gofiber/fiber · error

rand.Read failed

Error message

rand.Read failed: %w

What it means

unsafeRandString reads n bytes from crypto/rand in one shot to build a random string (used for multipart boundaries). This error wraps the rare case where rand.Read fails on the very first bulk read, meaning the system random source is unavailable.

Solutions

1. Ensure /dev/urandom is available and readable inside the container/sandbox.
2. If running under seccomp/AppArmor, allow the getrandom syscall.
3. Treat the error as fatal for the request rather than retrying — the source itself is broken.

When it happens

Trigger: The OS entropy pool is exhausted or /dev/urandom is unreadable; running in a severely locked-down sandbox or container that blocks the random source; an OS-level error from getrandom(2).

Common situations: Heavily restricted containers/seccomp filters that deny getrandom; chroots without /dev/urandom mounted; very early boot on embedded systems.

Related errors

• boundary generation
• set boundary error
• create file error
• failed to close multipart writer
• failed to copy file data

AI-assisted analysis of gofiber/fiber@a105acad6c (2026-08-11). Data as JSON: /api/errors/9125460c050782f8. Report an issue: GitHub.

Appendix: source

Thrown at client/hooks.go:53

	letterBytes = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789"
)

// unsafeRandString returns a random string of length n.
// An error is returned if the random source fails.
func unsafeRandString(n int) (string, error) {
	inputLength := byte(len(letterBytes))

	// Compute the largest multiple of inputLength ≤ 256 to avoid modulo bias.
	// Any byte ≥ max will be rejected and re‑read.
	maxLength := byte(256 - (256 % int(inputLength))) //nolint:gosec // G115: integer overflow conversion int -> byte

	out := make([]byte, n)
	buf := make([]byte, n)

	// Read n raw bytes in one shot
	if _, err := rand.Read(buf); err != nil {
		return "", fmt.Errorf("rand.Read failed: %w", err)
	}

	for i, b := range buf {
		// Reject values ≥ maxLength
		for b >= maxLength {
			if _, err := rand.Read(buf[i : i+1]); err != nil {
				return "", fmt.Errorf("rand.Read failed: %w", err)
			}
			b = buf[i]
		}
		out[i] = letterBytes[b%inputLength]
	}

	return utils.UnsafeString(out), nil
}

// parserRequestURL sets options for the hostclient and normalizes the URL.
// It merges the baseURL with the request URI if needed and applies query and path parameters.

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