feat(fuzz): enhance MultiPartForm with metadata APIs (#6486)

* feat(fuzz): enhance `MultiPartForm` with metadata APIs

* add `SetFileMetadata`/`GetFileMetadata` APIs for
  file metadata management.
* implement RFC-2046 boundary validation
  (max 70 chars).
* add boundary validation in `Decode` method.

* fix `filesMetadata` initialization.
* fix mem leak by removing defer from file reading
  loop.
* fix file metadata overwriting by storing first
  file's metadata instead of last.

Closes #6405, #6406

Signed-off-by: Dwi Siswanto <git@dw1.io>

* chore(fuzz): satisfy lint errs

Signed-off-by: Dwi Siswanto <git@dw1.io>

---------

Signed-off-by: Dwi Siswanto <git@dw1.io>

pkg/fuzz/dataformat/multipart.go

@@ -27,7 +27,29 @@ var (
 
 // NewMultiPartForm returns a new MultiPartForm encoder
 func NewMultiPartForm() *MultiPartForm {
-	return &MultiPartForm{}
+	return &MultiPartForm{
+		filesMetadata: make(map[string]FileMetadata),
+	}
+}
+
+// SetFileMetadata sets the file metadata for a given field name
+func (m *MultiPartForm) SetFileMetadata(fieldName string, metadata FileMetadata) {
+	if m.filesMetadata == nil {
+		m.filesMetadata = make(map[string]FileMetadata)
+	}
+
+	m.filesMetadata[fieldName] = metadata
+}
+
+// GetFileMetadata gets the file metadata for a given field name
+func (m *MultiPartForm) GetFileMetadata(fieldName string) (FileMetadata, bool) {
+	if m.filesMetadata == nil {
+		return FileMetadata{}, false
+	}
+
+	metadata, exists := m.filesMetadata[fieldName]
+
+	return metadata, exists
 }
 
 // IsType returns true if the data is MultiPartForm encoded
@@ -125,16 +147,24 @@ func (m *MultiPartForm) ParseBoundary(contentType string) error {
 	if m.boundary == "" {
 		return fmt.Errorf("no boundary found in the content type")
 	}
+
+	// NOTE(dwisiswant0): boundary cannot exceed 70 characters according to
+	// RFC-2046.
+	if len(m.boundary) > 70 {
+		return fmt.Errorf("boundary exceeds maximum length of 70 characters")
+	}
+
 	return nil
 }
 
 // Decode decodes the data from MultiPartForm format
 func (m *MultiPartForm) Decode(data string) (KV, error) {
+	if m.boundary == "" {
+		return KV{}, fmt.Errorf("boundary not set, call ParseBoundary first")
+	}
+
 	// Create a buffer from the string data
 	b := bytes.NewBufferString(data)
-	// The boundary parameter should be extracted from the Content-Type header of the HTTP request
-	// which is not available in this context, so this is a placeholder for demonstration.
-	// You will need to pass the actual boundary value to this function.
 	r := multipart.NewReader(b, m.boundary)
 
 	form, err := r.ReadForm(32 << 20) // 32MB is the max memory used to parse the form
@@ -153,30 +183,44 @@ func (m *MultiPartForm) Decode(data string) (KV, error) {
 			result.Set(key, values[0])
 		}
 	}
-	m.filesMetadata = make(map[string]FileMetadata)
+
+	if m.filesMetadata == nil {
+		m.filesMetadata = make(map[string]FileMetadata)
+	}
+
 	for key, files := range form.File {
 		fileContents := []interface{}{}
+		var fileMetadataList []FileMetadata
+
 		for _, fileHeader := range files {
 			file, err := fileHeader.Open()
 			if err != nil {
 				return KV{}, err
 			}
-			defer func() {
-				_ = file.Close()
-			}()
 
 			buffer := new(bytes.Buffer)
 			if _, err := buffer.ReadFrom(file); err != nil {
+				_ = file.Close()
+
 				return KV{}, err
 			}
+			_ = file.Close()
+
 			fileContents = append(fileContents, buffer.String())
 
-			m.filesMetadata[key] = FileMetadata{
+			fileMetadataList = append(fileMetadataList, FileMetadata{
 				ContentType: fileHeader.Header.Get("Content-Type"),
 				Filename:    fileHeader.Filename,
-			}
+			})
 		}
+
 		result.Set(key, fileContents)
+
+		// NOTE(dwisiswant0): store the first file's metadata instead of the
+		// last one
+		if len(fileMetadataList) > 0 {
+			m.filesMetadata[key] = fileMetadataList[0]
+		}
 	}
 	return KVOrderedMap(&result), nil
 }

pkg/fuzz/dataformat/multipart_test.go

@@ -240,3 +240,131 @@ Python
 	assert.Contains(t, documentsArray, "fake_pdf_content_1")
 	assert.Contains(t, documentsArray, "fake_pdf_content_2")
 }
+
+func TestMultiPartForm_SetGetFileMetadata(t *testing.T) {
+	form := NewMultiPartForm()
+	metadata := FileMetadata{
+		ContentType: "image/jpeg",
+		Filename:    "test.jpg",
+	}
+	form.SetFileMetadata("avatar", metadata)
+
+	// Test GetFileMetadata for existing field
+	retrievedMetadata, exists := form.GetFileMetadata("avatar")
+	assert.True(t, exists)
+	assert.Equal(t, metadata.ContentType, retrievedMetadata.ContentType)
+	assert.Equal(t, metadata.Filename, retrievedMetadata.Filename)
+
+	// Test GetFileMetadata for non-existing field
+	_, exists = form.GetFileMetadata("nonexistent")
+	assert.False(t, exists)
+}
+
+func TestMultiPartForm_FilesMetadataInitialization(t *testing.T) {
+	form := NewMultiPartForm()
+	assert.NotNil(t, form.filesMetadata)
+
+	metadata := FileMetadata{
+		ContentType: "text/plain",
+		Filename:    "test.txt",
+	}
+	form.SetFileMetadata("file", metadata)
+
+	retrievedMetadata, exists := form.GetFileMetadata("file")
+	assert.True(t, exists)
+	assert.Equal(t, metadata, retrievedMetadata)
+}
+
+func TestMultiPartForm_BoundaryValidation(t *testing.T) {
+	form := NewMultiPartForm()
+
+	// Test valid boundary
+	err := form.ParseBoundary("multipart/form-data; boundary=testboundary")
+	assert.NoError(t, err)
+	assert.Equal(t, "testboundary", form.boundary)
+
+	// Test missing boundary
+	err = form.ParseBoundary("multipart/form-data")
+	assert.Error(t, err)
+	assert.Contains(t, err.Error(), "no boundary found")
+
+	// Test boundary too long (over 70 characters)
+	longBoundary := "multipart/form-data; boundary=" + string(make([]byte, 71))
+	for i := range longBoundary[len("multipart/form-data; boundary="):] {
+		longBoundary = longBoundary[:len("multipart/form-data; boundary=")+i] + "a" + longBoundary[len("multipart/form-data; boundary=")+i+1:]
+	}
+
+	err = form.ParseBoundary(longBoundary)
+	assert.Error(t, err)
+	assert.Contains(t, err.Error(), "boundary exceeds maximum length")
+}
+
+func TestMultiPartForm_DecodeRequiresBoundary(t *testing.T) {
+	form := NewMultiPartForm()
+
+	// Decode should fail if boundary is not set
+	_, err := form.Decode("some data")
+	assert.Error(t, err)
+	assert.Contains(t, err.Error(), "boundary not set")
+}
+
+func TestMultiPartForm_MultipleFilesMetadata(t *testing.T) {
+	form := NewMultiPartForm()
+	form.boundary = "----WebKitFormBoundaryMultiFileTest"
+
+	// Test with multiple files having the same field name
+	multipartData := `------WebKitFormBoundaryMultiFileTest
+Content-Disposition: form-data; name="documents"; filename="file1.txt"
+Content-Type: text/plain
+
+content1
+------WebKitFormBoundaryMultiFileTest
+Content-Disposition: form-data; name="documents"; filename="file2.txt"
+Content-Type: text/plain
+
+content2
+------WebKitFormBoundaryMultiFileTest--
+`
+
+	decoded, err := form.Decode(multipartData)
+	require.NoError(t, err)
+
+	// Verify files are decoded correctly
+	documents := decoded.Get("documents")
+	require.NotNil(t, documents)
+	documentsArray, ok := documents.([]interface{})
+	require.True(t, ok)
+	require.Len(t, documentsArray, 2)
+	assert.Contains(t, documentsArray, "content1")
+	assert.Contains(t, documentsArray, "content2")
+
+	// Verify metadata for the field exists (should be from the first file)
+	metadata, exists := form.GetFileMetadata("documents")
+	assert.True(t, exists)
+	assert.Equal(t, "text/plain", metadata.ContentType)
+	assert.Equal(t, "file1.txt", metadata.Filename) // Should be from first file, not last
+}
+
+func TestMultiPartForm_SetFileMetadataWithNilMap(t *testing.T) {
+	form := &MultiPartForm{}
+
+	// SetFileMetadata should handle nil filesMetadata
+	metadata := FileMetadata{
+		ContentType: "application/pdf",
+		Filename:    "document.pdf",
+	}
+	form.SetFileMetadata("doc", metadata)
+
+	// Should be able to retrieve the metadata
+	retrievedMetadata, exists := form.GetFileMetadata("doc")
+	assert.True(t, exists)
+	assert.Equal(t, metadata, retrievedMetadata)
+}
+
+func TestMultiPartForm_GetFileMetadataWithNilMap(t *testing.T) {
+	form := &MultiPartForm{}
+
+	// GetFileMetadata should handle nil filesMetadata gracefully
+	_, exists := form.GetFileMetadata("anything")
+	assert.False(t, exists)
+}