blob: bc374c2c7688b4e2c143b7a7ea2e706a69bd9e30 [file] [log] [blame]
// Copyright 2011 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.
// This file is called cgo_unix.go, but to allow syscalls-to-libc-based
// implementations to share the code, it does not use cgo directly.
// Instead of C.foo it uses _C_foo, which is defined in either
// cgo_unix_cgo.go or cgo_unix_syscall.go
//go:build !netgo && ((cgo && unix) || darwin)
package net
import (
"context"
"errors"
"internal/bytealg"
"net/netip"
"syscall"
"unsafe"
"golang.org/x/net/dns/dnsmessage"
)
// cgoAvailable set to true to indicate that the cgo resolver
// is available on this system.
const cgoAvailable = true
// An addrinfoErrno represents a getaddrinfo, getnameinfo-specific
// error number. It's a signed number and a zero value is a non-error
// by convention.
type addrinfoErrno int
func (eai addrinfoErrno) Error() string { return _C_gai_strerror(_C_int(eai)) }
func (eai addrinfoErrno) Temporary() bool { return eai == _C_EAI_AGAIN }
func (eai addrinfoErrno) Timeout() bool { return false }
// isAddrinfoErrno is just for testing purposes.
func (eai addrinfoErrno) isAddrinfoErrno() {}
// doBlockingWithCtx executes a blocking function in a separate goroutine when the provided
// context is cancellable. It is intended for use with calls that don't support context
// cancellation (cgo, syscalls). blocking func may still be running after this function finishes.
// For the duration of the execution of the blocking function, the thread is 'acquired' using [acquireThread],
// blocking might not be executed when the context gets canceled early.
func doBlockingWithCtx[T any](ctx context.Context, lookupName string, blocking func() (T, error)) (T, error) {
if err := acquireThread(ctx); err != nil {
var zero T
return zero, &DNSError{
Name: lookupName,
Err: mapErr(err).Error(),
IsTimeout: err == context.DeadlineExceeded,
}
}
if ctx.Done() == nil {
defer releaseThread()
return blocking()
}
type result struct {
res T
err error
}
res := make(chan result, 1)
go func() {
defer releaseThread()
var r result
r.res, r.err = blocking()
res <- r
}()
select {
case r := <-res:
return r.res, r.err
case <-ctx.Done():
var zero T
return zero, &DNSError{
Name: lookupName,
Err: mapErr(ctx.Err()).Error(),
IsTimeout: ctx.Err() == context.DeadlineExceeded,
}
}
}
func cgoLookupHost(ctx context.Context, name string) (hosts []string, err error) {
addrs, err := cgoLookupIP(ctx, "ip", name)
if err != nil {
return nil, err
}
for _, addr := range addrs {
hosts = append(hosts, addr.String())
}
return hosts, nil
}
func cgoLookupPort(ctx context.Context, network, service string) (port int, err error) {
var hints _C_struct_addrinfo
switch network {
case "ip": // no hints
case "tcp", "tcp4", "tcp6":
*_C_ai_socktype(&hints) = _C_SOCK_STREAM
*_C_ai_protocol(&hints) = _C_IPPROTO_TCP
case "udp", "udp4", "udp6":
*_C_ai_socktype(&hints) = _C_SOCK_DGRAM
*_C_ai_protocol(&hints) = _C_IPPROTO_UDP
default:
return 0, &DNSError{Err: "unknown network", Name: network + "/" + service}
}
switch ipVersion(network) {
case '4':
*_C_ai_family(&hints) = _C_AF_INET
case '6':
*_C_ai_family(&hints) = _C_AF_INET6
}
return doBlockingWithCtx(ctx, network+"/"+service, func() (int, error) {
return cgoLookupServicePort(&hints, network, service)
})
}
func cgoLookupServicePort(hints *_C_struct_addrinfo, network, service string) (port int, err error) {
cservice, err := syscall.ByteSliceFromString(service)
if err != nil {
return 0, &DNSError{Err: err.Error(), Name: network + "/" + service}
}
// Lowercase the C service name.
for i, b := range cservice[:len(service)] {
cservice[i] = lowerASCII(b)
}
var res *_C_struct_addrinfo
gerrno, err := _C_getaddrinfo(nil, (*_C_char)(unsafe.Pointer(&cservice[0])), hints, &res)
if gerrno != 0 {
switch gerrno {
case _C_EAI_SYSTEM:
if err == nil { // see golang.org/issue/6232
err = syscall.EMFILE
}
return 0, newDNSError(err, network+"/"+service, "")
case _C_EAI_SERVICE, _C_EAI_NONAME: // Darwin returns EAI_NONAME.
return 0, newDNSError(errUnknownPort, network+"/"+service, "")
default:
return 0, newDNSError(addrinfoErrno(gerrno), network+"/"+service, "")
}
}
defer _C_freeaddrinfo(res)
for r := res; r != nil; r = *_C_ai_next(r) {
switch *_C_ai_family(r) {
case _C_AF_INET:
sa := (*syscall.RawSockaddrInet4)(unsafe.Pointer(*_C_ai_addr(r)))
p := (*[2]byte)(unsafe.Pointer(&sa.Port))
return int(p[0])<<8 | int(p[1]), nil
case _C_AF_INET6:
sa := (*syscall.RawSockaddrInet6)(unsafe.Pointer(*_C_ai_addr(r)))
p := (*[2]byte)(unsafe.Pointer(&sa.Port))
return int(p[0])<<8 | int(p[1]), nil
}
}
return 0, newDNSError(errUnknownPort, network+"/"+service, "")
}
func cgoLookupHostIP(network, name string) (addrs []IPAddr, err error) {
var hints _C_struct_addrinfo
*_C_ai_flags(&hints) = cgoAddrInfoFlags
*_C_ai_socktype(&hints) = _C_SOCK_STREAM
*_C_ai_family(&hints) = _C_AF_UNSPEC
switch ipVersion(network) {
case '4':
*_C_ai_family(&hints) = _C_AF_INET
case '6':
*_C_ai_family(&hints) = _C_AF_INET6
}
h, err := syscall.BytePtrFromString(name)
if err != nil {
return nil, &DNSError{Err: err.Error(), Name: name}
}
var res *_C_struct_addrinfo
gerrno, err := _C_getaddrinfo((*_C_char)(unsafe.Pointer(h)), nil, &hints, &res)
if gerrno != 0 {
switch gerrno {
case _C_EAI_SYSTEM:
if err == nil {
// err should not be nil, but sometimes getaddrinfo returns
// gerrno == _C_EAI_SYSTEM with err == nil on Linux.
// The report claims that it happens when we have too many
// open files, so use syscall.EMFILE (too many open files in system).
// Most system calls would return ENFILE (too many open files),
// so at the least EMFILE should be easy to recognize if this
// comes up again. golang.org/issue/6232.
err = syscall.EMFILE
}
return nil, newDNSError(err, name, "")
case _C_EAI_NONAME, _C_EAI_NODATA:
return nil, newDNSError(errNoSuchHost, name, "")
default:
return nil, newDNSError(addrinfoErrno(gerrno), name, "")
}
}
defer _C_freeaddrinfo(res)
for r := res; r != nil; r = *_C_ai_next(r) {
// We only asked for SOCK_STREAM, but check anyhow.
if *_C_ai_socktype(r) != _C_SOCK_STREAM {
continue
}
switch *_C_ai_family(r) {
case _C_AF_INET:
sa := (*syscall.RawSockaddrInet4)(unsafe.Pointer(*_C_ai_addr(r)))
addr := IPAddr{IP: copyIP(sa.Addr[:])}
addrs = append(addrs, addr)
case _C_AF_INET6:
sa := (*syscall.RawSockaddrInet6)(unsafe.Pointer(*_C_ai_addr(r)))
addr := IPAddr{IP: copyIP(sa.Addr[:]), Zone: zoneCache.name(int(sa.Scope_id))}
addrs = append(addrs, addr)
}
}
return addrs, nil
}
func cgoLookupIP(ctx context.Context, network, name string) (addrs []IPAddr, err error) {
return doBlockingWithCtx(ctx, name, func() ([]IPAddr, error) {
return cgoLookupHostIP(network, name)
})
}
// These are roughly enough for the following:
//
// Source Encoding Maximum length of single name entry
// Unicast DNS ASCII or <=253 + a NUL terminator
// Unicode in RFC 5892 252 * total number of labels + delimiters + a NUL terminator
// Multicast DNS UTF-8 in RFC 5198 or <=253 + a NUL terminator
// the same as unicast DNS ASCII <=253 + a NUL terminator
// Local database various depends on implementation
const (
nameinfoLen = 64
maxNameinfoLen = 4096
)
func cgoLookupPTR(ctx context.Context, addr string) (names []string, err error) {
ip, err := netip.ParseAddr(addr)
if err != nil {
return nil, &DNSError{Err: "invalid address", Name: addr}
}
sa, salen := cgoSockaddr(IP(ip.AsSlice()), ip.Zone())
if sa == nil {
return nil, &DNSError{Err: "invalid address " + ip.String(), Name: addr}
}
return doBlockingWithCtx(ctx, addr, func() ([]string, error) {
return cgoLookupAddrPTR(addr, sa, salen)
})
}
func cgoLookupAddrPTR(addr string, sa *_C_struct_sockaddr, salen _C_socklen_t) (names []string, err error) {
var gerrno int
var b []byte
for l := nameinfoLen; l <= maxNameinfoLen; l *= 2 {
b = make([]byte, l)
gerrno, err = cgoNameinfoPTR(b, sa, salen)
if gerrno == 0 || gerrno != _C_EAI_OVERFLOW {
break
}
}
if gerrno != 0 {
switch gerrno {
case _C_EAI_SYSTEM:
if err == nil { // see golang.org/issue/6232
err = syscall.EMFILE
}
return nil, newDNSError(err, addr, "")
case _C_EAI_NONAME:
return nil, newDNSError(errNoSuchHost, addr, "")
default:
return nil, newDNSError(addrinfoErrno(gerrno), addr, "")
}
}
if i := bytealg.IndexByte(b, 0); i != -1 {
b = b[:i]
}
return []string{absDomainName(string(b))}, nil
}
func cgoSockaddr(ip IP, zone string) (*_C_struct_sockaddr, _C_socklen_t) {
if ip4 := ip.To4(); ip4 != nil {
return cgoSockaddrInet4(ip4), _C_socklen_t(syscall.SizeofSockaddrInet4)
}
if ip6 := ip.To16(); ip6 != nil {
return cgoSockaddrInet6(ip6, zoneCache.index(zone)), _C_socklen_t(syscall.SizeofSockaddrInet6)
}
return nil, 0
}
func cgoLookupCNAME(ctx context.Context, name string) (cname string, err error, completed bool) {
resources, err := resSearch(ctx, name, int(dnsmessage.TypeCNAME), int(dnsmessage.ClassINET))
if err != nil {
return
}
cname, err = parseCNAMEFromResources(resources)
if err != nil {
return "", err, false
}
return cname, nil, true
}
// resSearch will make a call to the 'res_nsearch' routine in the C library
// and parse the output as a slice of DNS resources.
func resSearch(ctx context.Context, hostname string, rtype, class int) ([]dnsmessage.Resource, error) {
return doBlockingWithCtx(ctx, hostname, func() ([]dnsmessage.Resource, error) {
return cgoResSearch(hostname, rtype, class)
})
}
func cgoResSearch(hostname string, rtype, class int) ([]dnsmessage.Resource, error) {
resStateSize := unsafe.Sizeof(_C_struct___res_state{})
var state *_C_struct___res_state
if resStateSize > 0 {
mem := _C_malloc(resStateSize)
defer _C_free(mem)
memSlice := unsafe.Slice((*byte)(mem), resStateSize)
clear(memSlice)
state = (*_C_struct___res_state)(unsafe.Pointer(&memSlice[0]))
}
if err := _C_res_ninit(state); err != nil {
return nil, errors.New("res_ninit failure: " + err.Error())
}
defer _C_res_nclose(state)
// Some res_nsearch implementations (like macOS) do not set errno.
// They set h_errno, which is not per-thread and useless to us.
// res_nsearch returns the size of the DNS response packet.
// But if the DNS response packet contains failure-like response codes,
// res_search returns -1 even though it has copied the packet into buf,
// giving us no way to find out how big the packet is.
// For now, we are willing to take res_search's word that there's nothing
// useful in the response, even though there *is* a response.
bufSize := maxDNSPacketSize
buf := (*_C_uchar)(_C_malloc(uintptr(bufSize)))
defer _C_free(unsafe.Pointer(buf))
s, err := syscall.BytePtrFromString(hostname)
if err != nil {
return nil, err
}
var size int
for {
size := _C_res_nsearch(state, (*_C_char)(unsafe.Pointer(s)), class, rtype, buf, bufSize)
if size <= 0 || size > 0xffff {
return nil, errors.New("res_nsearch failure")
}
if size <= bufSize {
break
}
// Allocate a bigger buffer to fit the entire msg.
_C_free(unsafe.Pointer(buf))
bufSize = size
buf = (*_C_uchar)(_C_malloc(uintptr(bufSize)))
}
var p dnsmessage.Parser
if _, err := p.Start(unsafe.Slice((*byte)(unsafe.Pointer(buf)), size)); err != nil {
return nil, err
}
p.SkipAllQuestions()
resources, err := p.AllAnswers()
if err != nil {
return nil, err
}
return resources, nil
}