net/http: using errors.Is in fs error detection

Compare error by errors.Is to detect wrapped fs errors.

Fixes #44923

Change-Id: Idf32b96a661728278b7006c3b3bcc581b8588259
GitHub-Last-Rev: dba01ddae06947fb8c6047ddfba108acd650f446
GitHub-Pull-Request: golang/go#45314
Reviewed-on: https://go-review.googlesource.com/c/go/+/306051
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Reviewed-by: Damien Neil <dneil@google.com>
Trust: Brad Fitzpatrick <bradfitz@golang.org>
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Go Bot <gobot@golang.org>

2 files changed, 9 insertions, 7 deletions

diff --git a/src/net/http/fs.go b/src/net/http/fs.go
index a28ae85958..57e731e481 100644
--- a/src/net/http/fs.go
+++ b/src/net/http/fs.go
@@ -46,7 +46,7 @@ type Dir string
 // to a possibly better non-nil error. In particular, it turns OS-specific errors
 // about opening files in non-directories into fs.ErrNotExist. See Issue 18984.
 func mapDirOpenError(originalErr error, name string) error {
-	if os.IsNotExist(originalErr) || os.IsPermission(originalErr) {
+	if errors.Is(originalErr, fs.ErrNotExist) || errors.Is(originalErr, fs.ErrPermission) {
 		return originalErr
 	}
 
@@ -670,10 +670,10 @@ func serveFile(w ResponseWriter, r *Request, fs FileSystem, name string, redirec
 // and historically Go's ServeContent always returned just "404 Not Found" for
 // all errors. We don't want to start leaking information in error messages.
 func toHTTPError(err error) (msg string, httpStatus int) {
-	if os.IsNotExist(err) {
+	if errors.Is(err, fs.ErrNotExist) {
 		return "404 page not found", StatusNotFound
 	}
-	if os.IsPermission(err) {
+	if errors.Is(err, fs.ErrPermission) {
 		return "403 Forbidden", StatusForbidden
 	}
 	// Default:
diff --git a/src/net/http/fs_test.go b/src/net/http/fs_test.go
index 1bf207e0f7..b42ade1e8a 100644
--- a/src/net/http/fs_test.go
+++ b/src/net/http/fs_test.go
@@ -1265,16 +1265,18 @@ func TestFileServerNotDirError(t *testing.T) {
 			if err == nil {
 				t.Fatal("err == nil; want != nil")
 			}
-			if !os.IsNotExist(err) {
-				t.Errorf("err = %v; os.IsNotExist(err) = %v; want true", err, os.IsNotExist(err))
+			if !errors.Is(err, fs.ErrNotExist) {
+				t.Errorf("err = %v; errors.Is(err, fs.ErrNotExist) = %v; want true", err,
+					errors.Is(err, fs.ErrNotExist))
 			}
 
 			_, err = dir.Open("/index.html/not-a-dir/not-a-file")
 			if err == nil {
 				t.Fatal("err == nil; want != nil")
 			}
-			if !os.IsNotExist(err) {
-				t.Errorf("err = %v; os.IsNotExist(err) = %v; want true", err, os.IsNotExist(err))
+			if !errors.Is(err, fs.ErrNotExist) {
+				t.Errorf("err = %v; errors.Is(err, fs.ErrNotExist) = %v; want true", err,
+					errors.Is(err, fs.ErrNotExist))
 			}
 		})
 	}