What causes "failed to write: %w" in charmbracelet/gum?

Increase the memory limit of the container/process running the command

failed to write: %w

Error message

failed to write: %w

What it means

Returned by internal/stdin.Read when b.Write(line) fails after a successful ReadLine in singleLine mode. Writing to a strings.Builder essentially only fails on out-of-memory, so this error is rare and indicates the process cannot allocate memory to buffer the line.

Source

Thrown at internal/stdin/stdin.go:57

		return "", fmt.Errorf("stdin is empty")
	}

	options := options{}
	for _, opt := range opts {
		opt(&options)
	}

	reader := bufio.NewReader(os.Stdin)
	var b strings.Builder

	if options.singleLine {
		line, _, err := reader.ReadLine()
		if err != nil {
			return "", fmt.Errorf("failed to read line: %w", err)
		}
		_, err = b.Write(line)
		if err != nil {
			return "", fmt.Errorf("failed to write: %w", err)
		}
	}

	for !options.singleLine {
		r, _, err := reader.ReadRune()
		if err != nil && err == io.EOF {
			break
		}
		_, err = b.WriteRune(r)
		if err != nil {
			return "", fmt.Errorf("failed to write rune: %w", err)
		}
	}

	s := strings.TrimSpace(b.String())
	if options.ansiStrip {
		return ansi.Strip(s), nil
	}

View on GitHub (pinned to 4d089f9550)

Solutions

Increase the memory limit of the container/process running the command
Check for pathologically large input lines being piped in
Use strings.Builder's available-memory diagnostics (b.Cap()) if profiling allocation
Handle the error and abort gracefully rather than retrying the same read

Example fix

// before
line, _ := stdin.Read(stdin.WithSingleLine())
// after
line, err := stdin.Read(stdin.WithSingleLine())
if err != nil {
    log.Fatalf("could not buffer line: %v", err)
}

Defensive patterns

Strategy: try-catch

Validate before calling

// No practical pre-check; strings.Builder fails only on OOM.
// Keep input lines bounded:
if len(rawLine) > 1<<20 { return fmt.Errorf("line too large") }

Try / catch

line, err := stdin.Read(stdin.WithSingleLine())
if err != nil {
    return fmt.Errorf("buffer write failed (OOM?): %w", err)
}

Prevention

Bound input line sizes before processing
Ensure adequate container memory limits
Avoid retrying identical reads after OOM errors

When it happens

Trigger: Calling Read with singleLine option where strings.Builder.Write returns an error — practically only under memory exhaustion in the Go runtime.

Common situations: Extremely constrained memory environments (containers with tight limits); a pathological single line consuming all available memory before the write fails.

Related errors

AI-assisted analysis of charmbracelet/gum@4d089f9550 (2026-08-31). Data as JSON: /api/errors/e2c0abc53d66dfce. Report an issue: GitHub.