crowdsecurity/crowdsec · error

structured data must start with '[' or be '-'

Error message

structured data must start with '[' or be '-'

What it means

Returned by parseStructuredData when the STRUCTURED-DATA element is neither the NIL value '-' nor begins with '[' as RFC5424 requires. The first byte at the parse position after MSGID is some other character.

Source

Thrown at pkg/acquisition/modules/syslog/internal/parser/rfc5424/parse.go:256

		return errors.New("msgid is empty")
	}

	if len(msgid) > 32 {
		return errors.New("msgid is too long")
	}

	r.MsgID = string(msgid)
	return nil
}

func (r *RFC5424) parseStructuredData() error {
	done := false
	if r.buf[r.position] == NIL_VALUE {
		r.position += 2
		return nil
	}
	if r.buf[r.position] != '[' {
		return errors.New("structured data must start with '[' or be '-'")
	}
	prev := byte(0)
	for r.position < r.len {
		done = false
		c := r.buf[r.position]
		if c == ']' && prev != '\\' {
			done = true
			r.position++
			if r.position < r.len && r.buf[r.position] == ' ' {
				break
			}
		}
		prev = c
		r.position++
	}
	r.position++
	if !done {
		return errors.New("structured data must end with ']'")

View on GitHub (pinned to 909b515798)

Solutions

1. Emit '-' when the message has no structured data
2. Start every STRUCTURED-DATA element with '[' and properly close it with ']'
3. Verify the MSGID field before it is correctly terminated by a single space

When it happens

Trigger: Thrown at pkg/acquisition/modules/syslog/internal/parser/rfc5424/parse.go:256 when the library encounters an invalid state.

Common situations: See trigger scenarios.

AI-assisted analysis of crowdsecurity/crowdsec@909b515798 (2026-09-06). Data as JSON: /api/errors/90825d9c97b625cb. Report an issue: GitHub.