GoogleContainerTools/skaffold · error

unexpected kind of os.Process. probably a bug: %s

Error message

unexpected kind of os.Process. probably a bug: %s

What it means

getHandleFromProcess uses reflection to read the unexported 'handle' field of os.Process on Windows. Before touching the field it asserts that the dereferenced *os.Process is actually a struct; if the Go runtime ever changes that representation, this guard fires with the observed reflect.Kind. It is an internal invariant check, not a condition a user can normally cause.

Source

Thrown at pkg/skaffold/kubectl/exec_windows.go:93

	c.handle = handle
	go func() {
		<-c.ctx.Done()
		c.Terminate()
	}()

	return nil
}

func getHandleFromProcess(p *os.Process) (windows.Handle, error) {
	// os.Process contains an unexported processHandle struct, which contains
	// a `handle uintptr` field.
	v := reflect.ValueOf(p)
	i := reflect.Indirect(v)

	k := i.Kind()
	if k != reflect.Struct {
		return windows.InvalidHandle, fmt.Errorf("unexpected kind of os.Process. probably a bug: %s", k)
	}

	f := i.FieldByName("handle")
	if f.IsZero() {
		return windows.InvalidHandle, fmt.Errorf("could not get 'handle' field from os.Process. probably a bug")
	}
	// Get the processHandle struct
	handlestruct := reflect.Indirect(f)
	handle := handlestruct.FieldByName("handle")

	return windows.Handle(handle.Uint()), nil
}

// Run starts the specified command in a job object and waits for it to complete
func (c *Cmd) Run() error {
	if err := c.Start(); err != nil {
		return err
	}

View on GitHub (pinned to a1189de023)

Solutions

1. Upgrade or pin to a Go toolchain version officially supported by this Skaffold release
2. Rebuild with the unmodified upstream Go toolchain (no -tags or stdlib overrides)
3. Report the Go version and reflect.Kind value to the Skaffold maintainers as a bug

// Not user-validatable: depends on Go stdlib internals. Assert toolchain before build:
// go version  # must match the version supported by the library release

h, err := getHandleFromProcess(proc)
if err != nil {
    return fmt.Errorf("io redirection unsupported on this Go build: %w", err)
}

When it happens

Trigger: Calling Start (which calls getHandleFromProcess) on Windows with a Go standard library whose os.Process is no longer a plain struct under reflection — e.g. building with an unusual/patched Go toolchain, GOOS=windows build, or future stdlib refactor.

Common situations: Building Skaffold with a forked or very new/patched Go release where runtime internals changed; exotic cross-compilation setups; essentially never in normal use.

Related errors

• could not get 'handle' field from os.Process. probably a bug
• upgrading main pipeline: %w
• lengths of old and new profiles differ
• opening %q in embedded filesystem: %w
• reading %q in embedded filesystem: %w

AI-assisted analysis of GoogleContainerTools/skaffold@a1189de023 (2026-09-05). Data as JSON: /api/errors/8435ff2851412e8e. Report an issue: GitHub.