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util.go
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util.go
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package mdns
import (
"fmt"
"net"
"os"
"strings"
"syscall"
// Modules
. "github.com/djthorpe/go-server"
multierror "github.com/hashicorp/go-multierror"
dns "github.com/miekg/dns"
ipv4 "golang.org/x/net/ipv4"
ipv6 "golang.org/x/net/ipv6"
)
///////////////////////////////////////////////////////////////////////////////
// PRIVATE METHODS
// interfaceForName returns a net.Interface or error
func interfaceForName(name string) (net.Interface, error) {
if name == "" {
return net.Interface{}, nil
}
ifaces, err := net.Interfaces()
if err != nil {
return net.Interface{}, err
}
for _, iface := range ifaces {
if iface.Name == name {
return iface, nil
}
}
return net.Interface{}, ErrBadParameter.With(name)
}
// multicastInterfaces returns one or more interfaces which should be bound
// for listening
func multicastInterfaces(iface net.Interface) ([]net.Interface, error) {
if iface.Name != "" {
if (iface.Flags&net.FlagUp) > 0 && (iface.Flags&net.FlagMulticast) > 0 {
return []net.Interface{iface}, nil
} else {
return nil, fmt.Errorf("Interface %v is not up and/or multicast-enabled", iface.Name)
}
}
if ifaces, err := net.Interfaces(); err != nil {
return nil, err
} else {
interfaces := make([]net.Interface, 0, len(ifaces))
for _, ifi := range ifaces {
if (ifi.Flags & net.FlagUp) == 0 {
continue
}
if (ifi.Flags & net.FlagMulticast) == 0 {
continue
}
if (ifi.Flags & net.FlagPointToPoint) != 0 {
continue
}
if addrs, err := ifi.MulticastAddrs(); err != nil || len(addrs) == 0 {
continue
}
interfaces = append(interfaces, ifi)
}
if len(interfaces) > 0 {
return interfaces, nil
} else {
return nil, fmt.Errorf("No multicast-enabled interface found")
}
}
}
// bindUdp4 binds to listen on a particular address for IPv4
func bindUdp4(ifaces []net.Interface, addr *net.UDPAddr) (*ipv4.PacketConn, error) {
var result error
if len(ifaces) == 0 {
return nil, ErrBadParameter
} else if conn, err := net.ListenUDP("udp4", addr); err != nil {
return nil, err
} else if packet_conn := ipv4.NewPacketConn(conn); packet_conn == nil {
return nil, conn.Close()
} else {
packet_conn.SetControlMessage(ipv4.FlagInterface, true)
for _, iface := range ifaces {
if err := packet_conn.JoinGroup(&iface, &net.UDPAddr{IP: addr.IP}); err != nil {
if err_, ok := err.(*os.SyscallError); ok && err_.Err == syscall.EAFNOSUPPORT {
continue
} else {
result = multierror.Append(result, fmt.Errorf("%v: %w", iface.Name, err))
}
}
}
if result != nil {
if err := conn.Close(); err != nil {
result = multierror.Append(result, err)
}
}
return packet_conn, result
}
}
// bindUdp6 binds to listen on a particular address for IPv6
func bindUdp6(ifaces []net.Interface, addr *net.UDPAddr) (*ipv6.PacketConn, error) {
var result error
if len(ifaces) == 0 {
return nil, ErrBadParameter
} else if conn, err := net.ListenUDP("udp6", addr); err != nil {
return nil, err
} else if packet_conn := ipv6.NewPacketConn(conn); packet_conn == nil {
return nil, conn.Close()
} else {
packet_conn.SetControlMessage(ipv6.FlagInterface, true)
for _, iface := range ifaces {
if err := packet_conn.JoinGroup(&iface, &net.UDPAddr{IP: addr.IP}); err != nil {
if err_, ok := err.(*os.SyscallError); ok && err_.Err == syscall.EAFNOSUPPORT {
continue
} else {
result = multierror.Append(result, fmt.Errorf("%v: %w", iface.Name, err))
}
}
}
if result != nil {
if err := conn.Close(); err != nil {
result = multierror.Append(result, err)
}
}
return packet_conn, result
}
}
// parseDnsPacket parses packets into DNS message
func parseDnsPacket(packet []byte) (*dns.Msg, error) {
var msg dns.Msg
if err := msg.Unpack(packet); err != nil {
return nil, err
}
if msg.Opcode != dns.OpcodeQuery {
return nil, fmt.Errorf("Query with invalid Opcode %v (expected %v)", msg.Opcode, dns.OpcodeQuery)
}
if msg.Rcode != 0 {
return nil, fmt.Errorf("Query with non-zero Rcode %v", msg.Rcode)
}
if msg.Truncated {
return nil, fmt.Errorf("Support for DNS requests with high truncated bit not implemented")
}
return &msg, nil
}
// Return fully-qualified value
func fqn(value string) string {
return strings.Trim(value, ".") + "."
}
// Transform from fully-qualified value
func unfqn(value string) string {
return strings.TrimSuffix(value, ".")
}
// Return a query message looking up all services
func msgQueryServices(zone string) *dns.Msg {
msg := new(dns.Msg)
msg.SetQuestion(fqn(ServicesQuery)+fqn(zone), dns.TypePTR)
msg.RecursionDesired = false
return msg
}
// Return a query message looking up a specific service record
func msgQueryInstances(srv, zone string) *dns.Msg {
msg := new(dns.Msg)
msg.SetQuestion(fqn(srv)+fqn(zone), dns.TypePTR)
msg.RecursionDesired = false
return msg
}