Recursively visit payloads inside ScheduleNexusOperationCommandAttributes when using system nexus (#290)

* Visit payloads inside system Nexus envelopes

* Fix a bug in defaultWellKnownAnyVisitor, which could return a result before all goroutines within it had finished

Author: dplyukhin

cmd/proxygenerator/interceptor.go

@@ -0,0 +1,72 @@
+package proxy
+
+import (
+	"fmt"
+
+	"go.temporal.io/api/command/v1"
+	"google.golang.org/protobuf/proto"
+	"google.golang.org/protobuf/reflect/protoreflect"
+	"google.golang.org/protobuf/reflect/protoregistry"
+)
+
+// visitSystemNexusEnvelope decodes the system Nexus envelope in attrs.Input,
+// visits the payloads inside the decoded request message, and re-encodes it.
+//
+// The envelope's proto message type is taken from the payload's "messageType"
+// metadata, so no operation registry is required. The envelope must be encoded
+// as binary/protobuf. The inner payloads (and only those) are passed to the
+// visitor, so external storage and codecs apply to them and not to the envelope
+// itself, which is never offloaded or codec-encoded.
+func visitSystemNexusEnvelope(
+	ctx *VisitPayloadsContext,
+	options *VisitPayloadsOptions,
+	concState *payloadConcurrencyState,
+	attrs *command.ScheduleNexusOperationCommandAttributes,
+) error {
+	input := attrs.Input
+
+	if encoding := string(input.GetMetadata()["encoding"]); encoding != "binary/protobuf" {
+		return fmt.Errorf(
+			"system nexus envelope for operation %q must be encoded as binary/protobuf but got %q",
+			attrs.GetOperation(), encoding,
+		)
+	}
+
+	messageType := string(input.GetMetadata()["messageType"])
+	if messageType == "" {
+		return fmt.Errorf(
+			"system nexus envelope for operation %q is missing the messageType metadata",
+			attrs.GetOperation(),
+		)
+	}
+
+	mt, err := protoregistry.GlobalTypes.FindMessageByName(protoreflect.FullName(messageType))
+	if err != nil {
+		return fmt.Errorf(
+			"system nexus envelope for operation %q references unknown message type %q: %w",
+			attrs.GetOperation(), messageType, err,
+		)
+	}
+	msg := mt.New().Interface()
+
+	if err := proto.Unmarshal(input.GetData(), msg); err != nil {
+		return fmt.Errorf(
+			"failed to unmarshal system nexus envelope for operation %q: %w",
+			attrs.GetOperation(), err,
+		)
+	}
+
+	if err := visitPayloadsAndWait(ctx, options, msg, concState, msg); err != nil {
+		return err
+	}
+
+	data, err := proto.Marshal(msg)
+	if err != nil {
+		return fmt.Errorf(
+			"failed to marshal system nexus envelope for operation %q: %w",
+			attrs.GetOperation(), err,
+		)
+	}
+	input.Data = data
+	return nil
+}