KV: changing discard policy would fail on srv upgrade

jsm.go

@@ -587,6 +587,9 @@ func (js *js) AddStream(cfg *StreamConfig, opts ...JSOpt) (*StreamInfo, error) {
 		return nil, err
 	}
 	if resp.Error != nil {
+		if resp.Error.ErrorCode == 10058 {
+			return nil, ErrStreamNameAlreadyInUse
+		}
 		return nil, errors.New(resp.Error.Description)
 	}
 

kv.go

@@ -17,6 +17,7 @@ import (
 	"context"
 	"errors"
 	"fmt"
+	"reflect"
 	"regexp"
 	"strconv"
 	"strings"
@@ -326,18 +327,31 @@ func (js *js) CreateKeyValue(cfg *KeyValueConfig) (KeyValue, error) {
 		replicas = 1
 	}
 
+	// We will set explicitly some values so that we can do comparison
+	// if we get an "already in use" error and need to check if it is same.
+	maxBytes := cfg.MaxBytes
+	if maxBytes == 0 {
+		maxBytes = -1
+	}
+	maxMsgSize := cfg.MaxValueSize
+	if maxMsgSize == 0 {
+		maxMsgSize = -1
+	}
 	scfg := &StreamConfig{
 		Name:              fmt.Sprintf(kvBucketNameTmpl, cfg.Bucket),
 		Description:       cfg.Description,
 		Subjects:          []string{fmt.Sprintf(kvSubjectsTmpl, cfg.Bucket)},
 		MaxMsgsPerSubject: history,
-		MaxBytes:          cfg.MaxBytes,
+		MaxBytes:          maxBytes,
 		MaxAge:            cfg.TTL,
-		MaxMsgSize:        cfg.MaxValueSize,
+		MaxMsgSize:        maxMsgSize,
 		Storage:           cfg.Storage,
 		Replicas:          replicas,
 		AllowRollup:       true,
 		DenyDelete:        true,
+		Duplicates:        2 * time.Minute,
+		MaxMsgs:           -1,
+		MaxConsumers:      -1,
 	}
 
 	// If we are at server version 2.7.2 or above use DiscardNew. We can not use DiscardNew for 2.7.1 or below.
@@ -346,7 +360,24 @@ func (js *js) CreateKeyValue(cfg *KeyValueConfig) (KeyValue, error) {
 	}
 
 	if _, err := js.AddStream(scfg); err != nil {
-		return nil, err
+		// If we have a failure to add, it could be because we have
+		// a config change if the KV was created against a pre 2.7.2
+		// and we are now moving to a v2.7.2+. If that is the case
+		// and the only difference is the discard policy, then update
+		// the stream.
+		if err == ErrStreamNameAlreadyInUse {
+			if si, _ := js.StreamInfo(scfg.Name); si != nil {
+				// To compare, make the server's stream info discard
+				// policy same than ours.
+				si.Config.Discard = scfg.Discard
+				if reflect.DeepEqual(&si.Config, scfg) {
+					_, err = js.UpdateStream(scfg)
+				}
+			}
+		}
+		if err != nil {
+			return nil, err
+		}
 	}
 
 	kv := &kvs{

kv_test.go

@@ -0,0 +1,69 @@
+// Copyright 2022 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 nats
+
+import (
+	"testing"
+)
+
+func TestKeyValueDiscardOldToDiscardNew(t *testing.T) {
+	s := RunBasicJetStreamServer()
+	defer shutdownJSServerAndRemoveStorage(t, s)
+
+	nc, js := jsClient(t, s)
+	defer nc.Close()
+
+	checkDiscard := func(expected DiscardPolicy) KeyValue {
+		t.Helper()
+		kv, err := js.CreateKeyValue(&KeyValueConfig{Bucket: "TEST", History: 1})
+		if err != nil {
+			t.Fatalf("Error creating store: %v", err)
+		}
+		si, err := js.StreamInfo("KV_TEST")
+		if err != nil {
+			t.Fatalf("Error getting stream info: %v", err)
+		}
+		if si.Config.Discard != expected {
+			t.Fatalf("Expected discard policy %v, got %+v", expected, si)
+		}
+		return kv
+	}
+
+	// We are going to go from 2.7.1->2.7.2->2.7.1 and 2.7.2 again.
+	for i := 0; i < 2; i++ {
+		// Change the server version in the connection to
+		// create as-if we were connecting to a v2.7.1 server.
+		nc.mu.Lock()
+		nc.info.Version = "2.7.1"
+		nc.mu.Unlock()
+
+		kv := checkDiscard(DiscardOld)
+		if i == 0 {
+			if _, err := kv.PutString("foo", "value"); err != nil {
+				t.Fatalf("Error adding key: %v", err)
+			}
+		}
+
+		// Now change version to 2.7.2
+		nc.mu.Lock()
+		nc.info.Version = "2.7.2"
+		nc.mu.Unlock()
+
+		kv = checkDiscard(DiscardNew)
+		// Make sure the key still exists
+		if e, err := kv.Get("foo"); err != nil || string(e.Value()) != "value" {
+			t.Fatalf("Error getting key: err=%v e=%+v", err, e)
+		}
+	}
+}

nats.go

@@ -160,6 +160,7 @@ var (
 	ErrMsgNotFound                  = errors.New("nats: message not found")
 	ErrMsgAlreadyAckd               = errors.New("nats: message was already acknowledged")
 	ErrStreamInfoMaxSubjects        = errors.New("nats: subject details would exceed maximum allowed")
+	ErrStreamNameAlreadyInUse       = errors.New("nats: stream name already in use")
 )
 
 func init() {

test/kv_test.go

@@ -18,7 +18,6 @@ import (
 	"fmt"
 	"os"
 	"reflect"
-	"regexp"
 	"strconv"
 	"strings"
 	"testing"
@@ -558,48 +557,6 @@ func TestKeyValueKeys(t *testing.T) {
 	}
 }
 
-func TestKeyValueDiscardNew(t *testing.T) {
-	s := RunBasicJetStreamServer()
-	defer shutdownJSServerAndRemoveStorage(t, s)
-
-	nc, js := jsClient(t, s)
-	defer nc.Close()
-
-	kv, err := js.CreateKeyValue(&nats.KeyValueConfig{Bucket: "TEST", History: 1, MaxBytes: 256})
-	expectOk(t, err)
-
-	vc := func() (major, minor, patch int) {
-		semVerRe := regexp.MustCompile(`\Av?([0-9]+)\.?([0-9]+)?\.?([0-9]+)?`)
-		m := semVerRe.FindStringSubmatch(nc.ConnectedServerVersion())
-		expectOk(t, err)
-		major, err = strconv.Atoi(m[1])
-		expectOk(t, err)
-		minor, err = strconv.Atoi(m[2])
-		expectOk(t, err)
-		patch, err = strconv.Atoi(m[3])
-		expectOk(t, err)
-		return major, minor, patch
-	}
-
-	major, minor, patch := vc()
-	status, err := kv.Status()
-	expectOk(t, err)
-	kvs := status.(*nats.KeyValueBucketStatus)
-	si := kvs.StreamInfo()
-
-	// If we are 2.7.1 or below DiscardOld should be used.
-	// If 2.7.2 or above should be DiscardNew
-	if major <= 2 && minor <= 7 && patch <= 1 {
-		if si.Config.Discard != nats.DiscardOld {
-			t.Fatalf("Expected Discard Old for server version %d.%d.%d", major, minor, patch)
-		}
-	} else {
-		if si.Config.Discard != nats.DiscardNew {
-			t.Fatalf("Expected Discard New for server version %d.%d.%d", major, minor, patch)
-		}
-	}
-}
-
 func TestKeyValueCrossAccounts(t *testing.T) {
 	conf := createConfFile(t, []byte(`
         jetstream: enabled