Source file src/net/cgo_unix.go

Documentation: net

     1  // Copyright 2011 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  // This file is called cgo_unix.go, but to allow syscalls-to-libc-based
     6  // implementations to share the code, it does not use cgo directly.
     7  // Instead of C.foo it uses _C_foo, which is defined in either
     8  // cgo_unix_cgo.go or cgo_unix_syscall.go
     9  
    10  //go:build !netgo && ((cgo && unix) || darwin)
    11  
    12  package net
    13  
    14  import (
    15  	"context"
    16  	"errors"
    17  	"net/netip"
    18  	"syscall"
    19  	"unsafe"
    20  
    21  	"golang.org/x/net/dns/dnsmessage"
    22  )
    23  
    24  // cgoAvailable set to true to indicate that the cgo resolver
    25  // is available on this system.
    26  const cgoAvailable = true
    27  
    28  // An addrinfoErrno represents a getaddrinfo, getnameinfo-specific
    29  // error number. It's a signed number and a zero value is a non-error
    30  // by convention.
    31  type addrinfoErrno int
    32  
    33  func (eai addrinfoErrno) Error() string   { return _C_gai_strerror(_C_int(eai)) }
    34  func (eai addrinfoErrno) Temporary() bool { return eai == _C_EAI_AGAIN }
    35  func (eai addrinfoErrno) Timeout() bool   { return false }
    36  
    37  // isAddrinfoErrno is just for testing purposes.
    38  func (eai addrinfoErrno) isAddrinfoErrno() {}
    39  
    40  // doBlockingWithCtx executes a blocking function in a separate goroutine when the provided
    41  // context is cancellable. It is intended for use with calls that don't support context
    42  // cancellation (cgo, syscalls). blocking func may still be running after this function finishes.
    43  func doBlockingWithCtx[T any](ctx context.Context, blocking func() (T, error)) (T, error) {
    44  	if ctx.Done() == nil {
    45  		return blocking()
    46  	}
    47  
    48  	type result struct {
    49  		res T
    50  		err error
    51  	}
    52  
    53  	res := make(chan result, 1)
    54  	go func() {
    55  		var r result
    56  		r.res, r.err = blocking()
    57  		res <- r
    58  	}()
    59  
    60  	select {
    61  	case r := <-res:
    62  		return r.res, r.err
    63  	case <-ctx.Done():
    64  		var zero T
    65  		return zero, mapErr(ctx.Err())
    66  	}
    67  }
    68  
    69  func cgoLookupHost(ctx context.Context, name string) (hosts []string, err error) {
    70  	addrs, err := cgoLookupIP(ctx, "ip", name)
    71  	if err != nil {
    72  		return nil, err
    73  	}
    74  	for _, addr := range addrs {
    75  		hosts = append(hosts, addr.String())
    76  	}
    77  	return hosts, nil
    78  }
    79  
    80  func cgoLookupPort(ctx context.Context, network, service string) (port int, err error) {
    81  	var hints _C_struct_addrinfo
    82  	switch network {
    83  	case "ip": // no hints
    84  	case "tcp", "tcp4", "tcp6":
    85  		*_C_ai_socktype(&hints) = _C_SOCK_STREAM
    86  		*_C_ai_protocol(&hints) = _C_IPPROTO_TCP
    87  	case "udp", "udp4", "udp6":
    88  		*_C_ai_socktype(&hints) = _C_SOCK_DGRAM
    89  		*_C_ai_protocol(&hints) = _C_IPPROTO_UDP
    90  	default:
    91  		return 0, &DNSError{Err: "unknown network", Name: network + "/" + service}
    92  	}
    93  	switch ipVersion(network) {
    94  	case '4':
    95  		*_C_ai_family(&hints) = _C_AF_INET
    96  	case '6':
    97  		*_C_ai_family(&hints) = _C_AF_INET6
    98  	}
    99  
   100  	return doBlockingWithCtx(ctx, func() (int, error) {
   101  		return cgoLookupServicePort(&hints, network, service)
   102  	})
   103  }
   104  
   105  func cgoLookupServicePort(hints *_C_struct_addrinfo, network, service string) (port int, err error) {
   106  	cservice, err := syscall.ByteSliceFromString(service)
   107  	if err != nil {
   108  		return 0, &DNSError{Err: err.Error(), Name: network + "/" + service}
   109  	}
   110  	// Lowercase the C service name.
   111  	for i, b := range cservice[:len(service)] {
   112  		cservice[i] = lowerASCII(b)
   113  	}
   114  	var res *_C_struct_addrinfo
   115  	gerrno, err := _C_getaddrinfo(nil, (*_C_char)(unsafe.Pointer(&cservice[0])), hints, &res)
   116  	if gerrno != 0 {
   117  		isTemporary := false
   118  		switch gerrno {
   119  		case _C_EAI_SYSTEM:
   120  			if err == nil { // see golang.org/issue/6232
   121  				err = syscall.EMFILE
   122  			}
   123  		case _C_EAI_SERVICE, _C_EAI_NONAME: // Darwin returns EAI_NONAME.
   124  			return 0, &DNSError{Err: "unknown port", Name: network + "/" + service, IsNotFound: true}
   125  		default:
   126  			err = addrinfoErrno(gerrno)
   127  			isTemporary = addrinfoErrno(gerrno).Temporary()
   128  		}
   129  		return 0, &DNSError{Err: err.Error(), Name: network + "/" + service, IsTemporary: isTemporary}
   130  	}
   131  	defer _C_freeaddrinfo(res)
   132  
   133  	for r := res; r != nil; r = *_C_ai_next(r) {
   134  		switch *_C_ai_family(r) {
   135  		case _C_AF_INET:
   136  			sa := (*syscall.RawSockaddrInet4)(unsafe.Pointer(*_C_ai_addr(r)))
   137  			p := (*[2]byte)(unsafe.Pointer(&sa.Port))
   138  			return int(p[0])<<8 | int(p[1]), nil
   139  		case _C_AF_INET6:
   140  			sa := (*syscall.RawSockaddrInet6)(unsafe.Pointer(*_C_ai_addr(r)))
   141  			p := (*[2]byte)(unsafe.Pointer(&sa.Port))
   142  			return int(p[0])<<8 | int(p[1]), nil
   143  		}
   144  	}
   145  	return 0, &DNSError{Err: "unknown port", Name: network + "/" + service, IsNotFound: true}
   146  }
   147  
   148  func cgoLookupHostIP(network, name string) (addrs []IPAddr, err error) {
   149  	acquireThread()
   150  	defer releaseThread()
   151  
   152  	var hints _C_struct_addrinfo
   153  	*_C_ai_flags(&hints) = cgoAddrInfoFlags
   154  	*_C_ai_socktype(&hints) = _C_SOCK_STREAM
   155  	*_C_ai_family(&hints) = _C_AF_UNSPEC
   156  	switch ipVersion(network) {
   157  	case '4':
   158  		*_C_ai_family(&hints) = _C_AF_INET
   159  	case '6':
   160  		*_C_ai_family(&hints) = _C_AF_INET6
   161  	}
   162  
   163  	h, err := syscall.BytePtrFromString(name)
   164  	if err != nil {
   165  		return nil, &DNSError{Err: err.Error(), Name: name}
   166  	}
   167  	var res *_C_struct_addrinfo
   168  	gerrno, err := _C_getaddrinfo((*_C_char)(unsafe.Pointer(h)), nil, &hints, &res)
   169  	if gerrno != 0 {
   170  		isErrorNoSuchHost := false
   171  		isTemporary := false
   172  		switch gerrno {
   173  		case _C_EAI_SYSTEM:
   174  			if err == nil {
   175  				// err should not be nil, but sometimes getaddrinfo returns
   176  				// gerrno == _C_EAI_SYSTEM with err == nil on Linux.
   177  				// The report claims that it happens when we have too many
   178  				// open files, so use syscall.EMFILE (too many open files in system).
   179  				// Most system calls would return ENFILE (too many open files),
   180  				// so at the least EMFILE should be easy to recognize if this
   181  				// comes up again. golang.org/issue/6232.
   182  				err = syscall.EMFILE
   183  			}
   184  		case _C_EAI_NONAME, _C_EAI_NODATA:
   185  			err = errNoSuchHost
   186  			isErrorNoSuchHost = true
   187  		default:
   188  			err = addrinfoErrno(gerrno)
   189  			isTemporary = addrinfoErrno(gerrno).Temporary()
   190  		}
   191  
   192  		return nil, &DNSError{Err: err.Error(), Name: name, IsNotFound: isErrorNoSuchHost, IsTemporary: isTemporary}
   193  	}
   194  	defer _C_freeaddrinfo(res)
   195  
   196  	for r := res; r != nil; r = *_C_ai_next(r) {
   197  		// We only asked for SOCK_STREAM, but check anyhow.
   198  		if *_C_ai_socktype(r) != _C_SOCK_STREAM {
   199  			continue
   200  		}
   201  		switch *_C_ai_family(r) {
   202  		case _C_AF_INET:
   203  			sa := (*syscall.RawSockaddrInet4)(unsafe.Pointer(*_C_ai_addr(r)))
   204  			addr := IPAddr{IP: copyIP(sa.Addr[:])}
   205  			addrs = append(addrs, addr)
   206  		case _C_AF_INET6:
   207  			sa := (*syscall.RawSockaddrInet6)(unsafe.Pointer(*_C_ai_addr(r)))
   208  			addr := IPAddr{IP: copyIP(sa.Addr[:]), Zone: zoneCache.name(int(sa.Scope_id))}
   209  			addrs = append(addrs, addr)
   210  		}
   211  	}
   212  	return addrs, nil
   213  }
   214  
   215  func cgoLookupIP(ctx context.Context, network, name string) (addrs []IPAddr, err error) {
   216  	return doBlockingWithCtx(ctx, func() ([]IPAddr, error) {
   217  		return cgoLookupHostIP(network, name)
   218  	})
   219  }
   220  
   221  // These are roughly enough for the following:
   222  //
   223  //	 Source		Encoding			Maximum length of single name entry
   224  //	 Unicast DNS		ASCII or			<=253 + a NUL terminator
   225  //				Unicode in RFC 5892		252 * total number of labels + delimiters + a NUL terminator
   226  //	 Multicast DNS	UTF-8 in RFC 5198 or		<=253 + a NUL terminator
   227  //				the same as unicast DNS ASCII	<=253 + a NUL terminator
   228  //	 Local database	various				depends on implementation
   229  const (
   230  	nameinfoLen    = 64
   231  	maxNameinfoLen = 4096
   232  )
   233  
   234  func cgoLookupPTR(ctx context.Context, addr string) (names []string, err error) {
   235  	ip, err := netip.ParseAddr(addr)
   236  	if err != nil {
   237  		return nil, &DNSError{Err: "invalid address", Name: addr}
   238  	}
   239  	sa, salen := cgoSockaddr(IP(ip.AsSlice()), ip.Zone())
   240  	if sa == nil {
   241  		return nil, &DNSError{Err: "invalid address " + ip.String(), Name: addr}
   242  	}
   243  
   244  	return doBlockingWithCtx(ctx, func() ([]string, error) {
   245  		return cgoLookupAddrPTR(addr, sa, salen)
   246  	})
   247  }
   248  
   249  func cgoLookupAddrPTR(addr string, sa *_C_struct_sockaddr, salen _C_socklen_t) (names []string, err error) {
   250  	acquireThread()
   251  	defer releaseThread()
   252  
   253  	var gerrno int
   254  	var b []byte
   255  	for l := nameinfoLen; l <= maxNameinfoLen; l *= 2 {
   256  		b = make([]byte, l)
   257  		gerrno, err = cgoNameinfoPTR(b, sa, salen)
   258  		if gerrno == 0 || gerrno != _C_EAI_OVERFLOW {
   259  			break
   260  		}
   261  	}
   262  	if gerrno != 0 {
   263  		isErrorNoSuchHost := false
   264  		isTemporary := false
   265  		switch gerrno {
   266  		case _C_EAI_SYSTEM:
   267  			if err == nil { // see golang.org/issue/6232
   268  				err = syscall.EMFILE
   269  			}
   270  		case _C_EAI_NONAME:
   271  			err = errNoSuchHost
   272  			isErrorNoSuchHost = true
   273  		default:
   274  			err = addrinfoErrno(gerrno)
   275  			isTemporary = addrinfoErrno(gerrno).Temporary()
   276  		}
   277  		return nil, &DNSError{Err: err.Error(), Name: addr, IsTemporary: isTemporary, IsNotFound: isErrorNoSuchHost}
   278  	}
   279  	for i := 0; i < len(b); i++ {
   280  		if b[i] == 0 {
   281  			b = b[:i]
   282  			break
   283  		}
   284  	}
   285  	return []string{absDomainName(string(b))}, nil
   286  }
   287  
   288  func cgoSockaddr(ip IP, zone string) (*_C_struct_sockaddr, _C_socklen_t) {
   289  	if ip4 := ip.To4(); ip4 != nil {
   290  		return cgoSockaddrInet4(ip4), _C_socklen_t(syscall.SizeofSockaddrInet4)
   291  	}
   292  	if ip6 := ip.To16(); ip6 != nil {
   293  		return cgoSockaddrInet6(ip6, zoneCache.index(zone)), _C_socklen_t(syscall.SizeofSockaddrInet6)
   294  	}
   295  	return nil, 0
   296  }
   297  
   298  func cgoLookupCNAME(ctx context.Context, name string) (cname string, err error, completed bool) {
   299  	resources, err := resSearch(ctx, name, int(dnsmessage.TypeCNAME), int(dnsmessage.ClassINET))
   300  	if err != nil {
   301  		return
   302  	}
   303  	cname, err = parseCNAMEFromResources(resources)
   304  	if err != nil {
   305  		return "", err, false
   306  	}
   307  	return cname, nil, true
   308  }
   309  
   310  // resSearch will make a call to the 'res_nsearch' routine in the C library
   311  // and parse the output as a slice of DNS resources.
   312  func resSearch(ctx context.Context, hostname string, rtype, class int) ([]dnsmessage.Resource, error) {
   313  	return doBlockingWithCtx(ctx, func() ([]dnsmessage.Resource, error) {
   314  		return cgoResSearch(hostname, rtype, class)
   315  	})
   316  }
   317  
   318  func cgoResSearch(hostname string, rtype, class int) ([]dnsmessage.Resource, error) {
   319  	acquireThread()
   320  	defer releaseThread()
   321  
   322  	resStateSize := unsafe.Sizeof(_C_struct___res_state{})
   323  	var state *_C_struct___res_state
   324  	if resStateSize > 0 {
   325  		mem := _C_malloc(resStateSize)
   326  		defer _C_free(mem)
   327  		memSlice := unsafe.Slice((*byte)(mem), resStateSize)
   328  		clear(memSlice)
   329  		state = (*_C_struct___res_state)(unsafe.Pointer(&memSlice[0]))
   330  	}
   331  	if err := _C_res_ninit(state); err != nil {
   332  		return nil, errors.New("res_ninit failure: " + err.Error())
   333  	}
   334  	defer _C_res_nclose(state)
   335  
   336  	// Some res_nsearch implementations (like macOS) do not set errno.
   337  	// They set h_errno, which is not per-thread and useless to us.
   338  	// res_nsearch returns the size of the DNS response packet.
   339  	// But if the DNS response packet contains failure-like response codes,
   340  	// res_search returns -1 even though it has copied the packet into buf,
   341  	// giving us no way to find out how big the packet is.
   342  	// For now, we are willing to take res_search's word that there's nothing
   343  	// useful in the response, even though there *is* a response.
   344  	bufSize := maxDNSPacketSize
   345  	buf := (*_C_uchar)(_C_malloc(uintptr(bufSize)))
   346  	defer _C_free(unsafe.Pointer(buf))
   347  
   348  	s, err := syscall.BytePtrFromString(hostname)
   349  	if err != nil {
   350  		return nil, err
   351  	}
   352  
   353  	var size int
   354  	for {
   355  		size, _ = _C_res_nsearch(state, (*_C_char)(unsafe.Pointer(s)), class, rtype, buf, bufSize)
   356  		if size <= 0 || size > 0xffff {
   357  			return nil, errors.New("res_nsearch failure")
   358  		}
   359  		if size <= bufSize {
   360  			break
   361  		}
   362  
   363  		// Allocate a bigger buffer to fit the entire msg.
   364  		_C_free(unsafe.Pointer(buf))
   365  		bufSize = size
   366  		buf = (*_C_uchar)(_C_malloc(uintptr(bufSize)))
   367  	}
   368  
   369  	var p dnsmessage.Parser
   370  	if _, err := p.Start(unsafe.Slice((*byte)(unsafe.Pointer(buf)), size)); err != nil {
   371  		return nil, err
   372  	}
   373  	p.SkipAllQuestions()
   374  	resources, err := p.AllAnswers()
   375  	if err != nil {
   376  		return nil, err
   377  	}
   378  	return resources, nil
   379  }
   380  

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