KV: changing discard policy would fail on srv upgrade

kv.go

@@ -17,6 +17,7 @@ import (
 	"context"
 	"errors"
 	"fmt"
+	"reflect"
 	"regexp"
 	"strconv"
 	"strings"
@@ -346,7 +347,21 @@ 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 strings.Contains(err.Error(), "already in use") {
+			if si, _ := js.StreamInfo(scfg.Name); si != nil {
+				if streamCfgSameSansDiscard(&si.Config, scfg) {
+					_, err = js.UpdateStream(scfg)
+				}
+			}
+		}
+		if err != nil {
+			return nil, err
+		}
 	}
 
 	kv := &kvs{
@@ -360,6 +375,25 @@ func (js *js) CreateKeyValue(cfg *KeyValueConfig) (KeyValue, error) {
 	return kv, nil
 }
 
+func streamCfgSameSansDiscard(srvCfg, ourCfg *StreamConfig) bool {
+	// The server sets some values (like -1) when sending 0.
+	// So we need to align to what the server may return to
+	// have a meaningfull comparison.
+	ours := *ourCfg
+	if ours.MaxMsgSize == 0 {
+		ours.MaxMsgSize = -1
+	}
+	if ours.MaxBytes == 0 {
+		ours.MaxBytes = -1
+	}
+	ours.Duplicates = 2 * time.Minute
+	ours.MaxMsgs = -1
+	ours.MaxConsumers = -1
+	// Set our discard to what server has for the comparison
+	ours.Discard = srvCfg.Discard
+	return reflect.DeepEqual(srvCfg, &ours)
+}
+
 // DeleteKeyValue will delete this KeyValue store (JetStream stream).
 func (js *js) DeleteKeyValue(bucket string) error {
 	if !validBucketRe.MatchString(bucket) {

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)
+		}
+	}
+}

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