net: add support for DNS SRV requests.

        Fixes #758.

R=rsc, adg
CC=golang-dev
https://golang.org/cl/1078041

diff --git a/src/pkg/net/dnsclient.go b/src/pkg/net/dnsclient.go
index 337c5544aa37ce2fe5ccdbc40a50c79f16f9edd5..ea21117e3c2e1047b3e218741b5130b3c81660c6 100644 (file)
--- a/src/pkg/net/dnsclient.go
+++ b/src/pkg/net/dnsclient.go
@@ -45,14 +45,14 @@ const noSuchHost = "no such host"
 
 // Send a request on the connection and hope for a reply.
 // Up to cfg.attempts attempts.
-func exchange(cfg *dnsConfig, c Conn, name string) (*dnsMsg, os.Error) {
+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{
-               dnsQuestion{name, dnsTypeA, dnsClassINET},
+               dnsQuestion{name, qtype, dnsClassINET},
        }
        out.recursion_desired = true
        msg, ok := out.Pack()
@@ -93,8 +93,8 @@ func exchange(cfg *dnsConfig, c Conn, name string) (*dnsMsg, os.Error) {
 
 // Find answer for name in dns message.
 // On return, if err == nil, addrs != nil.
-func answer(name, server string, dns *dnsMsg) (addrs []string, err os.Error) {
-       addrs = make([]string, 0, len(dns.answer))
+func answer(name, server string, dns *dnsMsg, qtype uint16) (addrs []dnsRR, err os.Error) {
+       addrs = make([]dnsRR, 0, len(dns.answer))
 
        if dns.rcode == dnsRcodeNameError && dns.recursion_available {
                return nil, &DNSError{Error: noSuchHost, Name: name}
@@ -120,11 +120,10 @@ Cname:
                        h := rr.Header()
                        if h.Class == dnsClassINET && h.Name == name {
                                switch h.Rrtype {
-                               case dnsTypeA:
+                               case qtype:
                                        n := len(addrs)
-                                       a := rr.(*dnsRR_A).A
                                        addrs = addrs[0 : n+1]
-                                       addrs[n] = IPv4(byte(a>>24), byte(a>>16), byte(a>>8), byte(a)).String()
+                                       addrs[n] = rr
                                case dnsTypeCNAME:
                                        // redirect to cname
                                        name = rr.(*dnsRR_CNAME).Cname
@@ -143,7 +142,7 @@ Cname:
 
 // Do a lookup for a single name, which must be rooted
 // (otherwise answer will not find the answers).
-func tryOneName(cfg *dnsConfig, name string) (addrs []string, err os.Error) {
+func tryOneName(cfg *dnsConfig, name string, qtype uint16) (addrs []dnsRR, err os.Error) {
        if len(cfg.servers) == 0 {
                return nil, &DNSError{Error: "no DNS servers", Name: name}
        }
@@ -160,13 +159,13 @@ func tryOneName(cfg *dnsConfig, name string) (addrs []string, err os.Error) {
                        err = cerr
                        continue
                }
-               msg, merr := exchange(cfg, c, name)
+               msg, merr := exchange(cfg, c, name, qtype)
                c.Close()
                if merr != nil {
                        err = merr
                        continue
                }
-               addrs, err = answer(name, server, msg)
+               addrs, err = answer(name, server, msg, qtype)
                if err == nil || err.(*DNSError).Error == noSuchHost {
                        break
                }
@@ -174,6 +173,16 @@ func tryOneName(cfg *dnsConfig, name string) (addrs []string, err os.Error) {
        return
 }
 
+func convertRR_A(records []dnsRR) []string {
+       addrs := make([]string, len(records))
+       for i := 0; i < len(records); i++ {
+               rr := records[i]
+               a := rr.(*dnsRR_A).A
+               addrs[i] = IPv4(byte(a>>24), byte(a>>16), byte(a>>8), byte(a)).String()
+       }
+       return addrs
+}
+
 var cfg *dnsConfig
 var dnserr os.Error
 
@@ -223,10 +232,7 @@ func isDomainName(s string) bool {
        return ok
 }
 
-// LookupHost looks for name using the local hosts file and DNS resolver.
-// It returns the canonical name for the host and an array of that
-// host's addresses.
-func LookupHost(name string) (cname string, addrs []string, err os.Error) {
+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}
        }
@@ -235,12 +241,6 @@ func LookupHost(name string) (cname string, addrs []string, err os.Error) {
                err = dnserr
                return
        }
-       // Use entries from /etc/hosts if they match.
-       addrs = lookupStaticHost(name)
-       if len(addrs) > 0 {
-               cname = name
-               return
-       }
        // If name is rooted (trailing dot) or has enough dots,
        // try it by itself first.
        rooted := len(name) > 0 && name[len(name)-1] == '.'
@@ -250,7 +250,7 @@ func LookupHost(name string) (cname string, addrs []string, err os.Error) {
                        rname += "."
                }
                // Can try as ordinary name.
-               addrs, err = tryOneName(cfg, rname)
+               addrs, err = tryOneName(cfg, rname, qtype)
                if err == nil {
                        cname = rname
                        return
@@ -266,7 +266,7 @@ func LookupHost(name string) (cname string, addrs []string, err os.Error) {
                if rname[len(rname)-1] != '.' {
                        rname += "."
                }
-               addrs, err = tryOneName(cfg, rname)
+               addrs, err = tryOneName(cfg, rname, qtype)
                if err == nil {
                        cname = rname
                        return
@@ -278,10 +278,55 @@ func LookupHost(name string) (cname string, addrs []string, err os.Error) {
        if !rooted {
                rname += "."
        }
-       addrs, err = tryOneName(cfg, rname)
+       addrs, err = tryOneName(cfg, rname, qtype)
        if err == nil {
                cname = rname
                return
        }
        return
 }
+
+// LookupHost looks for name using the local hosts file and DNS resolver.
+// It returns the canonical name for the host and an array of that
+// host's addresses.
+func LookupHost(name string) (cname string, addrs []string, err os.Error) {
+       once.Do(loadConfig)
+       if dnserr != nil || cfg == nil {
+               err = dnserr
+               return
+       }
+       // Use entries from /etc/hosts if they match.
+       addrs = lookupStaticHost(name)
+       if len(addrs) > 0 {
+               cname = name
+               return
+       }
+       var records []dnsRR
+       cname, records, err = lookup(name, dnsTypeA)
+       if err != nil {
+               return
+       }
+       addrs = convertRR_A(records)
+       return
+}
+
+type SRV struct {
+       Target   string
+       Port     uint16
+       Priority uint16
+       Weight   uint16
+}
+
+func LookupSRV(name string) (cname string, addrs []*SRV, err os.Error) {
+       var records []dnsRR
+       cname, records, err = lookup(name, dnsTypeSRV)
+       if err != nil {
+               return
+       }
+       addrs = make([]*SRV, len(records))
+       for i := 0; i < len(records); i++ {
+               r := records[i].(*dnsRR_SRV)
+               addrs[i] = &SRV{r.Target, r.Port, r.Priority, r.Weight}
+       }
+       return
+}

diff --git a/src/pkg/net/dnsmsg.go b/src/pkg/net/dnsmsg.go
index f136b8c0862388fc0277a51b6d788ba1497b12b7..1d1b62eebb5c1e3c107887764184cd07a863d894 100644 (file)
--- a/src/pkg/net/dnsmsg.go
+++ b/src/pkg/net/dnsmsg.go
@@ -50,6 +50,7 @@ const (
        dnsTypeMINFO = 14
        dnsTypeMX    = 15
        dnsTypeTXT   = 16
+       dnsTypeSRV   = 33
 
        // valid dnsQuestion.qtype only
        dnsTypeAXFR  = 252
@@ -226,6 +227,18 @@ func (rr *dnsRR_TXT) Header() *dnsRR_Header {
        return &rr.Hdr
 }
 
+type dnsRR_SRV struct {
+       Hdr      dnsRR_Header
+       Priority uint16
+       Weight   uint16
+       Port     uint16
+       Target   string "domain-name"
+}
+
+func (rr *dnsRR_SRV) Header() *dnsRR_Header {
+       return &rr.Hdr
+}
+
 type dnsRR_A struct {
        Hdr dnsRR_Header
        A   uint32 "ipv4"
@@ -255,6 +268,7 @@ var rr_mk = map[int]func() dnsRR{
        dnsTypePTR:   func() dnsRR { return new(dnsRR_PTR) },
        dnsTypeSOA:   func() dnsRR { return new(dnsRR_SOA) },
        dnsTypeTXT:   func() dnsRR { return new(dnsRR_TXT) },
+       dnsTypeSRV:   func() dnsRR { return new(dnsRR_SRV) },
        dnsTypeA:     func() dnsRR { return new(dnsRR_A) },
 }