grpc/grpc-go · error

fault: incorrect config type provided (%T)

Error message

fault: incorrect config type provided (%T): %v

What it means

BuildClientInterceptor (fault.go:124) requires cfg to be the filter's internal config struct (the unexported type returned by parseConfig). Any other concrete type fails the assertion — usually because a config from a different filter builder was passed in.

Solutions

1. Use the config value returned by the fault builder's ParseFilterConfig as the cfg argument.
2. Do not mix configs across filter builders; each builder produces its own internal type.
3. Add a unit test that asserts the cfg type matches the builder that produced it.

Example fix

// before
ic, err := faultCF.BuildClientInterceptor(rbacConfig, override)

// after
ic, err := faultCF.BuildClientInterceptor(faultConfig, override)

// Internal type is unexported, so guard by ensuring the same builder produced cfg.
// Caller-side: keep a reference to the builder and use it for both parse and build.

// The error is returned from BuildClientInterceptor; surface it during filter setup.
ic, err := cf.BuildClientInterceptor(cfg, override)
if err != nil && strings.Contains(err.Error(), "incorrect config type") {
    // re-parse cfg with the correct builder
}

When it happens

Trigger: BuildClientInterceptor is called with a FilterConfig value that is not the fault filter's internal config struct (e.g., an rbac or gcp_authn config, or a custom implementation of the FilterConfig interface).

Common situations: Cross-filter wiring mistake; a wrapper that re-implements httpfilter.FilterConfig and passes its own type; refactoring that swapped builders.

Related errors

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

AI-assisted analysis of grpc/grpc-go@0c51461d27 (2026-08-11). Data as JSON: /api/errors/02a6498a2b5cf709. Report an issue: GitHub.

Appendix: source

Thrown at internal/xds/httpfilter/fault/fault.go:125

func (builder) BuildClientFilter(httpfilter.ClientFilterOptions) httpfilter.ClientFilter {
	return clientFilter{}
}

var _ httpfilter.ClientFilterBuilder = builder{}

type clientFilter struct{}

func (clientFilter) Close() {}

func (clientFilter) BuildClientInterceptor(cfg, override httpfilter.FilterConfig) (httpfilter.ClientInterceptor, error) {
	if cfg == nil {
		return nil, fmt.Errorf("fault: nil config provided")
	}

	c, ok := cfg.(config)
	if !ok {
		return nil, fmt.Errorf("fault: incorrect config type provided (%T): %v", cfg, cfg)
	}

	if override != nil {
		// override completely replaces the listener configuration; but we
		// still validate the listener config type.
		c, ok = override.(config)
		if !ok {
			return nil, fmt.Errorf("fault: incorrect override config type provided (%T): %v", override, override)
		}
	}

	icfg := c.config
	if (icfg.GetMaxActiveFaults() != nil && icfg.GetMaxActiveFaults().GetValue() == 0) ||
		(icfg.GetDelay() == nil && icfg.GetAbort() == nil) {
		return nil, nil
	}
	return &interceptor{config: icfg}, nil
}

View on GitHub (pinned to 0c51461d27)