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net/{neterror,dns/resolver}: move PacketWasTruncated to neterror from DNS code

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And delete the unused code in net/dns/resolver/neterr_*.go.

Change-Id: Ibe62c486bacce2733eb9968c96a98cbbdb2758bd
Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>
This commit is contained in:
Brad Fitzpatrick
2022-01-03 10:49:56 -08:00
committed by Brad Fitzpatrick
parent dd45bba76b
commit 2513d2d728
6 changed files with 37 additions and 90 deletions
Download Patch File Download Diff File Expand all files Collapse all files

3
net/dns/resolver/forwarder.go
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@@ -25,6 +25,7 @@ import (
dns "golang.org/x/net/dns/dnsmessage" dns "golang.org/x/net/dns/dnsmessage"
"inet.af/netaddr" "inet.af/netaddr"
"tailscale.com/hostinfo" "tailscale.com/hostinfo"
"tailscale.com/net/neterror"
"tailscale.com/net/netns" "tailscale.com/net/netns"
"tailscale.com/net/tsdial" "tailscale.com/net/tsdial"
"tailscale.com/types/dnstype" "tailscale.com/types/dnstype"
@@ -482,7 +483,7 @@ func (f *forwarder) send(ctx context.Context, fq *forwardQuery, rr resolverAndDe
if err := ctx.Err(); err != nil { if err := ctx.Err(); err != nil {
return nil, err return nil, err
} }
if packetWasTruncated(err) { if neterror.PacketWasTruncated(err) {
err = nil err = nil
} else { } else {
metricDNSFwdUDPErrorRead.Add(1) metricDNSFwdUDPErrorRead.Add(1)

30
net/dns/resolver/neterr_darwin.go
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@@ -1,30 +0,0 @@
// Copyright (c) 2020 Tailscale Inc & AUTHORS All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
package resolver
import (
"errors"
"syscall"
)
// Avoid allocation when calling errors.Is below
// by converting syscall.Errno to error here.
var (
networkDown error = syscall.ENETDOWN
networkUnreachable error = syscall.ENETUNREACH
)
func networkIsDown(err error) bool {
return errors.Is(err, networkDown)
}
func networkIsUnreachable(err error) bool {
return errors.Is(err, networkUnreachable)
}
// packetWasTruncated returns true if err indicates truncation but the RecvFrom
// that generated err was otherwise successful. It always returns false on this
// platform.
func packetWasTruncated(err error) bool { return false }

16
net/dns/resolver/neterr_other.go
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@@ -1,16 +0,0 @@
// Copyright (c) 2020 Tailscale Inc & AUTHORS All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
//go:build !darwin && !windows
// +build !darwin,!windows
package resolver
func networkIsDown(err error) bool { return false }
func networkIsUnreachable(err error) bool { return false }
// packetWasTruncated returns true if err indicates truncation but the RecvFrom
// that generated err was otherwise successful. It always returns false on this
// platform.
func packetWasTruncated(err error) bool { return false }

43
net/dns/resolver/neterr_windows.go
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@@ -1,43 +0,0 @@
// Copyright (c) 2020 Tailscale Inc & AUTHORS All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
package resolver
import (
"errors"
"net"
"os"
"golang.org/x/sys/windows"
)
func networkIsDown(err error) bool {
if oe, ok := err.(*net.OpError); ok && oe.Op == "write" {
if se, ok := oe.Err.(*os.SyscallError); ok {
if se.Syscall == "wsasendto" && se.Err == windows.WSAENETUNREACH {
return true
}
}
}
return false
}
func networkIsUnreachable(err error) bool {
// TODO(bradfitz,josharian): something here? what is the
// difference between down and unreachable? Add comments.
return false
}
// packetWasTruncated returns true if err indicates truncation but the RecvFrom
// that generated err was otherwise successful. On Windows, Go's UDP RecvFrom
// calls WSARecvFrom which returns the WSAEMSGSIZE error code when the received
// datagram is larger than the provided buffer. When that happens, both a valid
// size and an error are returned (as per the partial fix for golang/go#14074).
// If the WSAEMSGSIZE error is returned, then we ignore the error to get
// semantics similar to the POSIX operating systems. One caveat is that it
// appears that the source address is not returned when WSAEMSGSIZE occurs, but
// we do not currently look at the source address.
func packetWasTruncated(err error) bool {
return errors.Is(err, windows.WSAEMSGSIZE)
}

18
net/neterror/neterror.go
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@@ -40,3 +40,21 @@ func TreatAsLostUDP(err error) bool {
} }
return false return false
} }
var packetWasTruncated func(error) bool // non-nil on Windows at least
// PacketWasTruncated reports whether err indicates truncation but the RecvFrom
// that generated err was otherwise successful. On Windows, Go's UDP RecvFrom
// calls WSARecvFrom which returns the WSAEMSGSIZE error code when the received
// datagram is larger than the provided buffer. When that happens, both a valid
// size and an error are returned (as per the partial fix for golang/go#14074).
// If the WSAEMSGSIZE error is returned, then we ignore the error to get
// semantics similar to the POSIX operating systems. One caveat is that it
// appears that the source address is not returned when WSAEMSGSIZE occurs, but
// we do not currently look at the source address.
func PacketWasTruncated(err error) bool {
if packetWasTruncated == nil {
return false
}
return packetWasTruncated(err)
}

17
net/neterror/neterror_windows.go Normal file
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@@ -0,0 +1,17 @@
// Copyright (c) 2021 Tailscale Inc & AUTHORS All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
package neterror
import (
"errors"
"golang.org/x/sys/windows"
)
func init() {
packetWasTruncated = func(err error) bool {
return errors.Is(err, windows.WSAEMSGSIZE)
}
}