Add error fieldname to multipart response

http/filestream/errors.go

@@ -0,0 +1,17 @@
+package filestream
+
+type MultipartError struct {
+	FileName string `json:"file_name"`
+	Message  string `json:"message"`
+}
+
+func (e MultipartError) Error() string {
+	return e.Message
+}
+
+func NewMultipartError(fileName, message string) *MultipartError {
+	return &MultipartError{
+		FileName: fileName,
+		Message:  message,
+	}
+}

http/filestream/filestream.go

@@ -1,6 +1,8 @@
 package filestream
 
 import (
+	"bytes"
+	"encoding/json"
 	"errors"
 	"fmt"
 	"io"
@@ -11,7 +13,8 @@ import (
 )
 
 const (
-	FileType = "file"
+	FileType  = "file"
+	ErrorType = "error"
 )
 
 // The expected type of function that should be provided to the ReadFilesFromStream func, that returns the writer that should handle each file
@@ -60,21 +63,22 @@ type FileInfo struct {
 }
 
 func WriteFilesToStream(multipartWriter *multipart.Writer, filesList []*FileInfo) (err error) {
+	// Close finishes the multipart message and writes the trailing
+	// boundary end line to the output.
+	defer ioutils.Close(multipartWriter, &err)
 	for _, file := range filesList {
 		if err = writeFile(multipartWriter, file); err != nil {
-			return
+			return writeErrPart(multipartWriter, file, err)
 		}
 	}
 
-	// Close finishes the multipart message and writes the trailing
-	// boundary end line to the output.
-	return multipartWriter.Close()
+	return nil
 }
 
 func writeFile(multipartWriter *multipart.Writer, file *FileInfo) (err error) {
 	fileReader, err := os.Open(file.Path)
 	if err != nil {
-		return fmt.Errorf("failed opening %q: %w", file, err)
+		return fmt.Errorf("failed opening %q: %w", file.Name, err)
 	}
 	defer ioutils.Close(fileReader, &err)
 	fileWriter, err := multipartWriter.CreateFormFile(FileType, file.Name)
@@ -84,3 +88,19 @@ func writeFile(multipartWriter *multipart.Writer, file *FileInfo) (err error) {
 	_, err = io.Copy(fileWriter, fileReader)
 	return err
 }
+
+func writeErrPart(multipartWriter *multipart.Writer, file *FileInfo, writeFileErr error) error {
+	fileWriter, err := multipartWriter.CreateFormField(ErrorType)
+	if err != nil {
+		return fmt.Errorf("failed to CreateFormField: %w", err)
+	}
+
+	multipartErr := NewMultipartError(file.Name, writeFileErr.Error())
+	multipartErrJSON, err := json.Marshal(multipartErr)
+	if err != nil {
+		return fmt.Errorf("failed to marshal multipart error: %w", err)
+	}
+
+	_, err = io.Copy(fileWriter, bytes.NewReader(multipartErrJSON))
+	return err
+}

http/filestream/filestream_test.go

@@ -2,6 +2,7 @@ package filestream
 
 import (
 	"bytes"
+	"encoding/json"
 	"io"
 	"mime/multipart"
 	"os"
@@ -46,6 +47,34 @@ func TestWriteFilesToStreamAndReadFilesFromStream(t *testing.T) {
 	assert.Equal(t, file2Content, content)
 }
 
+func TestWriteFilesToStreamWithError(t *testing.T) {
+	// Create a temporary directory for the test
+	sourceDir := t.TempDir()
+
+	nonExistentFileName := "nonexistent.txt"
+	// Create a FileInfo with a non-existent file
+	file := &FileInfo{Name: nonExistentFileName, Path: filepath.Join(sourceDir, nonExistentFileName)}
+
+	// Create a buffer and a multipart writer
+	body := &bytes.Buffer{}
+	multipartWriter := multipart.NewWriter(body)
+
+	// Call WriteFilesToStream and expect an error
+	err := WriteFilesToStream(multipartWriter, []*FileInfo{file})
+	assert.NoError(t, err)
+
+	multipartReader := multipart.NewReader(body, multipartWriter.Boundary())
+	form, err := multipartReader.ReadForm(1024)
+	assert.NoError(t, err)
+
+	assert.Len(t, form.Value[ErrorType], 1)
+	var multipartErr MultipartError
+	assert.NoError(t, json.Unmarshal([]byte(form.Value[ErrorType][0]), &multipartErr))
+
+	assert.Equal(t, nonExistentFileName, multipartErr.FileName)
+	assert.NotEmpty(t, multipartErr.Error())
+}
+
 func simpleFileWriter(fileName string) (fileWriter []io.WriteCloser, err error) {
 	writer, err := os.Create(filepath.Join(targetDir, fileName))
 	if err != nil {