Source file src/net/ipsock.go

Documentation: net

  // Copyright 2009 The Go Authors. All rights reserved.
  // Use of this source code is governed by a BSD-style
  // license that can be found in the LICENSE file.
  
  package net
  
  import (
  	"context"
  	"sync"
  )
  
  // BUG(rsc,mikio): On DragonFly BSD and OpenBSD, listening on the
  // "tcp" and "udp" networks does not listen for both IPv4 and IPv6
  // connections. This is due to the fact that IPv4 traffic will not be
  // routed to an IPv6 socket - two separate sockets are required if
  // both address families are to be supported.
  // See inet6(4) for details.
  
  type ipStackCapabilities struct {
  	sync.Once             // guards following
  	ipv4Enabled           bool
  	ipv6Enabled           bool
  	ipv4MappedIPv6Enabled bool
  }
  
  var ipStackCaps ipStackCapabilities
  
  // supportsIPv4 reports whether the platform supports IPv4 networking
  // functionality.
  func supportsIPv4() bool {
  	ipStackCaps.Once.Do(ipStackCaps.probe)
  	return ipStackCaps.ipv4Enabled
  }
  
  // supportsIPv6 reports whether the platform supports IPv6 networking
  // functionality.
  func supportsIPv6() bool {
  	ipStackCaps.Once.Do(ipStackCaps.probe)
  	return ipStackCaps.ipv6Enabled
  }
  
  // supportsIPv4map reports whether the platform supports mapping an
  // IPv4 address inside an IPv6 address at transport layer
  // protocols. See RFC 4291, RFC 4038 and RFC 3493.
  func supportsIPv4map() bool {
  	ipStackCaps.Once.Do(ipStackCaps.probe)
  	return ipStackCaps.ipv4MappedIPv6Enabled
  }
  
  // An addrList represents a list of network endpoint addresses.
  type addrList []Addr
  
  // isIPv4 reports whether addr contains an IPv4 address.
  func isIPv4(addr Addr) bool {
  	switch addr := addr.(type) {
  	case *TCPAddr:
  		return addr.IP.To4() != nil
  	case *UDPAddr:
  		return addr.IP.To4() != nil
  	case *IPAddr:
  		return addr.IP.To4() != nil
  	}
  	return false
  }
  
  // isNotIPv4 reports whether addr does not contain an IPv4 address.
  func isNotIPv4(addr Addr) bool { return !isIPv4(addr) }
  
  // forResolve returns the most appropriate address in address for
  // a call to ResolveTCPAddr, ResolveUDPAddr, or ResolveIPAddr.
  // IPv4 is preferred, unless addr contains an IPv6 literal.
  func (addrs addrList) forResolve(network, addr string) Addr {
  	var want6 bool
  	switch network {
  	case "ip":
  		// IPv6 literal (addr does NOT contain a port)
  		want6 = count(addr, ':') > 0
  	case "tcp", "udp":
  		// IPv6 literal. (addr contains a port, so look for '[')
  		want6 = count(addr, '[') > 0
  	}
  	if want6 {
  		return addrs.first(isNotIPv4)
  	}
  	return addrs.first(isIPv4)
  }
  
  // first returns the first address which satisfies strategy, or if
  // none do, then the first address of any kind.
  func (addrs addrList) first(strategy func(Addr) bool) Addr {
  	for _, addr := range addrs {
  		if strategy(addr) {
  			return addr
  		}
  	}
  	return addrs[0]
  }
  
  // partition divides an address list into two categories, using a
  // strategy function to assign a boolean label to each address.
  // The first address, and any with a matching label, are returned as
  // primaries, while addresses with the opposite label are returned
  // as fallbacks. For non-empty inputs, primaries is guaranteed to be
  // non-empty.
  func (addrs addrList) partition(strategy func(Addr) bool) (primaries, fallbacks addrList) {
  	var primaryLabel bool
  	for i, addr := range addrs {
  		label := strategy(addr)
  		if i == 0 || label == primaryLabel {
  			primaryLabel = label
  			primaries = append(primaries, addr)
  		} else {
  			fallbacks = append(fallbacks, addr)
  		}
  	}
  	return
  }
  
  // filterAddrList applies a filter to a list of IP addresses,
  // yielding a list of Addr objects. Known filters are nil, ipv4only,
  // and ipv6only. It returns every address when the filter is nil.
  // The result contains at least one address when error is nil.
  func filterAddrList(filter func(IPAddr) bool, ips []IPAddr, inetaddr func(IPAddr) Addr, originalAddr string) (addrList, error) {
  	var addrs addrList
  	for _, ip := range ips {
  		if filter == nil || filter(ip) {
  			addrs = append(addrs, inetaddr(ip))
  		}
  	}
  	if len(addrs) == 0 {
  		return nil, &AddrError{Err: errNoSuitableAddress.Error(), Addr: originalAddr}
  	}
  	return addrs, nil
  }
  
  // ipv4only reports whether addr is an IPv4 address.
  func ipv4only(addr IPAddr) bool {
  	return addr.IP.To4() != nil
  }
  
  // ipv6only reports whether addr is an IPv6 address except IPv4-mapped IPv6 address.
  func ipv6only(addr IPAddr) bool {
  	return len(addr.IP) == IPv6len && addr.IP.To4() == nil
  }
  
  // SplitHostPort splits a network address of the form "host:port",
  // "host%zone:port", "[host]:port" or "[host%zone]:port" into host or
  // host%zone and port.
  //
  // A literal IPv6 address in hostport must be enclosed in square
  // brackets, as in "[::1]:80", "[::1%lo0]:80".
  //
  // See func Dial for a description of the hostport parameter, and host
  // and port results.
  func SplitHostPort(hostport string) (host, port string, err error) {
  	const (
  		missingPort   = "missing port in address"
  		tooManyColons = "too many colons in address"
  	)
  	addrErr := func(addr, why string) (host, port string, err error) {
  		return "", "", &AddrError{Err: why, Addr: addr}
  	}
  	j, k := 0, 0
  
  	// The port starts after the last colon.
  	i := last(hostport, ':')
  	if i < 0 {
  		return addrErr(hostport, missingPort)
  	}
  
  	if hostport[0] == '[' {
  		// Expect the first ']' just before the last ':'.
  		end := byteIndex(hostport, ']')
  		if end < 0 {
  			return addrErr(hostport, "missing ']' in address")
  		}
  		switch end + 1 {
  		case len(hostport):
  			// There can't be a ':' behind the ']' now.
  			return addrErr(hostport, missingPort)
  		case i:
  			// The expected result.
  		default:
  			// Either ']' isn't followed by a colon, or it is
  			// followed by a colon that is not the last one.
  			if hostport[end+1] == ':' {
  				return addrErr(hostport, tooManyColons)
  			}
  			return addrErr(hostport, missingPort)
  		}
  		host = hostport[1:end]
  		j, k = 1, end+1 // there can't be a '[' resp. ']' before these positions
  	} else {
  		host = hostport[:i]
  		if byteIndex(host, ':') >= 0 {
  			return addrErr(hostport, tooManyColons)
  		}
  	}
  	if byteIndex(hostport[j:], '[') >= 0 {
  		return addrErr(hostport, "unexpected '[' in address")
  	}
  	if byteIndex(hostport[k:], ']') >= 0 {
  		return addrErr(hostport, "unexpected ']' in address")
  	}
  
  	port = hostport[i+1:]
  	return host, port, nil
  }
  
  func splitHostZone(s string) (host, zone string) {
  	// The IPv6 scoped addressing zone identifier starts after the
  	// last percent sign.
  	if i := last(s, '%'); i > 0 {
  		host, zone = s[:i], s[i+1:]
  	} else {
  		host = s
  	}
  	return
  }
  
  // JoinHostPort combines host and port into a network address of the
  // form "host:port". If host contains a colon, as found in literal
  // IPv6 addresses, then JoinHostPort returns "[host]:port".
  //
  // See func Dial for a description of the host and port parameters.
  func JoinHostPort(host, port string) string {
  	// We assume that host is a literal IPv6 address if host has
  	// colons.
  	if byteIndex(host, ':') >= 0 {
  		return "[" + host + "]:" + port
  	}
  	return host + ":" + port
  }
  
  // internetAddrList resolves addr, which may be a literal IP
  // address or a DNS name, and returns a list of internet protocol
  // family addresses. The result contains at least one address when
  // error is nil.
  func (r *Resolver) internetAddrList(ctx context.Context, net, addr string) (addrList, error) {
  	var (
  		err        error
  		host, port string
  		portnum    int
  	)
  	switch net {
  	case "tcp", "tcp4", "tcp6", "udp", "udp4", "udp6":
  		if addr != "" {
  			if host, port, err = SplitHostPort(addr); err != nil {
  				return nil, err
  			}
  			if portnum, err = r.LookupPort(ctx, net, port); err != nil {
  				return nil, err
  			}
  		}
  	case "ip", "ip4", "ip6":
  		if addr != "" {
  			host = addr
  		}
  	default:
  		return nil, UnknownNetworkError(net)
  	}
  	inetaddr := func(ip IPAddr) Addr {
  		switch net {
  		case "tcp", "tcp4", "tcp6":
  			return &TCPAddr{IP: ip.IP, Port: portnum, Zone: ip.Zone}
  		case "udp", "udp4", "udp6":
  			return &UDPAddr{IP: ip.IP, Port: portnum, Zone: ip.Zone}
  		case "ip", "ip4", "ip6":
  			return &IPAddr{IP: ip.IP, Zone: ip.Zone}
  		default:
  			panic("unexpected network: " + net)
  		}
  	}
  	if host == "" {
  		return addrList{inetaddr(IPAddr{})}, nil
  	}
  
  	// Try as a literal IP address, then as a DNS name.
  	var ips []IPAddr
  	if ip := parseIPv4(host); ip != nil {
  		ips = []IPAddr{{IP: ip}}
  	} else if ip, zone := parseIPv6(host, true); ip != nil {
  		ips = []IPAddr{{IP: ip, Zone: zone}}
  		// Issue 18806: if the machine has halfway configured
  		// IPv6 such that it can bind on "::" (IPv6unspecified)
  		// but not connect back to that same address, fall
  		// back to dialing 0.0.0.0.
  		if ip.Equal(IPv6unspecified) {
  			ips = append(ips, IPAddr{IP: IPv4zero})
  		}
  	} else {
  		// Try as a DNS name.
  		ips, err = r.LookupIPAddr(ctx, host)
  		if err != nil {
  			return nil, err
  		}
  	}
  
  	var filter func(IPAddr) bool
  	if net != "" && net[len(net)-1] == '4' {
  		filter = ipv4only
  	}
  	if net != "" && net[len(net)-1] == '6' {
  		filter = ipv6only
  	}
  	return filterAddrList(filter, ips, inetaddr, host)
  }
  
  func loopbackIP(net string) IP {
  	if net != "" && net[len(net)-1] == '6' {
  		return IPv6loopback
  	}
  	return IP{127, 0, 0, 1}
  }
  

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