Fix open append (#370)

* Fix append in file_cache by saving flags and using append correctly

* Add unit test for file append

* Cleanup comment, revert change to OpenFile

component/file_cache/file_cache.go

@@ -965,6 +965,11 @@ func (fc *FileCache) OpenFile(options internal.OpenFileOptions) (*handlemap.Hand
 	// create handle and record openFileOptions for later
 	handle := handlemap.NewHandle(options.Name)
 	handle.SetValue("openFileOptions", openFileOptions{flags: options.Flags, fMode: options.Mode})
+
+	if options.Flags&os.O_APPEND != 0 {
+		handle.Flags.Set(handlemap.HandleOpenedAppend)
+	}
+
 	// Increment the handle count in this lock item as there is one handle open for this now
 	flock.Inc()
 
@@ -1117,7 +1122,13 @@ func (fc *FileCache) WriteFile(options internal.WriteFileOptions) (int, error) {
 
 	// Removing Pwrite as it is not supported on Windows
 	// bytesWritten, err := syscall.Pwrite(options.Handle.FD(), options.Data, options.Offset)
-	bytesWritten, err := f.WriteAt(options.Data, options.Offset)
+
+	var bytesWritten int
+	if options.Handle.Flags.IsSet(handlemap.HandleOpenedAppend) {
+		bytesWritten, err = f.Write(options.Data)
+	} else {
+		bytesWritten, err = f.WriteAt(options.Data, options.Offset)
+	}
 
 	if err == nil {
 		// Mark the handle dirty so the file is written back to storage on FlushFile.

internal/handlemap/handle_map.go

@@ -43,10 +43,11 @@ const InvalidHandleID HandleID = 0
 
 // Flags represented in BitMap for various flags in the handle
 const (
-	HandleFlagUnknown uint16 = iota
-	HandleFlagDirty          // File has been modified with write operation or is a new file
-	HandleFlagFSynced        // User has called fsync on the file explicitly
-	HandleFlagCached         // File is cached in the local system by cloudfuse
+	HandleFlagUnknown  uint16 = iota
+	HandleFlagDirty           // File has been modified with write operation or is a new file
+	HandleFlagFSynced         // User has called fsync on the file explicitly
+	HandleFlagCached          // File is cached in the local system by cloudfuse
+	HandleOpenedAppend        // File is opened for Append
 )
 
 // Structure to hold in memory cache for streaming layer

test/e2e_tests/file_test.go

@@ -254,6 +254,34 @@ func (suite *fileTestSuite) TestFileCreateLabel() {
 	suite.fileTestCleanup([]string{fileName})
 }
 
+func (suite *fileTestSuite) TestFileAppend() {
+	fileName := filepath.Join(suite.testPath, "append_test.txt")
+	initialContent := []byte("Initial content\n")
+	appendContent := []byte("Appended content\n")
+
+	// Create and write initial content to the file
+	srcFile, err := os.OpenFile(fileName, os.O_CREATE|os.O_WRONLY, 0777)
+	suite.NoError(err)
+	_, err = srcFile.Write(initialContent)
+	suite.NoError(err)
+	srcFile.Close()
+
+	// Open the file with O_APPEND and append new content
+	appendFile, err := os.OpenFile(fileName, os.O_APPEND|os.O_WRONLY, 0777)
+	suite.NoError(err)
+	_, err = appendFile.Write(appendContent)
+	suite.NoError(err)
+	appendFile.Close()
+
+	// Read the file and verify the content
+	data, err := os.ReadFile(fileName)
+	suite.NoError(err)
+	expectedContent := append(initialContent, appendContent...)
+	suite.Equal(expectedContent, data)
+
+	suite.fileTestCleanup([]string{fileName})
+}
+
 // # Write a small file
 func (suite *fileTestSuite) TestFileWriteSmall() {
 	fileName := filepath.Join(suite.testPath, "small_write.txt")