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net: stop multiple sends into single capacity channel in lookupIP

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ch is of size 1, and has only one read. But current code can
write to ch more than once. This makes goroutines that do network
name lookups block forever. Only 500 goroutines are allowed, and
we eventually run out of goroutines.

Rewrite the code to only write into ch once.

Fixes #24178

Change-Id: Ifbd37db377c8b05e69eca24cc9147e7f86f899d8
Reviewed-on: https://go-review.googlesource.com/111718
Run-TryBot: Alex Brainman <alex.brainman@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
This commit is contained in:
Alex Brainman 2018-05-05 17:03:21 +10:00
parent f94b5a8105
commit 33b2b17201
2 changed files with 56 additions and 9 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

40
src/net/lookup_test.go
View File

@ -911,3 +911,43 @@ func TestNilResolverLookup(t *testing.T) {
r.LookupSRV(ctx, "service", "proto", "name")
r.LookupTXT(ctx, "gmail.com")
}
// TestLookupHostCancel verifies that lookup works even after many
// canceled lookups (see golang.org/issue/24178 for details).
func TestLookupHostCancel(t *testing.T) {
if testenv.Builder() == "" {
testenv.MustHaveExternalNetwork(t)
}
if runtime.GOOS == "nacl" {
t.Skip("skip on nacl")
}
const (
google = "www.google.com"
invalidDomain = "nonexistentdomain.golang.org"
n = 600 // this needs to be larger than threadLimit size
)
_, err := LookupHost(google)
if err != nil {
t.Fatal(err)
}
ctx, cancel := context.WithCancel(context.Background())
cancel()
for i := 0; i < n; i++ {
addr, err := DefaultResolver.LookupHost(ctx, invalidDomain)
if err == nil {
t.Fatalf("LookupHost(%q): returns %v, but should fail", invalidDomain, addr)
}
if !strings.Contains(err.Error(), "canceled") {
t.Fatalf("LookupHost(%q): failed with unexpected error: %v", invalidDomain, err)
}
time.Sleep(time.Millisecond * 1)
}
_, err = LookupHost(google)
if err != nil {
t.Fatal(err)
}
}

25
src/net/lookup_windows.go
View File

@ -79,12 +79,7 @@ func (r *Resolver) lookupHost(ctx context.Context, name string) ([]string, error
func (r *Resolver) lookupIP(ctx context.Context, name string) ([]IPAddr, error) {
// TODO(bradfitz,brainman): use ctx more. See TODO below.
type ret struct {
addrs []IPAddr
err error
}
ch := make(chan ret, 1)
go func() {
getaddr := func() ([]IPAddr, error) {
acquireThread()
defer releaseThread()
hints := syscall.AddrinfoW{
@ -95,7 +90,7 @@ func (r *Resolver) lookupIP(ctx context.Context, name string) ([]IPAddr, error)
var result *syscall.AddrinfoW
e := syscall.GetAddrInfoW(syscall.StringToUTF16Ptr(name), nil, &hints, &result)
if e != nil {
ch <- ret{err: &DNSError{Err: winError("getaddrinfow", e).Error(), Name: name}}
return nil, &DNSError{Err: winError("getaddrinfow", e).Error(), Name: name}
}
defer syscall.FreeAddrInfoW(result)
addrs := make([]IPAddr, 0, 5)
@ -110,11 +105,23 @@ func (r *Resolver) lookupIP(ctx context.Context, name string) ([]IPAddr, error)
zone := zoneCache.name(int((*syscall.RawSockaddrInet6)(addr).Scope_id))
addrs = append(addrs, IPAddr{IP: IP{a[0], a[1], a[2], a[3], a[4], a[5], a[6], a[7], a[8], a[9], a[10], a[11], a[12], a[13], a[14], a[15]}, Zone: zone})
default:
ch <- ret{err: &DNSError{Err: syscall.EWINDOWS.Error(), Name: name}}
return nil, &DNSError{Err: syscall.EWINDOWS.Error(), Name: name}
}
}
ch <- ret{addrs: addrs}
return addrs, nil
}
type ret struct {
addrs []IPAddr
err error
}
ch := make(chan ret, 1)
go func() {
addr, err := getaddr()
ch <- ret{addrs: addr, err: err}
}()
select {
case r := <-ch:
return r.addrs, r.err