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// Copyright 2022-2025 The NATS Authors
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
package jetstream
import (
"context"
"encoding/json"
"errors"
"fmt"
"math"
"slices"
"sync"
"sync/atomic"
"time"
"github.com/nats-io/nats.go"
"github.com/nats-io/nats.go/internal/syncx"
"github.com/nats-io/nuid"
)
type (
// MessagesContext supports iterating over a messages on a stream.
// It is returned by [Consumer.Messages] method.
MessagesContext interface {
// Next retrieves next message on a stream. It will block until the next
// message is available. If the context is canceled, Next will return
// ErrMsgIteratorClosed error. An optional timeout or context can be
// provided using NextOpt options. If none are provided, Next will block
// indefinitely until a message is available, iterator is closed or a
// heartbeat error occurs.
Next(opts ...NextOpt) (Msg, error)
// Stop unsubscribes from the stream and cancels subscription. Calling
// Next after calling Stop will return ErrMsgIteratorClosed error.
// All messages that are already in the buffer are discarded.
Stop()
// Drain unsubscribes from the stream and cancels subscription. All
// messages that are already in the buffer will be available on
// subsequent calls to Next. After the buffer is drained, Next will
// return ErrMsgIteratorClosed error.
Drain()
}
// ConsumeContext supports processing incoming messages from a stream.
// It is returned by [Consumer.Consume] method.
ConsumeContext interface {
// Stop unsubscribes from the stream and cancels subscription.
// No more messages will be received after calling this method.
// All messages that are already in the buffer are discarded.
Stop()
// Drain unsubscribes from the stream and cancels subscription.
// All messages that are already in the buffer will be processed in callback function.
Drain()
// Closed returns a channel that is closed when the consuming is
// fully stopped/drained. When the channel is closed, no more messages
// will be received and processing is complete.
Closed() <-chan struct{}
}
// MessageHandler is a handler function used as callback in [Consume].
MessageHandler func(msg Msg)
// PullConsumeOpt represent additional options used in [Consume] for pull consumers.
PullConsumeOpt interface {
configureConsume(*consumeOpts) error
}
// PullMessagesOpt represent additional options used in [Messages] for pull consumers.
PullMessagesOpt interface {
configureMessages(*consumeOpts) error
}
pullConsumer struct {
sync.Mutex
js *jetStream
stream string
durable bool
name string
info *ConsumerInfo
subs syncx.Map[string, *pullSubscription]
pinID string
}
pullRequest struct {
Expires time.Duration `json:"expires,omitempty"`
Batch int `json:"batch,omitempty"`
MaxBytes int `json:"max_bytes,omitempty"`
NoWait bool `json:"no_wait,omitempty"`
Heartbeat time.Duration `json:"idle_heartbeat,omitempty"`
MinPending int64 `json:"min_pending,omitempty"`
MinAckPending int64 `json:"min_ack_pending,omitempty"`
PinID string `json:"id,omitempty"`
Group string `json:"group,omitempty"`
Priority uint8 `json:"priority,omitempty"`
ctx context.Context `json:"-"`
maxWaitSet bool `json:"-"`
}
consumeOpts struct {
Expires time.Duration
MaxMessages int
MaxBytes int
LimitSize bool
MinPending int64
MinAckPending int64
Priority uint8
Group string
Heartbeat time.Duration
ErrHandler ConsumeErrHandler
ReportMissingHeartbeats bool
ThresholdMessages int
ThresholdBytes int
StopAfter int
stopAfterMsgsLeft chan int
notifyOnReconnect bool
}
ConsumeErrHandlerFunc func(consumeCtx ConsumeContext, err error)
pullSubscription struct {
sync.Mutex
id string
consumer *pullConsumer
subscription *nats.Subscription
msgs chan *nats.Msg
errs chan error
pending pendingMsgs
hbMonitor *hbMonitor
fetchInProgress atomic.Uint32
closed atomic.Uint32
draining atomic.Uint32
done chan struct{}
connStatusChanged chan nats.Status
fetchNext chan *pullRequest
consumeOpts *consumeOpts
delivered int
closedCh chan struct{}
}
pendingMsgs struct {
msgCount int
byteCount int
}
MessageBatch interface {
Messages() <-chan Msg
Error() error
}
fetchResult struct {
sync.Mutex
msgs chan Msg
err error
done bool
sseq uint64
}
FetchOpt func(*pullRequest) error
hbMonitor struct {
timer *time.Timer
sync.Mutex
}
// NextOpt is an option for configuring the behavior of MessagesContext.Next.
NextOpt interface {
configureNext(*nextOpts)
}
nextOpts struct {
timeout time.Duration
ctx context.Context
}
)
const (
DefaultMaxMessages = 500
DefaultExpires = 30 * time.Second
defaultBatchMaxBytesOnly = 1_000_000
unset = -1
)
func min(x, y int) int {
if x < y {
return x
}
return y
}
// Consume can be used to continuously receive messages and handle them
// with the provided callback function. Consume cannot be used concurrently
// when using ordered consumer.
//
// See [Consumer.Consume] for more details.
func (p *pullConsumer) Consume(handler MessageHandler, opts ...PullConsumeOpt) (ConsumeContext, error) {
if handler == nil {
return nil, ErrHandlerRequired
}
consumeOpts, err := parseConsumeOpts(false, opts...)
if err != nil {
return nil, fmt.Errorf("%w: %s", ErrInvalidOption, err)
}
if len(p.info.Config.PriorityGroups) != 0 {
if consumeOpts.Group == "" {
return nil, fmt.Errorf("%w: %s", ErrInvalidOption, "priority group is required for priority consumer")
}
if !slices.Contains(p.info.Config.PriorityGroups, consumeOpts.Group) {
return nil, fmt.Errorf("%w: %s", ErrInvalidOption, "invalid priority group")
}
} else if consumeOpts.Group != "" {
return nil, fmt.Errorf("%w: %s", ErrInvalidOption, "priority group is not supported for this consumer")
}
p.Lock()
subject := p.js.apiSubject(fmt.Sprintf(apiRequestNextT, p.stream, p.name))
consumeID := nuid.Next()
sub := &pullSubscription{
id: consumeID,
consumer: p,
errs: make(chan error, 10),
done: make(chan struct{}, 1),
fetchNext: make(chan *pullRequest, 1),
consumeOpts: consumeOpts,
}
sub.connStatusChanged = p.js.conn.StatusChanged(nats.CONNECTED, nats.RECONNECTING, nats.CLOSED)
sub.hbMonitor = sub.scheduleHeartbeatCheck(consumeOpts.Heartbeat)
p.subs.Store(sub.id, sub)
p.Unlock()
internalHandler := func(msg *nats.Msg) {
if sub.hbMonitor != nil {
sub.hbMonitor.Stop()
}
userMsg, msgErr := checkMsg(msg)
if !userMsg && msgErr == nil {
if sub.hbMonitor != nil {
sub.hbMonitor.Reset(2 * consumeOpts.Heartbeat)
}
return
}
defer func() {
sub.Lock()
sub.checkPending()
if sub.hbMonitor != nil {
sub.hbMonitor.Reset(2 * consumeOpts.Heartbeat)
}
sub.Unlock()
}()
if !userMsg {
// heartbeat message
if msgErr == nil {
return
}
sub.Lock()
err := sub.handleStatusMsg(msg, msgErr)
sub.Unlock()
if err != nil {
if sub.closed.Load() == 1 {
return
}
if sub.consumeOpts.ErrHandler != nil {
sub.consumeOpts.ErrHandler(sub, err)
}
sub.Stop()
}
return
}
if pinId := msg.Header.Get("Nats-Pin-Id"); pinId != "" {
p.setPinID(pinId)
}
handler(p.js.toJSMsg(msg))
sub.Lock()
sub.decrementPendingMsgs(msg)
sub.incrementDeliveredMsgs()
sub.Unlock()
if sub.consumeOpts.StopAfter > 0 && sub.consumeOpts.StopAfter == sub.delivered {
sub.Stop()
}
}
inbox := p.js.conn.NewInbox()
sub.subscription, err = p.js.conn.Subscribe(inbox, internalHandler)
if err != nil {
return nil, err
}
sub.subscription.SetClosedHandler(func(sid string) func(string) {
return func(subject string) {
p.subs.Delete(sid)
sub.draining.CompareAndSwap(1, 0)
sub.Lock()
if sub.closedCh != nil {
close(sub.closedCh)
sub.closedCh = nil
}
sub.Unlock()
}
}(sub.id))
sub.Lock()
// initial pull
sub.resetPendingMsgs()
batchSize := sub.consumeOpts.MaxMessages
if sub.consumeOpts.StopAfter > 0 {
batchSize = min(batchSize, sub.consumeOpts.StopAfter-sub.delivered)
}
if err := sub.pull(&pullRequest{
Expires: consumeOpts.Expires,
Batch: batchSize,
MaxBytes: consumeOpts.MaxBytes,
Heartbeat: consumeOpts.Heartbeat,
MinPending: consumeOpts.MinPending,
MinAckPending: consumeOpts.MinAckPending,
Priority: consumeOpts.Priority,
Group: consumeOpts.Group,
PinID: p.getPinID(),
}, subject); err != nil {
sub.errs <- err
}
sub.Unlock()
go func() {
isConnected := true
for {
if sub.closed.Load() == 1 {
return
}
select {
case status, ok := <-sub.connStatusChanged:
if !ok {
continue
}
switch status {
case nats.RECONNECTING:
if sub.hbMonitor != nil {
sub.hbMonitor.Stop()
}
isConnected = false
case nats.CONNECTED:
sub.Lock()
if !isConnected {
isConnected = true
if sub.consumeOpts.notifyOnReconnect {
sub.errs <- errConnected
}
sub.fetchNext <- &pullRequest{
Expires: sub.consumeOpts.Expires,
Batch: sub.consumeOpts.MaxMessages,
MaxBytes: sub.consumeOpts.MaxBytes,
Heartbeat: sub.consumeOpts.Heartbeat,
MinPending: sub.consumeOpts.MinPending,
MinAckPending: sub.consumeOpts.MinAckPending,
Priority: sub.consumeOpts.Priority,
Group: sub.consumeOpts.Group,
PinID: p.getPinID(),
}
if sub.hbMonitor != nil {
sub.hbMonitor.Reset(2 * sub.consumeOpts.Heartbeat)
}
sub.resetPendingMsgs()
}
sub.Unlock()
case nats.CLOSED:
sub.errs <- ErrConnectionClosed
}
case err := <-sub.errs:
sub.Lock()
if sub.consumeOpts.ErrHandler != nil {
sub.consumeOpts.ErrHandler(sub, err)
}
if errors.Is(err, ErrNoHeartbeat) {
batchSize := sub.consumeOpts.MaxMessages
if sub.consumeOpts.StopAfter > 0 {
batchSize = min(batchSize, sub.consumeOpts.StopAfter-sub.delivered)
}
sub.fetchNext <- &pullRequest{
Expires: sub.consumeOpts.Expires,
Batch: batchSize,
MaxBytes: sub.consumeOpts.MaxBytes,
Heartbeat: sub.consumeOpts.Heartbeat,
MinPending: sub.consumeOpts.MinPending,
MinAckPending: sub.consumeOpts.MinAckPending,
Priority: sub.consumeOpts.Priority,
Group: sub.consumeOpts.Group,
PinID: p.getPinID(),
}
if sub.hbMonitor != nil {
sub.hbMonitor.Reset(2 * sub.consumeOpts.Heartbeat)
}
sub.resetPendingMsgs()
}
sub.Unlock()
if errors.Is(err, ErrConnectionClosed) {
sub.Stop()
}
case <-sub.done:
return
}
}
}()
go sub.pullMessages(subject)
return sub, nil
}
// resetPendingMsgs resets pending message count and byte count
// to the values set in consumeOpts
// lock should be held before calling this method
func (s *pullSubscription) resetPendingMsgs() {
s.pending.msgCount = s.consumeOpts.MaxMessages
s.pending.byteCount = s.consumeOpts.MaxBytes
}
// decrementPendingMsgs decrements pending message count and byte count
// lock should be held before calling this method
func (s *pullSubscription) decrementPendingMsgs(msg *nats.Msg) {
s.pending.msgCount--
if s.consumeOpts.MaxBytes != 0 && !s.consumeOpts.LimitSize {
s.pending.byteCount -= msg.Size()
}
}
// incrementDeliveredMsgs increments delivered message count
// lock should be held before calling this method
func (s *pullSubscription) incrementDeliveredMsgs() {
s.delivered++
}
// checkPending verifies whether there are enough messages in
// the buffer to trigger a new pull request.
// lock should be held before calling this method
func (s *pullSubscription) checkPending() {
// check if we went below any threshold
// we don't want to track bytes threshold if either it's not set or we used
// PullMaxMessagesWithBytesLimit
if (s.pending.msgCount < s.consumeOpts.ThresholdMessages ||
(s.pending.byteCount < s.consumeOpts.ThresholdBytes && s.consumeOpts.MaxBytes != 0 && !s.consumeOpts.LimitSize)) &&
s.fetchInProgress.Load() == 0 {
var batchSize, maxBytes int
batchSize = s.consumeOpts.MaxMessages - s.pending.msgCount
if s.consumeOpts.MaxBytes != 0 {
if s.consumeOpts.LimitSize {
maxBytes = s.consumeOpts.MaxBytes
} else {
maxBytes = s.consumeOpts.MaxBytes - s.pending.byteCount
// when working with max bytes only, always ask for full batch
batchSize = s.consumeOpts.MaxMessages
}
}
if s.consumeOpts.StopAfter > 0 {
batchSize = min(batchSize, s.consumeOpts.StopAfter-s.delivered-s.pending.msgCount)
}
if batchSize > 0 {
pinID := ""
if s.consumer != nil {
pinID = s.consumer.getPinID()
}
s.fetchNext <- &pullRequest{
Expires: s.consumeOpts.Expires,
Batch: batchSize,
MaxBytes: maxBytes,
Heartbeat: s.consumeOpts.Heartbeat,
PinID: pinID,
Group: s.consumeOpts.Group,
MinPending: s.consumeOpts.MinPending,
MinAckPending: s.consumeOpts.MinAckPending,
Priority: s.consumeOpts.Priority,
}
s.pending.msgCount = s.consumeOpts.MaxMessages
s.pending.byteCount = s.consumeOpts.MaxBytes
}
}
}
// Messages returns MessagesContext, allowing continuously iterating
// over messages on a stream. Messages cannot be used concurrently
// when using ordered consumer.
//
// See [Consumer.Messages] for more details.
func (p *pullConsumer) Messages(opts ...PullMessagesOpt) (MessagesContext, error) {
consumeOpts, err := parseMessagesOpts(false, opts...)
if err != nil {
return nil, fmt.Errorf("%w: %s", ErrInvalidOption, err)
}
if len(p.info.Config.PriorityGroups) != 0 {
if consumeOpts.Group == "" {
return nil, fmt.Errorf("%w: %s", ErrInvalidOption, "priority group is required for priority consumer")
}
if !slices.Contains(p.info.Config.PriorityGroups, consumeOpts.Group) {
return nil, fmt.Errorf("%w: %s", ErrInvalidOption, "invalid priority group")
}
} else if consumeOpts.Group != "" {
return nil, fmt.Errorf("%w: %s", ErrInvalidOption, "priority group is not supported for this consumer")
}
p.Lock()
subject := p.js.apiSubject(fmt.Sprintf(apiRequestNextT, p.stream, p.name))
msgs := make(chan *nats.Msg, consumeOpts.MaxMessages)
consumeID := nuid.Next()
sub := &pullSubscription{
id: consumeID,
consumer: p,
done: make(chan struct{}, 1),
msgs: msgs,
errs: make(chan error, 10),
fetchNext: make(chan *pullRequest, 1),
consumeOpts: consumeOpts,
}
sub.connStatusChanged = p.js.conn.StatusChanged(nats.CONNECTED, nats.RECONNECTING)
inbox := p.js.conn.NewInbox()
sub.subscription, err = p.js.conn.ChanSubscribe(inbox, sub.msgs)
if err != nil {
p.Unlock()
return nil, err
}
sub.subscription.SetClosedHandler(func(sid string) func(string) {
return func(subject string) {
if sub.draining.Load() != 1 {
// if we're not draining, subscription can be closed as soon
// as closed handler is called
// otherwise, we need to wait until all messages are drained
// in Next
p.subs.Delete(sid)
}
close(msgs)
}
}(sub.id))
p.subs.Store(sub.id, sub)
p.Unlock()
go sub.pullMessages(subject)
go func() {
for {
select {
case status, ok := <-sub.connStatusChanged:
if !ok {
return
}
if status == nats.CONNECTED {
sub.errs <- errConnected
}
if status == nats.RECONNECTING {
sub.errs <- errDisconnected
}
case <-sub.done:
return
}
}
}()
return sub, nil
}
var (
errConnected = errors.New("connected")
errDisconnected = errors.New("disconnected")
)
// Next retrieves next message on a stream. It will block until the next
// message is available. If the context is canceled, Next will return
// ErrMsgIteratorClosed error.
func (s *pullSubscription) Next(opts ...NextOpt) (Msg, error) {
var nextOpts nextOpts
for _, opt := range opts {
opt.configureNext(&nextOpts)
}
if nextOpts.timeout > 0 && nextOpts.ctx != nil {
return nil, fmt.Errorf("%w: cannot specify both NextMaxWait and NextContext", ErrInvalidOption)
}
// Create timeout channel if needed
var timeoutCh <-chan time.Time
if nextOpts.timeout > 0 {
timer := time.NewTimer(nextOpts.timeout)
defer timer.Stop()
timeoutCh = timer.C
}
// Use context if provided
var ctxDone <-chan struct{}
if nextOpts.ctx != nil {
ctxDone = nextOpts.ctx.Done()
}
s.Lock()
defer s.Unlock()
drainMode := s.draining.Load() == 1
closed := s.closed.Load() == 1
if closed && !drainMode {
// Check if iterator was closed due to connection closure
if s.consumer.js.conn.IsClosed() {
return nil, fmt.Errorf("%w: %w", ErrMsgIteratorClosed, ErrConnectionClosed)
}
return nil, ErrMsgIteratorClosed
}
hbMonitor := s.scheduleHeartbeatCheck(s.consumeOpts.Heartbeat)
defer func() {
if hbMonitor != nil {
hbMonitor.Stop()
}
}()
isConnected := true
if s.consumeOpts.StopAfter > 0 && s.delivered >= s.consumeOpts.StopAfter {
s.Stop()
return nil, ErrMsgIteratorClosed
}
for {
s.checkPending()
select {
case msg, ok := <-s.msgs:
if !ok {
// if msgs channel is closed, it means that subscription was either drained or stopped
s.consumer.subs.Delete(s.id)
s.draining.CompareAndSwap(1, 0)
// Check if iterator was closed due to connection closure
if s.consumer.js.conn.IsClosed() {
return nil, fmt.Errorf("%w: %w", ErrMsgIteratorClosed, ErrConnectionClosed)
}
return nil, ErrMsgIteratorClosed
}
if hbMonitor != nil {
hbMonitor.Reset(2 * s.consumeOpts.Heartbeat)
}
userMsg, msgErr := checkMsg(msg)
if !userMsg {
// heartbeat message
if msgErr == nil {
continue
}
if err := s.handleStatusMsg(msg, msgErr); err != nil {
s.Stop()
return nil, err
}
continue
}
if pinId := msg.Header.Get("Nats-Pin-Id"); pinId != "" {
s.consumer.setPinID(pinId)
}
s.decrementPendingMsgs(msg)
s.incrementDeliveredMsgs()
return s.consumer.js.toJSMsg(msg), nil
case err := <-s.errs:
if errors.Is(err, ErrNoHeartbeat) {
s.pending.msgCount = 0
s.pending.byteCount = 0
if s.consumeOpts.ReportMissingHeartbeats {
return nil, err
}
if hbMonitor != nil {
hbMonitor.Reset(2 * s.consumeOpts.Heartbeat)
}
}
if errors.Is(err, errConnected) {
if !isConnected {
isConnected = true
if s.consumeOpts.notifyOnReconnect {
return nil, errConnected
}
s.pending.msgCount = 0
s.pending.byteCount = 0
if hbMonitor != nil {
hbMonitor.Reset(2 * s.consumeOpts.Heartbeat)
}
}
}
if errors.Is(err, errDisconnected) {
if hbMonitor != nil {
hbMonitor.Stop()
}
isConnected = false
}
case <-timeoutCh:
return nil, nats.ErrTimeout
case <-ctxDone:
return nil, nextOpts.ctx.Err()
}
}
}
func (s *pullSubscription) handleStatusMsg(msg *nats.Msg, msgErr error) error {
if !errors.Is(msgErr, nats.ErrTimeout) && !errors.Is(msgErr, ErrMaxBytesExceeded) && !errors.Is(msgErr, ErrBatchCompleted) {
if errors.Is(msgErr, ErrConsumerDeleted) || errors.Is(msgErr, ErrBadRequest) {
return msgErr
}
if errors.Is(msgErr, ErrPinIDMismatch) {
s.consumer.setPinID("")
s.pending.msgCount = 0
s.pending.byteCount = 0
}
if s.consumeOpts.ErrHandler != nil {
s.consumeOpts.ErrHandler(s, msgErr)
}
if errors.Is(msgErr, ErrConsumerLeadershipChanged) {
s.pending.msgCount = 0
s.pending.byteCount = 0
}
return nil
}
msgsLeft, bytesLeft, err := parsePending(msg)
if err != nil {
return err
}
s.pending.msgCount -= msgsLeft
if s.pending.msgCount < 0 {
s.pending.msgCount = 0
}
if s.consumeOpts.MaxBytes > 0 && !s.consumeOpts.LimitSize {
s.pending.byteCount -= bytesLeft
if s.pending.byteCount < 0 {
s.pending.byteCount = 0
}
}
return nil
}
func (hb *hbMonitor) Stop() {
hb.Lock()
hb.timer.Stop()
hb.Unlock()
}
func (hb *hbMonitor) Reset(dur time.Duration) {
hb.Lock()
hb.timer.Reset(dur)
hb.Unlock()
}
// Stop unsubscribes from the stream and cancels subscription. Calling
// Next after calling Stop will return ErrMsgIteratorClosed error.
// All messages that are already in the buffer are discarded.
func (s *pullSubscription) Stop() {
if !s.closed.CompareAndSwap(0, 1) {
return
}
close(s.done)
if s.consumeOpts.stopAfterMsgsLeft != nil {
if s.delivered >= s.consumeOpts.StopAfter {
close(s.consumeOpts.stopAfterMsgsLeft)
} else {
s.consumeOpts.stopAfterMsgsLeft <- s.consumeOpts.StopAfter - s.delivered
}
}
}
// Drain unsubscribes from the stream and cancels subscription. All
// messages that are already in the buffer will be available on
// subsequent calls to Next. After the buffer is drained, Next will
// return ErrMsgIteratorClosed error.
func (s *pullSubscription) Drain() {
if !s.closed.CompareAndSwap(0, 1) {
return
}
s.draining.Store(1)
close(s.done)
if s.consumeOpts.stopAfterMsgsLeft != nil {
if s.delivered >= s.consumeOpts.StopAfter {
close(s.consumeOpts.stopAfterMsgsLeft)
} else {
s.consumeOpts.stopAfterMsgsLeft <- s.consumeOpts.StopAfter - s.delivered
}
}
}
// Closed returns a channel that is closed when consuming is
// fully stopped/drained. When the channel is closed, no more messages
// will be received and processing is complete.
func (s *pullSubscription) Closed() <-chan struct{} {
s.Lock()
defer s.Unlock()
closedCh := s.closedCh
if closedCh == nil {
closedCh = make(chan struct{})
s.closedCh = closedCh
}
if !s.subscription.IsValid() {
close(s.closedCh)
s.closedCh = nil
}
return closedCh
}
// Fetch sends a single request to retrieve given number of messages.
// It will wait up to provided expiry time if not all messages are available.
func (p *pullConsumer) Fetch(batch int, opts ...FetchOpt) (MessageBatch, error) {
req := &pullRequest{
Batch: batch,
Expires: DefaultExpires,
Heartbeat: unset,
}
for _, opt := range opts {
if err := opt(req); err != nil {
return nil, err
}
}
if req.ctx != nil && req.maxWaitSet {
return nil, fmt.Errorf("%w: cannot specify both FetchContext and FetchMaxWait", ErrInvalidOption)
}
// if heartbeat was not explicitly set, set it to 5 seconds for longer pulls
// and disable it for shorter pulls
if req.Heartbeat == unset {
if req.Expires >= 10*time.Second {
req.Heartbeat = 5 * time.Second
} else {
req.Heartbeat = 0
}
}
if req.Expires < 2*req.Heartbeat {
return nil, fmt.Errorf("%w: expiry time should be at least 2 times the heartbeat", ErrInvalidOption)
}
return p.fetch(req)
}
// FetchBytes is used to retrieve up to a provided bytes from the stream.
func (p *pullConsumer) FetchBytes(maxBytes int, opts ...FetchOpt) (MessageBatch, error) {
req := &pullRequest{
Batch: defaultBatchMaxBytesOnly,
MaxBytes: maxBytes,
Expires: DefaultExpires,
Heartbeat: unset,
}
for _, opt := range opts {
if err := opt(req); err != nil {
return nil, err
}
}
if req.ctx != nil && req.maxWaitSet {
return nil, fmt.Errorf("%w: cannot specify both FetchContext and FetchMaxWait", ErrInvalidOption)
}
// if heartbeat was not explicitly set, set it to 5 seconds for longer pulls
// and disable it for shorter pulls
if req.Heartbeat == unset {
if req.Expires >= 10*time.Second {
req.Heartbeat = 5 * time.Second
} else {
req.Heartbeat = 0
}
}
if req.Expires < 2*req.Heartbeat {
return nil, fmt.Errorf("%w: expiry time should be at least 2 times the heartbeat", ErrInvalidOption)
}
return p.fetch(req)
}
// FetchNoWait sends a single request to retrieve given number of messages.
// FetchNoWait will only return messages that are available at the time of the
// request. It will not wait for more messages to arrive.
func (p *pullConsumer) FetchNoWait(batch int) (MessageBatch, error) {
req := &pullRequest{
Batch: batch,
NoWait: true,
}
return p.fetch(req)
}
func (p *pullConsumer) fetch(req *pullRequest) (MessageBatch, error) {
res := &fetchResult{
msgs: make(chan Msg, req.Batch),
}
msgs := make(chan *nats.Msg, 2*req.Batch)
subject := p.js.apiSubject(fmt.Sprintf(apiRequestNextT, p.stream, p.name))
sub := &pullSubscription{
consumer: p,
done: make(chan struct{}, 1),
msgs: msgs,
errs: make(chan error, 10),
}
inbox := p.js.conn.NewInbox()
var err error
sub.subscription, err = p.js.conn.ChanSubscribe(inbox, sub.msgs)
if err != nil {
return nil, err
}
req.PinID = p.getPinID()
if err := sub.pull(req, subject); err != nil {
return nil, err
}
var receivedMsgs, receivedBytes int
hbTimer := sub.scheduleHeartbeatCheck(req.Heartbeat)
// Use context if provided
var ctxDone <-chan struct{}
if req.ctx != nil {
ctxDone = req.ctx.Done()
}
go func(res *fetchResult) {
defer sub.subscription.Unsubscribe()
defer close(res.msgs)
for {
select {
case msg := <-msgs:
res.Lock()
if hbTimer != nil {
hbTimer.Reset(2 * req.Heartbeat)
}
userMsg, err := checkMsg(msg)
if err != nil {
errNotTimeoutOrNoMsgs := !errors.Is(err, nats.ErrTimeout) && !errors.Is(err, ErrNoMessages)
if errNotTimeoutOrNoMsgs && !errors.Is(err, ErrMaxBytesExceeded) {
res.err = err
}
if errors.Is(err, ErrPinIDMismatch) {
p.setPinID("")
}
res.done = true
res.Unlock()
return
}
if !userMsg {
res.Unlock()
continue
}
if pinId := msg.Header.Get("Nats-Pin-Id"); pinId != "" {
p.setPinID(pinId)
}
res.msgs <- p.js.toJSMsg(msg)
meta, err := msg.Metadata()
if err != nil {
res.err = fmt.Errorf("parsing message metadata: %s", err)
res.done = true
res.Unlock()
return
}
res.sseq = meta.Sequence.Stream
receivedMsgs++
if req.MaxBytes != 0 {
receivedBytes += msg.Size()
}
if receivedMsgs == req.Batch || (req.MaxBytes != 0 && receivedBytes >= req.MaxBytes) {
res.done = true
res.Unlock()
return
}
res.Unlock()
case err := <-sub.errs:
res.Lock()
res.err = err
res.done = true
res.Unlock()
return
case <-time.After(req.Expires + 1*time.Second):
res.Lock()
res.done = true
res.Unlock()
return
case <-ctxDone:
res.Lock()
res.err = req.ctx.Err()
res.done = true
res.Unlock()
return
}
}
}(res)
return res, nil
}
func (fr *fetchResult) Messages() <-chan Msg {
fr.Lock()
defer fr.Unlock()
return fr.msgs
}
func (fr *fetchResult) Error() error {
fr.Lock()
defer fr.Unlock()
return fr.err
}
func (fr *fetchResult) closed() bool {
fr.Lock()
defer fr.Unlock()
return fr.done
}
// Next is used to retrieve the next message from the stream. This
// method will block until the message is retrieved or timeout is
// reached.
func (p *pullConsumer) Next(opts ...FetchOpt) (Msg, error) {
res, err := p.Fetch(1, opts...)
if err != nil {
return nil, err
}
msg := <-res.Messages()
if msg != nil {
return msg, nil
}
if res.Error() == nil {
return nil, nats.ErrTimeout
}
return nil, res.Error()
}
func (s *pullSubscription) pullMessages(subject string) {
for {
select {
case req := <-s.fetchNext:
s.fetchInProgress.Store(1)
if err := s.pull(req, subject); err != nil {
if errors.Is(err, ErrMsgIteratorClosed) {
s.cleanup()
return
}
s.errs <- err
}
s.fetchInProgress.Store(0)
case <-s.done:
s.cleanup()
return
}
}
}
func (s *pullSubscription) scheduleHeartbeatCheck(dur time.Duration) *hbMonitor {
if dur == 0 {
return nil
}
return &hbMonitor{
timer: time.AfterFunc(2*dur, func() {
s.errs <- ErrNoHeartbeat
}),
}
}
func (s *pullSubscription) cleanup() {
// For now this function does not need to hold the lock.
// Holding the lock here might cause a deadlock if Next()
// is already holding the lock and waiting.
// The fields that are read (subscription, hbMonitor)
// are read only (Only written on creation of pullSubscription).
if s.subscription == nil || !s.subscription.IsValid() {
return
}
if s.hbMonitor != nil {
s.hbMonitor.Stop()
}
drainMode := s.draining.Load() == 1
if drainMode {
s.subscription.Drain()
} else {
s.subscription.Unsubscribe()
}
s.closed.Store(1)
}
// pull sends a pull request to the server and waits for messages using a subscription from [pullSubscription].
// Messages will be fetched up to given batch_size or until there are no more messages or timeout is returned
func (s *pullSubscription) pull(req *pullRequest, subject string) error {
s.consumer.Lock()
defer s.consumer.Unlock()
if s.closed.Load() == 1 {
return ErrMsgIteratorClosed
}
if req.Batch < 1 {
return fmt.Errorf("%w: batch size must be at least 1", nats.ErrInvalidArg)
}
reqJSON, err := json.Marshal(req)
if err != nil {
return err
}
reply := s.subscription.Subject
if err := s.consumer.js.conn.PublishRequest(subject, reply, reqJSON); err != nil {
return err
}
return nil
}
func parseConsumeOpts(ordered bool, opts ...PullConsumeOpt) (*consumeOpts, error) {
consumeOpts := &consumeOpts{
MaxMessages: unset,
MaxBytes: unset,
Expires: DefaultExpires,
Heartbeat: unset,
ReportMissingHeartbeats: true,
StopAfter: unset,
}
for _, opt := range opts {
if err := opt.configureConsume(consumeOpts); err != nil {
return nil, err
}
}
if err := consumeOpts.setDefaults(ordered); err != nil {
return nil, err
}
return consumeOpts, nil
}
func parseMessagesOpts(ordered bool, opts ...PullMessagesOpt) (*consumeOpts, error) {
consumeOpts := &consumeOpts{
MaxMessages: unset,
MaxBytes: unset,
Expires: DefaultExpires,
Heartbeat: unset,
ReportMissingHeartbeats: true,
StopAfter: unset,
}
for _, opt := range opts {
if err := opt.configureMessages(consumeOpts); err != nil {
return nil, err
}
}
if err := consumeOpts.setDefaults(ordered); err != nil {
return nil, err
}
return consumeOpts, nil
}
func (consumeOpts *consumeOpts) setDefaults(ordered bool) error {
// we cannot use both max messages and max bytes unless we're using max bytes as fetch size limiter
if consumeOpts.MaxBytes != unset && consumeOpts.MaxMessages != unset && !consumeOpts.LimitSize {
return errors.New("only one of MaxMessages and MaxBytes can be specified")
}
if consumeOpts.MaxBytes != unset && !consumeOpts.LimitSize {
// we used PullMaxBytes setting, set MaxMessages to a high value
consumeOpts.MaxMessages = defaultBatchMaxBytesOnly
} else if consumeOpts.MaxMessages == unset {
// otherwise, if max messages is not set, set it to default value
consumeOpts.MaxMessages = DefaultMaxMessages
}
// if user did not set max bytes, set it to 0
if consumeOpts.MaxBytes == unset {
consumeOpts.MaxBytes = 0
}
if consumeOpts.ThresholdMessages == 0 {
// half of the max messages, rounded up
consumeOpts.ThresholdMessages = int(math.Ceil(float64(consumeOpts.MaxMessages) / 2))
}
if consumeOpts.ThresholdBytes == 0 {
// half of the max bytes, rounded up
consumeOpts.ThresholdBytes = int(math.Ceil(float64(consumeOpts.MaxBytes) / 2))
}
// set default heartbeats
if consumeOpts.Heartbeat == unset {
// by default, use 50% of expiry time
consumeOpts.Heartbeat = consumeOpts.Expires / 2
if ordered {
// for ordered consumers, the default heartbeat is 5 seconds
if consumeOpts.Expires < 10*time.Second {
consumeOpts.Heartbeat = consumeOpts.Expires / 2
} else {
consumeOpts.Heartbeat = 5 * time.Second
}
} else if consumeOpts.Heartbeat > 30*time.Second {
// cap the heartbeat to 30 seconds
consumeOpts.Heartbeat = 30 * time.Second
}
}
if consumeOpts.Heartbeat > consumeOpts.Expires/2 {
return fmt.Errorf("%w: the value of Heartbeat must be less than 50%% of expiry", ErrInvalidOption)
}
return nil
}
func (c *pullConsumer) getPinID() string {
c.Lock()
defer c.Unlock()
return c.pinID
}
func (c *pullConsumer) setPinID(pinID string) {
c.Lock()
defer c.Unlock()
c.pinID = pinID
}
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