host.go

package k8sresolver

import (
	"errors"
	"fmt"
	"net"
)

var (
	errMissingAddr = errors.New("k8s resolver: missing address")

	// Addresses ending with a colon that is supposed to be the separator
	// between host and port is not allowed.  E.g. "::" is a valid address as
	// it is an IPv6 address (host only) and "[::]:" is invalid as it ends with
	// a colon as the host and port separator
	errEndsWithColon = errors.New("k8s resolver: missing port after port-separator colon")
)

// parseTarget takes the user input target string and default port, returns formatted host and port info.
// If target doesn't specify a port, set the port to be the defaultPort.
// If target is in IPv6 format and host-name is enclosed in square brackets, brackets
// are stripped when setting the host.
// examples:
// target: "www.google.com" defaultPort: "443" returns host: "www.google.com", port: "443"
// target: "ipv4-host:80" defaultPort: "443" returns host: "ipv4-host", port: "80"
// target: "[ipv6-host]" defaultPort: "443" returns host: "ipv6-host", port: "443"
// target: ":80" defaultPort: "443" returns host: "localhost", port: "80"
func parseTarget(target, defaultPort string) (host, port string, err error) {
	if target == "" {
		return "", "", errMissingAddr
	}
	if ip := net.ParseIP(target); ip != nil {
		// target is an IPv4 or IPv6(without brackets) address
		return target, defaultPort, nil
	}
	if host, port, err = net.SplitHostPort(target); err == nil {
		if port == "" {
			// If the port field is empty (target ends with colon), e.g. "[::1]:", this is an error.
			return "", "", errEndsWithColon
		}
		// target has port, i.e ipv4-host:port, [ipv6-host]:port, host-name:port
		if host == "" {
			// Keep consistent with net.Dial(): If the host is empty, as in ":80", the local system is assumed.
			host = "localhost"
		}
		return host, port, nil
	}
	if host, port, err = net.SplitHostPort(target + ":" + defaultPort); err == nil {
		// target doesn't have port
		return host, port, nil
	}
	return "", "", fmt.Errorf("invalid target address %v, error info: %v", target, err)
}