nats-io/nats-server · error

processLeafHeaderMsgArgs Header Size larger then TotalSize:

Error message

processLeafHeaderMsgArgs Header Size larger then TotalSize: '%s'

What it means

Leaf-node protocol parse guard: the parsed header size exceeds the parsed total message size in an incoming header message, which is inconsistent and indicates a malformed or corrupted protocol line.

Source

Thrown at server/leafnode.go:3217

		// Grab size.
		c.pa.szb = args[len(args)-1]
		c.pa.size = parseSize(c.pa.szb)

		// Grab queue names.
		if c.pa.reply != nil {
			c.pa.queues = args[3 : len(args)-2]
		} else {
			c.pa.queues = args[2 : len(args)-2]
		}
	}
	if c.pa.hdr < 0 {
		return fmt.Errorf("processLeafHeaderMsgArgs Bad or Missing Header Size: '%s'", arg)
	}
	if c.pa.size < 0 {
		return fmt.Errorf("processLeafHeaderMsgArgs Bad or Missing Size: '%s'", args)
	}
	if c.pa.hdr > c.pa.size {
		return fmt.Errorf("processLeafHeaderMsgArgs Header Size larger then TotalSize: '%s'", arg)
	}
	maxPayload := atomic.LoadInt32(&c.mpay)
	if maxPayload != jwt.NoLimit && int64(c.pa.size) > int64(maxPayload) {
		c.maxPayloadViolation(c.pa.size, maxPayload)
		return ErrMaxPayload
	}

	// Common ones processed after check for arg length
	c.pa.subject = args[0]

	return nil
}

func (c *client) processLeafMsgArgs(arg []byte) error {
	// Unroll splitArgs to avoid runtime/heap issues
	args := c.argsa[:0]
	start := -1
	for i, b := range arg {

View on GitHub (pinned to 3a66a489d2)

Solutions

1. Check protocol corruption or a buggy peer emitting wrong sizes
2. Verify intermediaries do not truncate protocol lines
3. Capture the offending line via trace logging

When it happens

Trigger: Thrown at server/leafnode.go:3217 when the library encounters an invalid state.

Common situations: See trigger scenarios.

AI-assisted analysis of nats-io/nats-server@3a66a489d2 (2026-09-02). Data as JSON: /api/errors/8b67441c9069f036. Report an issue: GitHub.