diff options
Diffstat (limited to 'src/pkg/net/dnsclient.go')
| -rw-r--r-- | src/pkg/net/dnsclient.go | 78 |
1 files changed, 63 insertions, 15 deletions
diff --git a/src/pkg/net/dnsclient.go b/src/pkg/net/dnsclient.go index 89f2409bf..ae9ca8430 100644 --- a/src/pkg/net/dnsclient.go +++ b/src/pkg/net/dnsclient.go @@ -121,15 +121,19 @@ func answer(name, server string, dns *dnsMsg, qtype uint16) (cname string, addrs Cname: for cnameloop := 0; cnameloop < 10; cnameloop++ { addrs = addrs[0:0] - for i := 0; i < len(dns.answer); i++ { - rr := dns.answer[i] + for _, rr := range dns.answer { + if _, justHeader := rr.(*dnsRR_Header); justHeader { + // Corrupt record: we only have a + // header. That header might say it's + // of type qtype, but we don't + // actually have it. Skip. + continue + } h := rr.Header() if h.Class == dnsClassINET && h.Name == name { switch h.Rrtype { case qtype: - n := len(addrs) - addrs = addrs[0 : n+1] - addrs[n] = rr + addrs = append(addrs, rr) case dnsTypeCNAME: // redirect to cname name = rr.(*dnsRR_CNAME).Cname @@ -181,8 +185,7 @@ func tryOneName(cfg *dnsConfig, name string, qtype uint16) (cname string, addrs func convertRR_A(records []dnsRR) []IP { addrs := make([]IP, len(records)) - for i := 0; i < len(records); i++ { - rr := records[i] + for i, rr := range records { a := rr.(*dnsRR_A).A addrs[i] = IPv4(byte(a>>24), byte(a>>16), byte(a>>8), byte(a)) } @@ -191,8 +194,7 @@ func convertRR_A(records []dnsRR) []IP { func convertRR_AAAA(records []dnsRR) []IP { addrs := make([]IP, len(records)) - for i := 0; i < len(records); i++ { - rr := records[i] + for i, rr := range records { a := make(IP, 16) copy(a, rr.(*dnsRR_AAAA).AAAA[:]) addrs[i] = a @@ -384,9 +386,7 @@ func goLookupCNAME(name string) (cname string, err os.Error) { if err != nil { return } - if len(rr) >= 0 { - cname = rr[0].(*dnsRR_CNAME).Cname - } + cname = rr[0].(*dnsRR_CNAME).Cname return } @@ -398,10 +398,49 @@ type SRV struct { Weight uint16 } +// byPriorityWeight sorts SRV records by ascending priority and weight. +type byPriorityWeight []*SRV + +func (s byPriorityWeight) Len() int { return len(s) } + +func (s byPriorityWeight) Swap(i, j int) { s[i], s[j] = s[j], s[i] } + +func (s byPriorityWeight) Less(i, j int) bool { + return s[i].Priority < s[j].Priority || + (s[i].Priority == s[j].Priority && s[i].Weight < s[j].Weight) +} + +// shuffleSRVByWeight shuffles SRV records by weight using the algorithm +// described in RFC 2782. +func shuffleSRVByWeight(addrs []*SRV) { + sum := 0 + for _, addr := range addrs { + sum += int(addr.Weight) + } + for sum > 0 && len(addrs) > 1 { + s := 0 + n := rand.Intn(sum + 1) + for i := range addrs { + s += int(addrs[i].Weight) + if s >= n { + if i > 0 { + t := addrs[i] + copy(addrs[1:i+1], addrs[0:i]) + addrs[0] = t + } + break + } + } + sum -= int(addrs[0].Weight) + addrs = addrs[1:] + } +} + // LookupSRV tries to resolve an SRV query of the given service, // protocol, and domain name, as specified in RFC 2782. In most cases // the proto argument can be the same as the corresponding -// Addr.Network(). +// Addr.Network(). The returned records are sorted by priority +// and randomized by weight within a priority. func LookupSRV(service, proto, name string) (cname string, addrs []*SRV, err os.Error) { target := "_" + service + "._" + proto + "." + name var records []dnsRR @@ -410,10 +449,19 @@ func LookupSRV(service, proto, name string) (cname string, addrs []*SRV, err os. return } addrs = make([]*SRV, len(records)) - for i := 0; i < len(records); i++ { - r := records[i].(*dnsRR_SRV) + for i, rr := range records { + r := rr.(*dnsRR_SRV) addrs[i] = &SRV{r.Target, r.Port, r.Priority, r.Weight} } + sort.Sort(byPriorityWeight(addrs)) + i := 0 + for j := 1; j < len(addrs); j++ { + if addrs[i].Priority != addrs[j].Priority { + shuffleSRVByWeight(addrs[i:j]) + i = j + } + } + shuffleSRVByWeight(addrs[i:len(addrs)]) return } |