nats-io/nats-server · error

processRoutedMsgArgs Bad or Missing Size: '%s'

Error message

processRoutedMsgArgs Bad or Missing Size: '%s'

What it means

After parsing a routed MSG's size field, the server checks that the resulting size is non-negative. parseSize returns -1 for a non-numeric or negative size value, so a bad or missing final size field triggers this error. It protects the server from allocating based on garbage lengths.

Source

Thrown at server/route.go:446

			c.pa.reply = args[3]
		case '|':
			c.pa.reply = nil
		default:
			return fmt.Errorf("processRoutedMsgArgs Bad or Missing Reply Indicator: '%s'", args[2])
		}
		// 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[4 : len(args)-1]
		} else {
			c.pa.queues = args[3 : len(args)-1]
		}
	}
	if c.pa.size < 0 {
		return fmt.Errorf("processRoutedMsgArgs Bad or Missing Size: '%s'", args)
	}

	// Common ones processed after check for arg length
	c.pa.account = args[0]
	c.pa.subject = args[1]
	if len(an) > 0 {
		c.pa.pacache = c.pa.subject
	} else {
		c.pa.pacache = arg[:len(args[0])+len(args[1])+1]
	}
	return nil
}

// processInboundRoutedMsg is called to process an inbound msg from a route.
func (c *client) processInboundRoutedMsg(msg []byte) {
	// Update statistics
	c.in.msgs++
	// The msg includes the CR_LF, so pull back out for accounting.

View on GitHub (pinned to 3a66a489d2)

Solutions

1. Ensure the last field of the routed MSG line is the decimal byte size of the payload
2. Fix the emitter to compute size as len(payload) exactly
3. Trace the raw protocol line to see which sender produced the malformed frame
4. Check route/TLS links for corruption and keep cluster servers on compatible versions

Example fix

// before
"MSG foo + reply 5 abc\r\n" // 'abc' where size should be
// after
"MSG foo + reply 5\r\n" + payload

// Validate the size field parses to a non-negative integer before sending
size, err := strconv.Atoi(lastField)
if err != nil || size < 0 {
    return fmt.Errorf("bad size field %q", lastField)
}
if size != len(payload) {
    return fmt.Errorf("size %d != payload len %d", size, len(payload))
}

When it happens

Trigger: Final arg of a routed MSG is not a valid non-negative integer (e.g. 'abc', '-5', or empty), causing parseSize to return -1.

Common situations: Corrupt cluster traffic, custom publishers writing wrong size fields, off-by-one in hand-built protocol emitters that put a queue name where the size belongs, or truncated frames after network errors.

Related errors

• processRoutedHeaderMsgArgs Header Size larger then TotalSize
• processRoutedMsgArgs Parse Error: '%s'
• processRoutedMsgArgs Bad or Missing Reply Indicator: '%s'
• invalid publish message, variable header exceeds remaining l
• restore for stream '%s > %s' requires reply subject for each

AI-assisted analysis of nats-io/nats-server@3a66a489d2 (2026-09-02). Data as JSON: /api/errors/b39da840e20593b4. Report an issue: GitHub.