XTLS/Xray-core · error

invalid IP format for :

Error message

invalid IP format for : 

What it means

formatLittleEndianString reports that the net.IP passed in produced no usable byte slice: To4() and To16() both returned nil, which for net.IP only happens when the input is nil (or a 4-byte/16-byte-malformed value). The message prints the original addr. The root cause is always an invalid or missing IP upstream — net.ParseIP never errors, it silently returns nil.

Source

Thrown at common/net/find_process_linux.go:94

	pid, err := strconv.Atoi(pidStr)
	if err != nil {
		return 0, "", "", errors.New("failed to parse PID: ", err)
	}

	return pid, procName, absPath, nil
}

func formatLittleEndianString(addr net.IP, port Port) (string, error) {
	ip := addr
	var ipBytes []byte
	if ip.To4() != nil {
		ipBytes = ip.To4()
	} else {
		ipBytes = ip.To16()
	}
	if ipBytes == nil {
		return "", errors.New("invalid IP format for ", addr, ": ", ip)
	}

	for i, j := 0, len(ipBytes)-1; i < j; i, j = i+1, j-1 {
		ipBytes[i], ipBytes[j] = ipBytes[j], ipBytes[i]
	}
	portHex := fmt.Sprintf("%04X", uint16(port))
	ipHex := strings.ToUpper(hex.EncodeToString(ipBytes))
	return fmt.Sprintf("%s:%s", ipHex, portHex), nil
}

func findInodeInFile(filePath, targetHexAddr string) (string, error) {
	file, err := os.Open(filePath)
	if err != nil {
		return "", err
	}
	defer file.Close()

	scanner := bufio.NewScanner(file)

View on GitHub (pinned to 7d214f8b09)

Solutions

1. Validate with net.ParseIP(srcIP) != nil before calling FindProcess
2. Normalize addresses upstream: strip CIDR length, zone IDs, and port suffixes
3. Fail fast at the boundary where srcIP enters your system rather than deep in process lookup

Example fix

// before
err := routeByProcess(srcIP, srcPort)

// after
ip := net.ParseIP(srcIP)
if ip == nil {
    return fmt.Errorf("invalid source IP %q", srcIP)
}
err := routeByProcess(ip.String(), srcPort)

if net.ParseIP(srcIP) == nil {
    return errors.New("invalid source IP: ", srcIP)
}

func isParsableIp(s string) bool {
    return net.ParseIP(s) != nil // nil in = nil out = guaranteed failure later
}

When it happens

Trigger: FindProcess called with srcIP that net.ParseIP cannot parse ('', hostname, '1.2.3.4/24', IPv6 with zone). The nil flows silently until this formatting step.

Common situations: Call sites passing empty metadata strings for direct connections, addresses taken from proxy headers without validation, or IPs with CIDR or zone suffixes.

Related errors

• failed to format address:
• failed to determine if address is local:
• could not search in
• connection for :: not found in
• could not find PID for inode :

AI-assisted analysis of XTLS/Xray-core@7d214f8b09 (2026-08-15). Data as JSON: /api/errors/a86a01c58773fad4. Report an issue: GitHub.