os: add a test case of copying a file itself via io.Copy

Change-Id: Ib9746cb4f27625cb22620271b280d2da242b2fba
Reviewed-on: https://go-review.googlesource.com/c/go/+/428437
Run-TryBot: Ian Lance Taylor <[email protected]>
Run-TryBot: Andy Pan <[email protected]>
TryBot-Result: Gopher Robot <[email protected]>
Reviewed-by: Michael Knyszek <[email protected]>
Reviewed-by: Ian Lance Taylor <[email protected]>
Auto-Submit: Ian Lance Taylor <[email protected]>

src/os/readfrom_linux_test.go

@@ -13,6 +13,7 @@ import (
  . "os"
  "path/filepath"
  "strconv"
+ "strings"
  "syscall"
  "testing"
  "time"
@@ -74,6 +75,56 @@ func TestCopyFileRange(t *testing.T) {
  mustSeekStart(t, dst2)
  mustContainData(t, dst2, data) // through traditional means
  })
+ t.Run("CopyFileItself", func(t *testing.T) {
+ hook := hookCopyFileRange(t)
+
+ f, err := os.CreateTemp("", "file-readfrom-itself-test")
+ if err != nil {
+ t.Fatalf("failed to create tmp file: %v", err)
+ }
+ t.Cleanup(func() {
+ f.Close()
+ os.Remove(f.Name())
+ })
+
+ data := []byte("hello world!")
+ if _, err := f.Write(data); err != nil {
+ t.Fatalf("failed to create and feed the file: %v", err)
+ }
+
+ if err := f.Sync(); err != nil {
+ t.Fatalf("failed to save the file: %v", err)
+ }
+
+ // Rewind it.
+ if _, err := f.Seek(0, io.SeekStart); err != nil {
+ t.Fatalf("failed to rewind the file: %v", err)
+ }
+
+ // Read data from the file itself.
+ if _, err := io.Copy(f, f); err != nil {
+ t.Fatalf("failed to read from the file: %v", err)
+ }
+
+ if !hook.called || hook.written != 0 || hook.handled || hook.err != nil {
+ t.Fatalf("poll.CopyFileRange should be called and return the EINVAL error, but got hook.called=%t, hook.err=%v", hook.called, hook.err)
+ }
+
+ // Rewind it.
+ if _, err := f.Seek(0, io.SeekStart); err != nil {
+ t.Fatalf("failed to rewind the file: %v", err)
+ }
+
+ data2, err := io.ReadAll(f)
+ if err != nil {
+ t.Fatalf("failed to read from the file: %v", err)
+ }
+
+ // It should wind up a double of the original data.
+ if strings.Repeat(string(data), 2) != string(data2) {
+ t.Fatalf("data mismatch: %s != %s", string(data), string(data2))
+ }
+ })
  t.Run("NotRegular", func(t *testing.T) {
  t.Run("BothPipes", func(t *testing.T) {
  hook := hookCopyFileRange(t)
@@ -344,6 +395,10 @@ type copyFileRangeHook struct {
  srcfd int
  remain int64
 
+ written int64
+ handled bool
+ err error
+
  original func(dst, src *poll.FD, remain int64) (int64, bool, error)
 }
 
@@ -354,7 +409,8 @@ func (h *copyFileRangeHook) install() {
  h.dstfd = dst.Sysfd
  h.srcfd = src.Sysfd
  h.remain = remain
- return h.original(dst, src, remain)
+ h.written, h.handled, h.err = h.original(dst, src, remain)
+ return h.written, h.handled, h.err
  }
 }