database's default level is used.
Isolation IsolationLevel
ReadOnly bool
}
// RawBytes is a byte slice that holds a reference to memory owned by
// the database itself. After a Scan into a RawBytes, the slice is only
// valid until the next call to Next, Scan, or Close.
type RawBytes []byte
// NullString represents a string that may be null.
// NullString implements the Scanner interface so
// it can be used as a scan destination:
//
// var s NullString
// err := db.QueryRow("SELECT name FROM foo WHERE id=?", id).Scan(&s)
// ...
// if s.Valid {
// // use s.String
// } else {
// // NULL value
// }
//
type NullString struct {
String string
Valid bool // Valid is true if String is not NULL
}
// Scan implements the Scanner interface.
func (ns *NullString) Scan(value interface{}) error {
if value == nil {
ns.String, ns.Valid = "", false
return nil
}
ns.Valid = true
return convertAssign(&ns.String, value)
}
// Value implements the driver Valuer interface.
func (ns NullString) Value() (driver.Value, error) {
if !ns.Valid {
return nil, nil
}
return ns.String, nil
}
// NullInt64 represents an int64 that may be null.
// NullInt64 implements the Scanner interface so
// it can be used as a scan destination, similar to NullString.
type NullInt64 struct {
Int64 int64
Valid bool // Valid is true if Int64 is not NULL
}
// Scan implements the Scanner interface.
func (n *NullInt64) Scan(value interface{}) error {
if value == nil {
n.Int64, n.Valid = 0, false
return nil
}
n.Valid = true
return convertAssign(&n.Int64, value)
}
// Value implements the driver Valuer interface.
func (n NullInt64) Value() (driver.Value, error) {
if !n.Valid {
return nil, nil
}
return n.Int64, nil
}
// NullInt32 represents an int32 that may be null.
// NullInt32 implements the Scanner interface so
// it can be used as a scan destination, similar to NullString.
type NullInt32 struct {
Int32 int32
Valid bool // Valid is true if Int32 is not NULL
}
// Scan implements the Scanner interface.
func (n *NullInt32) Scan(value interface{}) error {
if value == nil {
n.Int32, n.Valid = 0, false
return nil
}
n.Valid = true
return convertAssign(&n.Int32, value)
}
// Value implements the driver Valuer interface.
func (n NullInt32) Value() (driver.Value, error) {
if !n.Valid {
return nil, nil
}
return int64(n.Int32), nil
}
// NullFloat64 represents a float64 that may be null.
// NullFloat64 implements the Scanner interface so
// it can be used as a scan destination, similar to NullString.
type NullFloat64 struct {
Float64 float64
Valid bool // Valid is true if Float64 is not NULL
}
// Scan implements the Scanner interface.
func (n *NullFloat64) Scan(value interface{}) error {
if value == nil {
n.Float64, n.Valid = 0, false
return nil
}
n.Valid = true
return convertAssign(&n.Float64, value)
}
// Value implements the driver Valuer interface.
func (n NullFloat64) Value() (driver.Value, error) {
if !n.Valid {
return nil, nil
}
return n.Float64, nil
}
// NullBool represents a bool that may be null.
// NullBool implements the Scanner interface so
// it can be used as a scan destination, similar to NullString.
type NullBool struct {
Bool bool
Valid bool // Valid is true if Bool is not NULL
}
// Scan implements the Scanner interface.
func (n *NullBool) Scan(value interface{}) error {
if value == nil {
n.Bool, n.Valid = false, false
return nil
}
n.Valid = true
return convertAssign(&n.Bool, value)
}
// Value implements the driver Valuer interface.
func (n NullBool) Value() (driver.Value, error) {
if !n.Valid {
return nil, nil
}
return n.Bool, nil
}
// NullTime represents a time.Time that may be null.
// NullTime implements the Scanner interface so
// it can be used as a scan destination, similar to NullString.
type NullTime struct {
Time time.Time
Valid bool // Valid is true if Time is not NULL
}
// Scan implements the Scanner interface.
func (n *NullTime) Scan(value interface{}) error {
if value == nil {
n.Time, n.Valid = time.Time{}, false
return nil
}
n.Valid = true
return convertAssign(&n.Time, value)
}
// Value implements the driver Valuer interface.
func (n NullTime) Value() (driver.Value, error) {
if !n.Valid {
return nil, nil
}
return n.Time, nil
}
// Scanner is an interface used by Scan.
type Scanner interface {
// Scan assigns a value from a database driver.
//
// The src value will be of one of the following types:
//
// int64
// float64
// bool
// []byte
// string
// time.Time
// nil - for NULL values
//
// An error should be returned if the value cannot be stored
// without loss of information.
//
// Reference types such as []byte are only valid until the next call to Scan
// and should not be retained. Their underlying memory is owned by the driver.
// If retention is necessary, copy their values before the next call to Scan.
Scan(src interface{}) error
}
// Out may be used to retrieve OUTPUT value parameters from stored procedures.
//
// Not all drivers and databases support OUTPUT value parameters.
//
// Example usage:
//
// var outArg string
// _, err := db.ExecContext(ctx, "ProcName", sql.Named("Arg1", sql.Out{Dest: &outArg}))
type Out struct {
_Named_Fields_Required struct{}
// Dest is a pointer to the value that will be set to the result of the
// stored procedure's OUTPUT parameter.
Dest interface{}
// In is whether the parameter is an INOUT parameter. If so, the input value to the stored
// procedure is the dereferenced value of Dest's pointer, which is then replaced with
// the output value.
In bool
}
// ErrNoRows is returned by Scan when QueryRow doesn't return a
// row. In such a case, QueryRow returns a placeholder *Row value that
// defers this error until a Scan.
var ErrNoRows = errors.New("sql: no rows in result set")
// DB is a database handle representing a pool of zero or more
// underlying connections. It's safe for concurrent use by multiple
// goroutines.
//
// The sql package creates and frees connections automatically; it
// also maintains a free pool of idle connections. If the database has
// a concept of per-connection state, such state can be reliably observed
// within a transaction (Tx) or connection (Conn). Once DB.Begin is called, the
// returned Tx is bound to a single connection. Once Commit or
// Rollback is called on the transaction, that transaction's
// connection is returned to DB's idle connection pool. The pool size
// can be controlled with SetMaxIdleConns.
type DB struct {
// Atomic access only. At top of struct to prevent mis-alignment
// on 32-bit platforms. Of type time.Duration.
waitDuration int64 // Total time waited for new connections.
connector driver.Connector
// numClosed is an atomic counter which represents a total number of
// closed connections. Stmt.openStmt checks it before cleaning closed
// connections in Stmt.css.
numClosed uint64
mu sync.Mutex // protects following fields
freeConn []*driverConn
connRequests map[uint64]chan connRequest
nextRequest uint64 // Next key to use in connRequests.
numOpen int // number of opened and pending open connections
// Used to signal the need for new connections
// a goroutine running connectionOpener() reads on this chan and
// maybeOpenNewConnections sends on the chan (one send per needed connection)
// It is closed during db.Close(). The close tells the connectionOpener
// goroutine to exit.
openerCh chan struct{}
resetterCh chan *driverConn
closed bool
dep map[finalCloser]depSet
lastPut map[*driverConn]string // stacktrace of last conn's put; debug only
maxIdle int // zero means defaultMaxIdleConns; negative means 0
maxOpen int // <= 0 means unlimited
maxLifetime time.Duration // maximum amount of time a connection may be reused
cleanerCh chan struct{}
waitCount int64 // Total number of connections waited for.
maxIdleClosed int64 // Total number of connections closed due to idle.
maxLifetimeClosed int64 // Total number of connections closed due to max free limit.
stop func() // stop cancels the connection opener and the session resetter.
}
// connReuseStrategy determines how (*DB).conn returns database connections.
type connReuseStrategy uint8
const (
// alwaysNewConn forces a new connection to the database.
alwaysNewConn connReuseStrategy = iota
// cachedOrNewConn returns a cached connection, if available, else waits
// for one to become available (if MaxOpenConns has been reached) or
// creates a new database connection.
cachedOrNewConn
)
// driverConn wraps a driver.Conn with a mutex, to
// be held during all calls into the Conn. (including any calls onto
// interfaces returned via that Conn, such as calls on Tx, Stmt,
// Result, Rows)
type driverConn struct {
db *DB
createdAt time.Time
sync.Mutex // guards following
ci driver.Conn
closed bool
finalClosed bool // ci.Close has been called
openStmt map[*driverStmt]bool
lastErr error // lastError captures the result of the session resetter.
// guarded by db.mu
inUse bool
onPut []func() // code (with db.mu held) run when conn is next returned
dbmuClosed bool // same as closed, but guarded by db.mu, for removeClosedStmtLocked
}
func (dc *driverConn) releaseConn(err error) {
dc.db.putConn(dc, err, true)
}
func (dc *driverConn) removeOpenStmt(ds *driverStmt) {
dc.Lock()
defer dc.Unlock()
delete(dc.openStmt, ds)
}
func (dc *driverConn) expired(timeout time.Duration) bool {
if timeout <= 0 {
return false
}
return dc.createdAt.Add(timeout).Before(nowFunc())
}
// prepareLocked prepares the query on dc. When cg == nil the dc must keep track of
// the prepared statements in a pool.
func (dc *driverConn) prepareLocked(ctx context.Context, cg stmtConnGrabber, query string) (*driverStmt, error) {
si, err := ctxDriverPrepare(ctx, dc.ci, query)
if err != nil {
return nil, err
}
ds := &driverStmt{Locker: dc, si: si}
// No need to manage open statements if there is a single connection grabber.
if cg != nil {
return ds, nil
}
// Track each driverConn's open statements, so we can close them
// before closing the conn.
//
// Wrap all driver.Stmt is *driverStmt to ensure they are only closed once.
if dc.openStmt == nil {
dc.openStmt = make(map[*driverStmt]bool)
}
dc.openStmt[ds] = true
return ds, nil
}
// resetSession resets the connection session and sets the lastErr
// that is checked before returning the connection to another query.
//
// resetSession assumes that the embedded mutex is locked when the connection
// was returned to the pool. This unlocks the mutex.
func (dc *driverConn) resetSession(ctx context.Context) {
defer dc.Unlock() // In case of panic.
if dc.closed { // Check if the database has been closed.
return
}
dc.lastErr = dc.ci.(driver.SessionResetter).ResetSession(ctx)
}
// the dc.db's Mutex is held.
func (dc *driverConn) closeDBLocked() func() error {
dc.Lock()
defer dc.Unlock()
if dc.closed {
return func() error { return errors.New("sql: duplicate driverConn close") }
}
dc.closed = true
return dc.db.removeDepLocked(dc, dc)
}
func (dc *driverConn) Close() error {
dc.Lock()
if dc.closed {
dc.Unlock()
return errors.New("sql: duplicate driverConn close")
}
dc.closed = true
dc.Unlock() // not defer; removeDep finalClose calls may need to lock
// And now updates that require holding dc.mu.Lock.
dc.db.mu.Lock()
dc.dbmuClosed = true
fn := dc.db.removeDepLocked(dc, dc)
dc.db.mu.Unlock()
return fn()
}
func (dc *driverConn) finalClose() error {
var err error
// Each *driverStmt has a lock to the dc. Copy the list out of the dc
// before calling close on each stmt.
var openStmt []*driverStmt
withLock(dc, func() {
openStmt = make([]*driverStmt, 0, len(dc.openStmt))
for ds := range dc.openStmt {
openStmt = append(openStmt, ds)
}
dc.openStmt = nil
})
for _, ds := range openStmt {
ds.Close()
}
withLock(dc, func() {
dc.finalClosed = true
err = dc.ci.Close()
dc.ci = nil
})
dc.db.mu.Lock()
dc.db.numOpen--
dc.db.maybeOpenNewConnections()
dc.db.mu.Unlock()
atomic.AddUint64(&dc.db.numClosed, 1)
return err
}
// driverStmt associates a driver.Stmt with the
// *driverConn from which it came, so the driverConn's lock can be
// held during calls.
type driverStmt struct {
sync.Locker // the *driverConn
si driver.Stmt
closed bool
closeErr error // return value of previous Close call
}
// Close ensures driver.Stmt is only closed once and always returns the same
// result.
func (ds *driverStmt) Close() error {
ds.Lock()
defer ds.Unlock()
if ds.closed {
return ds.closeErr
}
ds.closed = true
ds.closeErr = ds.si.Close()
return ds.closeErr
}
// depSet is a finalCloser's outstanding dependencies
type depSet map[interface{}]bool // set of true bools
// The finalCloser interface is used by (*DB).addDep and related
// dependency reference counting.
type finalCloser interface {
// finalClose is called when the reference count of an object
// goes to zero. (*DB).mu is not held while calling it.
finalClose() error
}
// addDep notes that x now depends on dep, and x's finalClose won't be
// called until all of x's dependencies are removed with removeDep.
func (db *DB) addDep(x finalCloser, dep interface{}) {
db.mu.Lock()
defer db.mu.Unlock()
db.addDepLocked(x, dep)
}
func (db *DB) addDepLocked(x finalCloser, dep interface{}) {
if db.dep == nil {
db.dep = make(map[finalCloser]depSet)
}
xdep := db.dep[x]
if xdep == nil {
xdep = make(depSet)
db.dep[x] = xdep
}
xdep[dep] = true
}
// removeDep notes that x no longer depends on dep.
// If x still has dependencies, nil is returned.
// If x no longer has any dependencies, its finalClose method will be
// called and its error value will be returned.
func (db *DB) removeDep(x finalCloser, dep interface{}) error {
db.mu.Lock()
fn := db.removeDepLocked(x, dep)
db.mu.Unlock()
return fn()
}
func (db *DB) removeDepLocked(x finalCloser, dep interface{}) func() error {
xdep, ok := db.dep[x]
if !ok {
panic(fmt.Sprintf("unpaired removeDep: no deps for %T", x))
}
l0 := len(xdep)
delete(xdep, dep)
switch len(xdep) {
case l0:
// Nothing removed. Shouldn't happen.
panic(fmt.Sprintf("unpaired removeDep: no %T dep on %T", dep, x))
case 0:
// No more dependencies.
delete(db.dep, x)
return x.finalClose
default:
// Dependencies remain.
return func() error { return nil }
}
}
// This is the size of the connectionOpener request chan (DB.openerCh).
// This value should be larger than the maximum typical value
// used for db.maxOpen. If maxOpen is significantly larger than
// connectionRequestQueueSize then it is possible for ALL calls into the *DB
// to block until the connectionOpener can satisfy the backlog of requests.
var connectionRequestQueueSize = 1000000
type dsnConnector struct {
dsn string
driver driver.Driver
}
func (t dsnConnector) Connect(_ context.Context) (driver.Conn, error) {
return t.driver.Open(t.dsn)
}
func (t dsnConnector) Driver() driver.Driver {
return t.driver
}
// OpenDB opens a database using a Connector, allowing drivers to
// bypass a string based data source name.
//
// Most users will open a database via a driver-specific connection
// helper function that returns a *DB. No database drivers are included
// in the Go standard library. See https://golang.org/s/sqldrivers for
// a list of third-party drivers.
//
// OpenDB may just validate its arguments without creating a connection
// to the database. To verify that the data source name is valid, call
// Ping.
//
// The returned DB is safe for concurrent use by multiple goroutines
// and maintains its own pool of idle connections. Thus, the OpenDB
// function should be called just once. It is rarely necessary to
// close a DB.
func OpenDB(c driver.Connector) *DB {
ctx, cancel := context.WithCancel(context.Background())
db := &DB{
connector: c,
openerCh: make(chan struct{}, connectionRequestQueueSize),
resetterCh: make(chan *driverConn, 50),
lastPut: make(map[*driverConn]string),
connRequests: make(map[uint64]chan connRequest),
stop: cancel,
}
go db.connectionOpener(ctx)
go db.connectionResetter(ctx)
return db
}
// Open opens a database specified by its database driver name and a
// driver-specific data source name, usually consisting of at least a
// database name and connection information.
//
// Most users will open a database via a driver-specific connection
// helper function that returns a *DB. No database drivers are included
// in the Go standard library. See https://golang.org/s/sqldrivers for
// a list of third-party drivers.
//
// Open may just validate its arguments without creating a connection
// to the database. To verify that the data source name is valid, call
// Ping.
//
// The returned DB is safe for concurrent use by multiple goroutines
// and maintains its own pool of idle connections. Thus, the Open
// function should be called just once. It is rarely necessary to
// close a DB.
func Open(driverName, dataSourceName string) (*DB, error) {
driversMu.RLock()
driveri, ok := drivers[driverName]
driversMu.RUnlock()
if !ok {
return nil, fmt.Errorf("sql: unknown driver %q (forgotten import?)", driverName)
}
if driverCtx, ok := driveri.(driver.DriverContext); ok {
connector, err := driverCtx.OpenConnector(dataSourceName)
if err != nil {
return nil, err
}
return OpenDB(connector), nil
}
return OpenDB(dsnConnector{dsn: dataSourceName, driver: driveri}), nil
}
func (db *DB) pingDC(ctx context.Context, dc *driverConn, release func(error)) error {
var err error
if pinger, ok := dc.ci.(driver.Pinger); ok {
withLock(dc, func() {
err = pinger.Ping(ctx)
})
}
release(err)
return err
}
// PingContext verifies a connection to the database is still alive,
// establishing a connection if necessary.
func (db *DB) PingContext(ctx context.Context) error {
var dc *driverConn
var err error
for i := 0; i < maxBadConnRetries; i++ {
dc, err = db.conn(ctx, cachedOrNewConn)
if err != driver.ErrBadConn {
break
}
}
if err == driver.ErrBadConn {
dc, err = db.conn(ctx, alwaysNewConn)
}
if err != nil {
return err
}
return db.pingDC(ctx, dc, dc.releaseConn)
}
// Ping verifies a connection to the database is still alive,
// establishing a connection if necessary.
func (db *DB) Ping() error {
return db.PingContext(context.Background())
}
// Close closes the database and prevents new queries from starting.
// Close then waits for all queries that have started processing on the server
// to finish.
//
// It is rare to Close a DB, as the DB handle is meant to be
// long-lived and shared between many goroutines.
func (db *DB) Close() error {
db.mu.Lock()
if db.closed { // Make DB.Close idempotent
db.mu.Unlock()
return nil
}
if db.cleanerCh != nil {
close(db.cleanerCh)
}
var err error
fns := make([]func() error, 0, len(db.freeConn))
for _, dc := range db.freeConn {
fns = append(fns, dc.closeDBLocked())
}
db.freeConn = nil
db.closed = true
for _, req := range db.connRequests {
close(req)
}
db.mu.Unlock()
for _, fn := range fns {
err1 := fn()
if err1 != nil {
err = err1
}
}
db.stop()
return err
}
const defaultMaxIdleConns = 2
func (db *DB) maxIdleConnsLocked() int {
n := db.maxIdle
switch {
case n == 0:
// TODO(bradfitz): ask driver, if supported, for its default preference
return defaultMaxIdleConns
case n < 0:
return 0
default:
return n
}
}
// SetMaxIdleConns sets the maximum number of connections in the idle
// connection pool.
//
// If MaxOpenConns is greater than 0 but less than the new MaxIdleConns,
// then the new MaxIdleConns will be reduced to match the MaxOpenConns limit.
//
// If n <= 0, no idle connections are retained.
//
// The default max idle connections is currently 2. This may change in
// a future release.
func (db *DB) SetMaxIdleConns(n int) {
db.mu.Lock()
if n > 0 {
db.maxIdle = n
} else {
// No idle connections.
db.maxIdle = -1
}
// Make sure maxIdle doesn't exceed maxOpen
if db.maxOpen > 0 && db.maxIdleConnsLocked() > db.maxOpen {
db.maxIdle = db.maxOpen
}
var closing []*driverConn
idleCount := len(db.freeConn)
maxIdle := db.maxIdleConnsLocked()
if idleCount > maxIdle {
closing = db.freeConn[maxIdle:]
db.freeConn = db.freeConn[:maxIdle]
}
db.maxIdleClosed += int64(len(closing))
db.mu.Unlock()
for _, c := range closing {
c.Close()
}
}
// SetMaxOpenConns sets the maximum number of open connections to the database.
//
// If MaxIdleConns is greater than 0 and the new MaxOpenConns is less than
// MaxIdleConns, then MaxIdleConns will be reduced to match the new
// MaxOpenConns limit.
//
// If n <= 0, then there is no limit on the number of open connections.
// The default is 0 (unlimited).
func (db *DB) SetMaxOpenConns(n int) {
db.mu.Lock()
db.maxOpen = n
if n < 0 {
db.maxOpen = 0
}
syncMaxIdle := db.maxOpen > 0 && db.maxIdleConnsLocked() > db.maxOpen
db.mu.Unlock()
if syncMaxIdle {
db.SetMaxIdleConns(n)
}
}
// SetConnMaxLifetime sets the maximum amount of time a connection may be reused.
//
// Expired connections may be closed lazily before reuse.
//
// If d <= 0, connections are reused forever.
func (db *DB) SetConnMaxLifetime(d time.Duration) {
if d < 0 {
d = 0
}
db.mu.Lock()
// wake cleaner up when lifetime is shortened.
if d > 0 && d < db.maxLifetime && db.cleanerCh != nil {
select {
case db.cleanerCh <- struct{}{}:
default:
}
}
db.maxLifetime = d
db.startCleanerLocked()
db.mu.Unlock()
}
// startCleanerLocked starts connectionCleaner if needed.
func (db *DB) startCleanerLocked() {
if db.maxLifetime > 0 && db.numOpen > 0 && db.cleanerCh == nil {
db.cleanerCh = make(chan struct{}, 1)
go db.connectionCleaner(db.maxLifetime)
}
}
func (db *DB) connectionCleaner(d time.Duration) {
const minInterval = time.Second
if d < minInterval {
d = minInterval
}
t := time.NewTimer(d)
for {
select {
case <-t.C:
case <-db.cleanerCh: // maxLifetime was changed or db was closed.
}
db.mu.Lock()
d = db.maxLifetime
if db.closed || db.numOpen == 0 || d <= 0 {
db.cleanerCh = nil
db.mu.Unlock()
return
}
expiredSince := nowFunc().Add(-d)
var closing []*driverConn
for i := 0; i < len(db.freeConn); i++ {
c := db.freeConn[i]
if c.createdAt.Before(expiredSince) {
closing = append(closing, c)
last := len(db.freeConn) - 1
db.freeConn[i] = db.freeConn[last]
db.freeConn[last] = nil
db.freeConn = db.freeConn[:last]
i--
}
}
db.maxLifetimeClosed += int64(len(closing))
db.mu.Unlock()
for _, c := range closing {
c.Close()
}
if d < minInterval {
d = minInterval
}
t.Reset(d)
}
}
// DBStats contains database statistics.
type DBStats struct {
MaxOpenConnections int // Maximum number of open connections to the database.
// Pool Status
OpenConnections int // The number of established connections both in use and idle.
InUse int // The number of connections currently in use.
Idle int // The number of idle connections.
// Counters
WaitCount int64 // The total number of connections waited for.
WaitDuration time.Duration // The total time blocked waiting for a new connection.
MaxIdleClosed int64 // The total number of connections closed due to SetMaxIdleConns.
MaxLifetimeClosed int64 // The total number of connections closed due to SetConnMaxLifetime.
}
// Stats returns database statistics.
func (db *DB) Stats() DBStats {
wait := atomic.LoadInt64(&db.waitDuration)
db.mu.Lock()
defer db.mu.Unlock()
stats := DBStats{
MaxOpenConnections: db.maxOpen,
Idle: len(db.freeConn),
OpenConnections: db.numOpen,
InUse: db.numOpen - len(db.freeConn),
WaitCount: db.waitCount,
WaitDuration: time.Duration(wait),
MaxIdleClosed: db.maxIdleClosed,
MaxLifetimeClosed: db.maxLifetimeClosed,
}
return stats
}
// Assumes db.mu is locked.
// If there are connRequests and the connection limit hasn't been reached,
// then tell the connectionOpener to open new connections.
func (db *DB) maybeOpenNewConnections() {
numRequests := len(db.connRequests)
if db.maxOpen > 0 {
numCanOpen := db.maxOpen - db.numOpen
if numRequests > numCanOpen {
numRequests = numCanOpen
}
}
for numRequests > 0 {
db.numOpen++ // optimistically
numRequests--
if db.closed {
return
}
db.openerCh <- struct{}{}
}
}
// Runs in a separate goroutine, opens new connections when requested.
func (db *DB) connectionOpener(ctx context.Context) {
for {
select {
case <-ctx.Done():
return
case <-db.openerCh:
db.openNewConnection(ctx)
}
}
}
// connectionResetter runs in a separate goroutine to reset connections async
// to exported API.
func (db *DB) connectionResetter(ctx context.Context) {
for {
select {
case <-ctx.Done():
close(db.resetterCh)
for dc := range db.resetterCh {
dc.Unlock()
}
return
case dc := <-db.resetterCh:
dc.resetSession(ctx)
}
}
}
// Open one new connection
func (db *DB) openNewConnection(ctx context.Context) {
// maybeOpenNewConnctions has already executed db.numOpen++ before it sent
// on db.openerCh. This function must execute db.numOpen-- if the
// connection fails or is closed before returning.
ci, err := db.connector.Connect(ctx)
db.mu.Lock()
defer db.mu.Unlock()
if db.closed {
if err == nil {
ci.Close()
}
db.numOpen--
return
}
if err != nil {
db.numOpen--
db.putConnDBLocked(nil, err)
db.maybeOpenNewConnections()
return
}
dc := &driverConn{
db: db,
createdAt: nowFunc(),
ci: ci,
}
if db.putConnDBLocked(dc, err) {
db.addDepLocked(dc, dc)
} else {
db.numOpen--
ci.Close()
}
}
// connRequest represents one request for a new connection
// When there are no idle connections available, DB.conn will create
// a new connRequest and put it on the db.connRequests list.
type connRequest struct {
conn *driverConn
err error
}
var errDBClosed = errors.New("sql: database is closed")
// nextRequestKeyLocked returns the next connection request key.
// It is assumed that nextRequest will not overflow.
func (db *DB) nextRequestKeyLocked() uint64 {
next := db.nextRequest
db.nextRequest++
return next
}
// conn returns a newly-opened or cached *driverConn.
func (db *DB) conn(ctx context.Context, strategy connReuseStrategy) (*driverConn, error) {
db.mu.Lock()
if db.closed {
db.mu.Unlock()
return nil, errDBClosed
}
// Check if the context is expired.
select {
default:
case <-ctx.Done():
db.mu.Unlock()
return nil, ctx.Err()
}
lifetime := db.maxLifetime
// Prefer a free connection, if possible.
numFree := len(db.freeConn)
if strategy == cachedOrNewConn && numFree > 0 {
conn := db.freeConn[0]
copy(db.freeConn, db.freeConn[1:])
db.freeConn = db.freeConn[:numFree-1]
conn.inUse = true
db.mu.Unlock()
if conn.expired(lifetime) {
conn.Close()
return nil, driver.ErrBadConn
}
// Lock around reading lastErr to ensure the session resetter finished.
conn.Lock()
err := conn.lastErr
conn.Unlock()
if err == driver.ErrBadConn {
conn.Close()
return nil, driver.ErrBadConn
}
return conn, nil
}
// Out of free connections or we were asked not to use one. If we're not
// allowed to open any more connections, make a request and wait.
if db.maxOpen > 0 && db.numOpen >= db.maxOpen {
// Make the connRequest channel. It's buffered so that the
// connectionOpener doesn't block while waiting for the req to be read.
req := make(chan connRequest, 1)
reqKey := db.nextRequestKeyLocked()
db.connRequests[reqKey] = req
db.waitCount++
db.mu.Unlock()
waitStart := time.Now()
// Timeout the connection request with the context.
select {
case <-ctx.Done():
// Remove the connection request and ensure no value has been sent
// on it after removing.
db.mu.Lock()
delete(db.connRequests, reqKey)
db.mu.Unlock()
atomic.AddInt64(&db.waitDuration, int64(time.Since(waitStart)))
select {
default:
case ret, ok := <-req:
if ok && ret.conn != nil {
db.putConn(ret.conn, ret.err, false)
}
}
return nil, ctx.Err()
case ret, ok := <-req:
atomic.AddInt64(&db.waitDuration, int64(time.Since(waitStart)))
if !ok {
return nil, errDBClosed
}
if ret.err == nil && ret.conn.expired(lifetime) {
ret.conn.Close()
return nil, driver.ErrBadConn
}
if ret.conn == nil {
return nil, ret.err
}
// Lock around reading lastErr to ensure the session resetter finished.
ret.conn.Lock()
err := ret.conn.lastErr
ret.conn.Unlock()
if err == driver.ErrBadConn {
ret.conn.Close()
return nil, driver.ErrBadConn
}
return ret.conn, ret.err
}
}
db.numOpen++ // optimistically
db.mu.Unlock()
ci, err := db.connector.Connect(ctx)
if err != nil {
db.mu.Lock()
db.numOpen-- // correct for earlier optimism
db.maybeOpenNewConnections()
db.mu.Unlock()
return nil, err
}
db.mu.Lock()
dc := &driverConn{
db: db,
createdAt: nowFunc(),
ci: ci,
inUse: true,
}
db.addDepLocked(dc, dc)
db.mu.Unlock()
return dc, nil
}
// putConnHook is a hook for testing.
var putConnHook func(*DB, *driverConn)
// noteUnusedDriverStatement notes that ds is no longer used and should
// be closed whenever possible (when c is next not in use), unless c is
// already closed.
func (db *DB) noteUnusedDriverStatement(c *driverConn, ds *driverStmt) {
db.mu.Lock()
defer db.mu.Unlock()
if c.inUse {
c.onPut = append(c.onPut, func() {
ds.Close()
})
} else {
c.Lock()
fc := c.finalClosed
c.Unlock()
if !fc {
ds.Close()
}
}
}
// debugGetPut determines whether getConn & putConn calls' stack traces
// are returned for more verbose crashes.
const debugGetPut = false
// putConn adds a connection to the db's free pool.
// err is optionally the last error that occurred on this connection.
func (db *DB) putConn(dc *driverConn, err error, resetSession bool) {
db.mu.Lock()
if !dc.inUse {
if debugGetPut {
fmt.Printf("putConn(%v) DUPLICATE was: %s\n\nPREVIOUS was: %s", dc, stack(), db.lastPut[dc])
}
panic("sql: connection returned that was never out")
}
if debugGetPut {
db.lastPut[dc] = stack()
}
dc.inUse = false
for _, fn := range dc.onPut {
fn()
}
dc.onPut = nil
if err == driver.ErrBadConn {
// Don't reuse bad connections.
// Since the conn is considered bad and is being discarded, treat it
// as closed. Don't decrement the open count here, finalClose will
// take care of that.
db.maybeOpenNewConnections()
db.mu.Unlock()
dc.Close()
return
}
if putConnHook != nil {
putConnHook(db, dc)
}
if db.closed {
// Connections do not need to be reset if they will be closed.
// Prevents writing to resetterCh after the DB has closed.
resetSession = false
}
if resetSession {
if _, resetSession = dc.ci.(driver.SessionResetter); resetSession {
// Lock the driverConn here so it isn't released until
// the connection is reset.
// The lock must be taken before the connection is put into
// the pool to prevent it from being taken out before it is reset.
dc.Lock()
}
}
added := db.putConnDBLocked(dc, nil)
db.mu.Unlock()
if !added {
if resetSession {
dc.Unlock()
}
dc.Close()
return
}
if !resetSession {
return
}
select {
default:
// If the resetterCh is blocking then mark the connection
// as bad and continue on.
dc.lastErr = driver.ErrBadConn
dc.Unlock()
case db.resetterCh <- dc:
}
}
// Satisfy a connRequest or put the driverConn in the idle pool and return true
// or return false.
// putConnDBLocked will satisfy a connRequest if there is one, or it will
// return the *driverConn to the freeConn list if err == nil and the idle
// connection limit will not be exceeded.
// If err != nil, the value of dc is ignored.
// If err == nil, then dc must not equal nil.
// If a connRequest was fulfilled or the *driverConn was placed in the
// freeConn list, then true is returned, otherwise false is returned.
func (db *DB) putConnDBLocked(dc *driverConn, err error) bool {
if db.closed {
return false
}
if db.maxOpen > 0 && db.numOpen > db.maxOpen {
return false
}
if c := len(db.connRequests); c > 0 {
var req chan connRequest
var reqKey uint64
for reqKey, req = range db.connRequests {
break
}
delete(db.connRequests, reqKey) // Remove from pending requests.
if err == nil {
dc.inUse = true
}
req <- connRequest{
conn: dc,
err: err,
}
return true
} else if err == nil && !db.closed {
if db.maxIdleConnsLocked() > len(db.freeConn) {
db.freeConn = append(db.freeConn, dc)
db.startCleanerLocked()
return true
}
db.maxIdleClosed++
}
return false
}
// maxBadConnRetries is the number of maximum retries if the driver returns
// driver.ErrBadConn to signal a broken connection before forcing a new
// connection to be opened.
const maxBadConnRetries = 2
// PrepareContext creates a prepared statement for later queries or executions.
// Multiple queries or executions may be run concurrently from the
// returned statement.
// The caller must call the statement's Close method
// when the statement is no longer needed.
//
// The provided context is used for the preparation of the statement, not for the
// execution of the statement.
func (db *DB) PrepareContext(ctx context.Context, query string) (*Stmt, error) {
var stmt *Stmt
var err error
for i := 0; i < maxBadConnRetries; i++ {
stmt, err = db.prepare(ctx, query, cachedOrNewConn)
if err != driver.ErrBadConn {
break
}
}
if err == driver.ErrBadConn {
return db.prepare(ctx, query, alwaysNewConn)
}
return stmt, err
}
// Prepare creates a prepared statement for later queries or executions.
// Multiple queries or executions may be run concurrently from the
// returned statement.
// The caller must call the statement's Close method
// when the statement is no longer needed.
func (db *DB) Prepare(query string) (*Stmt, error) {
return db.PrepareContext(context.Background(), query)
}
func (db *DB) prepare(ctx context.Context, query string, strategy connReuseStrategy) (*Stmt, error) {
// TODO: check if db.driver supports an optional
// driver.Preparer interface and call that instead, if so,
// otherwise we make a prepared statement that's bound
// to a connection, and to execute this prepared statement
// we either need to use this connection (if it's free), else
// get a new connection + re-prepare + execute on that one.
dc, err := db.conn(ctx, strategy)
if err != nil {
return nil, err
}
return db.prepareDC(ctx, dc, dc.releaseConn, nil, query)
}
// prepareDC prepares a query on the driverConn and calls release before
// returning. When cg == nil it implies that a connection pool is used, and
// when cg != nil only a single driver connection is used.
func (db *DB) prepareDC(ctx context.Context, dc *driverConn, release func(error), cg stmtConnGrabber, query string) (*Stmt, error) {
var ds *driverStmt
var err error
defer func() {
release(err)
}()
withLock(dc, func() {
ds, err = dc.prepareLocked(ctx, cg, query)
})
if err != nil {
return nil, err
}
stmt := &Stmt{
db: db,
query: query,
cg: cg,
cgds: ds,
}
// When cg == nil this statement will need to keep track of various
// connections they are prepared on and record the stmt dependency on
// the DB.
if cg == nil {
stmt.css = []connStmt{{dc, ds}}
stmt.lastNumClosed = atomic.LoadUint64(&db.numClosed)
db.addDep(stmt, stmt)
}
return stmt, nil
}
// ExecContext executes a query without returning any rows.
// The args are for any placeholder parameters in the query.
func (db *DB) ExecContext(ctx context.Context, query string, args ...interface{}) (Result, error) {
var res Result
var err error
for i := 0; i < maxBadConnRetries; i++ {
res, err = db.exec(ctx, query, args, cachedOrNewConn)
if err != driver.ErrBadConn {
break
}
}
if err == driver.ErrBadConn {
return db.exec(ctx, query, args, alwaysNewConn)
}
return res, err
}
// Exec executes a query without returning any rows.
// The args are for any placeholder parameters in the query.
func (db *DB) Exec(query string, args ...interface{}) (Result, error) {
return db.ExecContext(context.Background(), query, args...)
}
func (db *DB) exec(ctx context.Context, query string, args []interface{}, strategy connReuseStrategy) (Result, error) {
dc, err := db.conn(ctx, strategy)
if err != nil {
return nil, err
}
return db.execDC(ctx, dc, dc.releaseConn, query, args)
}
func (db *DB) execDC(ctx context.Context, dc *driverConn, release func(error), query string, args []interface{}) (res Result, err error) {
defer func() {
release(err)
}()
execerCtx, ok := dc.ci.(driver.ExecerContext)
var execer driver.Execer
if !ok {
execer, ok = dc.ci.(driver.Execer)
}
if ok {
var nvdargs []driver.NamedValue
var resi driver.Result
withLock(dc, func() {
nvdargs, err = driverArgsConnLocked(dc.ci, nil, args)
if err != nil {
return
}
resi, err = ctxDriverExec(ctx, execerCtx, execer, query, nvdargs)
})
if err != driver.ErrSkip {
if err != nil {
return nil, err
}
return driverResult{dc, resi}, nil
}
}
var si driver.Stmt
withLock(dc, func() {
si, err = ctxDriverPrepare(ctx, dc.ci, query)
})
if err != nil {
return nil, err
}
ds := &driverStmt{Locker: dc, si: si}
defer ds.Close()
return resultFromStatement(ctx, dc.ci, ds, args...)
}
// QueryContext executes a query that returns rows, typically a SELECT.
// The args are for any placeholder parameters in the query.
func (db *DB) QueryContext(ctx context.Context, query string, args ...interface{}) (*Rows, error) {
var rows *Rows
var err error
for i := 0; i < maxBadConnRetries; i++ {
rows, err = db.query(ctx, query, args, cachedOrNewConn)
if err != driver.ErrBadConn {
break
}
}
if err == driver.ErrBadConn {
return db.query(ctx, query, args, alwaysNewConn)
}
return rows, err
}
// Query executes a query that returns rows, typically a SELECT.
// The args are for any placeholder parameters in the query.
func (db *DB) Query(query string, args ...interface{}) (*Rows, error) {
return db.QueryContext(context.Background(), query, args...)
}
func (db *DB) query(ctx context.Context, query string, args []interface{}, strategy connReuseStrategy) (*Rows, error) {
dc, err := db.conn(ctx, strategy)
if err != nil {
return nil, err
}
return db.queryDC(ctx, nil, dc, dc.releaseConn, query, args)
}
// queryDC executes a query on the given connection.
// The connection gets released by the releaseConn function.
// The ctx context is from a query method and the txctx context is from an
// optional transaction context.
func (db *DB) queryDC(ctx, txctx context.Context, dc *driverConn, releaseConn func(error), query string, args []interface{}) (*Rows, error) {
queryerCtx, ok := dc.ci.(driver.QueryerContext)
var queryer driver.Queryer
if !ok {
queryer, ok = dc.ci.(driver.Queryer)
}
if ok {
var nvdargs []driver.NamedValue
var rowsi driver.Rows
var err error
withLock(dc, func() {
nvdargs, err = driverArgsConnLocked(dc.ci, nil, args)
if err != nil {
return
}
rowsi, err = ctxDriverQuery(ctx, queryerCtx, queryer, query, nvdargs)
})
if err != driver.ErrSkip {
if err != nil {
releaseConn(err)
return nil, err
}
// Note: ownership of dc passes to the *Rows, to be freed
// with releaseConn.
rows := &Rows{
dc: dc,
releaseConn: releaseConn,
rowsi: rowsi,
}
rows.initContextClose(ctx, txctx)
return rows, nil
}
}
var si driver.Stmt
var err error
withLock(dc, func() {
si, err = ctxDriverPrepare(ctx, dc.ci, query)
})
if err != nil {
releaseConn(err)
return nil, err
}
ds := &driverStmt{Locker: dc, si: si}
rowsi, err := rowsiFromStatement(ctx, dc.ci, ds, args...)
if err != nil {
ds.Close()
releaseConn(err)
return nil, err
}
// Note: ownership of ci passes to the *Rows, to be freed
// with releaseConn.
rows := &Rows{
dc: dc,
releaseConn: releaseConn,
rowsi: rowsi,
closeStmt: ds,
}
rows.initContextClose(ctx, txctx)
return rows, nil
}
// QueryRowContext executes a query that is expected to return at most one row.
// QueryRowContext always returns a non-nil value. Errors are deferred until
// Row's Scan method is called.
// If the query selects no rows, the *Row's Scan will return ErrNoRows.
// Otherwise, the *Row's Scan scans the first selected row and discards
// the rest.
func (db *DB) QueryRowContext(ctx context.Context, query string, args ...interface{}) *Row {
rows, err := db.QueryContext(ctx, query, args...)
return &Row{rows: rows, err: err}
}
// QueryRow executes a query that is expected to return at most one row.
// QueryRow always returns a non-nil value. Errors are deferred until
// Row's Scan method is called.
// If the query selects no rows, the *Row's Scan will return ErrNoRows.
// Otherwise, the *Row's Scan scans the first selected row and discards
// the rest.
func (db *DB) QueryRow(query string, args ...interface{}) *Row {
return db.QueryRowContext(context.Background(), query, args...)
}
// BeginTx starts a transaction.
//
// The provided context is used until the transaction is committed or rolled back.
// If the context is canceled, the sql package will roll back
// the transaction. Tx.Commit will return an error if the context provided to
// BeginTx is canceled.
//
// The provided TxOptions is optional and may be nil if defaults should be used.
// If a non-default isolation level is used that the driver doesn't support,
// an error will be returned.
func (db *DB) BeginTx(ctx context.Context, opts *TxOptions) (*Tx, error) {
var tx *Tx
var err error
for i := 0; i < maxBadConnRetries; i++ {
tx, err = db.begin(ctx, opts, cachedOrNewConn)
if err != driver.ErrBadConn {
break
}
}
if err == driver.ErrBadConn {
return db.begin(ctx, opts, alwaysNewConn)
}
return tx, err
}
// Begin starts a transaction. The default isolation level is dependent on
// the driver.
func (db *DB) Begin() (*Tx, error) {
return db.BeginTx(context.Background(), nil)
}
func (db *DB) begin(ctx context.Context, opts *TxOptions, strategy connReuseStrategy) (tx *Tx, err error) {
dc, err := db.conn(ctx, strategy)
if err != nil {
return nil, err
}
return db.beginDC(ctx, dc, dc.releaseConn, opts)
}
// beginDC starts a transaction. The provided dc must be valid and ready to use.
func (db *DB) beginDC(ctx context.Context, dc *driverConn, release func(error), opts *TxOptions) (tx *Tx, err error) {
var txi driver.Tx
withLock(dc, func() {
txi, err = ctxDriverBegin(ctx, opts, dc.ci)
})
if err != nil {
release(err)
return nil, err
}
// Schedule the transaction to rollback when the context is cancelled.
// The cancel function in Tx will be called after done is set to true.
ctx, cancel := context.WithCancel(ctx)
tx = &Tx{
db: db,
dc: dc,
releaseConn: release,
txi: txi,
cancel: cancel,
ctx: ctx,
}
go tx.awaitDone()
return tx, nil
}
// Driver returns the database's underlying driver.
func (db *DB) Driver() driver.Driver {
return db.connector.Driver()
}
// ErrConnDone is returned by any operation that is performed on a connection
// that has already been returned to the connection pool.
var ErrConnDone = errors.New("sql: connection is already closed")
// Conn returns a single connection by either opening a new connection
// or returning an existing connection from the connection pool. Conn will
// block until either a connection is returned or ctx is canceled.
// Queries run on the same Conn will be run in the same database session.
//
// Every Conn must be returned to the database pool after use by
// calling Conn.Close.
func (db *DB) Conn(ctx context.Context) (*Conn, error) {
var dc *driverConn
var err error
for i := 0; i < maxBadConnRetries; i++ {
dc, err = db.conn(ctx, cachedOrNewConn)
if err != driver.ErrBadConn {
break
}
}
if err == driver.ErrBadConn {
dc, err = db.conn(ctx, alwaysNewConn)
}
if err != nil {
return nil, err
}
conn := &Conn{
db: db,
dc: dc,
}
return conn, nil
}
type releaseConn func(error)
// Conn represents a single database connection rather than a pool of database
// connections. Prefer running queries from DB unless there is a specific
// need for a continuous single database connection.
//
// A Conn must call Close to return the connection to the database pool
// and may do so concurrently with a running query.
//
// After a call to Close, all operations on the
// connection fail with ErrConnDone.
type Conn struct {
db *DB
// closemu prevents the connection from closing while there
// is an active query. It is held for read during queries
// and exclusively during close.
closemu sync.RWMutex
// dc is owned until close, at which point
// it's returned to the connection pool.
dc *driverConn
// done transitions from 0 to 1 exactly once, on close.
// Once done, all operations fail with ErrConnDone.
// Use atomic operations on value when checking value.
done int32
}
// grabConn takes a context to implement stmtConnGrabber
// but the context is not used.
func (c *Conn) grabConn(context.Context) (*driverConn, releaseConn, error) {
if atomic.LoadInt32(&c.done) != 0 {
return nil, nil, ErrConnDone
}
c.closemu.RLock()
return c.dc, c.closemuRUnlockCondReleaseConn, nil
}
// PingContext verifies the connection to the database is still alive.
func (c *Conn) PingContext(ctx context.Context) error {
dc, release, err := c.grabConn(ctx)
if err != nil {
return err
}
return c.db.pingDC(ctx, dc, release)
}
// ExecContext executes a query without returning any rows.
// The args are for any placeholder parameters in the query.
func (c *Conn) ExecContext(ctx context.Context, query string, args ...interface{}) (Result, error) {
dc, release, err := c.grabConn(ctx)
if err != nil {
return nil, err
}
return c.db.execDC(ctx, dc, release, query, args)
}
// QueryContext executes a query that returns rows, typically a SELECT.
// The args are for any placeholder parameters in the query.
func (c *Conn) QueryContext(ctx context.Context, query string, args ...interface{}) (*Rows, error) {
dc, release, err := c.grabConn(ctx)
if err != nil {
return nil, err
}
return c.db.queryDC(ctx, nil, dc, release, query, args)
}
// QueryRowContext executes a query that is expected to return at most one row.
// QueryRowContext always returns a non-nil value. Errors are deferred until
// Row's Scan method is called.
// If the query selects no rows, the *Row's Scan will return ErrNoRows.
// Otherwise, the *Row's Scan scans the first selected row and discards
// the rest.
func (c *Conn) QueryRowContext(ctx context.Context, query string, args ...interface{}) *Row {
rows, err := c.QueryContext(ctx, query, args...)
return &Row{rows: rows, err: err}
}
// PrepareContext creates a prepared statement for later queries or executions.
// Multiple queries or executions may be run concurrently from the
// returned statement.
// The caller must call the statement's Close method
// when the statement is no longer needed.
//
// The provided context is used for the preparation of the statement, not for the
// execution of the statement.
func (c *Conn) PrepareContext(ctx context.Context, query string) (*Stmt, error) {
dc, release, err := c.grabConn(ctx)
if err != nil {
return nil, err
}
return c.db.prepareDC(ctx, dc, release, c, query)
}
// Raw executes f exposing the underlying driver connection for the
// duration of f. The driverConn must not be used outside of f.
//
// Once f returns and err is nil, the Conn will continue to be usable
// until Conn.Close is called.
func (c *Conn) Raw(f func(driverConn interface{}) error) (err error) {
var dc *driverConn
var release releaseConn
// grabConn takes a context to implement stmtConnGrabber, but the context is not used.
dc, release, err = c.grabConn(nil)
if err != nil {
return
}
fPanic := true
dc.Mutex.Lock()
defer func() {
dc.Mutex.Unlock()
// If f panics fPanic will remain true.
// Ensure an error is passed to release so the connection
// may be discarded.
if fPanic {
err = driver.ErrBadConn
}
release(err)
}()
err = f(dc.ci)
fPanic = false
return
}
// BeginTx starts a transaction.
//
// The provided context is used until the transaction is committed or rolled back.
// If the context is canceled, the sql package will roll back
// the transaction. Tx.Commit will return an error if the context provided to
// BeginTx is canceled.
//
// The provided TxOptions is optional and may be nil if defaults should be used.
// If a non-default isolation level is used that the driver doesn't support,
// an error will be returned.
func (c *Conn) BeginTx(ctx context.Context, opts *TxOptions) (*Tx, error) {
dc, release, err := c.grabConn(ctx)
if err != nil {
return nil, err
}
return c.db.beginDC(ctx, dc, release, opts)
}
// closemuRUnlockCondReleaseConn read unlocks closemu
// as the sql operation is done with the dc.
func (c *Conn) closemuRUnlockCondReleaseConn(err error) {
c.closemu.RUnlock()
if err == driver.ErrBadConn {
c.close(err)
}
}
func (c *Conn) txCtx() context.Context {
return nil
}
func (c *Conn) close(err error) error {
if !atomic.CompareAndSwapInt32(&c.done, 0, 1) {
return ErrConnDone
}
// Lock around releasing the driver connection
// to ensure all queries have been stopped before doing so.
c.closemu.Lock()
defer c.closemu.Unlock()
c.dc.releaseConn(err)
c.dc = nil
c.db = nil
return err
}
// Close returns the connection to the connection pool.
// All operations after a Close will return with ErrConnDone.
// Close is safe to call concurrently with other operations and will
// block until all other operations finish. It may be useful to first
// cancel any used context and then call close directly after.
func (c *Conn) Close() error {
return c.close(nil)
}
// Tx is an in-progress database transaction.
//
// A transaction must end with a call to Commit or Rollback.
//
// After a call to Commit or Rollback, all operations on the
// transaction fail with ErrTxDone.
//
// The statements prepared for a transaction by calling
// the transaction's Prepare or Stmt methods are closed
// by the call to Commit or Rollback.
type Tx struct {
db *DB
// closemu prevents the transaction from closing while there
// is an active query. It is held for read during queries
// and exclusively during close.
closemu sync.RWMutex
// dc is owned exclusively until Commit or Rollback, at which point
// it's returned with putConn.
dc *driverConn
txi driver.Tx
// releaseConn is called once the Tx is closed to release
// any held driverConn back to the pool.
releaseConn func(error)
// done transitions from 0 to 1 exactly once, on Commit
// or Rollback. once done, all operations fail with
// ErrTxDone.
// Use atomic operations on value when checking value.
done int32
// All Stmts prepared for this transaction. These will be closed after the
// transaction has been committed or rolled back.
stmts struct {
sync.Mutex
v []*Stmt
}
// cancel is called after done transitions from 0 to 1.
cancel func()
// ctx lives for the life of the transaction.
ctx context.Context
}
// awaitDone blocks until the context in Tx is canceled and rolls back
// the transaction if it's not already done.
func (tx *Tx) awaitDone() {
// Wait for either the transaction to be committed or rolled
// back, or for the associated context to be closed.
<-tx.ctx.Done()
// Discard and close the connection used to ensure the
// transaction is closed and the resources are released. This
// rollback does nothing if the transaction has already been
// committed or rolled back.
tx.rollback(true)
}
func (tx *Tx) isDone() bool {
return atomic.LoadInt32(&tx.done) != 0
}
// ErrTxDone is returned by any operation that is performed on a transaction
// that has already been committed or rolled back.
var ErrTxDone = errors.New("sql: transaction has already been committed or rolled back")
// close returns the connection to the pool and
// must only be called by Tx.rollback or Tx.Commit.
func (tx *Tx) close(err error) {
tx.cancel()
tx.closemu.Lock()
defer tx.closemu.Unlock()
tx.releaseConn(err)
tx.dc = nil
tx.txi = nil
}
// hookTxGrabConn specifies an optional hook to be called on
// a successful call to (*Tx).grabConn. For tests.
var hookTxGrabConn func()
func (tx *Tx) grabConn(ctx context.Context) (*driverConn, releaseConn, error) {
select {
default:
case <-ctx.Done():
return nil, nil, ctx.Err()
}
// closeme.RLock must come before the check for isDone to prevent the Tx from
// closing while a query is executing.
tx.closemu.RLock()
if tx.isDone() {
tx.closemu.RUnlock()
return nil, nil, ErrTxDone
}
if hookTxGrabConn != nil { // test hook
hookTxGrabConn()
}
return tx.dc, tx.closemuRUnlockRelease, nil
}
func (tx *Tx) txCtx() context.Context {
return tx.ctx
}
// closemuRUnlockRelease is used as a func(error) method value in
// ExecContext and QueryContext. Unlocking in the releaseConn keeps
// the driver conn from being returned to the connection pool until
// the Rows has been closed.
func (tx *Tx) closemuRUnlockRelease(error) {
tx.closemu.RUnlock()
}
// Closes all Stmts prepared for this transaction.
func (tx *Tx) closePrepared() {
tx.stmts.Lock()
defer tx.stmts.Unlock()
for _, stmt := range tx.stmts.v {
stmt.Close()
}
}
// Commit commits the transaction.
func (tx *Tx) Commit() error {
// Check context first to avoid transaction leak.
// If put it behind tx.done CompareAndSwap statement, we can't ensure
// the consistency between tx.done and the real COMMIT operation.
select {
default:
case <-tx.ctx.Done():
if atomic.LoadInt32(&tx.done) == 1 {
return ErrTxDone
}
return tx.ctx.Err()
}
if !atomic.CompareAndSwapInt32(&tx.done, 0, 1) {
return ErrTxDone
}
var err error
withLock(tx.dc, func() {
err = tx.txi.Commit()
})
if err != driver.ErrBadConn {
tx.closePrepared()
}
tx.close(err)
return err
}
// rollback aborts the transaction and optionally forces the pool to discard
// the connection.
func (tx *Tx) rollback(discardConn bool) error {
if !atomic.CompareAndSwapInt32(&tx.done, 0, 1) {
return ErrTxDone
}
var err error
withLock(tx.dc, func() {
err = tx.txi.Rollback()
})
if err != driver.ErrBadConn {
tx.closePrepared()
}
if discardConn {
err = driver.ErrBadConn
}
tx.close(err)
return err
}
// Rollback aborts the transaction.
func (tx *Tx) Rollback() error {
return tx.rollback(false)
}
// PrepareContext creates a prepared statement for use within a transaction.
//
// The returned statement operates within the transaction and will be closed
// when the transaction has been committed or rolled back.
//
// To use an existing prepared statement on this transaction, see Tx.Stmt.
//
// The provided context will be used for the preparation of the context, not
// for the execution of the returned statement. The returned statement
// will run in the transaction context.
func (tx *Tx) PrepareContext(ctx context.Context, query string) (*Stmt, error) {
dc, release, err := tx.grabConn(ctx)
if err != nil {
return nil, err
}
stmt, err := tx.db.prepareDC(ctx, dc, release, tx, query)
if err != nil {
return nil, err
}
tx.stmts.Lock()
tx.stmts.v = append(tx.stmts.v, stmt)
tx.stmts.Unlock()
return stmt, nil
}
// Prepare creates a prepared statement for use within a transaction.
//
// The returned statement operates within the transaction and can no longer
// be used once the transaction has been committed or rolled back.
//
// To use an existing prepared statement on this transaction, see Tx.Stmt.
func (tx *Tx) Prepare(query string) (*Stmt, error) {
return tx.PrepareContext(context.Background(), query)
}
// StmtContext returns a transaction-specific prepared statement from
// an existing statement.
//
// Example:
// updateMoney, err := db.Prepare("UPDATE balance SET money=money+? WHERE id=?")
// ...
// tx, err := db.Begin()
// ...
// res, err := tx.StmtContext(ctx, updateMoney).Exec(123.45, 98293203)
//
// The provided context is used for the preparation of the statement, not for the
// execution of the statement.
//
// The returned statement operates within the transaction and will be closed
// when the transaction has been committed or rolled back.
func (tx *Tx) StmtContext(ctx context.Context, stmt *Stmt) *Stmt {
dc, release, err := tx.grabConn(ctx)
if err != nil {
return &Stmt{stickyErr: err}
}
defer release(nil)
if tx.db != stmt.db {
return &Stmt{stickyErr: errors.New("sql: Tx.Stmt: statement from different database used")}
}
var si driver.Stmt
var parentStmt *Stmt
stmt.mu.Lock()
if stmt.closed || stmt.cg != nil {
// If the statement has been closed or already belongs to a
// transaction, we can't reuse it in this connection.
// Since tx.StmtContext should never need to be called with a
// Stmt already belonging to tx, we ignore this edge case and
// re-prepare the statement in this case. No need to add
// code-complexity for this.
stmt.mu.Unlock()
withLock(dc, func() {
si, err = ctxDriverPrepare(ctx, dc.ci, stmt.query)
})
if err != nil {
return &Stmt{stickyErr: err}
}
} else {
stmt.removeClosedStmtLocked()
// See if the statement has already been prepared on this connection,
// and reuse it if possible.
for _, v := range stmt.css {
if v.dc == dc {
si = v.ds.si
break
}
}
stmt.mu.Unlock()
if si == nil {
var ds *driverStmt
withLock(dc, func() {
ds, err = stmt.prepareOnConnLocked(ctx, dc)
})
if err != nil {
return &Stmt{stickyErr: err}
}
si = ds.si
}
parentStmt = stmt
}
txs := &Stmt{
db: tx.db,
cg: tx,
cgds: &driverStmt{
Locker: dc,
si: si,
},
parentStmt: parentStmt,
query: stmt.query,
}
if parentStmt != nil {
tx.db.addDep(parentStmt, txs)
}
tx.stmts.Lock()
tx.stmts.v = append(tx.stmts.v, txs)
tx.stmts.Unlock()
return txs
}
// Stmt returns a transaction-specific prepared statement from
// an existing statement.
//
// Example:
// updateMoney, err := db.Prepare("UPDATE balance SET money=money+? WHERE id=?")
// ...
// tx, err := db.Begin()
// ...
// res, err := tx.Stmt(updateMoney).Exec(123.45, 98293203)
//
// The returned statement operates within the transaction and will be closed
// when the transaction has been committed or rolled back.
func (tx *Tx) Stmt(stmt *Stmt) *Stmt {
return tx.StmtContext(context.Background(), stmt)
}
// ExecContext executes a query that doesn't return rows.
// For example: an INSERT and UPDATE.
func (tx *Tx) ExecContext(ctx context.Context, query string, args ...interface{}) (Result, error) {
dc, release, err := tx.grabConn(ctx)
if err != nil {
return nil, err
}
return tx.db.execDC(ctx, dc, release, query, args)
}
// Exec executes a query that doesn't return rows.
// For example: an INSERT and UPDATE.
func (tx *Tx) Exec(query string, args ...interface{}) (Result, error) {
return tx.ExecContext(context.Background(), query, args...)
}
// QueryContext executes a query that returns rows, typically a SELECT.
func (tx *Tx) QueryContext(ctx context.Context, query string, args ...interface{}) (*Rows, error) {
dc, release, err := tx.grabConn(ctx)
if err != nil {
return nil, err
}
return tx.db.queryDC(ctx, tx.ctx, dc, release, query, args)
}
// Query executes a query that returns rows, typically a SELECT.
func (tx *Tx) Query(query string, args ...interface{}) (*Rows, error) {
return tx.QueryContext(context.Background(), query, args...)
}
// QueryRowContext executes a query that is expected to return at most one row.
// QueryRowContext always returns a non-nil value. Errors are deferred until
// Row's Scan method is called.
// If the query selects no rows, the *Row's Scan will return ErrNoRows.
// Otherwise, the *Row's Scan scans the first selected row and discards
// the rest.
func (tx *Tx) QueryRowContext(ctx context.Context, query string, args ...interface{}) *Row {
rows, err := tx.QueryContext(ctx, query, args...)
return &Row{rows: rows, err: err}
}
// QueryRow executes a query that is expected to return at most one row.
// QueryRow always returns a non-nil value. Errors are deferred until
// Row's Scan method is called.
// If the query selects no rows, the *Row's Scan will return ErrNoRows.
// Otherwise, the *Row's Scan scans the first selected row and discards
// the rest.
func (tx *Tx) QueryRow(query string, args ...interface{}) *Row {
return tx.QueryRowContext(context.Background(), query, args...)
}
// connStmt is a prepared statement on a particular connection.
type connStmt struct {
dc *driverConn
ds *driverStmt
}
// stmtConnGrabber represents a Tx or Conn that will return the underlying
// driverConn and release function.
type stmtConnGrabber interface {
// grabConn returns the driverConn and the associated release function
// that must be called when the operation completes.
grabConn(context.Context) (*driverConn, releaseConn, error)
// txCtx returns the transaction context if available.
// The returned context should be selected on along with
// any query context when awaiting a cancel.
txCtx() context.Context
}
var (
_ stmtConnGrabber = &Tx{}
_ stmtConnGrabber = &Conn{}
)
// Stmt is a prepared statement.
// A Stmt is safe for concurrent use by multiple goroutines.
//
// If a Stmt is prepared on a Tx or Conn, it will be bound to a single
// underlying connection forever. If the Tx or Conn closes, the Stmt will
// become unusable and all operations will return an error.
// If a Stmt is prepared on a DB, it will remain usable for the lifetime of the
// DB. When the Stmt needs to execute on a new underlying connection, it will
// prepare itself on the new connection automatically.
type Stmt struct {
// Immutable:
db *DB // where we came from
query string // that created the Stmt
stickyErr error // if non-nil, this error is returned for all operations
closemu sync.RWMutex // held exclusively during close, for read otherwise.
// If Stmt is prepared on a Tx or Conn then cg is present and will
// only ever grab a connection from cg.
// If cg is nil then the Stmt must grab an arbitrary connection
// from db and determine if it must prepare the stmt again by
// inspecting css.
cg stmtConnGrabber
cgds *driverStmt
// parentStmt is set when a transaction-specific statement
// is requested from an identical statement prepared on the same
// conn. parentStmt is used to track the dependency of this statement
// on its originating ("parent") statement so that parentStmt may
// be closed by the user without them having to know whether or not
// any transactions are still using it.
parentStmt *Stmt
mu sync.Mutex // protects the rest of the fields
closed bool
// css is a list of underlying driver statement interfaces
// that are valid on particular connections. This is only
// used if cg == nil and one is found that has idle
// connections. If cg != nil, cgds is always used.
css []connStmt
// lastNumClosed is copied from db.numClosed when Stmt is created
// without tx and closed connections in css are removed.
lastNumClosed uint64
}
// ExecContext executes a prepared statement with the given arguments and
// returns a Result summarizing the effect of the statement.
func (s *Stmt) ExecContext(ctx context.Context, args ...interface{}) (Result, error) {
s.closemu.RLock()
defer s.closemu.RUnlock()
var res Result
strategy := cachedOrNewConn
for i := 0; i < maxBadConnRetries+1; i++ {
if i == maxBadConnRetries {
strategy = alwaysNewConn
}
dc, releaseConn, ds, err := s.connStmt(ctx, strategy)
if err != nil {
if err == driver.ErrBadConn {
continue
}
return nil, err
}
res, err = resultFromStatement(ctx, dc.ci, ds, args...)
releaseConn(err)
if err != driver.ErrBadConn {
return res, err
}
}
return nil, driver.ErrBadConn
}
// Exec executes a prepared statement with the given arguments and
// returns a Result summarizing the effect of the statement.
func (s *Stmt) Exec(args ...interface{}) (Result, error) {
return s.ExecContext(context.Background(), args...)
}
func resultFromStatement(ctx context.Context, ci driver.Conn, ds *driverStmt, args ...interface{}) (Result, error) {
ds.Lock()
defer ds.Unlock()
dargs, err := driverArgsConnLocked(ci, ds, args)
if err != nil {
return nil, err
}
resi, err := ctxDriverStmtExec(ctx, ds.si, dargs)
if err != nil {
return nil, err
}
return driverResult{ds.Locker, resi}, nil
}
// removeClosedStmtLocked removes closed conns in s.css.
//
// To avoid lock contention on DB.mu, we do it only when
// s.db.numClosed - s.lastNum is large enough.
func (s *Stmt) removeClosedStmtLocked() {
t := len(s.css)/2 + 1
if t > 10 {
t = 10
}
dbClosed := atomic.LoadUint64(&s.db.numClosed)
if dbClosed-s.lastNumClosed < uint64(t) {
return
}
s.db.mu.Lock()
for i := 0; i < len(s.css); i++ {
if s.css[i].dc.dbmuClosed {
s.css[i] = s.css[len(s.css)-1]
s.css = s.css[:len(s.css)-1]
i--
}
}
s.db.mu.Unlock()
s.lastNumClosed = dbClosed
}
// connStmt returns a free driver connection on which to execute the
// statement, a function to call to release the connection, and a
// statement bound to that connection.
func (s *Stmt) connStmt(ctx context.Context, strategy connReuseStrategy) (dc *driverConn, releaseConn func(error), ds *driverStmt, err error) {
if err = s.stickyErr; err != nil {
return
}
s.mu.Lock()
if s.closed {
s.mu.Unlock()
err = errors.New("sql: statement is closed")
return
}
// In a transaction or connection, we always use the connection that the
// stmt was created on.
if s.cg != nil {
s.mu.Unlock()
dc, releaseConn, err = s.cg.grabConn(ctx) // blocks, waiting for the connection.
if err != nil {
return
}
return dc, releaseConn, s.cgds, nil
}
s.removeClosedStmtLocked()
s.mu.Unlock()
dc, err = s.db.conn(ctx, strategy)
if err != nil {
return nil, nil, nil, err
}
s.mu.Lock()
for _, v := range s.css {
if v.dc == dc {
s.mu.Unlock()
return dc, dc.releaseConn, v.ds, nil
}
}
s.mu.Unlock()
// No luck; we need to prepare the statement on this connection
withLock(dc, func() {
ds, err = s.prepareOnConnLocked(ctx, dc)
})
if err != nil {
dc.releaseConn(err)
return nil, nil, nil, err
}
return dc, dc.releaseConn, ds, nil
}
// prepareOnConnLocked prepares the query in Stmt s on dc and adds it to the list of
// open connStmt on the statement. It assumes the caller is holding the lock on dc.
func (s *Stmt) prepareOnConnLocked(ctx context.Context, dc *driverConn) (*driverStmt, error) {
si, err := dc.prepareLocked(ctx, s.cg, s.query)
if err != nil {
return nil, err
}
cs := connStmt{dc, si}
s.mu.Lock()
s.css = append(s.css, cs)
s.mu.Unlock()
return cs.ds, nil
}
// QueryContext executes a prepared query statement with the given arguments
// and returns the query results as a *Rows.
func (s *Stmt) QueryContext(ctx context.Context, args ...interface{}) (*Rows, error) {
s.closemu.RLock()
defer s.closemu.RUnlock()
var rowsi driver.Rows
strategy := cachedOrNewConn
for i := 0; i < maxBadConnRetries+1; i++ {
if i == maxBadConnRetries {
strategy = alwaysNewConn
}
dc, releaseConn, ds, err := s.connStmt(ctx, strategy)
if err != nil {
if err == driver.ErrBadConn {
continue
}
return nil, err
}
rowsi, err = rowsiFromStatement(ctx, dc.ci, ds, args...)
if err == nil {
// Note: ownership of ci passes to the *Rows, to be freed
// with releaseConn.
rows := &Rows{
dc: dc,
rowsi: rowsi,
// releaseConn set below
}
// addDep must be added before initContextClose or it could attempt
// to removeDep before it has been added.
s.db.addDep(s, rows)
// releaseConn must be set before initContextClose or it could
// release the connection before it is set.
rows.releaseConn = func(err error) {
releaseConn(err)
s.db.removeDep(s, rows)
}
var txctx context.Context
if s.cg != nil {
txctx = s.cg.txCtx()
}
rows.initContextClose(ctx, txctx)
return rows, nil
}
releaseConn(err)
if err != driver.ErrBadConn {
return nil, err
}
}
return nil, driver.ErrBadConn
}
// Query executes a prepared query statement with the given arguments
// and returns the query results as a *Rows.
func (s *Stmt) Query(args ...interface{}) (*Rows, error) {
return s.QueryContext(context.Background(), args...)
}
func rowsiFromStatement(ctx context.Context, ci driver.Conn, ds *driverStmt, args ...interface{}) (driver.Rows, error) {
ds.Lock()
defer ds.Unlock()
dargs, err := driverArgsConnLocked(ci, ds, args)
if err != nil {
return nil, err
}
return ctxDriverStmtQuery(ctx, ds.si, dargs)
}
// QueryRowContext executes a prepared query statement with the given arguments.
// If an error occurs during the execution of the statement, that error will
// be returned by a call to Scan on the returned *Row, which is always non-nil.
// If the query selects no rows, the *Row's Scan will return ErrNoRows.
// Otherwise, the *Row's Scan scans the first selected row and discards
// the rest.
func (s *Stmt) QueryRowContext(ctx context.Context, args ...interface{}) *Row {
rows, err := s.QueryContext(ctx, args...)
if err != nil {
return &Row{err: err}
}
return &Row{rows: rows}
}
// QueryRow executes a prepared query statement with the given arguments.
// If an error occurs during the execution of the statement, that error will
// be returned by a call to Scan on the returned *Row, which is always non-nil.
// If the query selects no rows, the *Row's Scan will return ErrNoRows.
// Otherwise, the *Row's Scan scans the first selected row and discards
// the rest.
//
// Example usage:
//
// var name string
// err := nameByUseridStmt.QueryRow(id).Scan(&name)
func (s *Stmt) QueryRow(args ...interface{}) *Row {
return s.QueryRowContext(context.Background(), args...)
}
// Close closes the statement.
func (s *Stmt) Close() error {
s.closemu.Lock()
defer s.closemu.Unlock()
if s.stickyErr != nil {
return s.stickyErr
}
s.mu.Lock()
if s.closed {
s.mu.Unlock()
return nil
}
s.closed = true
txds := s.cgds
s.cgds = nil
s.mu.Unlock()
if s.cg == nil {
return s.db.removeDep(s, s)
}
if s.parentStmt != nil {
// If parentStmt is set, we must not close s.txds since it's stored
// in the css array of the parentStmt.
return s.db.removeDep(s.parentStmt, s)
}
return txds.Close()
}
func (s *Stmt) finalClose() error {
s.mu.Lock()
defer s.mu.Unlock()
if s.css != nil {
for _, v := range s.css {
s.db.noteUnusedDriverStatement(v.dc, v.ds)
v.dc.removeOpenStmt(v.ds)
}
s.css = nil
}
return nil
}
// Rows is the result of a query. Its cursor starts before the first row
// of the result set. Use Next to advance from row to row.
type Rows struct {
dc *driverConn // owned; must call releaseConn when closed to release
releaseConn func(error)
rowsi driver.Rows
cancel func() // called when Rows is closed, may be nil.
closeStmt *driverStmt // if non-nil, statement to Close on close
// closemu prevents Rows from closing while there
// is an active streaming result. It is held for read during non-close operations
// and exclusively during close.
//
// closemu guards lasterr and closed.
closemu sync.RWMutex
closed bool
lasterr error // non-nil only if closed is true
// lastcols is only used in Scan, Next, and NextResultSet which are expected
// not to be called concurrently.
lastcols []driver.Value
}
// lasterrOrErrLocked returns either lasterr or the provided err.
// rs.closemu must be read-locked.
func (rs *Rows) lasterrOrErrLocked(err error) error {
if rs.lasterr != nil && rs.lasterr != io.EOF {
return rs.lasterr
}
return err
}
func (rs *Rows) initContextClose(ctx, txctx context.Context) {
if ctx.Done() == nil && (txctx == nil || txctx.Done() == nil) {
return
}
ctx, rs.cancel = context.WithCancel(ctx)
go rs.awaitDone(ctx, txctx)
}
// awaitDone blocks until either ctx or txctx is canceled. The ctx is provided
// from the query context and is canceled when the query Rows is closed.
// If the query was issued in a transaction, the transaction's context
// is also provided in txctx to ensure Rows is closed if the Tx is closed.
func (rs *Rows) awaitDone(ctx, txctx context.Context) {
var txctxDone <-chan struct{}
if txctx != nil {
txctxDone = txctx.Done()
}
select {
case <-ctx.Done():
case <-txctxDone:
}
rs.close(ctx.Err())
}
// Next prepares the next result row for reading with the Scan method. It
// returns true on success, or false if there is no next result row or an error
// happened while preparing it. Err should be consulted to distinguish between
// the two cases.
//
// Every call to Scan, even the first one, must be preceded by a call to Next.
func (rs *Rows) Next() bool {
var doClose, ok bool
withLock(rs.closemu.RLocker(), func() {
doClose, ok = rs.nextLocked()
})
if doClose {
rs.Close()
}
return ok
}
func (rs *Rows) nextLocked() (doClose, ok bool) {
if rs.closed {
return false, false
}
// Lock the driver connection before calling the driver interface
// rowsi to prevent a Tx from rolling back the connection at the same time.
rs.dc.Lock()
defer rs.dc.Unlock()
if rs.lastcols == nil {
rs.lastcols = make([]driver.Value, len(rs.rowsi.Columns()))
}
rs.lasterr = rs.rowsi.Next(rs.lastcols)
if rs.lasterr != nil {
// Close the connection if there is a driver error.
if rs.lasterr != io.EOF {
return true, false
}
nextResultSet, ok := rs.rowsi.(driver.RowsNextResultSet)
if !ok {
return true, false
}
// The driver is at the end of the current result set.
// Test to see if there is another result set after the current one.
// Only close Rows if there is no further result sets to read.
if !nextResultSet.HasNextResultSet() {
doClose = true
}
return doClose, false
}
return false, true
}
// NextResultSet prepares the next result set for reading. It reports whether
// there is further result sets, or false if there is no further result set
// or if there is an error advancing to it. The Err method should be consulted
// to distinguish between the two cases.
//
// After calling NextResultSet, the Next method should always be called before
// scanning. If there are further result sets they may not have rows in the result
// set.
func (rs *Rows) NextResultSet() bool {
var doClose bool
defer func() {
if doClose {
rs.Close()
}
}()
rs.closemu.RLock()
defer rs.closemu.RUnlock()
if rs.closed {
return false
}
rs.lastcols = nil
nextResultSet, ok := rs.rowsi.(driver.RowsNextResultSet)
if !ok {
doClose = true
return false
}
// Lock the driver connection before calling the driver interface
// rowsi to prevent a Tx from rolling back the connection at the same time.
rs.dc.Lock()
defer rs.dc.Unlock()
rs.lasterr = nextResultSet.NextResultSet()
if rs.lasterr != nil {
doClose = true
return false
}
return true
}
// Err returns the error, if any, that was encountered during iteration.
// Err may be called after an explicit or implicit Close.
func (rs *Rows) Err() error {
rs.closemu.RLock()
defer rs.closemu.RUnlock()
return rs.lasterrOrErrLocked(nil)
}
var errRowsClosed = errors.New("sql: Rows are closed")
var errNoRows = errors.New("sql: no Rows available")
// Columns returns the column names.
// Columns returns an error if the rows are closed.
func (rs *Rows) Columns() ([]string, error) {
rs.closemu.RLock()
defer rs.closemu.RUnlock()
if rs.closed {
return nil, rs.lasterrOrErrLocked(errRowsClosed)
}
if rs.rowsi == nil {
return nil, rs.lasterrOrErrLocked(errNoRows)
}
rs.dc.Lock()
defer rs.dc.Unlock()
return rs.rowsi.Columns(), nil
}
// ColumnTypes returns column information such as column type, length,
// and nullable. Some information may not be available from some drivers.
func (rs *Rows) ColumnTypes() ([]*ColumnType, error) {
rs.closemu.RLock()
defer rs.closemu.RUnlock()
if rs.closed {
return nil, rs.lasterrOrErrLocked(errRowsClosed)
}
if rs.rowsi == nil {
return nil, rs.lasterrOrErrLocked(errNoRows)
}
rs.dc.Lock()
defer rs.dc.Unlock()
return rowsColumnInfoSetupConnLocked(rs.rowsi), nil
}
// ColumnType contains the name and type of a column.
type ColumnType struct {
name string
hasNullable bool
hasLength bool
hasPrecisionScale bool
nullable bool
length int64
databaseType string
precision int64
scale int64
scanType reflect.Type
}
// Name returns the name or alias of the column.
func (ci *ColumnType) Name() string {
return ci.name
}
// Length returns the column type length for variable length column types such
// as text and binary field types. If the type length is unbounded the value will
// be math.MaxInt64 (any database limits will still apply).
// If the column type is not variable length, such as an int, or if not supported
// by the driver ok is false.
func (ci *ColumnType) Length() (length int64, ok bool) {
return ci.length, ci.hasLength
}
// DecimalSize returns the scale and precision of a decimal type.
// If not applicable or if not supported ok is false.
func (ci *ColumnType) DecimalSize() (precision, scale int64, ok bool) {
return ci.precision, ci.scale, ci.hasPrecisionScale
}
// ScanType returns a Go type suitable for scanning into using Rows.Scan.
// If a driver does not support this property ScanType will return
// the type of an empty interface.
func (ci *ColumnType) ScanType() reflect.Type {
return ci.scanType
}
// Nullable reports whether the column may be null.
// If a driver does not support this property ok will be false.
func (ci *ColumnType) Nullable() (nullable, ok bool) {
return ci.nullable, ci.hasNullable
}
// DatabaseTypeName returns the database system name of the column type. If an empty
// string is returned the driver type name is not supported.
// Consult your driver documentation for a list of driver data types. Length specifiers
// are not included.
// Common type include "VARCHAR", "TEXT", "NVARCHAR", "DECIMAL", "BOOL", "INT", "BIGINT".
func (ci *ColumnType) DatabaseTypeName() string {
return ci.databaseType
}
func rowsColumnInfoSetupConnLocked(rowsi driver.Rows) []*ColumnType {
names := rowsi.Columns()
list := make([]*ColumnType, len(names))
for i := range list {
ci := &ColumnType{
name: names[i],
}
list[i] = ci
if prop, ok := rowsi.(driver.RowsColumnTypeScanType); ok {
ci.scanType = prop.ColumnTypeScanType(i)
} else {
ci.scanType = reflect.TypeOf(new(interface{})).Elem()
}
if prop, ok := rowsi.(driver.RowsColumnTypeDatabaseTypeName); ok {
ci.databaseType = prop.ColumnTypeDatabaseTypeName(i)
}
if prop, ok := rowsi.(driver.RowsColumnTypeLength); ok {
ci.length, ci.hasLength = prop.ColumnTypeLength(i)
}
if prop, ok := rowsi.(driver.RowsColumnTypeNullable); ok {
ci.nullable, ci.hasNullable = prop.ColumnTypeNullable(i)
}
if prop, ok := rowsi.(driver.RowsColumnTypePrecisionScale); ok {
ci.precision, ci.scale, ci.hasPrecisionScale = prop.ColumnTypePrecisionScale(i)
}
}
return list
}
// Scan copies the columns in the current row into the values pointed
// at by dest. The number of values in dest must be the same as the
// number of columns in Rows.
//
// Scan converts columns read from the database into the following
// common Go types and special types provided by the sql package:
//
// *string
// *[]byte
// *int, *int8, *int16, *int32, *int64
// *uint, *uint8, *uint16, *uint32, *uint64
// *bool
// *float32, *float64
// *interface{}
// *RawBytes
// *Rows (cursor value)
// any type implementing Scanner (see Scanner docs)
//
// In the most simple case, if the type of the value from the source
// column is an integer, bool or string type T and dest is of type *T,
// Scan simply assigns the value through the pointer.
//
// Scan also converts between string and numeric types, as long as no
// information would be lost. While Scan stringifies all numbers
// scanned from numeric database columns into *string, scans into
// numeric types are checked for overflow. For example, a float64 with
// value 300 or a string with value "300" can scan into a uint16, but
// not into a uint8, though float64(255) or "255" can scan into a
// uint8. One exception is that scans of some float64 numbers to
// strings may lose information when stringifying. In general, scan
// floating point columns into *float64.
//
// If a dest argument has type *[]byte, Scan saves in that argument a
// copy of the corresponding data. The copy is owned by the caller and
// can be modified and held indefinitely. The copy can be avoided by
// using an argument of type *RawBytes instead; see the documentation
// for RawBytes for restrictions on its use.
//
// If an argument has type *interface{}, Scan copies the value
// provided by the underlying driver without conversion. When scanning
// from a source value of type []byte to *interface{}, a copy of the
// slice is made and the caller owns the result.
//
// Source values of type time.Time may be scanned into values of type
// *time.Time, *interface{}, *string, or *[]byte. When converting to
// the latter two, time.RFC3339Nano is used.
//
// Source values of type bool may be scanned into types *bool,
// *interface{}, *string, *[]byte, or *RawBytes.
//
// For scanning into *bool, the source may be true, false, 1, 0, or
// string inputs parseable by strconv.ParseBool.
//
// Scan can also convert a cursor returned from a query, such as
// "select cursor(select * from my_table) from dual", into a
// *Rows value that can itself be scanned from. The parent
// select query will close any cursor *Rows if the parent *Rows is closed.
func (rs *Rows) Scan(dest ...interface{}) error {
rs.closemu.RLock()
if rs.lasterr != nil && rs.lasterr != io.EOF {
rs.closemu.RUnlock()
return rs.lasterr
}
if rs.closed {
err := rs.lasterrOrErrLocked(errRowsClosed)
rs.closemu.RUnlock()
return err
}
rs.closemu.RUnlock()
if rs.lastcols == nil {
return errors.New("sql: Scan called without calling Next")
}
if len(dest) != len(rs.lastcols) {
return fmt.Errorf("sql: expected %d destination arguments in Scan, not %d", len(rs.lastcols), len(dest))
}
for i, sv := range rs.lastcols {
err := convertAssignRows(dest[i], sv, rs)
if err != nil {
return fmt.Errorf(`sql: Scan error on column index %d, name %q: %v`, i, rs.rowsi.Columns()[i], err)
}
}
return nil
}
// rowsCloseHook returns a function so tests may install the
// hook through a test only mutex.
var rowsCloseHook = func() func(*Rows, *error) { return nil }
// Close closes the Rows, preventing further enumeration. If Next is called
// and returns false and there are no further result sets,
// the Rows are closed automatically and it will suffice to check the
// result of Err. Close is idempotent and does not affect the result of Err.
func (rs *Rows) Close() error {
return rs.close(nil)
}
func (rs *Rows) close(err error) error {
rs.closemu.Lock()
defer rs.closemu.Unlock()
if rs.closed {
return nil
}
rs.closed = true
if rs.lasterr == nil {
rs.lasterr = err
}
withLock(rs.dc, func() {
err = rs.rowsi.Close()
})
if fn := rowsCloseHook(); fn != nil {
fn(rs, &err)
}
if rs.cancel != nil {
rs.cancel()
}
if rs.closeStmt != nil {
rs.closeStmt.Close()
}
rs.releaseConn(err)
return err
}
// Row is the result of calling QueryRow to select a single row.
type Row struct {
// One of these two will be non-nil:
err error // deferred error for easy chaining
rows *Rows
}
// Scan copies the columns from the matched row into the values
// pointed at by dest. See the documentation on Rows.Scan for details.
// If more than one row matches the query,
// Scan uses the first row and discards the rest. If no row matches
// the query, Scan returns ErrNoRows.
func (r *Row) Scan(dest ...interface{}) error {
if r.err != nil {
return r.err
}
// TODO(bradfitz): for now we need to defensively clone all
// []byte that the driver returned (not permitting
// *RawBytes in Rows.Scan), since we're about to close
// the Rows in our defer, when we return from this function.
// the contract with the driver.Next(...) interface is that it
// can return slices into read-only temporary memory that's
// only valid until the next Scan/Close. But the TODO is that
// for a lot of drivers, this copy will be unnecessary. We
// should provide an optional interface for drivers to
// implement to say, "don't worry, the []bytes that I return
// from Next will not be modified again." (for instance, if
// they were obtained from the network anyway) But for now we
// don't care.
defer r.rows.Close()
for _, dp := range dest {
if _, ok := dp.(*RawBytes); ok {
return errors.New("sql: RawBytes isn't allowed on Row.Scan")
}
}
if !r.rows.Next() {
if err := r.rows.Err(); err != nil {
return err
}
return ErrNoRows
}
err := r.rows.Scan(dest...)
if err != nil {
return err
}
// Make sure the query can be processed to completion with no errors.
return r.rows.Close()
}
// A Result summarizes an executed SQL command.
type Result interface {
// LastInsertId returns the integer generated by the database
// in response to a command. Typically this will be from an
// "auto increment" column when inserting a new row. Not all
// databases support this feature, and the syntax of such
// statements varies.
LastInsertId() (int64, error)
// RowsAffected returns the number of rows affected by an
// update, insert, or delete. Not every database or database
// driver may support this.
RowsAffected() (int64, error)
}
type driverResult struct {
sync.Locker // the *driverConn
resi driver.Result
}
func (dr driverResult) LastInsertId() (int64, error) {
dr.Lock()
defer dr.Unlock()
return dr.resi.LastInsertId()
}
func (dr driverResult) RowsAffected() (int64, error) {
dr.Lock()
defer dr.Unlock()
return dr.resi.RowsAffected()
}
func stack() string {
var buf [2 << 10]byte
return string(buf[:runtime.Stack(buf[:], false)])
}
// withLock runs while holding lk.
func withLock(lk sync.Locker, fn func()) {
lk.Lock()
defer lk.Unlock() // in case fn panics
fn()
}
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