Source file src/net/ipsock.go

     1	// Copyright 2009 The Go Authors. All rights reserved.
     2	// Use of this source code is governed by a BSD-style
     3	// license that can be found in the LICENSE file.
     4	
     5	package net
     6	
     7	import (
     8		"context"
     9		"internal/bytealg"
    10		"sync"
    11	)
    12	
    13	// BUG(rsc,mikio): On DragonFly BSD and OpenBSD, listening on the
    14	// "tcp" and "udp" networks does not listen for both IPv4 and IPv6
    15	// connections. This is due to the fact that IPv4 traffic will not be
    16	// routed to an IPv6 socket - two separate sockets are required if
    17	// both address families are to be supported.
    18	// See inet6(4) for details.
    19	
    20	type ipStackCapabilities struct {
    21		sync.Once             // guards following
    22		ipv4Enabled           bool
    23		ipv6Enabled           bool
    24		ipv4MappedIPv6Enabled bool
    25	}
    26	
    27	var ipStackCaps ipStackCapabilities
    28	
    29	// supportsIPv4 reports whether the platform supports IPv4 networking
    30	// functionality.
    31	func supportsIPv4() bool {
    32		ipStackCaps.Once.Do(ipStackCaps.probe)
    33		return ipStackCaps.ipv4Enabled
    34	}
    35	
    36	// supportsIPv6 reports whether the platform supports IPv6 networking
    37	// functionality.
    38	func supportsIPv6() bool {
    39		ipStackCaps.Once.Do(ipStackCaps.probe)
    40		return ipStackCaps.ipv6Enabled
    41	}
    42	
    43	// supportsIPv4map reports whether the platform supports mapping an
    44	// IPv4 address inside an IPv6 address at transport layer
    45	// protocols. See RFC 4291, RFC 4038 and RFC 3493.
    46	func supportsIPv4map() bool {
    47		ipStackCaps.Once.Do(ipStackCaps.probe)
    48		return ipStackCaps.ipv4MappedIPv6Enabled
    49	}
    50	
    51	// An addrList represents a list of network endpoint addresses.
    52	type addrList []Addr
    53	
    54	// isIPv4 reports whether addr contains an IPv4 address.
    55	func isIPv4(addr Addr) bool {
    56		switch addr := addr.(type) {
    57		case *TCPAddr:
    58			return addr.IP.To4() != nil
    59		case *UDPAddr:
    60			return addr.IP.To4() != nil
    61		case *IPAddr:
    62			return addr.IP.To4() != nil
    63		}
    64		return false
    65	}
    66	
    67	// isNotIPv4 reports whether addr does not contain an IPv4 address.
    68	func isNotIPv4(addr Addr) bool { return !isIPv4(addr) }
    69	
    70	// forResolve returns the most appropriate address in address for
    71	// a call to ResolveTCPAddr, ResolveUDPAddr, or ResolveIPAddr.
    72	// IPv4 is preferred, unless addr contains an IPv6 literal.
    73	func (addrs addrList) forResolve(network, addr string) Addr {
    74		var want6 bool
    75		switch network {
    76		case "ip":
    77			// IPv6 literal (addr does NOT contain a port)
    78			want6 = count(addr, ':') > 0
    79		case "tcp", "udp":
    80			// IPv6 literal. (addr contains a port, so look for '[')
    81			want6 = count(addr, '[') > 0
    82		}
    83		if want6 {
    84			return addrs.first(isNotIPv4)
    85		}
    86		return addrs.first(isIPv4)
    87	}
    88	
    89	// first returns the first address which satisfies strategy, or if
    90	// none do, then the first address of any kind.
    91	func (addrs addrList) first(strategy func(Addr) bool) Addr {
    92		for _, addr := range addrs {
    93			if strategy(addr) {
    94				return addr
    95			}
    96		}
    97		return addrs[0]
    98	}
    99	
   100	// partition divides an address list into two categories, using a
   101	// strategy function to assign a boolean label to each address.
   102	// The first address, and any with a matching label, are returned as
   103	// primaries, while addresses with the opposite label are returned
   104	// as fallbacks. For non-empty inputs, primaries is guaranteed to be
   105	// non-empty.
   106	func (addrs addrList) partition(strategy func(Addr) bool) (primaries, fallbacks addrList) {
   107		var primaryLabel bool
   108		for i, addr := range addrs {
   109			label := strategy(addr)
   110			if i == 0 || label == primaryLabel {
   111				primaryLabel = label
   112				primaries = append(primaries, addr)
   113			} else {
   114				fallbacks = append(fallbacks, addr)
   115			}
   116		}
   117		return
   118	}
   119	
   120	// filterAddrList applies a filter to a list of IP addresses,
   121	// yielding a list of Addr objects. Known filters are nil, ipv4only,
   122	// and ipv6only. It returns every address when the filter is nil.
   123	// The result contains at least one address when error is nil.
   124	func filterAddrList(filter func(IPAddr) bool, ips []IPAddr, inetaddr func(IPAddr) Addr, originalAddr string) (addrList, error) {
   125		var addrs addrList
   126		for _, ip := range ips {
   127			if filter == nil || filter(ip) {
   128				addrs = append(addrs, inetaddr(ip))
   129			}
   130		}
   131		if len(addrs) == 0 {
   132			return nil, &AddrError{Err: errNoSuitableAddress.Error(), Addr: originalAddr}
   133		}
   134		return addrs, nil
   135	}
   136	
   137	// ipv4only reports whether addr is an IPv4 address.
   138	func ipv4only(addr IPAddr) bool {
   139		return addr.IP.To4() != nil
   140	}
   141	
   142	// ipv6only reports whether addr is an IPv6 address except IPv4-mapped IPv6 address.
   143	func ipv6only(addr IPAddr) bool {
   144		return len(addr.IP) == IPv6len && addr.IP.To4() == nil
   145	}
   146	
   147	// SplitHostPort splits a network address of the form "host:port",
   148	// "host%zone:port", "[host]:port" or "[host%zone]:port" into host or
   149	// host%zone and port.
   150	//
   151	// A literal IPv6 address in hostport must be enclosed in square
   152	// brackets, as in "[::1]:80", "[::1%lo0]:80".
   153	//
   154	// See func Dial for a description of the hostport parameter, and host
   155	// and port results.
   156	func SplitHostPort(hostport string) (host, port string, err error) {
   157		const (
   158			missingPort   = "missing port in address"
   159			tooManyColons = "too many colons in address"
   160		)
   161		addrErr := func(addr, why string) (host, port string, err error) {
   162			return "", "", &AddrError{Err: why, Addr: addr}
   163		}
   164		j, k := 0, 0
   165	
   166		// The port starts after the last colon.
   167		i := last(hostport, ':')
   168		if i < 0 {
   169			return addrErr(hostport, missingPort)
   170		}
   171	
   172		if hostport[0] == '[' {
   173			// Expect the first ']' just before the last ':'.
   174			end := bytealg.IndexByteString(hostport, ']')
   175			if end < 0 {
   176				return addrErr(hostport, "missing ']' in address")
   177			}
   178			switch end + 1 {
   179			case len(hostport):
   180				// There can't be a ':' behind the ']' now.
   181				return addrErr(hostport, missingPort)
   182			case i:
   183				// The expected result.
   184			default:
   185				// Either ']' isn't followed by a colon, or it is
   186				// followed by a colon that is not the last one.
   187				if hostport[end+1] == ':' {
   188					return addrErr(hostport, tooManyColons)
   189				}
   190				return addrErr(hostport, missingPort)
   191			}
   192			host = hostport[1:end]
   193			j, k = 1, end+1 // there can't be a '[' resp. ']' before these positions
   194		} else {
   195			host = hostport[:i]
   196			if bytealg.IndexByteString(host, ':') >= 0 {
   197				return addrErr(hostport, tooManyColons)
   198			}
   199		}
   200		if bytealg.IndexByteString(hostport[j:], '[') >= 0 {
   201			return addrErr(hostport, "unexpected '[' in address")
   202		}
   203		if bytealg.IndexByteString(hostport[k:], ']') >= 0 {
   204			return addrErr(hostport, "unexpected ']' in address")
   205		}
   206	
   207		port = hostport[i+1:]
   208		return host, port, nil
   209	}
   210	
   211	func splitHostZone(s string) (host, zone string) {
   212		// The IPv6 scoped addressing zone identifier starts after the
   213		// last percent sign.
   214		if i := last(s, '%'); i > 0 {
   215			host, zone = s[:i], s[i+1:]
   216		} else {
   217			host = s
   218		}
   219		return
   220	}
   221	
   222	// JoinHostPort combines host and port into a network address of the
   223	// form "host:port". If host contains a colon, as found in literal
   224	// IPv6 addresses, then JoinHostPort returns "[host]:port".
   225	//
   226	// See func Dial for a description of the host and port parameters.
   227	func JoinHostPort(host, port string) string {
   228		// We assume that host is a literal IPv6 address if host has
   229		// colons.
   230		if bytealg.IndexByteString(host, ':') >= 0 {
   231			return "[" + host + "]:" + port
   232		}
   233		return host + ":" + port
   234	}
   235	
   236	// internetAddrList resolves addr, which may be a literal IP
   237	// address or a DNS name, and returns a list of internet protocol
   238	// family addresses. The result contains at least one address when
   239	// error is nil.
   240	func (r *Resolver) internetAddrList(ctx context.Context, net, addr string) (addrList, error) {
   241		var (
   242			err        error
   243			host, port string
   244			portnum    int
   245		)
   246		switch net {
   247		case "tcp", "tcp4", "tcp6", "udp", "udp4", "udp6":
   248			if addr != "" {
   249				if host, port, err = SplitHostPort(addr); err != nil {
   250					return nil, err
   251				}
   252				if portnum, err = r.LookupPort(ctx, net, port); err != nil {
   253					return nil, err
   254				}
   255			}
   256		case "ip", "ip4", "ip6":
   257			if addr != "" {
   258				host = addr
   259			}
   260		default:
   261			return nil, UnknownNetworkError(net)
   262		}
   263		inetaddr := func(ip IPAddr) Addr {
   264			switch net {
   265			case "tcp", "tcp4", "tcp6":
   266				return &TCPAddr{IP: ip.IP, Port: portnum, Zone: ip.Zone}
   267			case "udp", "udp4", "udp6":
   268				return &UDPAddr{IP: ip.IP, Port: portnum, Zone: ip.Zone}
   269			case "ip", "ip4", "ip6":
   270				return &IPAddr{IP: ip.IP, Zone: ip.Zone}
   271			default:
   272				panic("unexpected network: " + net)
   273			}
   274		}
   275		if host == "" {
   276			return addrList{inetaddr(IPAddr{})}, nil
   277		}
   278	
   279		// Try as a literal IP address, then as a DNS name.
   280		ips, err := r.lookupIPAddr(ctx, net, host)
   281		if err != nil {
   282			return nil, err
   283		}
   284		// Issue 18806: if the machine has halfway configured
   285		// IPv6 such that it can bind on "::" (IPv6unspecified)
   286		// but not connect back to that same address, fall
   287		// back to dialing 0.0.0.0.
   288		if len(ips) == 1 && ips[0].IP.Equal(IPv6unspecified) {
   289			ips = append(ips, IPAddr{IP: IPv4zero})
   290		}
   291	
   292		var filter func(IPAddr) bool
   293		if net != "" && net[len(net)-1] == '4' {
   294			filter = ipv4only
   295		}
   296		if net != "" && net[len(net)-1] == '6' {
   297			filter = ipv6only
   298		}
   299		return filterAddrList(filter, ips, inetaddr, host)
   300	}
   301	
   302	func loopbackIP(net string) IP {
   303		if net != "" && net[len(net)-1] == '6' {
   304			return IPv6loopback
   305		}
   306		return IP{127, 0, 0, 1}
   307	}
   308	

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