Fix package upload for files >32mb (#20622)

* Rewind file before first read.
* Added tests.

Co-authored-by: Lunny Xiao <xiaolunwen@gmail.com>

2 files changed, 51 insertions, 5 deletions

diff --git a/modules/util/filebuffer/file_backed_buffer.go b/modules/util/filebuffer/file_backed_buffer.go
index 128030b4c5..8e3e138e04 100644
--- a/modules/util/filebuffer/file_backed_buffer.go
+++ b/modules/util/filebuffer/file_backed_buffer.go
@@ -103,35 +103,45 @@ func (b *FileBackedBuffer) Size() int64 {
 	return b.size
 }
 
-func (b *FileBackedBuffer) switchToReader() {
+func (b *FileBackedBuffer) switchToReader() error {
 	if b.reader != nil {
-		return
+		return nil
 	}
 
 	if b.file != nil {
+		if _, err := b.file.Seek(0, io.SeekStart); err != nil {
+			return err
+		}
 		b.reader = b.file
 	} else {
 		b.reader = bytes.NewReader(b.buffer.Bytes())
 	}
+	return nil
 }
 
 // Read implements io.Reader
 func (b *FileBackedBuffer) Read(p []byte) (int, error) {
-	b.switchToReader()
+	if err := b.switchToReader(); err != nil {
+		return 0, err
+	}
 
 	return b.reader.Read(p)
 }
 
 // ReadAt implements io.ReaderAt
 func (b *FileBackedBuffer) ReadAt(p []byte, off int64) (int, error) {
-	b.switchToReader()
+	if err := b.switchToReader(); err != nil {
+		return 0, err
+	}
 
 	return b.reader.ReadAt(p, off)
 }
 
 // Seek implements io.Seeker
 func (b *FileBackedBuffer) Seek(offset int64, whence int) (int64, error) {
-	b.switchToReader()
+	if err := b.switchToReader(); err != nil {
+		return 0, err
+	}
 
 	return b.reader.Seek(offset, whence)
 }
diff --git a/modules/util/filebuffer/file_backed_buffer_test.go b/modules/util/filebuffer/file_backed_buffer_test.go
new file mode 100644
index 0000000000..83ef58561d
--- /dev/null
+++ b/modules/util/filebuffer/file_backed_buffer_test.go
@@ -0,0 +1,36 @@
+// Copyright 2022 The Gitea Authors. All rights reserved.
+// Use of this source code is governed by a MIT-style
+// license that can be found in the LICENSE file.
+
+package filebuffer
+
+import (
+	"io"
+	"strings"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func TestFileBackedBuffer(t *testing.T) {
+	cases := []struct {
+		MaxMemorySize int
+		Data          string
+	}{
+		{5, "test"},
+		{5, "testtest"},
+	}
+
+	for _, c := range cases {
+		buf, err := CreateFromReader(strings.NewReader(c.Data), c.MaxMemorySize)
+		assert.NoError(t, err)
+
+		assert.EqualValues(t, len(c.Data), buf.Size())
+
+		data, err := io.ReadAll(buf)
+		assert.NoError(t, err)
+		assert.Equal(t, c.Data, string(data))
+
+		assert.NoError(t, buf.Close())
+	}
+}