1 files changed, 262 insertions, 0 deletions
diff --git a/src/pkg/net/dnsclient_unix.go b/src/pkg/net/dnsclient_unix.go
new file mode 100644
index 000000000..7f3ef2878
--- /dev/null
+++ b/src/pkg/net/dnsclient_unix.go
@@ -0,0 +1,262 @@
+// 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.
+
+// DNS client: see RFC 1035.
+// Has to be linked into package net for Dial.
+
+// TODO(rsc):
+//	Check periodically whether /etc/resolv.conf has changed.
+//	Could potentially handle many outstanding lookups faster.
+//	Could have a small cache.
+//	Random UDP source port (net.Dial should do that for us).
+//	Random request IDs.
+
+package net
+
+import (
+	"os"
+	"rand"
+	"sync"
+	"time"
+)
+
+// Send a request on the connection and hope for a reply.
+// Up to cfg.attempts attempts.
+func exchange(cfg *dnsConfig, c Conn, name string, qtype uint16) (*dnsMsg, os.Error) {
+	if len(name) >= 256 {
+		return nil, &DNSError{Error: "name too long", Name: name}
+	}
+	out := new(dnsMsg)
+	out.id = uint16(rand.Int()) ^ uint16(time.Nanoseconds())
+	out.question = []dnsQuestion{
+		{name, qtype, dnsClassINET},
+	}
+	out.recursion_desired = true
+	msg, ok := out.Pack()
+	if !ok {
+		return nil, &DNSError{Error: "internal error - cannot pack message", Name: name}
+	}
+
+	for attempt := 0; attempt < cfg.attempts; attempt++ {
+		n, err := c.Write(msg)
+		if err != nil {
+			return nil, err
+		}
+
+		c.SetReadTimeout(int64(cfg.timeout) * 1e9) // nanoseconds
+
+		buf := make([]byte, 2000) // More than enough.
+		n, err = c.Read(buf)
+		if err != nil {
+			if e, ok := err.(Error); ok && e.Timeout() {
+				continue
+			}
+			return nil, err
+		}
+		buf = buf[0:n]
+		in := new(dnsMsg)
+		if !in.Unpack(buf) || in.id != out.id {
+			continue
+		}
+		return in, nil
+	}
+	var server string
+	if a := c.RemoteAddr(); a != nil {
+		server = a.String()
+	}
+	return nil, &DNSError{Error: "no answer from server", Name: name, Server: server, IsTimeout: true}
+}
+
+
+// Do a lookup for a single name, which must be rooted
+// (otherwise answer will not find the answers).
+func tryOneName(cfg *dnsConfig, name string, qtype uint16) (cname string, addrs []dnsRR, err os.Error) {
+	if len(cfg.servers) == 0 {
+		return "", nil, &DNSError{Error: "no DNS servers", Name: name}
+	}
+	for i := 0; i < len(cfg.servers); i++ {
+		// Calling Dial here is scary -- we have to be sure
+		// not to dial a name that will require a DNS lookup,
+		// or Dial will call back here to translate it.
+		// The DNS config parser has already checked that
+		// all the cfg.servers[i] are IP addresses, which
+		// Dial will use without a DNS lookup.
+		server := cfg.servers[i] + ":53"
+		c, cerr := Dial("udp", server)
+		if cerr != nil {
+			err = cerr
+			continue
+		}
+		msg, merr := exchange(cfg, c, name, qtype)
+		c.Close()
+		if merr != nil {
+			err = merr
+			continue
+		}
+		cname, addrs, err = answer(name, server, msg, qtype)
+		if err == nil || err.(*DNSError).Error == noSuchHost {
+			break
+		}
+	}
+	return
+}
+
+func convertRR_A(records []dnsRR) []IP {
+	addrs := make([]IP, len(records))
+	for i, rr := range records {
+		a := rr.(*dnsRR_A).A
+		addrs[i] = IPv4(byte(a>>24), byte(a>>16), byte(a>>8), byte(a))
+	}
+	return addrs
+}
+
+func convertRR_AAAA(records []dnsRR) []IP {
+	addrs := make([]IP, len(records))
+	for i, rr := range records {
+		a := make(IP, 16)
+		copy(a, rr.(*dnsRR_AAAA).AAAA[:])
+		addrs[i] = a
+	}
+	return addrs
+}
+
+var cfg *dnsConfig
+var dnserr os.Error
+
+func loadConfig() { cfg, dnserr = dnsReadConfig() }
+
+var onceLoadConfig sync.Once
+
+func lookup(name string, qtype uint16) (cname string, addrs []dnsRR, err os.Error) {
+	if !isDomainName(name) {
+		return name, nil, &DNSError{Error: "invalid domain name", Name: name}
+	}
+	onceLoadConfig.Do(loadConfig)
+	if dnserr != nil || cfg == nil {
+		err = dnserr
+		return
+	}
+	// If name is rooted (trailing dot) or has enough dots,
+	// try it by itself first.
+	rooted := len(name) > 0 && name[len(name)-1] == '.'
+	if rooted || count(name, '.') >= cfg.ndots {
+		rname := name
+		if !rooted {
+			rname += "."
+		}
+		// Can try as ordinary name.
+		cname, addrs, err = tryOneName(cfg, rname, qtype)
+		if err == nil {
+			return
+		}
+	}
+	if rooted {
+		return
+	}
+
+	// Otherwise, try suffixes.
+	for i := 0; i < len(cfg.search); i++ {
+		rname := name + "." + cfg.search[i]
+		if rname[len(rname)-1] != '.' {
+			rname += "."
+		}
+		cname, addrs, err = tryOneName(cfg, rname, qtype)
+		if err == nil {
+			return
+		}
+	}
+
+	// Last ditch effort: try unsuffixed.
+	rname := name
+	if !rooted {
+		rname += "."
+	}
+	cname, addrs, err = tryOneName(cfg, rname, qtype)
+	if err == nil {
+		return
+	}
+	return
+}
+
+// goLookupHost is the native Go implementation of LookupHost.
+// Used only if cgoLookupHost refuses to handle the request
+// (that is, only if cgoLookupHost is the stub in cgo_stub.go).
+// Normally we let cgo use the C library resolver instead of
+// depending on our lookup code, so that Go and C get the same
+// answers.
+func goLookupHost(name string) (addrs []string, err os.Error) {
+	// Use entries from /etc/hosts if they match.
+	addrs = lookupStaticHost(name)
+	if len(addrs) > 0 {
+		return
+	}
+	onceLoadConfig.Do(loadConfig)
+	if dnserr != nil || cfg == nil {
+		err = dnserr
+		return
+	}
+	ips, err := goLookupIP(name)
+	if err != nil {
+		return
+	}
+	addrs = make([]string, 0, len(ips))
+	for _, ip := range ips {
+		addrs = append(addrs, ip.String())
+	}
+	return
+}
+
+// goLookupIP is the native Go implementation of LookupIP.
+// Used only if cgoLookupIP refuses to handle the request
+// (that is, only if cgoLookupIP is the stub in cgo_stub.go).
+// Normally we let cgo use the C library resolver instead of
+// depending on our lookup code, so that Go and C get the same
+// answers.
+func goLookupIP(name string) (addrs []IP, err os.Error) {
+	onceLoadConfig.Do(loadConfig)
+	if dnserr != nil || cfg == nil {
+		err = dnserr
+		return
+	}
+	var records []dnsRR
+	var cname string
+	cname, records, err = lookup(name, dnsTypeA)
+	if err != nil {
+		return
+	}
+	addrs = convertRR_A(records)
+	if cname != "" {
+		name = cname
+	}
+	_, records, err = lookup(name, dnsTypeAAAA)
+	if err != nil && len(addrs) > 0 {
+		// Ignore error because A lookup succeeded.
+		err = nil
+	}
+	if err != nil {
+		return
+	}
+	addrs = append(addrs, convertRR_AAAA(records)...)
+	return
+}
+
+// goLookupCNAME is the native Go implementation of LookupCNAME.
+// Used only if cgoLookupCNAME refuses to handle the request
+// (that is, only if cgoLookupCNAME is the stub in cgo_stub.go).
+// Normally we let cgo use the C library resolver instead of
+// depending on our lookup code, so that Go and C get the same
+// answers.
+func goLookupCNAME(name string) (cname string, err os.Error) {
+	onceLoadConfig.Do(loadConfig)
+	if dnserr != nil || cfg == nil {
+		err = dnserr
+		return
+	}
+	_, rr, err := lookup(name, dnsTypeCNAME)
+	if err != nil {
+		return
+	}
+	cname = rr[0].(*dnsRR_CNAME).Cname
+	return
+}