internal/poll: in SendFile treat ENOTSUP like EOPNOTSUPP

Fixes #70763

Change-Id: Ifb79b5b0529f7977df0fe1b59d224b8b31df2c9b
Reviewed-on: https://go-review.googlesource.com/c/go/+/635396
Reviewed-by: Ian Lance Taylor <iant@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Damien Neil <dneil@google.com>
Auto-Submit: Ian Lance Taylor <iant@google.com>

src/internal/poll/sendfile_unix.go

@@ -110,12 +110,20 @@ func sendFile(dstFD *FD, src int, offset *int64, size int64) (written int64, err
 			// Retry.
 		case syscall.ENOSYS, syscall.EOPNOTSUPP, syscall.EINVAL:
 			// ENOSYS indicates no kernel support for sendfile.
-			// EINVAL indicates a FD type which does not support sendfile.
+			// EINVAL indicates a FD type that does not support sendfile.
 			//
 			// On Linux, copy_file_range can return EOPNOTSUPP when copying
 			// to a NFS file (issue #40731); check for it here just in case.
 			return written, err, written > 0
 		default:
+			// We want to handle ENOTSUP like EOPNOTSUPP.
+			// It's a pain to put it as a switch case
+			// because on Linux systems ENOTSUP == EOPNOTSUPP,
+			// so the compiler complains about a duplicate case.
+			if err == syscall.ENOTSUP {
+				return written, err, written > 0
+			}
+
 			// Not a retryable error.
 			return written, err, true
 		}

src/net/sendfile_unix_test.go

@@ -0,0 +1,86 @@
+// Copyright 2024 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 unix
+
+package net
+
+import (
+	"internal/testpty"
+	"io"
+	"os"
+	"sync"
+	"syscall"
+	"testing"
+)
+
+// Issue 70763: test that we don't fail on sendfile from a tty.
+func TestCopyFromTTY(t *testing.T) {
+	pty, ttyName, err := testpty.Open()
+	if err != nil {
+		t.Skipf("skipping test because pty open failed: %v", err)
+	}
+	defer pty.Close()
+
+	// Use syscall.Open so that the tty is blocking.
+	ttyFD, err := syscall.Open(ttyName, syscall.O_RDWR, 0)
+	if err != nil {
+		t.Skipf("skipping test because tty open failed: %v", err)
+	}
+	defer syscall.Close(ttyFD)
+
+	tty := os.NewFile(uintptr(ttyFD), "tty")
+	defer tty.Close()
+
+	ln := newLocalListener(t, "tcp")
+	defer ln.Close()
+
+	ch := make(chan bool)
+
+	const data = "data\n"
+
+	var wg sync.WaitGroup
+	defer wg.Wait()
+
+	wg.Add(1)
+	go func() {
+		defer wg.Done()
+		conn, err := ln.Accept()
+		if err != nil {
+			t.Error(err)
+			return
+		}
+		defer conn.Close()
+
+		buf := make([]byte, len(data))
+		if _, err := io.ReadFull(conn, buf); err != nil {
+			t.Error(err)
+		}
+
+		ch <- true
+	}()
+
+	conn, err := Dial("tcp", ln.Addr().String())
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer conn.Close()
+
+	wg.Add(1)
+	go func() {
+		defer wg.Done()
+		if _, err := pty.Write([]byte(data)); err != nil {
+			t.Error(err)
+		}
+		<-ch
+		if err := pty.Close(); err != nil {
+			t.Error(err)
+		}
+	}()
+
+	lr := io.LimitReader(tty, int64(len(data)))
+	if _, err := io.Copy(conn, lr); err != nil {
+		t.Error(err)
+	}
+}