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Diffstat (limited to 'vendor/github.com/lib/pq/notify.go')
| -rw-r--r-- | vendor/github.com/lib/pq/notify.go | 858 |
1 files changed, 858 insertions, 0 deletions
diff --git a/vendor/github.com/lib/pq/notify.go b/vendor/github.com/lib/pq/notify.go new file mode 100644 index 0000000..5c421fd --- /dev/null +++ b/vendor/github.com/lib/pq/notify.go @@ -0,0 +1,858 @@ +package pq + +// Package pq is a pure Go Postgres driver for the database/sql package. +// This module contains support for Postgres LISTEN/NOTIFY. + +import ( + "context" + "database/sql/driver" + "errors" + "fmt" + "sync" + "sync/atomic" + "time" +) + +// Notification represents a single notification from the database. +type Notification struct { + // Process ID (PID) of the notifying postgres backend. + BePid int + // Name of the channel the notification was sent on. + Channel string + // Payload, or the empty string if unspecified. + Extra string +} + +func recvNotification(r *readBuf) *Notification { + bePid := r.int32() + channel := r.string() + extra := r.string() + + return &Notification{bePid, channel, extra} +} + +// SetNotificationHandler sets the given notification handler on the given +// connection. A runtime panic occurs if c is not a pq connection. A nil handler +// may be used to unset it. +// +// Note: Notification handlers are executed synchronously by pq meaning commands +// won't continue to be processed until the handler returns. +func SetNotificationHandler(c driver.Conn, handler func(*Notification)) { + c.(*conn).notificationHandler = handler +} + +// NotificationHandlerConnector wraps a regular connector and sets a notification handler +// on it. +type NotificationHandlerConnector struct { + driver.Connector + notificationHandler func(*Notification) +} + +// Connect calls the underlying connector's connect method and then sets the +// notification handler. +func (n *NotificationHandlerConnector) Connect(ctx context.Context) (driver.Conn, error) { + c, err := n.Connector.Connect(ctx) + if err == nil { + SetNotificationHandler(c, n.notificationHandler) + } + return c, err +} + +// ConnectorNotificationHandler returns the currently set notification handler, if any. If +// the given connector is not a result of ConnectorWithNotificationHandler, nil is +// returned. +func ConnectorNotificationHandler(c driver.Connector) func(*Notification) { + if c, ok := c.(*NotificationHandlerConnector); ok { + return c.notificationHandler + } + return nil +} + +// ConnectorWithNotificationHandler creates or sets the given handler for the given +// connector. If the given connector is a result of calling this function +// previously, it is simply set on the given connector and returned. Otherwise, +// this returns a new connector wrapping the given one and setting the notification +// handler. A nil notification handler may be used to unset it. +// +// The returned connector is intended to be used with database/sql.OpenDB. +// +// Note: Notification handlers are executed synchronously by pq meaning commands +// won't continue to be processed until the handler returns. +func ConnectorWithNotificationHandler(c driver.Connector, handler func(*Notification)) *NotificationHandlerConnector { + if c, ok := c.(*NotificationHandlerConnector); ok { + c.notificationHandler = handler + return c + } + return &NotificationHandlerConnector{Connector: c, notificationHandler: handler} +} + +const ( + connStateIdle int32 = iota + connStateExpectResponse + connStateExpectReadyForQuery +) + +type message struct { + typ byte + err error +} + +var errListenerConnClosed = errors.New("pq: ListenerConn has been closed") + +// ListenerConn is a low-level interface for waiting for notifications. You +// should use Listener instead. +type ListenerConn struct { + // guards cn and err + connectionLock sync.Mutex + cn *conn + err error + + connState int32 + + // the sending goroutine will be holding this lock + senderLock sync.Mutex + + notificationChan chan<- *Notification + + replyChan chan message +} + +// NewListenerConn creates a new ListenerConn. Use NewListener instead. +func NewListenerConn(name string, notificationChan chan<- *Notification) (*ListenerConn, error) { + return newDialListenerConn(defaultDialer{}, name, notificationChan) +} + +func newDialListenerConn(d Dialer, name string, c chan<- *Notification) (*ListenerConn, error) { + cn, err := DialOpen(d, name) + if err != nil { + return nil, err + } + + l := &ListenerConn{ + cn: cn.(*conn), + notificationChan: c, + connState: connStateIdle, + replyChan: make(chan message, 2), + } + + go l.listenerConnMain() + + return l, nil +} + +// We can only allow one goroutine at a time to be running a query on the +// connection for various reasons, so the goroutine sending on the connection +// must be holding senderLock. +// +// Returns an error if an unrecoverable error has occurred and the ListenerConn +// should be abandoned. +func (l *ListenerConn) acquireSenderLock() error { + // we must acquire senderLock first to avoid deadlocks; see ExecSimpleQuery + l.senderLock.Lock() + + l.connectionLock.Lock() + err := l.err + l.connectionLock.Unlock() + if err != nil { + l.senderLock.Unlock() + return err + } + return nil +} + +func (l *ListenerConn) releaseSenderLock() { + l.senderLock.Unlock() +} + +// setState advances the protocol state to newState. Returns false if moving +// to that state from the current state is not allowed. +func (l *ListenerConn) setState(newState int32) bool { + var expectedState int32 + + switch newState { + case connStateIdle: + expectedState = connStateExpectReadyForQuery + case connStateExpectResponse: + expectedState = connStateIdle + case connStateExpectReadyForQuery: + expectedState = connStateExpectResponse + default: + panic(fmt.Sprintf("unexpected listenerConnState %d", newState)) + } + + return atomic.CompareAndSwapInt32(&l.connState, expectedState, newState) +} + +// Main logic is here: receive messages from the postgres backend, forward +// notifications and query replies and keep the internal state in sync with the +// protocol state. Returns when the connection has been lost, is about to go +// away or should be discarded because we couldn't agree on the state with the +// server backend. +func (l *ListenerConn) listenerConnLoop() (err error) { + defer errRecoverNoErrBadConn(&err) + + r := &readBuf{} + for { + t, err := l.cn.recvMessage(r) + if err != nil { + return err + } + + switch t { + case 'A': + // recvNotification copies all the data so we don't need to worry + // about the scratch buffer being overwritten. + l.notificationChan <- recvNotification(r) + + case 'T', 'D': + // only used by tests; ignore + + case 'E': + // We might receive an ErrorResponse even when not in a query; it + // is expected that the server will close the connection after + // that, but we should make sure that the error we display is the + // one from the stray ErrorResponse, not io.ErrUnexpectedEOF. + if !l.setState(connStateExpectReadyForQuery) { + return parseError(r) + } + l.replyChan <- message{t, parseError(r)} + + case 'C', 'I': + if !l.setState(connStateExpectReadyForQuery) { + // protocol out of sync + return fmt.Errorf("unexpected CommandComplete") + } + // ExecSimpleQuery doesn't need to know about this message + + case 'Z': + if !l.setState(connStateIdle) { + // protocol out of sync + return fmt.Errorf("unexpected ReadyForQuery") + } + l.replyChan <- message{t, nil} + + case 'S': + // ignore + case 'N': + if n := l.cn.noticeHandler; n != nil { + n(parseError(r)) + } + default: + return fmt.Errorf("unexpected message %q from server in listenerConnLoop", t) + } + } +} + +// This is the main routine for the goroutine receiving on the database +// connection. Most of the main logic is in listenerConnLoop. +func (l *ListenerConn) listenerConnMain() { + err := l.listenerConnLoop() + + // listenerConnLoop terminated; we're done, but we still have to clean up. + // Make sure nobody tries to start any new queries by making sure the err + // pointer is set. It is important that we do not overwrite its value; a + // connection could be closed by either this goroutine or one sending on + // the connection -- whoever closes the connection is assumed to have the + // more meaningful error message (as the other one will probably get + // net.errClosed), so that goroutine sets the error we expose while the + // other error is discarded. If the connection is lost while two + // goroutines are operating on the socket, it probably doesn't matter which + // error we expose so we don't try to do anything more complex. + l.connectionLock.Lock() + if l.err == nil { + l.err = err + } + l.cn.Close() + l.connectionLock.Unlock() + + // There might be a query in-flight; make sure nobody's waiting for a + // response to it, since there's not going to be one. + close(l.replyChan) + + // let the listener know we're done + close(l.notificationChan) + + // this ListenerConn is done +} + +// Listen sends a LISTEN query to the server. See ExecSimpleQuery. +func (l *ListenerConn) Listen(channel string) (bool, error) { + return l.ExecSimpleQuery("LISTEN " + QuoteIdentifier(channel)) +} + +// Unlisten sends an UNLISTEN query to the server. See ExecSimpleQuery. +func (l *ListenerConn) Unlisten(channel string) (bool, error) { + return l.ExecSimpleQuery("UNLISTEN " + QuoteIdentifier(channel)) +} + +// UnlistenAll sends an `UNLISTEN *` query to the server. See ExecSimpleQuery. +func (l *ListenerConn) UnlistenAll() (bool, error) { + return l.ExecSimpleQuery("UNLISTEN *") +} + +// Ping the remote server to make sure it's alive. Non-nil error means the +// connection has failed and should be abandoned. +func (l *ListenerConn) Ping() error { + sent, err := l.ExecSimpleQuery("") + if !sent { + return err + } + if err != nil { + // shouldn't happen + panic(err) + } + return nil +} + +// Attempt to send a query on the connection. Returns an error if sending the +// query failed, and the caller should initiate closure of this connection. +// The caller must be holding senderLock (see acquireSenderLock and +// releaseSenderLock). +func (l *ListenerConn) sendSimpleQuery(q string) (err error) { + defer errRecoverNoErrBadConn(&err) + + // must set connection state before sending the query + if !l.setState(connStateExpectResponse) { + panic("two queries running at the same time") + } + + // Can't use l.cn.writeBuf here because it uses the scratch buffer which + // might get overwritten by listenerConnLoop. + b := &writeBuf{ + buf: []byte("Q\x00\x00\x00\x00"), + pos: 1, + } + b.string(q) + l.cn.send(b) + + return nil +} + +// ExecSimpleQuery executes a "simple query" (i.e. one with no bindable +// parameters) on the connection. The possible return values are: +// 1) "executed" is true; the query was executed to completion on the +// database server. If the query failed, err will be set to the error +// returned by the database, otherwise err will be nil. +// 2) If "executed" is false, the query could not be executed on the remote +// server. err will be non-nil. +// +// After a call to ExecSimpleQuery has returned an executed=false value, the +// connection has either been closed or will be closed shortly thereafter, and +// all subsequently executed queries will return an error. +func (l *ListenerConn) ExecSimpleQuery(q string) (executed bool, err error) { + if err = l.acquireSenderLock(); err != nil { + return false, err + } + defer l.releaseSenderLock() + + err = l.sendSimpleQuery(q) + if err != nil { + // We can't know what state the protocol is in, so we need to abandon + // this connection. + l.connectionLock.Lock() + // Set the error pointer if it hasn't been set already; see + // listenerConnMain. + if l.err == nil { + l.err = err + } + l.connectionLock.Unlock() + l.cn.c.Close() + return false, err + } + + // now we just wait for a reply.. + for { + m, ok := <-l.replyChan + if !ok { + // We lost the connection to server, don't bother waiting for a + // a response. err should have been set already. + l.connectionLock.Lock() + err := l.err + l.connectionLock.Unlock() + return false, err + } + switch m.typ { + case 'Z': + // sanity check + if m.err != nil { + panic("m.err != nil") + } + // done; err might or might not be set + return true, err + + case 'E': + // sanity check + if m.err == nil { + panic("m.err == nil") + } + // server responded with an error; ReadyForQuery to follow + err = m.err + + default: + return false, fmt.Errorf("unknown response for simple query: %q", m.typ) + } + } +} + +// Close closes the connection. +func (l *ListenerConn) Close() error { + l.connectionLock.Lock() + if l.err != nil { + l.connectionLock.Unlock() + return errListenerConnClosed + } + l.err = errListenerConnClosed + l.connectionLock.Unlock() + // We can't send anything on the connection without holding senderLock. + // Simply close the net.Conn to wake up everyone operating on it. + return l.cn.c.Close() +} + +// Err returns the reason the connection was closed. It is not safe to call +// this function until l.Notify has been closed. +func (l *ListenerConn) Err() error { + return l.err +} + +var errListenerClosed = errors.New("pq: Listener has been closed") + +// ErrChannelAlreadyOpen is returned from Listen when a channel is already +// open. +var ErrChannelAlreadyOpen = errors.New("pq: channel is already open") + +// ErrChannelNotOpen is returned from Unlisten when a channel is not open. +var ErrChannelNotOpen = errors.New("pq: channel is not open") + +// ListenerEventType is an enumeration of listener event types. +type ListenerEventType int + +const ( + // ListenerEventConnected is emitted only when the database connection + // has been initially initialized. The err argument of the callback + // will always be nil. + ListenerEventConnected ListenerEventType = iota + + // ListenerEventDisconnected is emitted after a database connection has + // been lost, either because of an error or because Close has been + // called. The err argument will be set to the reason the database + // connection was lost. + ListenerEventDisconnected + + // ListenerEventReconnected is emitted after a database connection has + // been re-established after connection loss. The err argument of the + // callback will always be nil. After this event has been emitted, a + // nil pq.Notification is sent on the Listener.Notify channel. + ListenerEventReconnected + + // ListenerEventConnectionAttemptFailed is emitted after a connection + // to the database was attempted, but failed. The err argument will be + // set to an error describing why the connection attempt did not + // succeed. + ListenerEventConnectionAttemptFailed +) + +// EventCallbackType is the event callback type. See also ListenerEventType +// constants' documentation. +type EventCallbackType func(event ListenerEventType, err error) + +// Listener provides an interface for listening to notifications from a +// PostgreSQL database. For general usage information, see section +// "Notifications". +// +// Listener can safely be used from concurrently running goroutines. +type Listener struct { + // Channel for receiving notifications from the database. In some cases a + // nil value will be sent. See section "Notifications" above. + Notify chan *Notification + + name string + minReconnectInterval time.Duration + maxReconnectInterval time.Duration + dialer Dialer + eventCallback EventCallbackType + + lock sync.Mutex + isClosed bool + reconnectCond *sync.Cond + cn *ListenerConn + connNotificationChan <-chan *Notification + channels map[string]struct{} +} + +// NewListener creates a new database connection dedicated to LISTEN / NOTIFY. +// +// name should be set to a connection string to be used to establish the +// database connection (see section "Connection String Parameters" above). +// +// minReconnectInterval controls the duration to wait before trying to +// re-establish the database connection after connection loss. After each +// consecutive failure this interval is doubled, until maxReconnectInterval is +// reached. Successfully completing the connection establishment procedure +// resets the interval back to minReconnectInterval. +// +// The last parameter eventCallback can be set to a function which will be +// called by the Listener when the state of the underlying database connection +// changes. This callback will be called by the goroutine which dispatches the +// notifications over the Notify channel, so you should try to avoid doing +// potentially time-consuming operations from the callback. +func NewListener(name string, + minReconnectInterval time.Duration, + maxReconnectInterval time.Duration, + eventCallback EventCallbackType) *Listener { + return NewDialListener(defaultDialer{}, name, minReconnectInterval, maxReconnectInterval, eventCallback) +} + +// NewDialListener is like NewListener but it takes a Dialer. +func NewDialListener(d Dialer, + name string, + minReconnectInterval time.Duration, + maxReconnectInterval time.Duration, + eventCallback EventCallbackType) *Listener { + + l := &Listener{ + name: name, + minReconnectInterval: minReconnectInterval, + maxReconnectInterval: maxReconnectInterval, + dialer: d, + eventCallback: eventCallback, + + channels: make(map[string]struct{}), + + Notify: make(chan *Notification, 32), + } + l.reconnectCond = sync.NewCond(&l.lock) + + go l.listenerMain() + + return l +} + +// NotificationChannel returns the notification channel for this listener. +// This is the same channel as Notify, and will not be recreated during the +// life time of the Listener. +func (l *Listener) NotificationChannel() <-chan *Notification { + return l.Notify +} + +// Listen starts listening for notifications on a channel. Calls to this +// function will block until an acknowledgement has been received from the +// server. Note that Listener automatically re-establishes the connection +// after connection loss, so this function may block indefinitely if the +// connection can not be re-established. +// +// Listen will only fail in three conditions: +// 1) The channel is already open. The returned error will be +// ErrChannelAlreadyOpen. +// 2) The query was executed on the remote server, but PostgreSQL returned an +// error message in response to the query. The returned error will be a +// pq.Error containing the information the server supplied. +// 3) Close is called on the Listener before the request could be completed. +// +// The channel name is case-sensitive. +func (l *Listener) Listen(channel string) error { + l.lock.Lock() + defer l.lock.Unlock() + + if l.isClosed { + return errListenerClosed + } + + // The server allows you to issue a LISTEN on a channel which is already + // open, but it seems useful to be able to detect this case to spot for + // mistakes in application logic. If the application genuinely does't + // care, it can check the exported error and ignore it. + _, exists := l.channels[channel] + if exists { + return ErrChannelAlreadyOpen + } + + if l.cn != nil { + // If gotResponse is true but error is set, the query was executed on + // the remote server, but resulted in an error. This should be + // relatively rare, so it's fine if we just pass the error to our + // caller. However, if gotResponse is false, we could not complete the + // query on the remote server and our underlying connection is about + // to go away, so we only add relname to l.channels, and wait for + // resync() to take care of the rest. + gotResponse, err := l.cn.Listen(channel) + if gotResponse && err != nil { + return err + } + } + + l.channels[channel] = struct{}{} + for l.cn == nil { + l.reconnectCond.Wait() + // we let go of the mutex for a while + if l.isClosed { + return errListenerClosed + } + } + + return nil +} + +// Unlisten removes a channel from the Listener's channel list. Returns +// ErrChannelNotOpen if the Listener is not listening on the specified channel. +// Returns immediately with no error if there is no connection. Note that you +// 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) +} |