Prevent creating files with illegal characters in name (#7)

src/main/java/net/kemitix/trello/AttachmentDirectoryImpl.java

@@ -17,19 +17,22 @@ public class AttachmentDirectoryImpl implements AttachmentDirectory {
     private static final Logger LOG =
             Logger.getLogger(
                     AttachmentDirectoryImpl.class.getName());
+    private static final String ILLEGAL_CHARS = "[\\\\/:*?\"<>|]";
 
     private Path dir;
     private List<File> toDelete = new ArrayList<>();
 
     @PostConstruct
-    void init() throws IOException {
+    public void init() throws IOException {
         dir = Files.createTempDirectory("attachments");
         LOG.info("Attachments directory: " + dir);
     }
 
     @Override
     public File createFile(File fileName) {
-        File file = dir.resolve(fileName.getName()).toFile();
+        String cleanFilename = fileName.getName()
+                .replaceAll(ILLEGAL_CHARS, "");
+        File file = dir.resolve(cleanFilename).toFile();
         LOG.info("Created attachment: " + file);
         toDelete.add(file);
         return file;

src/test/java/net/kemitix/trello/AttachmentDirectoryImplTest.java

@@ -0,0 +1,32 @@
+package net.kemitix.trello;
+
+import org.assertj.core.api.WithAssertions;
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.DisplayName;
+import org.junit.jupiter.api.Test;
+
+import java.io.File;
+import java.io.IOException;
+
+public class AttachmentDirectoryImplTest
+        implements WithAssertions {
+
+    AttachmentDirectoryImpl attachmentDirectory =
+            new AttachmentDirectoryImpl();
+
+    @BeforeEach
+    public void setUp() throws IOException {
+        attachmentDirectory.init();
+    }
+
+    @Test
+    @DisplayName("Creates safe filenames")
+    public void createsSafeFilenames() {
+        //given
+        String filename = "x\\y";
+        //when
+        File result = attachmentDirectory.createFile(new File(filename));
+        //then
+        assertThat(result.getName()).isEqualTo("xy");
+    }
+}