jetstream: add option to pass arbitrary headers on publish

This will allow callers to pass custom header values without needing to
import anything beyond the jetstream sub-package.

jetstream/jetstream_test.go

@@ -16,6 +16,7 @@ package jetstream
 import (
 	"errors"
 	"fmt"
+	"reflect"
 	"testing"
 	"time"
 
@@ -116,3 +117,26 @@ func TestValidateSubject(t *testing.T) {
 		})
 	}
 }
+
+func TestOptions(t *testing.T) {
+	t.Run("publish", func(t *testing.T) {
+		t.Run("WithHeader", func(t *testing.T) {
+			customHeader := "test"
+			customHeaderValues := []string{"some", "values"}
+			po := pubOpts{}
+			sut := WithHeader(customHeader, customHeaderValues)
+
+			err := sut(&po)
+			if err != nil {
+				t.Fatalf("expected nil error got: %s", err)
+			}
+			if po.headerValues == nil {
+				t.Fatal("nil headerValues")
+			}
+
+			if got := po.headerValues.Values(customHeader); !reflect.DeepEqual(got, customHeaderValues) {
+				t.Fatalf("header %s not set - expected %+v got %+v", customHeader, customHeaderValues, got)
+			}
+		})
+	})
+}

jetstream/options.go

@@ -16,6 +16,8 @@ package jetstream
 import (
 	"fmt"
 	"time"
+
+	"github.com/nats-io/nats.go"
 )
 
 type pullOptFunc func(*consumeOpts) error
@@ -250,6 +252,17 @@ func WithStreamListSubject(subject string) StreamListOpt {
 	}
 }
 
+// WithHeader adds an arbitrary header to the underlying message.
+func WithHeader(key string, value []string) PublishOpt {
+	return func(opts *pubOpts) error {
+		if opts.headerValues == nil {
+			opts.headerValues = nats.Header{}
+		}
+		opts.headerValues[key] = value
+		return nil
+	}
+}
+
 // WithMsgID sets the message ID used for deduplication.
 func WithMsgID(id string) PublishOpt {
 	return func(opts *pubOpts) error {

jetstream/publish.go

@@ -52,6 +52,9 @@ type (
 
 		// stallWait is the max wait of a async pub ack.
 		stallWait time.Duration
+
+		// headerValues contains any arbitrary headers provided by the caller
+		headerValues nats.Header
 	}
 
 	// PubAckFuture is a future for a PubAck.
@@ -171,6 +174,12 @@ func (js *jetStream) PublishMsg(ctx context.Context, m *nats.Msg, opts ...Publis
 		m.Header.Set(ExpectedLastSubjSeqHeader, strconv.FormatUint(*o.lastSubjectSeq, 10))
 	}
 
+	if o.headerValues != nil {
+		for k, v := range o.headerValues {
+			m.Header[k] = v
+		}
+	}
+
 	var resp *nats.Msg
 	var err error