grpc/grpc-go · error

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

Error message

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

What it means

BuildClientInterceptor asserts the base config is the internal fault config type produced by parseConfig (fault.go:123). A different concrete type means the build step received a config not created by this builder, indicating a wiring mismatch.

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 03255a9237)

Solutions

1. Pass only the httpfilter.FilterConfig returned by the fault builder's ParseFilterConfig into BuildClientInterceptor.
2. Do not reconstruct or re-type the config between parse and build.
3. Add a build-time check that the builder and config originate from the same package.

Example fix

// before: passing a raw *fpb.HTTPFault
ic, err := cf.BuildClientInterceptor(rawHTTPFault, nil)

// after: pass the FilterConfig produced by the fault builder
parsed, err := faultBuilder.ParseFilterConfig(anyMsg)
ic, err := cf.BuildClientInterceptor(parsed, nil)

// cfg must come from the fault builder's ParseFilterConfig
// (the concrete type is unexported, so never reconstruct it by hand)

// Internal type; callers can only assert it round-tripped through ParseFilterConfig:
func isFaultConfig(c httpfilter.FilterConfig) bool {
    // no public way to name the unexported config; rely on builder pairing
    return c != nil
}

ic, err := cf.BuildClientInterceptor(cfg, override)
if err != nil {
    return err
}

When it happens

Trigger: cfg passed to BuildClientInterceptor does not implement/assert as the unexported fault config struct (e.g. it is the raw *fpb.HTTPFault or a config from another filter).

Common situations: Mixing filter builders and configs across filters; a custom filter framework that re-wraps configs; refactor that changed the config struct without updating the build path.

Related errors

• fault: error parsing config %v: unknown type %T
• 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/02a6498a2b5cf709. Report an issue: GitHub.