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Source file src/net/ipsock_posix.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.
  
  // +build darwin dragonfly freebsd linux nacl netbsd openbsd solaris windows
  
  package net
  
  import (
  	"context"
  	"internal/poll"
  	"runtime"
  	"syscall"
  )
  
  // Probe probes IPv4, IPv6 and IPv4-mapped IPv6 communication
  // capabilities which are controlled by the IPV6_V6ONLY socket option
  // and kernel configuration.
  //
  // Should we try to use the IPv4 socket interface if we're only
  // dealing with IPv4 sockets? As long as the host system understands
  // IPv4-mapped IPv6, it's okay to pass IPv4-mapeed IPv6 addresses to
  // the IPv6 interface. That simplifies our code and is most
  // general. Unfortunately, we need to run on kernels built without
  // IPv6 support too. So probe the kernel to figure it out.
  func (p *ipStackCapabilities) probe() {
  	s, err := socketFunc(syscall.AF_INET, syscall.SOCK_STREAM, syscall.IPPROTO_TCP)
  	switch err {
  	case syscall.EAFNOSUPPORT, syscall.EPROTONOSUPPORT:
  	case nil:
  		poll.CloseFunc(s)
  		p.ipv4Enabled = true
  	}
  	var probes = []struct {
  		laddr TCPAddr
  		value int
  	}{
  		// IPv6 communication capability
  		{laddr: TCPAddr{IP: ParseIP("::1")}, value: 1},
  		// IPv4-mapped IPv6 address communication capability
  		{laddr: TCPAddr{IP: IPv4(127, 0, 0, 1)}, value: 0},
  	}
  	switch runtime.GOOS {
  	case "dragonfly", "openbsd":
  		// The latest DragonFly BSD and OpenBSD kernels don't
  		// support IPV6_V6ONLY=0. They always return an error
  		// and we don't need to probe the capability.
  		probes = probes[:1]
  	}
  	for i := range probes {
  		s, err := socketFunc(syscall.AF_INET6, syscall.SOCK_STREAM, syscall.IPPROTO_TCP)
  		if err != nil {
  			continue
  		}
  		defer poll.CloseFunc(s)
  		syscall.SetsockoptInt(s, syscall.IPPROTO_IPV6, syscall.IPV6_V6ONLY, probes[i].value)
  		sa, err := probes[i].laddr.sockaddr(syscall.AF_INET6)
  		if err != nil {
  			continue
  		}
  		if err := syscall.Bind(s, sa); err != nil {
  			continue
  		}
  		if i == 0 {
  			p.ipv6Enabled = true
  		} else {
  			p.ipv4MappedIPv6Enabled = true
  		}
  	}
  }
  
  // favoriteAddrFamily returns the appropriate address family for the
  // given network, laddr, raddr and mode.
  //
  // If mode indicates "listen" and laddr is a wildcard, we assume that
  // the user wants to make a passive-open connection with a wildcard
  // address family, both AF_INET and AF_INET6, and a wildcard address
  // like the following:
  //
  //	- A listen for a wildcard communication domain, "tcp" or
  //	  "udp", with a wildcard address: If the platform supports
  //	  both IPv6 and IPv4-mapped IPv6 communication capabilities,
  //	  or does not support IPv4, we use a dual stack, AF_INET6 and
  //	  IPV6_V6ONLY=0, wildcard address listen. The dual stack
  //	  wildcard address listen may fall back to an IPv6-only,
  //	  AF_INET6 and IPV6_V6ONLY=1, wildcard address listen.
  //	  Otherwise we prefer an IPv4-only, AF_INET, wildcard address
  //	  listen.
  //
  //	- A listen for a wildcard communication domain, "tcp" or
  //	  "udp", with an IPv4 wildcard address: same as above.
  //
  //	- A listen for a wildcard communication domain, "tcp" or
  //	  "udp", with an IPv6 wildcard address: same as above.
  //
  //	- A listen for an IPv4 communication domain, "tcp4" or "udp4",
  //	  with an IPv4 wildcard address: We use an IPv4-only, AF_INET,
  //	  wildcard address listen.
  //
  //	- A listen for an IPv6 communication domain, "tcp6" or "udp6",
  //	  with an IPv6 wildcard address: We use an IPv6-only, AF_INET6
  //	  and IPV6_V6ONLY=1, wildcard address listen.
  //
  // Otherwise guess: If the addresses are IPv4 then returns AF_INET,
  // or else returns AF_INET6. It also returns a boolean value what
  // designates IPV6_V6ONLY option.
  //
  // Note that the latest DragonFly BSD and OpenBSD kernels allow
  // neither "net.inet6.ip6.v6only=1" change nor IPPROTO_IPV6 level
  // IPV6_V6ONLY socket option setting.
  func favoriteAddrFamily(network string, laddr, raddr sockaddr, mode string) (family int, ipv6only bool) {
  	switch network[len(network)-1] {
  	case '4':
  		return syscall.AF_INET, false
  	case '6':
  		return syscall.AF_INET6, true
  	}
  
  	if mode == "listen" && (laddr == nil || laddr.isWildcard()) {
  		if supportsIPv4map() || !supportsIPv4() {
  			return syscall.AF_INET6, false
  		}
  		if laddr == nil {
  			return syscall.AF_INET, false
  		}
  		return laddr.family(), false
  	}
  
  	if (laddr == nil || laddr.family() == syscall.AF_INET) &&
  		(raddr == nil || raddr.family() == syscall.AF_INET) {
  		return syscall.AF_INET, false
  	}
  	return syscall.AF_INET6, false
  }
  
  func internetSocket(ctx context.Context, net string, laddr, raddr sockaddr, sotype, proto int, mode string) (fd *netFD, err error) {
  	if (runtime.GOOS == "windows" || runtime.GOOS == "openbsd" || runtime.GOOS == "nacl") && mode == "dial" && raddr.isWildcard() {
  		raddr = raddr.toLocal(net)
  	}
  	family, ipv6only := favoriteAddrFamily(net, laddr, raddr, mode)
  	return socket(ctx, net, family, sotype, proto, ipv6only, laddr, raddr)
  }
  
  func ipToSockaddr(family int, ip IP, port int, zone string) (syscall.Sockaddr, error) {
  	switch family {
  	case syscall.AF_INET:
  		if len(ip) == 0 {
  			ip = IPv4zero
  		}
  		ip4 := ip.To4()
  		if ip4 == nil {
  			return nil, &AddrError{Err: "non-IPv4 address", Addr: ip.String()}
  		}
  		sa := &syscall.SockaddrInet4{Port: port}
  		copy(sa.Addr[:], ip4)
  		return sa, nil
  	case syscall.AF_INET6:
  		// In general, an IP wildcard address, which is either
  		// "0.0.0.0" or "::", means the entire IP addressing
  		// space. For some historical reason, it is used to
  		// specify "any available address" on some operations
  		// of IP node.
  		//
  		// When the IP node supports IPv4-mapped IPv6 address,
  		// we allow an listener to listen to the wildcard
  		// address of both IP addressing spaces by specifying
  		// IPv6 wildcard address.
  		if len(ip) == 0 || ip.Equal(IPv4zero) {
  			ip = IPv6zero
  		}
  		// We accept any IPv6 address including IPv4-mapped
  		// IPv6 address.
  		ip6 := ip.To16()
  		if ip6 == nil {
  			return nil, &AddrError{Err: "non-IPv6 address", Addr: ip.String()}
  		}
  		sa := &syscall.SockaddrInet6{Port: port, ZoneId: uint32(zoneCache.index(zone))}
  		copy(sa.Addr[:], ip6)
  		return sa, nil
  	}
  	return nil, &AddrError{Err: "invalid address family", Addr: ip.String()}
  }
  

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