Hopefully avoid panic in DescribeWorkflowExecution (#5057)

**What changed?**

Clone suspected mutating fields after a returning from
DescribeWorkflowExecution.

**Why?**

Noticed panics in serialization of the
`DescribeWorkflowExecutionResponse` object.

**How did you test it?**

No tests added, assuming that normal test coverage is enough.
Haven't reproduced the issue, this is based on a hunch.

**Potential risks**

None that I can foresee.

**Is hotfix candidate?**

Yes.

service/history/api/describeworkflow/api.go

@@ -46,6 +46,21 @@ import (
 	"go.temporal.io/server/service/history/workflow"
 )
 
+func clonePayloadMap(source map[string]*commonpb.Payload) map[string]*commonpb.Payload {
+	target := make(map[string]*commonpb.Payload, len(source))
+	for k, v := range source {
+		metadata := make(map[string][]byte, len(v.GetMetadata()))
+		for mk, mv := range v.GetMetadata() {
+			metadata[mk] = mv
+		}
+		target[k] = &commonpb.Payload{
+			Metadata: metadata,
+			Data:     v.GetData(),
+		}
+	}
+	return target
+}
+
 func Invoke(
 	ctx context.Context,
 	req *historyservice.DescribeWorkflowExecutionRequest,
@@ -73,11 +88,29 @@ func Invoke(
 	if err != nil {
 		return nil, err
 	}
+	// We release the lock on this workflow just before we return from this method, at which point mutable state might
+	// be mutated. Take extra care to clone all response methods as marshalling happens after we return and it is unsafe
+	// to mutate proto fields during marshalling.
 	defer func() { weCtx.GetReleaseFn()(retError) }()
 
 	mutableState := weCtx.GetMutableState()
 	executionInfo := mutableState.GetExecutionInfo()
 	executionState := mutableState.GetExecutionState()
+
+	resetPoints := &workflowpb.ResetPoints{
+		Points: make([]*workflowpb.ResetPointInfo, len(executionInfo.AutoResetPoints.GetPoints())),
+	}
+	for i, p := range executionInfo.AutoResetPoints.GetPoints() {
+		resetPoints.Points[i] = &workflowpb.ResetPointInfo{
+			BinaryChecksum:               p.BinaryChecksum,
+			RunId:                        p.RunId,
+			FirstWorkflowTaskCompletedId: p.FirstWorkflowTaskCompletedId,
+			CreateTime:                   p.CreateTime,
+			ExpireTime:                   p.ExpireTime,
+			Resettable:                   p.Resettable,
+		}
+	}
+
 	result := &historyservice.DescribeWorkflowExecutionResponse{
 		ExecutionConfig: &workflowpb.WorkflowExecutionConfig{
 			TaskQueue: &taskqueuepb.TaskQueue{
@@ -93,14 +126,13 @@ func Invoke(
 				WorkflowId: executionInfo.WorkflowId,
 				RunId:      executionState.RunId,
 			},
-			Type:                 &commonpb.WorkflowType{Name: executionInfo.WorkflowTypeName},
-			StartTime:            executionInfo.StartTime,
-			Status:               executionState.Status,
-			HistoryLength:        mutableState.GetNextEventID() - common.FirstEventID,
-			ExecutionTime:        executionInfo.ExecutionTime,
-			Memo:                 &commonpb.Memo{Fields: executionInfo.Memo},
-			SearchAttributes:     &commonpb.SearchAttributes{IndexedFields: executionInfo.SearchAttributes},
-			AutoResetPoints:      executionInfo.AutoResetPoints,
+			Type:          &commonpb.WorkflowType{Name: executionInfo.WorkflowTypeName},
+			StartTime:     executionInfo.StartTime,
+			Status:        executionState.Status,
+			HistoryLength: mutableState.GetNextEventID() - common.FirstEventID,
+			ExecutionTime: executionInfo.ExecutionTime,
+			// Memo and SearchAttributes are set below
+			AutoResetPoints:      resetPoints,
 			TaskQueue:            executionInfo.TaskQueue,
 			StateTransitionCount: executionInfo.StateTransitionCount,
 			HistorySizeBytes:     executionInfo.GetExecutionStats().GetHistorySize(),
@@ -208,8 +240,12 @@ func Invoke(
 		)
 		return nil, serviceerror.NewInternal("Failed to fetch memo and search attributes")
 	}
-	result.WorkflowExecutionInfo.Memo = relocatableAttributes.Memo
-	result.WorkflowExecutionInfo.SearchAttributes = relocatableAttributes.SearchAttributes
+	result.WorkflowExecutionInfo.Memo = &commonpb.Memo{
+		Fields: clonePayloadMap(relocatableAttributes.Memo.GetFields()),
+	}
+	result.WorkflowExecutionInfo.SearchAttributes = &commonpb.SearchAttributes{
+		IndexedFields: clonePayloadMap(relocatableAttributes.SearchAttributes.GetIndexedFields()),
+	}
 
 	return result, nil
 }