// 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. package net import ( "context" "errors" "internal/bytealg" "internal/itoa" "io" "os" ) func query(ctx context.Context, filename, query string, bufSize int) (addrs []string, err error) { queryAddrs := func() (addrs []string, err error) { file, err := os.OpenFile(filename, os.O_RDWR, 0) if err != nil { return nil, err } defer file.Close() _, err = file.Seek(0, io.SeekStart) if err != nil { return nil, err } _, err = file.WriteString(query) if err != nil { return nil, err } _, err = file.Seek(0, io.SeekStart) if err != nil { return nil, err } buf := make([]byte, bufSize) for { n, _ := file.Read(buf) if n <= 0 { break } addrs = append(addrs, string(buf[:n])) } return addrs, nil } type ret struct { addrs []string err error } ch := make(chan ret, 1) go func() { addrs, err := queryAddrs() ch <- ret{addrs: addrs, err: err} }() select { case r := <-ch: return r.addrs, r.err case <-ctx.Done(): return nil, &DNSError{ Name: query, Err: ctx.Err().Error(), IsTimeout: ctx.Err() == context.DeadlineExceeded, } } } func queryCS(ctx context.Context, net, host, service string) (res []string, err error) { switch net { case "tcp4", "tcp6": net = "tcp" case "udp4", "udp6": net = "udp" } if host == "" { host = "*" } return query(ctx, netdir+"/cs", net+"!"+host+"!"+service, 128) } func queryCS1(ctx context.Context, net string, ip IP, port int) (clone, dest string, err error) { ips := "*" if len(ip) != 0 && !ip.IsUnspecified() { ips = ip.String() } lines, err := queryCS(ctx, net, ips, itoa.Itoa(port)) if err != nil { return } f := getFields(lines[0]) if len(f) < 2 { return "", "", errors.New("bad response from ndb/cs") } clone, dest = f[0], f[1] return } func queryDNS(ctx context.Context, addr string, typ string) (res []string, err error) { return query(ctx, netdir+"/dns", addr+" "+typ, 1024) } // toLower returns a lower-case version of in. Restricting us to // ASCII is sufficient to handle the IP protocol names and allow // us to not depend on the strings and unicode packages. func toLower(in string) string { for _, c := range in { if 'A' <= c && c <= 'Z' { // Has upper case; need to fix. out := []byte(in) for i := 0; i < len(in); i++ { c := in[i] if 'A' <= c && c <= 'Z' { c += 'a' - 'A' } out[i] = c } return string(out) } } return in } // lookupProtocol looks up IP protocol name and returns // the corresponding protocol number. func lookupProtocol(ctx context.Context, name string) (proto int, err error) { lines, err := query(ctx, netdir+"/cs", "!protocol="+toLower(name), 128) if err != nil { return 0, err } if len(lines) == 0 { return 0, UnknownNetworkError(name) } f := getFields(lines[0]) if len(f) < 2 { return 0, UnknownNetworkError(name) } s := f[1] if n, _, ok := dtoi(s[bytealg.IndexByteString(s, '=')+1:]); ok { return n, nil } return 0, UnknownNetworkError(name) } func (*Resolver) lookupHost(ctx context.Context, host string) (addrs []string, err error) { // Use netdir/cs instead of netdir/dns because cs knows about // host names in local network (e.g. from /lib/ndb/local) lines, err := queryCS(ctx, "net", host, "1") if err != nil { dnsError := &DNSError{Err: err.Error(), Name: host} if stringsHasSuffix(err.Error(), "dns failure") { dnsError.Err = errNoSuchHost.Error() dnsError.IsNotFound = true } return nil, dnsError } loop: for _, line := range lines { f := getFields(line) if len(f) < 2 { continue } addr := f[1] if i := bytealg.IndexByteString(addr, '!'); i >= 0 { addr = addr[:i] // remove port } if ParseIP(addr) == nil { continue } // only return unique addresses for _, a := range addrs { if a == addr { continue loop } } addrs = append(addrs, addr) } return } // preferGoOverPlan9 reports whether the resolver should use the // "PreferGo" implementation rather than asking plan9 services // for the answers. func (r *Resolver) preferGoOverPlan9() bool { _, _, res := r.preferGoOverPlan9WithOrderAndConf() return res } func (r *Resolver) preferGoOverPlan9WithOrderAndConf() (hostLookupOrder, *dnsConfig, bool) { order, conf := systemConf().hostLookupOrder(r, "") // name is unused // TODO(bradfitz): for now we only permit use of the PreferGo // implementation when there's a non-nil Resolver with a // non-nil Dialer. This is a sign that they the code is trying // to use their DNS-speaking net.Conn (such as an in-memory // DNS cache) and they don't want to actually hit the network. // Once we add support for looking the default DNS servers // from plan9, though, then we can relax this. return order, conf, order != hostLookupCgo && r != nil && r.Dial != nil } func (r *Resolver) lookupIP(ctx context.Context, network, host string) (addrs []IPAddr, err error) { if r.preferGoOverPlan9() { return r.goLookupIP(ctx, network, host) } lits, err := r.lookupHost(ctx, host) if err != nil { return } for _, lit := range lits { host, zone := splitHostZone(lit) if ip := ParseIP(host); ip != nil { addr := IPAddr{IP: ip, Zone: zone} addrs = append(addrs, addr) } } return } func (*Resolver) lookupPort(ctx context.Context, network, service string) (port int, err error) { switch network { case "tcp4", "tcp6": network = "tcp" case "udp4", "udp6": network = "udp" } lines, err := queryCS(ctx, network, "127.0.0.1", toLower(service)) if err != nil { return } unknownPortError := &AddrError{Err: "unknown port", Addr: network + "/" + service} if len(lines) == 0 { return 0, unknownPortError } f := getFields(lines[0]) if len(f) < 2 { return 0, unknownPortError } s := f[1] if i := bytealg.IndexByteString(s, '!'); i >= 0 { s = s[i+1:] // remove address } if n, _, ok := dtoi(s); ok { return n, nil } return 0, unknownPortError } func (r *Resolver) lookupCNAME(ctx context.Context, name string) (cname string, err error) { if order, conf, preferGo := r.preferGoOverPlan9WithOrderAndConf(); preferGo { return r.goLookupCNAME(ctx, name, order, conf) } lines, err := queryDNS(ctx, name, "cname") if err != nil { if stringsHasSuffix(err.Error(), "dns failure") || stringsHasSuffix(err.Error(), "resource does not exist; negrcode 0") { cname = name + "." err = nil } return } if len(lines) > 0 { if f := getFields(lines[0]); len(f) >= 3 { return f[2] + ".", nil } } return "", errors.New("bad response from ndb/dns") } func (r *Resolver) lookupSRV(ctx context.Context, service, proto, name string) (cname string, addrs []*SRV, err error) { if r.preferGoOverPlan9() { return r.goLookupSRV(ctx, service, proto, name) } var target string if service == "" && proto == "" { target = name } else { target = "_" + service + "._" + proto + "." + name } lines, err := queryDNS(ctx, target, "srv") if err != nil { return } for _, line := range lines { f := getFields(line) if len(f) < 6 { continue } port, _, portOk := dtoi(f[4]) priority, _, priorityOk := dtoi(f[3]) weight, _, weightOk := dtoi(f[2]) if !(portOk && priorityOk && weightOk) { continue } addrs = append(addrs, &SRV{absDomainName(f[5]), uint16(port), uint16(priority), uint16(weight)}) cname = absDomainName(f[0]) } byPriorityWeight(addrs).sort() return } func (r *Resolver) lookupMX(ctx context.Context, name string) (mx []*MX, err error) { if r.preferGoOverPlan9() { return r.goLookupMX(ctx, name) } lines, err := queryDNS(ctx, name, "mx") if err != nil { return } for _, line := range lines { f := getFields(line) if len(f) < 4 { continue } if pref, _, ok := dtoi(f[2]); ok { mx = append(mx, &MX{absDomainName(f[3]), uint16(pref)}) } } byPref(mx).sort() return } func (r *Resolver) lookupNS(ctx context.Context, name string) (ns []*NS, err error) { if r.preferGoOverPlan9() { return r.goLookupNS(ctx, name) } lines, err := queryDNS(ctx, name, "ns") if err != nil { return } for _, line := range lines { f := getFields(line) if len(f) < 3 { continue } ns = append(ns, &NS{absDomainName(f[2])}) } return } func (r *Resolver) lookupTXT(ctx context.Context, name string) (txt []string, err error) { if r.preferGoOverPlan9() { return r.goLookupTXT(ctx, name) } lines, err := queryDNS(ctx, name, "txt") if err != nil { return } for _, line := range lines { if i := bytealg.IndexByteString(line, '\t'); i >= 0 { txt = append(txt, line[i+1:]) } } return } func (r *Resolver) lookupAddr(ctx context.Context, addr string) (name []string, err error) { if _, conf, preferGo := r.preferGoOverPlan9WithOrderAndConf(); preferGo { return r.goLookupPTR(ctx, addr, conf) } arpa, err := reverseaddr(addr) if err != nil { return } lines, err := queryDNS(ctx, arpa, "ptr") if err != nil { return } for _, line := range lines { f := getFields(line) if len(f) < 3 { continue } name = append(name, absDomainName(f[2])) } return } // concurrentThreadsLimit returns the number of threads we permit to // run concurrently doing DNS lookups. func concurrentThreadsLimit() int { return 500 }