[FIXED] Stream config idempotency (#4292)

- [X] Branch rebased on top of current main (`git pull --rebase origin
main`)
- [X] Changes squashed to a single commit (described
[here](http://gitready.com/advanced/2009/02/10/squashing-commits-with-rebase.html))
 - [x] Build is green in Travis CI
- [X] You have certified that the contribution is your original work and
that you license the work to the project under the [Apache 2
license](https://github.com/nats-io/nats-server/blob/main/LICENSE)

Fixes a behavior where idempotency of re-defining the same stream more
than once (with the same attributes) was broken due to the DeepEqual
failing due to the StreamSource struct received from the client app not
having a value for the `iname` structure field (as it's internal) but
the StreamSource struct return from `mset.config()` would have it set.

Signed-off-by: Jean-Noël Moyne <jnmoyne@gmail.com>

server/stream.go

@@ -409,6 +409,12 @@ func (a *Account) addStreamWithAssignment(config *StreamConfig, fsConfig *FileSt
 		jsa.mu.Unlock()
 		// Check to see if configs are same.
 		ocfg := mset.config()
+
+		// set the index name on cfg since it would not contain a value for iname while the return from mset.config() does to ensure the DeepEqual works
+		for _, s := range cfg.Sources {
+			s.setIndexName()
+		}
+
 		if reflect.DeepEqual(ocfg, cfg) {
 			if sa != nil {
 				mset.setStreamAssignment(sa)
@@ -449,20 +455,18 @@ func (a *Account) addStreamWithAssignment(config *StreamConfig, fsConfig *FileSt
 	}
 
 	// Setup our internal indexed names here for sources and check if the transform (if any) is valid.
-	if len(cfg.Sources) > 0 {
-		for _, ssi := range cfg.Sources {
-			ssi.setIndexName()
-			// check the filter, if any, is valid
-			if ssi.FilterSubject != _EMPTY_ && !IsValidSubject(ssi.FilterSubject) {
+
+	for _, ssi := range cfg.Sources {
+		// check the filter, if any, is valid
+		if ssi.FilterSubject != _EMPTY_ && !IsValidSubject(ssi.FilterSubject) {
+			jsa.mu.Unlock()
+			return nil, fmt.Errorf("subject filter '%s' for the source %w", ssi.FilterSubject, ErrBadSubject)
+		}
+		// check the transform, if any, is valid
+		if ssi.SubjectTransformDest != _EMPTY_ {
+			if _, err = NewSubjectTransform(ssi.FilterSubject, ssi.SubjectTransformDest); err != nil {
 				jsa.mu.Unlock()
-				return nil, fmt.Errorf("subject filter '%s' for the source %w", ssi.FilterSubject, ErrBadSubject)
-			}
-			// check the transform, if any, is valid
-			if ssi.SubjectTransformDest != _EMPTY_ {
-				if _, err = NewSubjectTransform(ssi.FilterSubject, ssi.SubjectTransformDest); err != nil {
-					jsa.mu.Unlock()
-					return nil, fmt.Errorf("subject transform from '%s' to '%s' for the source %w", ssi.FilterSubject, ssi.SubjectTransformDest, err)
-				}
+				return nil, fmt.Errorf("subject transform from '%s' to '%s' for the source %w", ssi.FilterSubject, ssi.SubjectTransformDest, err)
 			}
 		}
 	}