grpc/grpc-go · error

fault: error parsing config %v: unknown type %T

Error message

fault: error parsing config %v: unknown type %T

What it means

parseConfig expects the incoming proto.Message to be an *anypb.Any (fault.go:85). Any other concrete type indicates the xDS decoding pipeline passed the wrong message type to the fault builder, which is a programmer/decoder contract violation.

Source

Thrown at internal/xds/httpfilter/fault/fault.go:87

}

type config struct {
	httpfilter.FilterConfig
	config *fpb.HTTPFault
}

func (builder) TypeURLs() []string {
	return []string{"type.googleapis.com/envoy.extensions.filters.http.fault.v3.HTTPFault"}
}

// Parsing is the same for the base config and the override config.
func parseConfig(cfg proto.Message) (httpfilter.FilterConfig, error) {
	if cfg == nil {
		return nil, fmt.Errorf("fault: nil configuration message provided")
	}
	m, ok := cfg.(*anypb.Any)
	if !ok {
		return nil, fmt.Errorf("fault: error parsing config %v: unknown type %T", cfg, cfg)
	}
	msg := new(fpb.HTTPFault)
	if err := m.UnmarshalTo(msg); err != nil {
		return nil, fmt.Errorf("fault: error parsing config %v: %v", cfg, err)
	}
	return config{config: msg}, nil
}

func (builder) ParseFilterConfig(cfg proto.Message) (httpfilter.FilterConfig, error) {
	return parseConfig(cfg)
}

func (builder) ParseFilterConfigOverride(override proto.Message) (httpfilter.FilterConfig, error) {
	return parseConfig(override)
}

func (builder) IsTerminal() bool {
	return false

View on GitHub (pinned to 03255a9237)

Solutions

1. Always pass an *anypb.Any whose TypeURL is type.googleapis.com/envoy.extensions.filters.http.fault.v3.HTTPFault.
2. Fix the resource decoder so it does not pre-unmarshal the filter config before the builder sees it.
3. Confirm the TypeURLs() of the fault builder match the resource type being routed to it.

Example fix

// before: passing the concrete HTTPFault directly
fc, err := faultBuilder.ParseFilterConfig(&fpb.HTTPFault{})

// after: wrap in *anypb.Any
anyMsg, _ := anypb.New(&fpb.HTTPFault{})
fc, err := faultBuilder.ParseFilterConfig(anyMsg)

if _, ok := cfg.(*anypb.Any); !ok {
    return nil, fmt.Errorf("expected *anypb.Any, got %T", cfg)
}
fc, err := faultBuilder.ParseFilterConfig(cfg)

func isAnyMsg(m proto.Message) bool {
    _, ok := m.(*anypb.Any)
    return ok
}

When it happens

Trigger: ParseFilterConfig receives a proto.Message that is not *anypb.Any (e.g. the already-unwrapped *fpb.HTTPFault or a raw struct message).

Common situations: A custom xdsclient/resource-decoder that pre-unwraps the Any before handing it to the filter builder; test harness passing the concrete type; type-url routing mismatch causing the wrong builder to handle the message.

Related errors

• fault: incorrect config type provided (%T): %v
• fault: incorrect override config type provided (%T): %v
• fault: nil configuration message provided
• fault: error parsing config %v: %v
• fault: nil config provided

AI-assisted analysis of grpc/grpc-go@03255a9237 (2026-08-07). Data as JSON: /api/errors/69ff11dd68512ea6. Report an issue: GitHub.