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* Migrate to go modules * make vendor * Update mvdan.cc/xurls * make vendor * Update code.gitea.io/git * make fmt-check * Update github.com/go-sql-driver/mysql * make vendor
798 lines
23 KiB
Go
798 lines
23 KiB
Go
package pq
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// Package pq is a pure Go Postgres driver for the database/sql package.
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// This module contains support for Postgres LISTEN/NOTIFY.
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import (
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"errors"
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"fmt"
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"sync"
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"sync/atomic"
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"time"
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)
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// Notification represents a single notification from the database.
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type Notification struct {
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// Process ID (PID) of the notifying postgres backend.
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BePid int
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// Name of the channel the notification was sent on.
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Channel string
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// Payload, or the empty string if unspecified.
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Extra string
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}
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func recvNotification(r *readBuf) *Notification {
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bePid := r.int32()
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channel := r.string()
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extra := r.string()
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return &Notification{bePid, channel, extra}
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}
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const (
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connStateIdle int32 = iota
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connStateExpectResponse
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connStateExpectReadyForQuery
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)
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type message struct {
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typ byte
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err error
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}
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var errListenerConnClosed = errors.New("pq: ListenerConn has been closed")
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// ListenerConn is a low-level interface for waiting for notifications. You
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// should use Listener instead.
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type ListenerConn struct {
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// guards cn and err
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connectionLock sync.Mutex
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cn *conn
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err error
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connState int32
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// the sending goroutine will be holding this lock
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senderLock sync.Mutex
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notificationChan chan<- *Notification
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replyChan chan message
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}
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// NewListenerConn creates a new ListenerConn. Use NewListener instead.
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func NewListenerConn(name string, notificationChan chan<- *Notification) (*ListenerConn, error) {
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return newDialListenerConn(defaultDialer{}, name, notificationChan)
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}
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func newDialListenerConn(d Dialer, name string, c chan<- *Notification) (*ListenerConn, error) {
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cn, err := DialOpen(d, name)
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if err != nil {
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return nil, err
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}
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l := &ListenerConn{
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cn: cn.(*conn),
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notificationChan: c,
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connState: connStateIdle,
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replyChan: make(chan message, 2),
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}
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go l.listenerConnMain()
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return l, nil
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}
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// We can only allow one goroutine at a time to be running a query on the
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// connection for various reasons, so the goroutine sending on the connection
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// must be holding senderLock.
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//
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// Returns an error if an unrecoverable error has occurred and the ListenerConn
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// should be abandoned.
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func (l *ListenerConn) acquireSenderLock() error {
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// we must acquire senderLock first to avoid deadlocks; see ExecSimpleQuery
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l.senderLock.Lock()
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l.connectionLock.Lock()
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err := l.err
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l.connectionLock.Unlock()
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if err != nil {
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l.senderLock.Unlock()
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return err
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}
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return nil
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}
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func (l *ListenerConn) releaseSenderLock() {
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l.senderLock.Unlock()
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}
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// setState advances the protocol state to newState. Returns false if moving
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// to that state from the current state is not allowed.
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func (l *ListenerConn) setState(newState int32) bool {
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var expectedState int32
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switch newState {
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case connStateIdle:
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expectedState = connStateExpectReadyForQuery
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case connStateExpectResponse:
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expectedState = connStateIdle
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case connStateExpectReadyForQuery:
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expectedState = connStateExpectResponse
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default:
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panic(fmt.Sprintf("unexpected listenerConnState %d", newState))
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}
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return atomic.CompareAndSwapInt32(&l.connState, expectedState, newState)
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}
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// Main logic is here: receive messages from the postgres backend, forward
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// notifications and query replies and keep the internal state in sync with the
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// protocol state. Returns when the connection has been lost, is about to go
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// away or should be discarded because we couldn't agree on the state with the
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// server backend.
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func (l *ListenerConn) listenerConnLoop() (err error) {
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defer errRecoverNoErrBadConn(&err)
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r := &readBuf{}
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for {
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t, err := l.cn.recvMessage(r)
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if err != nil {
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return err
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}
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switch t {
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case 'A':
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// recvNotification copies all the data so we don't need to worry
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// about the scratch buffer being overwritten.
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l.notificationChan <- recvNotification(r)
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case 'T', 'D':
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// only used by tests; ignore
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case 'E':
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// We might receive an ErrorResponse even when not in a query; it
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// is expected that the server will close the connection after
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// that, but we should make sure that the error we display is the
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// one from the stray ErrorResponse, not io.ErrUnexpectedEOF.
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if !l.setState(connStateExpectReadyForQuery) {
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return parseError(r)
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}
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l.replyChan <- message{t, parseError(r)}
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case 'C', 'I':
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if !l.setState(connStateExpectReadyForQuery) {
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// protocol out of sync
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return fmt.Errorf("unexpected CommandComplete")
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}
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// ExecSimpleQuery doesn't need to know about this message
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case 'Z':
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if !l.setState(connStateIdle) {
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// protocol out of sync
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return fmt.Errorf("unexpected ReadyForQuery")
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}
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l.replyChan <- message{t, nil}
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case 'N', 'S':
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// ignore
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default:
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return fmt.Errorf("unexpected message %q from server in listenerConnLoop", t)
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}
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}
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}
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// This is the main routine for the goroutine receiving on the database
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// connection. Most of the main logic is in listenerConnLoop.
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func (l *ListenerConn) listenerConnMain() {
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err := l.listenerConnLoop()
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// listenerConnLoop terminated; we're done, but we still have to clean up.
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// Make sure nobody tries to start any new queries by making sure the err
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// pointer is set. It is important that we do not overwrite its value; a
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// connection could be closed by either this goroutine or one sending on
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// the connection -- whoever closes the connection is assumed to have the
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// more meaningful error message (as the other one will probably get
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// net.errClosed), so that goroutine sets the error we expose while the
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// other error is discarded. If the connection is lost while two
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// goroutines are operating on the socket, it probably doesn't matter which
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// error we expose so we don't try to do anything more complex.
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l.connectionLock.Lock()
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if l.err == nil {
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l.err = err
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}
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l.cn.Close()
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l.connectionLock.Unlock()
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// There might be a query in-flight; make sure nobody's waiting for a
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// response to it, since there's not going to be one.
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close(l.replyChan)
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// let the listener know we're done
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close(l.notificationChan)
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// this ListenerConn is done
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}
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// Listen sends a LISTEN query to the server. See ExecSimpleQuery.
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func (l *ListenerConn) Listen(channel string) (bool, error) {
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return l.ExecSimpleQuery("LISTEN " + QuoteIdentifier(channel))
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}
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// Unlisten sends an UNLISTEN query to the server. See ExecSimpleQuery.
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func (l *ListenerConn) Unlisten(channel string) (bool, error) {
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return l.ExecSimpleQuery("UNLISTEN " + QuoteIdentifier(channel))
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}
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// UnlistenAll sends an `UNLISTEN *` query to the server. See ExecSimpleQuery.
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func (l *ListenerConn) UnlistenAll() (bool, error) {
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return l.ExecSimpleQuery("UNLISTEN *")
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}
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// Ping the remote server to make sure it's alive. Non-nil error means the
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// connection has failed and should be abandoned.
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func (l *ListenerConn) Ping() error {
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sent, err := l.ExecSimpleQuery("")
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if !sent {
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return err
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}
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if err != nil {
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// shouldn't happen
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panic(err)
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}
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return nil
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}
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// Attempt to send a query on the connection. Returns an error if sending the
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// query failed, and the caller should initiate closure of this connection.
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// The caller must be holding senderLock (see acquireSenderLock and
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// releaseSenderLock).
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func (l *ListenerConn) sendSimpleQuery(q string) (err error) {
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defer errRecoverNoErrBadConn(&err)
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// must set connection state before sending the query
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if !l.setState(connStateExpectResponse) {
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panic("two queries running at the same time")
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}
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// Can't use l.cn.writeBuf here because it uses the scratch buffer which
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// might get overwritten by listenerConnLoop.
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b := &writeBuf{
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buf: []byte("Q\x00\x00\x00\x00"),
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pos: 1,
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}
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b.string(q)
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l.cn.send(b)
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return nil
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}
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// ExecSimpleQuery executes a "simple query" (i.e. one with no bindable
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// parameters) on the connection. The possible return values are:
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// 1) "executed" is true; the query was executed to completion on the
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// database server. If the query failed, err will be set to the error
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// returned by the database, otherwise err will be nil.
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// 2) If "executed" is false, the query could not be executed on the remote
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// server. err will be non-nil.
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//
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// After a call to ExecSimpleQuery has returned an executed=false value, the
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// connection has either been closed or will be closed shortly thereafter, and
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// all subsequently executed queries will return an error.
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func (l *ListenerConn) ExecSimpleQuery(q string) (executed bool, err error) {
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if err = l.acquireSenderLock(); err != nil {
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return false, err
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}
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defer l.releaseSenderLock()
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err = l.sendSimpleQuery(q)
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if err != nil {
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// We can't know what state the protocol is in, so we need to abandon
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// this connection.
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l.connectionLock.Lock()
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// Set the error pointer if it hasn't been set already; see
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// listenerConnMain.
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if l.err == nil {
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l.err = err
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}
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l.connectionLock.Unlock()
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l.cn.c.Close()
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return false, err
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}
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// now we just wait for a reply..
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for {
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m, ok := <-l.replyChan
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if !ok {
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// We lost the connection to server, don't bother waiting for a
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// a response. err should have been set already.
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l.connectionLock.Lock()
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err := l.err
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l.connectionLock.Unlock()
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return false, err
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}
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switch m.typ {
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case 'Z':
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// sanity check
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if m.err != nil {
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panic("m.err != nil")
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}
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// done; err might or might not be set
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return true, err
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case 'E':
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// sanity check
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if m.err == nil {
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panic("m.err == nil")
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}
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// server responded with an error; ReadyForQuery to follow
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err = m.err
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default:
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return false, fmt.Errorf("unknown response for simple query: %q", m.typ)
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}
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}
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}
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// Close closes the connection.
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func (l *ListenerConn) Close() error {
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l.connectionLock.Lock()
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if l.err != nil {
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l.connectionLock.Unlock()
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return errListenerConnClosed
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}
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l.err = errListenerConnClosed
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l.connectionLock.Unlock()
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// We can't send anything on the connection without holding senderLock.
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// Simply close the net.Conn to wake up everyone operating on it.
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return l.cn.c.Close()
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}
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// Err returns the reason the connection was closed. It is not safe to call
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// this function until l.Notify has been closed.
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func (l *ListenerConn) Err() error {
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return l.err
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}
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var errListenerClosed = errors.New("pq: Listener has been closed")
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// ErrChannelAlreadyOpen is returned from Listen when a channel is already
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// open.
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var ErrChannelAlreadyOpen = errors.New("pq: channel is already open")
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// ErrChannelNotOpen is returned from Unlisten when a channel is not open.
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var ErrChannelNotOpen = errors.New("pq: channel is not open")
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// ListenerEventType is an enumeration of listener event types.
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type ListenerEventType int
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const (
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// ListenerEventConnected is emitted only when the database connection
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// has been initially initialized. The err argument of the callback
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// will always be nil.
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ListenerEventConnected ListenerEventType = iota
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// ListenerEventDisconnected is emitted after a database connection has
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// been lost, either because of an error or because Close has been
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// called. The err argument will be set to the reason the database
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// connection was lost.
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ListenerEventDisconnected
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// ListenerEventReconnected is emitted after a database connection has
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// been re-established after connection loss. The err argument of the
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// callback will always be nil. After this event has been emitted, a
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// nil pq.Notification is sent on the Listener.Notify channel.
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ListenerEventReconnected
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// ListenerEventConnectionAttemptFailed is emitted after a connection
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// to the database was attempted, but failed. The err argument will be
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// set to an error describing why the connection attempt did not
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// succeed.
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ListenerEventConnectionAttemptFailed
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)
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// EventCallbackType is the event callback type. See also ListenerEventType
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// constants' documentation.
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type EventCallbackType func(event ListenerEventType, err error)
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// Listener provides an interface for listening to notifications from a
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// PostgreSQL database. For general usage information, see section
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// "Notifications".
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//
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// Listener can safely be used from concurrently running goroutines.
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type Listener struct {
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// Channel for receiving notifications from the database. In some cases a
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// nil value will be sent. See section "Notifications" above.
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Notify chan *Notification
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name string
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minReconnectInterval time.Duration
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maxReconnectInterval time.Duration
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dialer Dialer
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eventCallback EventCallbackType
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lock sync.Mutex
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isClosed bool
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reconnectCond *sync.Cond
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cn *ListenerConn
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connNotificationChan <-chan *Notification
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channels map[string]struct{}
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}
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// NewListener creates a new database connection dedicated to LISTEN / NOTIFY.
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//
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// name should be set to a connection string to be used to establish the
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// database connection (see section "Connection String Parameters" above).
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//
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// minReconnectInterval controls the duration to wait before trying to
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// re-establish the database connection after connection loss. After each
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// consecutive failure this interval is doubled, until maxReconnectInterval is
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// reached. Successfully completing the connection establishment procedure
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// resets the interval back to minReconnectInterval.
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//
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// The last parameter eventCallback can be set to a function which will be
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// called by the Listener when the state of the underlying database connection
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// changes. This callback will be called by the goroutine which dispatches the
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// notifications over the Notify channel, so you should try to avoid doing
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// potentially time-consuming operations from the callback.
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func NewListener(name string,
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minReconnectInterval time.Duration,
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maxReconnectInterval time.Duration,
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eventCallback EventCallbackType) *Listener {
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return NewDialListener(defaultDialer{}, name, minReconnectInterval, maxReconnectInterval, eventCallback)
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}
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// NewDialListener is like NewListener but it takes a Dialer.
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func NewDialListener(d Dialer,
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name string,
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minReconnectInterval time.Duration,
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maxReconnectInterval time.Duration,
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eventCallback EventCallbackType) *Listener {
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l := &Listener{
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name: name,
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minReconnectInterval: minReconnectInterval,
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maxReconnectInterval: maxReconnectInterval,
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dialer: d,
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eventCallback: eventCallback,
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channels: make(map[string]struct{}),
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Notify: make(chan *Notification, 32),
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}
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l.reconnectCond = sync.NewCond(&l.lock)
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go l.listenerMain()
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return l
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}
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// NotificationChannel returns the notification channel for this listener.
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// This is the same channel as Notify, and will not be recreated during the
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// life time of the Listener.
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func (l *Listener) NotificationChannel() <-chan *Notification {
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return l.Notify
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}
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// Listen starts listening for notifications on a channel. Calls to this
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// function will block until an acknowledgement has been received from the
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// server. Note that Listener automatically re-establishes the connection
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// after connection loss, so this function may block indefinitely if the
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// connection can not be re-established.
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//
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// Listen will only fail in three conditions:
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// 1) The channel is already open. The returned error will be
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// ErrChannelAlreadyOpen.
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// 2) The query was executed on the remote server, but PostgreSQL returned an
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// error message in response to the query. The returned error will be a
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// pq.Error containing the information the server supplied.
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// 3) Close is called on the Listener before the request could be completed.
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//
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// The channel name is case-sensitive.
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func (l *Listener) Listen(channel string) error {
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l.lock.Lock()
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defer l.lock.Unlock()
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if l.isClosed {
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return errListenerClosed
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}
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// The server allows you to issue a LISTEN on a channel which is already
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// open, but it seems useful to be able to detect this case to spot for
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// mistakes in application logic. If the application genuinely does't
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// care, it can check the exported error and ignore it.
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_, exists := l.channels[channel]
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if exists {
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return ErrChannelAlreadyOpen
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}
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if l.cn != nil {
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// If gotResponse is true but error is set, the query was executed on
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// the remote server, but resulted in an error. This should be
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// relatively rare, so it's fine if we just pass the error to our
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// caller. However, if gotResponse is false, we could not complete the
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// query on the remote server and our underlying connection is about
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// to go away, so we only add relname to l.channels, and wait for
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// resync() to take care of the rest.
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gotResponse, err := l.cn.Listen(channel)
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if gotResponse && err != nil {
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return err
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}
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}
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l.channels[channel] = struct{}{}
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for l.cn == nil {
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l.reconnectCond.Wait()
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// we let go of the mutex for a while
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if l.isClosed {
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return errListenerClosed
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}
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}
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return nil
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}
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// Unlisten removes a channel from the Listener's channel list. Returns
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// ErrChannelNotOpen if the Listener is not listening on the specified channel.
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// Returns immediately with no error if there is no connection. Note that you
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// might still get notifications for this channel even after Unlisten has
|
|
// returned.
|
|
//
|
|
// The channel name is case-sensitive.
|
|
func (l *Listener) Unlisten(channel string) error {
|
|
l.lock.Lock()
|
|
defer l.lock.Unlock()
|
|
|
|
if l.isClosed {
|
|
return errListenerClosed
|
|
}
|
|
|
|
// Similarly to LISTEN, this is not an error in Postgres, but it seems
|
|
// useful to distinguish from the normal conditions.
|
|
_, exists := l.channels[channel]
|
|
if !exists {
|
|
return ErrChannelNotOpen
|
|
}
|
|
|
|
if l.cn != nil {
|
|
// Similarly to Listen (see comment in that function), the caller
|
|
// should only be bothered with an error if it came from the backend as
|
|
// a response to our query.
|
|
gotResponse, err := l.cn.Unlisten(channel)
|
|
if gotResponse && err != nil {
|
|
return err
|
|
}
|
|
}
|
|
|
|
// Don't bother waiting for resync if there's no connection.
|
|
delete(l.channels, channel)
|
|
return nil
|
|
}
|
|
|
|
// UnlistenAll removes all channels from the Listener's channel list. Returns
|
|
// immediately with no error if there is no connection. Note that you might
|
|
// still get notifications for any of the deleted channels even after
|
|
// UnlistenAll has returned.
|
|
func (l *Listener) UnlistenAll() error {
|
|
l.lock.Lock()
|
|
defer l.lock.Unlock()
|
|
|
|
if l.isClosed {
|
|
return errListenerClosed
|
|
}
|
|
|
|
if l.cn != nil {
|
|
// Similarly to Listen (see comment in that function), the caller
|
|
// should only be bothered with an error if it came from the backend as
|
|
// a response to our query.
|
|
gotResponse, err := l.cn.UnlistenAll()
|
|
if gotResponse && err != nil {
|
|
return err
|
|
}
|
|
}
|
|
|
|
// Don't bother waiting for resync if there's no connection.
|
|
l.channels = make(map[string]struct{})
|
|
return nil
|
|
}
|
|
|
|
// Ping the remote server to make sure it's alive. Non-nil return value means
|
|
// that there is no active connection.
|
|
func (l *Listener) Ping() error {
|
|
l.lock.Lock()
|
|
defer l.lock.Unlock()
|
|
|
|
if l.isClosed {
|
|
return errListenerClosed
|
|
}
|
|
if l.cn == nil {
|
|
return errors.New("no connection")
|
|
}
|
|
|
|
return l.cn.Ping()
|
|
}
|
|
|
|
// Clean up after losing the server connection. Returns l.cn.Err(), which
|
|
// should have the reason the connection was lost.
|
|
func (l *Listener) disconnectCleanup() error {
|
|
l.lock.Lock()
|
|
defer l.lock.Unlock()
|
|
|
|
// sanity check; can't look at Err() until the channel has been closed
|
|
select {
|
|
case _, ok := <-l.connNotificationChan:
|
|
if ok {
|
|
panic("connNotificationChan not closed")
|
|
}
|
|
default:
|
|
panic("connNotificationChan not closed")
|
|
}
|
|
|
|
err := l.cn.Err()
|
|
l.cn.Close()
|
|
l.cn = nil
|
|
return err
|
|
}
|
|
|
|
// Synchronize the list of channels we want to be listening on with the server
|
|
// after the connection has been established.
|
|
func (l *Listener) resync(cn *ListenerConn, notificationChan <-chan *Notification) error {
|
|
doneChan := make(chan error)
|
|
go func(notificationChan <-chan *Notification) {
|
|
for channel := range l.channels {
|
|
// If we got a response, return that error to our caller as it's
|
|
// going to be more descriptive than cn.Err().
|
|
gotResponse, err := cn.Listen(channel)
|
|
if gotResponse && err != nil {
|
|
doneChan <- err
|
|
return
|
|
}
|
|
|
|
// If we couldn't reach the server, wait for notificationChan to
|
|
// close and then return the error message from the connection, as
|
|
// per ListenerConn's interface.
|
|
if err != nil {
|
|
for range notificationChan {
|
|
}
|
|
doneChan <- cn.Err()
|
|
return
|
|
}
|
|
}
|
|
doneChan <- nil
|
|
}(notificationChan)
|
|
|
|
// Ignore notifications while synchronization is going on to avoid
|
|
// deadlocks. We have to send a nil notification over Notify anyway as
|
|
// we can't possibly know which notifications (if any) were lost while
|
|
// the connection was down, so there's no reason to try and process
|
|
// these messages at all.
|
|
for {
|
|
select {
|
|
case _, ok := <-notificationChan:
|
|
if !ok {
|
|
notificationChan = nil
|
|
}
|
|
|
|
case err := <-doneChan:
|
|
return err
|
|
}
|
|
}
|
|
}
|
|
|
|
// caller should NOT be holding l.lock
|
|
func (l *Listener) closed() bool {
|
|
l.lock.Lock()
|
|
defer l.lock.Unlock()
|
|
|
|
return l.isClosed
|
|
}
|
|
|
|
func (l *Listener) connect() error {
|
|
notificationChan := make(chan *Notification, 32)
|
|
cn, err := newDialListenerConn(l.dialer, l.name, notificationChan)
|
|
if err != nil {
|
|
return err
|
|
}
|
|
|
|
l.lock.Lock()
|
|
defer l.lock.Unlock()
|
|
|
|
err = l.resync(cn, notificationChan)
|
|
if err != nil {
|
|
cn.Close()
|
|
return err
|
|
}
|
|
|
|
l.cn = cn
|
|
l.connNotificationChan = notificationChan
|
|
l.reconnectCond.Broadcast()
|
|
|
|
return nil
|
|
}
|
|
|
|
// Close disconnects the Listener from the database and shuts it down.
|
|
// Subsequent calls to its methods will return an error. Close returns an
|
|
// error if the connection has already been closed.
|
|
func (l *Listener) Close() error {
|
|
l.lock.Lock()
|
|
defer l.lock.Unlock()
|
|
|
|
if l.isClosed {
|
|
return errListenerClosed
|
|
}
|
|
|
|
if l.cn != nil {
|
|
l.cn.Close()
|
|
}
|
|
l.isClosed = true
|
|
|
|
// Unblock calls to Listen()
|
|
l.reconnectCond.Broadcast()
|
|
|
|
return nil
|
|
}
|
|
|
|
func (l *Listener) emitEvent(event ListenerEventType, err error) {
|
|
if l.eventCallback != nil {
|
|
l.eventCallback(event, err)
|
|
}
|
|
}
|
|
|
|
// Main logic here: maintain a connection to the server when possible, wait
|
|
// for notifications and emit events.
|
|
func (l *Listener) listenerConnLoop() {
|
|
var nextReconnect time.Time
|
|
|
|
reconnectInterval := l.minReconnectInterval
|
|
for {
|
|
for {
|
|
err := l.connect()
|
|
if err == nil {
|
|
break
|
|
}
|
|
|
|
if l.closed() {
|
|
return
|
|
}
|
|
l.emitEvent(ListenerEventConnectionAttemptFailed, err)
|
|
|
|
time.Sleep(reconnectInterval)
|
|
reconnectInterval *= 2
|
|
if reconnectInterval > l.maxReconnectInterval {
|
|
reconnectInterval = l.maxReconnectInterval
|
|
}
|
|
}
|
|
|
|
if nextReconnect.IsZero() {
|
|
l.emitEvent(ListenerEventConnected, nil)
|
|
} else {
|
|
l.emitEvent(ListenerEventReconnected, nil)
|
|
l.Notify <- nil
|
|
}
|
|
|
|
reconnectInterval = l.minReconnectInterval
|
|
nextReconnect = time.Now().Add(reconnectInterval)
|
|
|
|
for {
|
|
notification, ok := <-l.connNotificationChan
|
|
if !ok {
|
|
// lost connection, loop again
|
|
break
|
|
}
|
|
l.Notify <- notification
|
|
}
|
|
|
|
err := l.disconnectCleanup()
|
|
if l.closed() {
|
|
return
|
|
}
|
|
l.emitEvent(ListenerEventDisconnected, err)
|
|
|
|
time.Sleep(time.Until(nextReconnect))
|
|
}
|
|
}
|
|
|
|
func (l *Listener) listenerMain() {
|
|
l.listenerConnLoop()
|
|
close(l.Notify)
|
|
}
|