Source file src/net/cgo_unix.go

     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  	"syscall"
    18  	"unsafe"
    19  
    20  	"golang.org/x/net/dns/dnsmessage"
    21  )
    22  
    23  // An addrinfoErrno represents a getaddrinfo, getnameinfo-specific
    24  // error number. It's a signed number and a zero value is a non-error
    25  // by convention.
    26  type addrinfoErrno int
    27  
    28  func (eai addrinfoErrno) Error() string   { return _C_gai_strerror(_C_int(eai)) }
    29  func (eai addrinfoErrno) Temporary() bool { return eai == _C_EAI_AGAIN }
    30  func (eai addrinfoErrno) Timeout() bool   { return false }
    31  
    32  type portLookupResult struct {
    33  	port int
    34  	err  error
    35  }
    36  
    37  type ipLookupResult struct {
    38  	addrs []IPAddr
    39  	cname string
    40  	err   error
    41  }
    42  
    43  type reverseLookupResult struct {
    44  	names []string
    45  	err   error
    46  }
    47  
    48  func cgoLookupHost(ctx context.Context, name string) (hosts []string, err error, completed bool) {
    49  	addrs, err, completed := cgoLookupIP(ctx, "ip", name)
    50  	for _, addr := range addrs {
    51  		hosts = append(hosts, addr.String())
    52  	}
    53  	return
    54  }
    55  
    56  func cgoLookupPort(ctx context.Context, network, service string) (port int, err error, completed bool) {
    57  	var hints _C_struct_addrinfo
    58  	switch network {
    59  	case "": // no hints
    60  	case "tcp", "tcp4", "tcp6":
    61  		*_C_ai_socktype(&hints) = _C_SOCK_STREAM
    62  		*_C_ai_protocol(&hints) = _C_IPPROTO_TCP
    63  	case "udp", "udp4", "udp6":
    64  		*_C_ai_socktype(&hints) = _C_SOCK_DGRAM
    65  		*_C_ai_protocol(&hints) = _C_IPPROTO_UDP
    66  	default:
    67  		return 0, &DNSError{Err: "unknown network", Name: network + "/" + service}, true
    68  	}
    69  	switch ipVersion(network) {
    70  	case '4':
    71  		*_C_ai_family(&hints) = _C_AF_INET
    72  	case '6':
    73  		*_C_ai_family(&hints) = _C_AF_INET6
    74  	}
    75  	if ctx.Done() == nil {
    76  		port, err := cgoLookupServicePort(&hints, network, service)
    77  		return port, err, true
    78  	}
    79  	result := make(chan portLookupResult, 1)
    80  	go cgoPortLookup(result, &hints, network, service)
    81  	select {
    82  	case r := <-result:
    83  		return r.port, r.err, true
    84  	case <-ctx.Done():
    85  		// Since there isn't a portable way to cancel the lookup,
    86  		// we just let it finish and write to the buffered channel.
    87  		return 0, mapErr(ctx.Err()), false
    88  	}
    89  }
    90  
    91  func cgoLookupServicePort(hints *_C_struct_addrinfo, network, service string) (port int, err error) {
    92  	cservice := make([]byte, len(service)+1)
    93  	copy(cservice, service)
    94  	// Lowercase the C service name.
    95  	for i, b := range cservice[:len(service)] {
    96  		cservice[i] = lowerASCII(b)
    97  	}
    98  	var res *_C_struct_addrinfo
    99  	gerrno, err := _C_getaddrinfo(nil, (*_C_char)(unsafe.Pointer(&cservice[0])), hints, &res)
   100  	if gerrno != 0 {
   101  		isTemporary := false
   102  		switch gerrno {
   103  		case _C_EAI_SYSTEM:
   104  			if err == nil { // see golang.org/issue/6232
   105  				err = syscall.EMFILE
   106  			}
   107  		default:
   108  			err = addrinfoErrno(gerrno)
   109  			isTemporary = addrinfoErrno(gerrno).Temporary()
   110  		}
   111  		return 0, &DNSError{Err: err.Error(), Name: network + "/" + service, IsTemporary: isTemporary}
   112  	}
   113  	defer _C_freeaddrinfo(res)
   114  
   115  	for r := res; r != nil; r = *_C_ai_next(r) {
   116  		switch *_C_ai_family(r) {
   117  		case _C_AF_INET:
   118  			sa := (*syscall.RawSockaddrInet4)(unsafe.Pointer(*_C_ai_addr(r)))
   119  			p := (*[2]byte)(unsafe.Pointer(&sa.Port))
   120  			return int(p[0])<<8 | int(p[1]), nil
   121  		case _C_AF_INET6:
   122  			sa := (*syscall.RawSockaddrInet6)(unsafe.Pointer(*_C_ai_addr(r)))
   123  			p := (*[2]byte)(unsafe.Pointer(&sa.Port))
   124  			return int(p[0])<<8 | int(p[1]), nil
   125  		}
   126  	}
   127  	return 0, &DNSError{Err: "unknown port", Name: network + "/" + service}
   128  }
   129  
   130  func cgoPortLookup(result chan<- portLookupResult, hints *_C_struct_addrinfo, network, service string) {
   131  	port, err := cgoLookupServicePort(hints, network, service)
   132  	result <- portLookupResult{port, err}
   133  }
   134  
   135  func cgoLookupIPCNAME(network, name string) (addrs []IPAddr, cname string, err error) {
   136  	acquireThread()
   137  	defer releaseThread()
   138  
   139  	var hints _C_struct_addrinfo
   140  	*_C_ai_flags(&hints) = cgoAddrInfoFlags
   141  	*_C_ai_socktype(&hints) = _C_SOCK_STREAM
   142  	*_C_ai_family(&hints) = _C_AF_UNSPEC
   143  	switch ipVersion(network) {
   144  	case '4':
   145  		*_C_ai_family(&hints) = _C_AF_INET
   146  	case '6':
   147  		*_C_ai_family(&hints) = _C_AF_INET6
   148  	}
   149  
   150  	h := make([]byte, len(name)+1)
   151  	copy(h, name)
   152  	var res *_C_struct_addrinfo
   153  	gerrno, err := _C_getaddrinfo((*_C_char)(unsafe.Pointer(&h[0])), nil, &hints, &res)
   154  	if gerrno != 0 {
   155  		isErrorNoSuchHost := false
   156  		isTemporary := false
   157  		switch gerrno {
   158  		case _C_EAI_SYSTEM:
   159  			if err == nil {
   160  				// err should not be nil, but sometimes getaddrinfo returns
   161  				// gerrno == _C_EAI_SYSTEM with err == nil on Linux.
   162  				// The report claims that it happens when we have too many
   163  				// open files, so use syscall.EMFILE (too many open files in system).
   164  				// Most system calls would return ENFILE (too many open files),
   165  				// so at the least EMFILE should be easy to recognize if this
   166  				// comes up again. golang.org/issue/6232.
   167  				err = syscall.EMFILE
   168  			}
   169  		case _C_EAI_NONAME:
   170  			err = errNoSuchHost
   171  			isErrorNoSuchHost = true
   172  		default:
   173  			err = addrinfoErrno(gerrno)
   174  			isTemporary = addrinfoErrno(gerrno).Temporary()
   175  		}
   176  
   177  		return nil, "", &DNSError{Err: err.Error(), Name: name, IsNotFound: isErrorNoSuchHost, IsTemporary: isTemporary}
   178  	}
   179  	defer _C_freeaddrinfo(res)
   180  
   181  	if res != nil {
   182  		cname = _C_GoString(*_C_ai_canonname(res))
   183  		if cname == "" {
   184  			cname = name
   185  		}
   186  		if len(cname) > 0 && cname[len(cname)-1] != '.' {
   187  			cname += "."
   188  		}
   189  	}
   190  	for r := res; r != nil; r = *_C_ai_next(r) {
   191  		// We only asked for SOCK_STREAM, but check anyhow.
   192  		if *_C_ai_socktype(r) != _C_SOCK_STREAM {
   193  			continue
   194  		}
   195  		switch *_C_ai_family(r) {
   196  		case _C_AF_INET:
   197  			sa := (*syscall.RawSockaddrInet4)(unsafe.Pointer(*_C_ai_addr(r)))
   198  			addr := IPAddr{IP: copyIP(sa.Addr[:])}
   199  			addrs = append(addrs, addr)
   200  		case _C_AF_INET6:
   201  			sa := (*syscall.RawSockaddrInet6)(unsafe.Pointer(*_C_ai_addr(r)))
   202  			addr := IPAddr{IP: copyIP(sa.Addr[:]), Zone: zoneCache.name(int(sa.Scope_id))}
   203  			addrs = append(addrs, addr)
   204  		}
   205  	}
   206  	return addrs, cname, nil
   207  }
   208  
   209  func cgoIPLookup(result chan<- ipLookupResult, network, name string) {
   210  	addrs, cname, err := cgoLookupIPCNAME(network, name)
   211  	result <- ipLookupResult{addrs, cname, err}
   212  }
   213  
   214  func cgoLookupIP(ctx context.Context, network, name string) (addrs []IPAddr, err error, completed bool) {
   215  	if ctx.Done() == nil {
   216  		addrs, _, err = cgoLookupIPCNAME(network, name)
   217  		return addrs, err, true
   218  	}
   219  	result := make(chan ipLookupResult, 1)
   220  	go cgoIPLookup(result, network, name)
   221  	select {
   222  	case r := <-result:
   223  		return r.addrs, r.err, true
   224  	case <-ctx.Done():
   225  		return nil, mapErr(ctx.Err()), false
   226  	}
   227  }
   228  
   229  // These are roughly enough for the following:
   230  //
   231  //	 Source		Encoding			Maximum length of single name entry
   232  //	 Unicast DNS		ASCII or			<=253 + a NUL terminator
   233  //				Unicode in RFC 5892		252 * total number of labels + delimiters + a NUL terminator
   234  //	 Multicast DNS	UTF-8 in RFC 5198 or		<=253 + a NUL terminator
   235  //				the same as unicast DNS ASCII	<=253 + a NUL terminator
   236  //	 Local database	various				depends on implementation
   237  const (
   238  	nameinfoLen    = 64
   239  	maxNameinfoLen = 4096
   240  )
   241  
   242  func cgoLookupPTR(ctx context.Context, addr string) (names []string, err error, completed bool) {
   243  	var zone string
   244  	ip := parseIPv4(addr)
   245  	if ip == nil {
   246  		ip, zone = parseIPv6Zone(addr)
   247  	}
   248  	if ip == nil {
   249  		return nil, &DNSError{Err: "invalid address", Name: addr}, true
   250  	}
   251  	sa, salen := cgoSockaddr(ip, zone)
   252  	if sa == nil {
   253  		return nil, &DNSError{Err: "invalid address " + ip.String(), Name: addr}, true
   254  	}
   255  	if ctx.Done() == nil {
   256  		names, err := cgoLookupAddrPTR(addr, sa, salen)
   257  		return names, err, true
   258  	}
   259  	result := make(chan reverseLookupResult, 1)
   260  	go cgoReverseLookup(result, addr, sa, salen)
   261  	select {
   262  	case r := <-result:
   263  		return r.names, r.err, true
   264  	case <-ctx.Done():
   265  		return nil, mapErr(ctx.Err()), false
   266  	}
   267  }
   268  
   269  func cgoLookupAddrPTR(addr string, sa *_C_struct_sockaddr, salen _C_socklen_t) (names []string, err error) {
   270  	acquireThread()
   271  	defer releaseThread()
   272  
   273  	var gerrno int
   274  	var b []byte
   275  	for l := nameinfoLen; l <= maxNameinfoLen; l *= 2 {
   276  		b = make([]byte, l)
   277  		gerrno, err = cgoNameinfoPTR(b, sa, salen)
   278  		if gerrno == 0 || gerrno != _C_EAI_OVERFLOW {
   279  			break
   280  		}
   281  	}
   282  	if gerrno != 0 {
   283  		isTemporary := false
   284  		switch gerrno {
   285  		case _C_EAI_SYSTEM:
   286  			if err == nil { // see golang.org/issue/6232
   287  				err = syscall.EMFILE
   288  			}
   289  		default:
   290  			err = addrinfoErrno(gerrno)
   291  			isTemporary = addrinfoErrno(gerrno).Temporary()
   292  		}
   293  		return nil, &DNSError{Err: err.Error(), Name: addr, IsTemporary: isTemporary}
   294  	}
   295  	for i := 0; i < len(b); i++ {
   296  		if b[i] == 0 {
   297  			b = b[:i]
   298  			break
   299  		}
   300  	}
   301  	return []string{absDomainName(string(b))}, nil
   302  }
   303  
   304  func cgoReverseLookup(result chan<- reverseLookupResult, addr string, sa *_C_struct_sockaddr, salen _C_socklen_t) {
   305  	names, err := cgoLookupAddrPTR(addr, sa, salen)
   306  	result <- reverseLookupResult{names, err}
   307  }
   308  
   309  func cgoSockaddr(ip IP, zone string) (*_C_struct_sockaddr, _C_socklen_t) {
   310  	if ip4 := ip.To4(); ip4 != nil {
   311  		return cgoSockaddrInet4(ip4), _C_socklen_t(syscall.SizeofSockaddrInet4)
   312  	}
   313  	if ip6 := ip.To16(); ip6 != nil {
   314  		return cgoSockaddrInet6(ip6, zoneCache.index(zone)), _C_socklen_t(syscall.SizeofSockaddrInet6)
   315  	}
   316  	return nil, 0
   317  }
   318  
   319  func cgoLookupCNAME(ctx context.Context, name string) (cname string, err error, completed bool) {
   320  	resources, err := resSearch(ctx, name, int(dnsmessage.TypeCNAME), int(dnsmessage.ClassINET))
   321  	if err != nil {
   322  		return
   323  	}
   324  	cname, err = parseCNAMEFromResources(resources)
   325  	if err != nil {
   326  		return "", err, false
   327  	}
   328  	return cname, nil, true
   329  }
   330  
   331  // resSearch will make a call to the 'res_nsearch' routine in the C library
   332  // and parse the output as a slice of DNS resources.
   333  func resSearch(ctx context.Context, hostname string, rtype, class int) ([]dnsmessage.Resource, error) {
   334  	if ctx.Done() == nil {
   335  		return cgoResSearch(hostname, rtype, class)
   336  	}
   337  
   338  	type result struct {
   339  		res []dnsmessage.Resource
   340  		err error
   341  	}
   342  
   343  	res := make(chan result, 1)
   344  	go func() {
   345  		r, err := cgoResSearch(hostname, rtype, class)
   346  		res <- result{
   347  			res: r,
   348  			err: err,
   349  		}
   350  	}()
   351  
   352  	select {
   353  	case res := <-res:
   354  		return res.res, res.err
   355  	case <-ctx.Done():
   356  		return nil, mapErr(ctx.Err())
   357  	}
   358  }
   359  
   360  func cgoResSearch(hostname string, rtype, class int) ([]dnsmessage.Resource, error) {
   361  	acquireThread()
   362  	defer releaseThread()
   363  
   364  	state := (*_C_struct___res_state)(_C_malloc(unsafe.Sizeof(_C_struct___res_state{})))
   365  	defer _C_free(unsafe.Pointer(state))
   366  	if err := _C_res_ninit(state); err != nil {
   367  		return nil, errors.New("res_ninit failure: " + err.Error())
   368  	}
   369  	defer _C_res_nclose(state)
   370  
   371  	// Some res_nsearch implementations (like macOS) do not set errno.
   372  	// They set h_errno, which is not per-thread and useless to us.
   373  	// res_nsearch returns the size of the DNS response packet.
   374  	// But if the DNS response packet contains failure-like response codes,
   375  	// res_search returns -1 even though it has copied the packet into buf,
   376  	// giving us no way to find out how big the packet is.
   377  	// For now, we are willing to take res_search's word that there's nothing
   378  	// useful in the response, even though there *is* a response.
   379  	bufSize := maxDNSPacketSize
   380  	buf := (*_C_uchar)(_C_malloc(uintptr(bufSize)))
   381  	defer _C_free(unsafe.Pointer(buf))
   382  
   383  	s := _C_CString(hostname)
   384  	defer _C_FreeCString(s)
   385  
   386  	var size int
   387  	for {
   388  		size, _ = _C_res_nsearch(state, s, class, rtype, buf, bufSize)
   389  		if size <= 0 || size > 0xffff {
   390  			return nil, errors.New("res_nsearch failure")
   391  		}
   392  		if size <= bufSize {
   393  			break
   394  		}
   395  
   396  		// Allocate a bigger buffer to fit the entire msg.
   397  		_C_free(unsafe.Pointer(buf))
   398  		bufSize = size
   399  		buf = (*_C_uchar)(_C_malloc(uintptr(bufSize)))
   400  	}
   401  
   402  	var p dnsmessage.Parser
   403  	if _, err := p.Start(unsafe.Slice((*byte)(unsafe.Pointer(buf)), size)); err != nil {
   404  		return nil, err
   405  	}
   406  	p.SkipAllQuestions()
   407  	resources, err := p.AllAnswers()
   408  	if err != nil {
   409  		return nil, err
   410  	}
   411  	return resources, nil
   412  }
   413  

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