From 3bcbab3f74ef4651264aef8be5fc76d0495943cd Mon Sep 17 00:00:00 2001
From: "Bryan C. Mills" <bcmills@google.com>
Date: Thu, 24 Feb 2022 16:00:15 -0500
Subject: [PATCH] ipv4: retry ENOBUFS errors in
 TestPacketConnConcurrentReadWriteUnicast
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This change is sheer speculation based on the failures observed in
golang/go#37319.

(A deadlock in the test prevented us from seeing the actual failure
mode of golang/go#51342 up until CL 387915, and it isn't obvious to me
that we should wait for another failure before trying a likely — and
otherwise harmless — fix.)

This is a port of CL 376095 to the "ipv4" package.

Fixes golang/go#51342.
(Maybe.)

Change-Id: Idd6d2d785dbb0c98404f99bd98a3c4ddc11cb2cf
Reviewed-on: https://go-review.googlesource.com/c/net/+/387916
Trust: Bryan Mills <bcmills@google.com>
Run-TryBot: Bryan Mills <bcmills@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>
---
 ipv4/errors_other_test.go | 14 +++++++++++
 ipv4/errors_unix_test.go  | 20 +++++++++++++++
 ipv4/readwrite_test.go    | 51 +++++++++++++++++++++++++++------------
 3 files changed, 70 insertions(+), 15 deletions(-)
 create mode 100644 ipv4/errors_other_test.go
 create mode 100644 ipv4/errors_unix_test.go

diff --git a/ipv4/errors_other_test.go b/ipv4/errors_other_test.go
new file mode 100644
index 00000000..61543539
--- /dev/null
+++ b/ipv4/errors_other_test.go
@@ -0,0 +1,14 @@
+// Copyright 2022 The Go 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 !(aix || darwin || dragonfly || freebsd || linux || netbsd || openbsd || solaris)
+// +build !aix,!darwin,!dragonfly,!freebsd,!linux,!netbsd,!openbsd,!solaris
+
+package ipv4_test
+
+// isENOBUFS reports whether err is unix.ENOBUFS.
+// (Always false on non-Unix platforms.)
+func isENOBUFS(err error) bool {
+	return false
+}
diff --git a/ipv4/errors_unix_test.go b/ipv4/errors_unix_test.go
new file mode 100644
index 00000000..566e070a
--- /dev/null
+++ b/ipv4/errors_unix_test.go
@@ -0,0 +1,20 @@
+// Copyright 2022 The Go 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 aix || darwin || dragonfly || freebsd || linux || netbsd || openbsd || solaris
+// +build aix darwin dragonfly freebsd linux netbsd openbsd solaris
+
+package ipv4_test
+
+import (
+	"errors"
+
+	"golang.org/x/sys/unix"
+)
+
+// isENOBUFS reports whether err is unix.ENOBUFS.
+// (Always false on non-Unix platforms.)
+func isENOBUFS(err error) bool {
+	return errors.Is(err, unix.ENOBUFS)
+}
diff --git a/ipv4/readwrite_test.go b/ipv4/readwrite_test.go
index e0176a2e..11281a44 100644
--- a/ipv4/readwrite_test.go
+++ b/ipv4/readwrite_test.go
@@ -12,6 +12,7 @@ import (
 	"strings"
 	"sync"
 	"testing"
+	"time"
 
 	"golang.org/x/net/internal/iana"
 	"golang.org/x/net/ipv4"
@@ -450,12 +451,22 @@ func testPacketConnConcurrentReadWriteUnicast(t *testing.T, p *ipv4.PacketConn,
 		if err := p.SetControlMessage(cf, toggle); err != nil {
 			fatalf("%v", err)
 		}
-		n, err := p.WriteTo(data, &cm, dst)
-		if err != nil {
-			fatalf("%v", err)
-		}
-		if n != len(data) {
-			fatalf("got %d; want %d", n, len(data))
+
+		backoff := time.Millisecond
+		for {
+			n, err := p.WriteTo(data, &cm, dst)
+			if err != nil {
+				if n == 0 && isENOBUFS(err) {
+					time.Sleep(backoff)
+					backoff *= 2
+					continue
+				}
+				fatalf("%v", err)
+			}
+			if n != len(data) {
+				fatalf("got %d; want %d", n, len(data))
+			}
+			break
 		}
 	}
 	batchWriter := func(toggle bool) {
@@ -476,15 +487,25 @@ func testPacketConnConcurrentReadWriteUnicast(t *testing.T, p *ipv4.PacketConn,
 				Addr:    dst,
 			},
 		}
-		n, err := p.WriteBatch(ms, 0)
-		if err != nil {
-			fatalf("%v", err)
-		}
-		if n != len(ms) {
-			fatalf("got %d; want %d", n, len(ms))
-		}
-		if ms[0].N != len(data) {
-			fatalf("got %d; want %d", ms[0].N, len(data))
+
+		backoff := time.Millisecond
+		for {
+			n, err := p.WriteBatch(ms, 0)
+			if err != nil {
+				if n == 0 && isENOBUFS(err) {
+					time.Sleep(backoff)
+					backoff *= 2
+					continue
+				}
+				fatalf("%v", err)
+			}
+			if n != len(ms) {
+				fatalf("got %d; want %d", n, len(ms))
+			}
+			if ms[0].N != len(data) {
+				fatalf("got %d; want %d", ms[0].N, len(data))
+			}
+			break
 		}
 	}