ipsock.go

Documentation: net

     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  	"runtime"
    11  	"sync"
    12  	_ "unsafe" // for linkname
    13  )
    14  
    15  // BUG(rsc,mikio): On DragonFly BSD and OpenBSD, listening on the
    16  // "tcp" and "udp" networks does not listen for both IPv4 and IPv6
    17  // connections. This is due to the fact that IPv4 traffic will not be
    18  // routed to an IPv6 socket - two separate sockets are required if
    19  // both address families are to be supported.
    20  // See inet6(4) for details.
    21  
    22  type ipStackCapabilities struct {
    23  	sync.Once             // guards following
    24  	ipv4Enabled           bool
    25  	ipv6Enabled           bool
    26  	ipv4MappedIPv6Enabled bool
    27  }
    28  
    29  var ipStackCaps ipStackCapabilities
    30  
    31  // supportsIPv4 reports whether the platform supports IPv4 networking
    32  // functionality.
    33  func supportsIPv4() bool {
    34  	ipStackCaps.Once.Do(ipStackCaps.probe)
    35  	return ipStackCaps.ipv4Enabled
    36  }
    37  
    38  // supportsIPv6 reports whether the platform supports IPv6 networking
    39  // functionality.
    40  func supportsIPv6() bool {
    41  	ipStackCaps.Once.Do(ipStackCaps.probe)
    42  	return ipStackCaps.ipv6Enabled
    43  }
    44  
    45  // supportsIPv4map reports whether the platform supports mapping an
    46  // IPv4 address inside an IPv6 address at transport layer
    47  // protocols. See RFC 4291, RFC 4038 and RFC 3493.
    48  func supportsIPv4map() bool {
    49  	// Some operating systems provide no support for mapping IPv4
    50  	// addresses to IPv6, and a runtime check is unnecessary.
    51  	switch runtime.GOOS {
    52  	case "dragonfly", "openbsd":
    53  		return false
    54  	}
    55  
    56  	ipStackCaps.Once.Do(ipStackCaps.probe)
    57  	return ipStackCaps.ipv4MappedIPv6Enabled
    58  }
    59  
    60  // An addrList represents a list of network endpoint addresses.
    61  type addrList []Addr
    62  
    63  // isIPv4 reports whether addr contains an IPv4 address.
    64  func isIPv4(addr Addr) bool {
    65  	switch addr := addr.(type) {
    66  	case *TCPAddr:
    67  		return addr.IP.To4() != nil
    68  	case *UDPAddr:
    69  		return addr.IP.To4() != nil
    70  	case *IPAddr:
    71  		return addr.IP.To4() != nil
    72  	}
    73  	return false
    74  }
    75  
    76  // isNotIPv4 reports whether addr does not contain an IPv4 address.
    77  func isNotIPv4(addr Addr) bool { return !isIPv4(addr) }
    78  
    79  // forResolve returns the most appropriate address in address for
    80  // a call to ResolveTCPAddr, ResolveUDPAddr, or ResolveIPAddr.
    81  // IPv4 is preferred, unless addr contains an IPv6 literal.
    82  func (addrs addrList) forResolve(network, addr string) Addr {
    83  	var want6 bool
    84  	switch network {
    85  	case "ip":
    86  		// IPv6 literal (addr does NOT contain a port)
    87  		want6 = bytealg.CountString(addr, ':') > 0
    88  	case "tcp", "udp":
    89  		// IPv6 literal. (addr contains a port, so look for '[')
    90  		want6 = bytealg.CountString(addr, '[') > 0
    91  	}
    92  	if want6 {
    93  		return addrs.first(isNotIPv4)
    94  	}
    95  	return addrs.first(isIPv4)
    96  }
    97  
    98  // first returns the first address which satisfies strategy, or if
    99  // none do, then the first address of any kind.
   100  func (addrs addrList) first(strategy func(Addr) bool) Addr {
   101  	for _, addr := range addrs {
   102  		if strategy(addr) {
   103  			return addr
   104  		}
   105  	}
   106  	return addrs[0]
   107  }
   108  
   109  // partition divides an address list into two categories, using a
   110  // strategy function to assign a boolean label to each address.
   111  // The first address, and any with a matching label, are returned as
   112  // primaries, while addresses with the opposite label are returned
   113  // as fallbacks. For non-empty inputs, primaries is guaranteed to be
   114  // non-empty.
   115  func (addrs addrList) partition(strategy func(Addr) bool) (primaries, fallbacks addrList) {
   116  	var primaryLabel bool
   117  	for i, addr := range addrs {
   118  		label := strategy(addr)
   119  		if i == 0 || label == primaryLabel {
   120  			primaryLabel = label
   121  			primaries = append(primaries, addr)
   122  		} else {
   123  			fallbacks = append(fallbacks, addr)
   124  		}
   125  	}
   126  	return
   127  }
   128  
   129  // filterAddrList applies a filter to a list of IP addresses,
   130  // yielding a list of Addr objects. Known filters are nil, ipv4only,
   131  // and ipv6only. It returns every address when the filter is nil.
   132  // The result contains at least one address when error is nil.
   133  func filterAddrList(filter func(IPAddr) bool, ips []IPAddr, inetaddr func(IPAddr) Addr, originalAddr string) (addrList, error) {
   134  	var addrs addrList
   135  	for _, ip := range ips {
   136  		if filter == nil || filter(ip) {
   137  			addrs = append(addrs, inetaddr(ip))
   138  		}
   139  	}
   140  	if len(addrs) == 0 {
   141  		return nil, &AddrError{Err: errNoSuitableAddress.Error(), Addr: originalAddr}
   142  	}
   143  	return addrs, nil
   144  }
   145  
   146  // ipv4only reports whether addr is an IPv4 address.
   147  func ipv4only(addr IPAddr) bool {
   148  	return addr.IP.To4() != nil
   149  }
   150  
   151  // ipv6only reports whether addr is an IPv6 address except IPv4-mapped IPv6 address.
   152  func ipv6only(addr IPAddr) bool {
   153  	return len(addr.IP) == IPv6len && addr.IP.To4() == nil
   154  }
   155  
   156  // SplitHostPort splits a network address of the form "host:port",
   157  // "host%zone:port", "[host]:port" or "[host%zone]:port" into host or
   158  // host%zone and port.
   159  //
   160  // A literal IPv6 address in hostport must be enclosed in square
   161  // brackets, as in "[::1]:80", "[::1%lo0]:80".
   162  //
   163  // See func Dial for a description of the hostport parameter, and host
   164  // and port results.
   165  func SplitHostPort(hostport string) (host, port string, err error) {
   166  	const (
   167  		missingPort   = "missing port in address"
   168  		tooManyColons = "too many colons in address"
   169  	)
   170  	addrErr := func(addr, why string) (host, port string, err error) {
   171  		return "", "", &AddrError{Err: why, Addr: addr}
   172  	}
   173  	j, k := 0, 0
   174  
   175  	// The port starts after the last colon.
   176  	i := bytealg.LastIndexByteString(hostport, ':')
   177  	if i < 0 {
   178  		return addrErr(hostport, missingPort)
   179  	}
   180  
   181  	if hostport[0] == '[' {
   182  		// Expect the first ']' just before the last ':'.
   183  		end := bytealg.IndexByteString(hostport, ']')
   184  		if end < 0 {
   185  			return addrErr(hostport, "missing ']' in address")
   186  		}
   187  		switch end + 1 {
   188  		case len(hostport):
   189  			// There can't be a ':' behind the ']' now.
   190  			return addrErr(hostport, missingPort)
   191  		case i:
   192  			// The expected result.
   193  		default:
   194  			// Either ']' isn't followed by a colon, or it is
   195  			// followed by a colon that is not the last one.
   196  			if hostport[end+1] == ':' {
   197  				return addrErr(hostport, tooManyColons)
   198  			}
   199  			return addrErr(hostport, missingPort)
   200  		}
   201  		host = hostport[1:end]
   202  		j, k = 1, end+1 // there can't be a '[' resp. ']' before these positions
   203  	} else {
   204  		host = hostport[:i]
   205  		if bytealg.IndexByteString(host, ':') >= 0 {
   206  			return addrErr(hostport, tooManyColons)
   207  		}
   208  	}
   209  	if bytealg.IndexByteString(hostport[j:], '[') >= 0 {
   210  		return addrErr(hostport, "unexpected '[' in address")
   211  	}
   212  	if bytealg.IndexByteString(hostport[k:], ']') >= 0 {
   213  		return addrErr(hostport, "unexpected ']' in address")
   214  	}
   215  
   216  	port = hostport[i+1:]
   217  	return host, port, nil
   218  }
   219  
   220  func splitHostZone(s string) (host, zone string) {
   221  	// The IPv6 scoped addressing zone identifier starts after the
   222  	// last percent sign.
   223  	if i := bytealg.LastIndexByteString(s, '%'); i > 0 {
   224  		host, zone = s[:i], s[i+1:]
   225  	} else {
   226  		host = s
   227  	}
   228  	return
   229  }
   230  
   231  // JoinHostPort combines host and port into a network address of the
   232  // form "host:port". If host contains a colon, as found in literal
   233  // IPv6 addresses, then JoinHostPort returns "[host]:port".
   234  //
   235  // See func Dial for a description of the host and port parameters.
   236  func JoinHostPort(host, port string) string {
   237  	// We assume that host is a literal IPv6 address if host has
   238  	// colons.
   239  	if bytealg.IndexByteString(host, ':') >= 0 {
   240  		return "[" + host + "]:" + port
   241  	}
   242  	return host + ":" + port
   243  }
   244  
   245  // internetAddrList resolves addr, which may be a literal IP
   246  // address or a DNS name, and returns a list of internet protocol
   247  // family addresses. The result contains at least one address when
   248  // error is nil.
   249  func (r *Resolver) internetAddrList(ctx context.Context, net, addr string) (addrList, error) {
   250  	var (
   251  		err        error
   252  		host, port string
   253  		portnum    int
   254  	)
   255  	switch net {
   256  	case "tcp", "tcp4", "tcp6", "udp", "udp4", "udp6":
   257  		if addr != "" {
   258  			if host, port, err = SplitHostPort(addr); err != nil {
   259  				return nil, err
   260  			}
   261  			if portnum, err = r.LookupPort(ctx, net, port); err != nil {
   262  				return nil, err
   263  			}
   264  		}
   265  	case "ip", "ip4", "ip6":
   266  		if addr != "" {
   267  			host = addr
   268  		}
   269  	default:
   270  		return nil, UnknownNetworkError(net)
   271  	}
   272  	inetaddr := func(ip IPAddr) Addr {
   273  		switch net {
   274  		case "tcp", "tcp4", "tcp6":
   275  			return &TCPAddr{IP: ip.IP, Port: portnum, Zone: ip.Zone}
   276  		case "udp", "udp4", "udp6":
   277  			return &UDPAddr{IP: ip.IP, Port: portnum, Zone: ip.Zone}
   278  		case "ip", "ip4", "ip6":
   279  			return &IPAddr{IP: ip.IP, Zone: ip.Zone}
   280  		default:
   281  			panic("unexpected network: " + net)
   282  		}
   283  	}
   284  	if host == "" {
   285  		return addrList{inetaddr(IPAddr{})}, nil
   286  	}
   287  
   288  	// Try as a literal IP address, then as a DNS name.
   289  	ips, err := r.lookupIPAddr(ctx, net, host)
   290  	if err != nil {
   291  		return nil, err
   292  	}
   293  	// Issue 18806: if the machine has halfway configured
   294  	// IPv6 such that it can bind on "::" (IPv6unspecified)
   295  	// but not connect back to that same address, fall
   296  	// back to dialing 0.0.0.0.
   297  	if len(ips) == 1 && ips[0].IP.Equal(IPv6unspecified) {
   298  		ips = append(ips, IPAddr{IP: IPv4zero})
   299  	}
   300  
   301  	var filter func(IPAddr) bool
   302  	if net != "" && net[len(net)-1] == '4' {
   303  		filter = ipv4only
   304  	}
   305  	if net != "" && net[len(net)-1] == '6' {
   306  		filter = ipv6only
   307  	}
   308  	return filterAddrList(filter, ips, inetaddr, host)
   309  }
   310  
   311  // loopbackIP should be an internal detail,
   312  // but widely used packages access it using linkname.
   313  // Notable members of the hall of shame include:
   314  //   - github.com/database64128/tfo-go/v2
   315  //   - github.com/metacubex/tfo-go
   316  //   - github.com/sagernet/tfo-go
   317  //
   318  // Do not remove or change the type signature.
   319  // See go.dev/issue/67401.
   320  //
   321  //go:linkname loopbackIP
   322  func loopbackIP(net string) IP {
   323  	if net != "" && net[len(net)-1] == '6' {
   324  		return IPv6loopback
   325  	}
   326  	return IP{127, 0, 0, 1}
   327  }
   328
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