Function validateSubject

nats.go:4390–4419

validateSubject checks if the subject contains characters that break the NATS protocol. Uses an adaptive algorithm: manual loop for short subjects (< 16 chars) and SIMD-optimized strings.IndexByte for longer subjects.

(subj string)

// Uses an adaptive algorithm: manual loop for short subjects (< 16 chars) and
// SIMD-optimized strings.IndexByte for longer subjects.
func validateSubject(subj string) error {
	if subj == "" {
		return ErrBadSubject
	}

	// Adaptive threshold based on benchmark data showing crossover at ~15-20 characters.
	const lengthThreshold = 16

	if len(subj) < lengthThreshold {
		// Fast path for short subjects (< 16 chars)
		// Short-circuit on non-control characters.
		for i := range len(subj) {
			c := subj[i]
			if c <= ' ' && (c == ' ' || c == '\t' || c == '\r' || c == '\n') {
				return ErrBadSubject
			}
		}
		return nil
	}

	// Optimized path for long subjects (>= 16 chars)
	// Uses SIMD-optimized strings.IndexByte (processes 16+ bytes per instruction)
	if strings.IndexByte(subj, ' ') >= 0 ||
		strings.IndexByte(subj, '\t') >= 0 ||
		strings.IndexByte(subj, '\r') >= 0 ||
		strings.IndexByte(subj, '\n') >= 0 {
		return ErrBadSubject
	}
	return nil
}

// publish is the internal function to publish messages to a nats-server.
// Sends a protocol data message by queuing into the bufio writer