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input.go
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input.go
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package nats
import (
"context"
"crypto/tls"
"errors"
"strings"
"sync"
"time"
"github.com/nats-io/nats.go"
"github.com/benthosdev/benthos/v4/internal/impl/nats/auth"
"github.com/benthosdev/benthos/v4/public/service"
)
func natsInputConfig() *service.ConfigSpec {
return service.NewConfigSpec().
Stable().
Categories("Services").
Summary(`Subscribe to a NATS subject.`).
Description(`
### Metadata
This input adds the following metadata fields to each message:
` + "``` text" + `
- nats_subject
- All message headers (when supported by the connection)
` + "```" + `
You can access these metadata fields using [function interpolation](/docs/configuration/interpolation#bloblang-queries).
` + ConnectionNameDescription() + auth.Description()).
Field(service.NewStringListField("urls").
Description("A list of URLs to connect to. If an item of the list contains commas it will be expanded into multiple URLs.").
Example([]string{"nats://127.0.0.1:4222"}).
Example([]string{"nats://username:password@127.0.0.1:4222"})).
Field(service.NewStringField("subject").
Description("A subject to consume from. Supports wildcards for consuming multiple subjects. Either a subject or stream must be specified.").
Example("foo.bar.baz").Example("foo.*.baz").Example("foo.bar.*").Example("foo.>")).
Field(service.NewStringField("queue").
Description("An optional queue group to consume as.").
Optional()).
Field(service.NewDurationField("nak_delay").
Description("An optional delay duration on redelivering a message when negatively acknowledged.").
Example("1m").
Advanced().
Optional()).
Field(service.NewIntField("prefetch_count").
Description("The maximum number of messages to pull at a time.").
Advanced().
Default(nats.DefaultSubPendingMsgsLimit).
LintRule(`root = if this < 0 { ["prefetch count must be greater than or equal to zero"] }`)).
Field(service.NewTLSToggledField("tls")).
Field(service.NewInternalField(auth.FieldSpec()))
}
func init() {
err := service.RegisterInput(
"nats", natsInputConfig(),
func(conf *service.ParsedConfig, mgr *service.Resources) (service.Input, error) {
input, err := newNATSReader(conf, mgr)
return service.AutoRetryNacks(input), err
},
)
if err != nil {
panic(err)
}
}
type natsReader struct {
label string
urls string
subject string
queue string
prefetchCount int
nakDelay time.Duration
authConf auth.Config
tlsConf *tls.Config
log *service.Logger
fs *service.FS
cMut sync.Mutex
natsConn *nats.Conn
natsSub *nats.Subscription
natsChan chan *nats.Msg
interruptChan chan struct{}
interruptOnce sync.Once
}
func newNATSReader(conf *service.ParsedConfig, mgr *service.Resources) (*natsReader, error) {
n := natsReader{
label: mgr.Label(),
log: mgr.Logger(),
fs: mgr.FS(),
interruptChan: make(chan struct{}),
}
urlList, err := conf.FieldStringList("urls")
if err != nil {
return nil, err
}
n.urls = strings.Join(urlList, ",")
if n.subject, err = conf.FieldString("subject"); err != nil {
return nil, err
}
if n.prefetchCount, err = conf.FieldInt("prefetch_count"); err != nil {
return nil, err
}
if n.prefetchCount < 0 {
return nil, errors.New("prefetch count must be greater than or equal to zero")
}
if conf.Contains("nak_delay") {
if n.nakDelay, err = conf.FieldDuration("nak_delay"); err != nil {
return nil, err
}
}
if conf.Contains("queue") {
if n.queue, err = conf.FieldString("queue"); err != nil {
return nil, err
}
}
tlsConf, tlsEnabled, err := conf.FieldTLSToggled("tls")
if err != nil {
return nil, err
}
if tlsEnabled {
n.tlsConf = tlsConf
}
if n.authConf, err = AuthFromParsedConfig(conf.Namespace("auth")); err != nil {
return nil, err
}
return &n, nil
}
func (n *natsReader) Connect(ctx context.Context) error {
n.cMut.Lock()
defer n.cMut.Unlock()
if n.natsConn != nil {
return nil
}
var natsConn *nats.Conn
var natsSub *nats.Subscription
var err error
var opts []nats.Option
if n.tlsConf != nil {
opts = append(opts, nats.Secure(n.tlsConf))
}
opts = append(opts, nats.Name(n.label))
opts = append(opts, authConfToOptions(n.authConf, n.fs)...)
opts = append(opts, errorHandlerOption(n.log))
if natsConn, err = nats.Connect(n.urls, opts...); err != nil {
return err
}
natsChan := make(chan *nats.Msg, n.prefetchCount)
if len(n.queue) > 0 {
natsSub, err = natsConn.ChanQueueSubscribe(n.subject, n.queue, natsChan)
} else {
natsSub, err = natsConn.ChanSubscribe(n.subject, natsChan)
}
if err != nil {
return err
}
n.log.Infof("Receiving NATS messages from subject: %v\n", n.subject)
n.natsConn = natsConn
n.natsSub = natsSub
n.natsChan = natsChan
return nil
}
func (n *natsReader) disconnect() {
n.cMut.Lock()
defer n.cMut.Unlock()
if n.natsSub != nil {
_ = n.natsSub.Unsubscribe()
n.natsSub = nil
}
if n.natsConn != nil {
n.natsConn.Close()
n.natsConn = nil
}
n.natsChan = nil
}
func (n *natsReader) Read(ctx context.Context) (*service.Message, service.AckFunc, error) {
n.cMut.Lock()
natsChan := n.natsChan
natsConn := n.natsConn
n.cMut.Unlock()
var msg *nats.Msg
var open bool
select {
case msg, open = <-natsChan:
case <-ctx.Done():
return nil, nil, ctx.Err()
case _, open = <-n.interruptChan:
}
if !open {
n.disconnect()
return nil, nil, service.ErrNotConnected
}
bmsg := service.NewMessage(msg.Data)
bmsg.MetaSetMut("nats_subject", msg.Subject)
// process message headers if server supports the feature
if natsConn.HeadersSupported() {
for key := range msg.Header {
value := msg.Header.Get(key)
bmsg.MetaSetMut(key, value)
}
}
return bmsg, func(_ context.Context, res error) error {
var ackErr error
if res != nil {
if n.nakDelay > 0 {
ackErr = msg.NakWithDelay(n.nakDelay)
} else {
ackErr = msg.Nak()
}
} else {
ackErr = msg.Ack()
}
if errors.Is(ackErr, nats.ErrMsgNoReply) {
ackErr = nil
}
return ackErr
}, nil
}
func (n *natsReader) Close(ctx context.Context) (err error) {
n.interruptOnce.Do(func() {
close(n.interruptChan)
})
return
}