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net: make LookupCNAME's native behavior match its cgo behavior

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Fixes #18172.

Change-Id: I4a21fb5c0753cced025a03d88a6dd1aa3ee01d05
Reviewed-on: https://go-review.googlesource.com/34650
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Run-TryBot: Matthew Dempsky <mdempsky@google.com>
This commit is contained in:
Matthew Dempsky 2016-12-19 13:05:53 -08:00
parent 0c942e8f2c
commit 2f9dee9293
6 changed files with 83 additions and 84 deletions
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44
src/net/dnsclient_unix.go
View file

@ -444,7 +444,7 @@ func goLookupHostOrder(ctx context.Context, name string, order hostLookupOrder)
return
}
}
ips, err := goLookupIPOrder(ctx, name, order)
ips, _, err := goLookupIPCNAMEOrder(ctx, name, order)
if err != nil {
return
}
@ -472,27 +472,28 @@ func goLookupIPFiles(name string) (addrs []IPAddr) {
// The libc versions are in cgo_*.go.
func goLookupIP(ctx context.Context, host string) (addrs []IPAddr, err error) {
order := systemConf().hostLookupOrder(host)
return goLookupIPOrder(ctx, host, order)
addrs, _, err = goLookupIPCNAMEOrder(ctx, host, order)
return
}
func goLookupIPOrder(ctx context.Context, name string, order hostLookupOrder) (addrs []IPAddr, err error) {
func goLookupIPCNAMEOrder(ctx context.Context, name string, order hostLookupOrder) (addrs []IPAddr, cname string, err error) {
if order == hostLookupFilesDNS || order == hostLookupFiles {
addrs = goLookupIPFiles(name)
if len(addrs) > 0 || order == hostLookupFiles {
return addrs, nil
return addrs, name, nil
}
}
if !isDomainName(name) {
// See comment in func lookup above about use of errNoSuchHost.
return nil, &DNSError{Err: errNoSuchHost.Error(), Name: name}
return nil, "", &DNSError{Err: errNoSuchHost.Error(), Name: name}
}
resolvConf.tryUpdate("/etc/resolv.conf")
resolvConf.mu.RLock()
conf := resolvConf.dnsConfig
resolvConf.mu.RUnlock()
type racer struct {
fqdn string
rrs []dnsRR
cname string
rrs []dnsRR
error
}
lane := make(chan racer, 1)
@ -501,20 +502,23 @@ func goLookupIPOrder(ctx context.Context, name string, order hostLookupOrder) (a
for _, fqdn := range conf.nameList(name) {
for _, qtype := range qtypes {
go func(qtype uint16) {
_, rrs, err := tryOneName(ctx, conf, fqdn, qtype)
lane <- racer{fqdn, rrs, err}
cname, rrs, err := tryOneName(ctx, conf, fqdn, qtype)
lane <- racer{cname, rrs, err}
}(qtype)
}
for range qtypes {
racer := <-lane
if racer.error != nil {
// Prefer error for original name.
if lastErr == nil || racer.fqdn == name+"." {
if lastErr == nil || fqdn == name+"." {
lastErr = racer.error
}
continue
}
addrs = append(addrs, addrRecordList(racer.rrs)...)
if cname == "" {
cname = racer.cname
}
}
if len(addrs) > 0 {
break
@ -532,24 +536,16 @@ func goLookupIPOrder(ctx context.Context, name string, order hostLookupOrder) (a
addrs = goLookupIPFiles(name)
}
if len(addrs) == 0 && lastErr != nil {
return nil, lastErr
return nil, "", lastErr
}
}
return addrs, nil
return addrs, cname, nil
}
// 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(ctx context.Context, name string) (cname string, err error) {
_, rrs, err := lookup(ctx, name, dnsTypeCNAME)
if err != nil {
return
}
cname = rrs[0].(*dnsRR_CNAME).Cname
// goLookupCNAME is the native Go (non-cgo) implementation of LookupCNAME.
func goLookupCNAME(ctx context.Context, host string) (cname string, err error) {
order := systemConf().hostLookupOrder(host)
_, cname, err = goLookupIPCNAMEOrder(ctx, host, order)
return
}