fix(core): fix path check with an invalid path (#394)

## AgentScope-Java Version

1.0.5-SNAPSHOT

## Description

* Fixes: #392 
 * fix path check with an invalid path

## Checklist

Please check the following items before code is ready to be reviewed.

- [x]  Code has been formatted with `mvn spotless:apply`
- [x]  All tests are passing (`mvn test`)
- [x]  Javadoc comments are complete and follow project conventions
- [x] Related documentation has been updated (e.g. links, examples,
etc.)
- [x]  Code is ready for review

Author: guanxuc

agentscope-core/src/main/java/io/agentscope/core/formatter/MediaUtils.java

@@ -26,6 +26,7 @@
 import java.net.URI;
 import java.net.URL;
 import java.nio.file.Files;
+import java.nio.file.InvalidPathException;
 import java.nio.file.Path;
 import java.util.Base64;
 import java.util.List;
@@ -175,10 +176,9 @@ public static String toFileProtocolUrl(String path) throws IOException {
      * @throws IOException If the resource read failed
      */
     public static InputStream urlToInputStream(String url) throws IOException {
-        Path path = Path.of(url);
-        if (Files.exists(path)) {
+        if (isFileExists(url)) {
             // Treat as local file
-            return Files.newInputStream(path);
+            return Files.newInputStream(Path.of(url));
         } else {
             // Treat as web URL
             return URI.create(url).toURL().openStream();
@@ -345,11 +345,18 @@ public static String getExtension(String path) {
 
     /**
      * Check if a file exists.
-     * @param path a local file path
-     * @return true: exists, false: not exists
+     * @param path a local file path or URL.
+     * @return true: exists, false: not exists or path is invalid
      */
     public static boolean isFileExists(String path) {
-        return Files.exists(Path.of(path));
+        if (!isLocalFile(path)) {
+            return false;
+        }
+        try {
+            return Files.exists(Path.of(path));
+        } catch (InvalidPathException e) {
+            return false;
+        }
     }
 
     /**

agentscope-core/src/test/java/io/agentscope/core/formatter/MediaUtilsTest.java

@@ -19,6 +19,7 @@
 import static org.junit.jupiter.api.Assertions.assertEquals;
 import static org.junit.jupiter.api.Assertions.assertFalse;
 import static org.junit.jupiter.api.Assertions.assertNotNull;
+import static org.junit.jupiter.api.Assertions.assertNull;
 import static org.junit.jupiter.api.Assertions.assertThrows;
 import static org.junit.jupiter.api.Assertions.assertTrue;
 
@@ -323,6 +324,20 @@ void testUrlToProtocolUrlWithUrl() throws IOException {
         assertEquals(url, protocolUrl);
     }
 
+    @Test
+    @DisplayName("Should return null or empty string with null or empty path")
+    void testUrlToProtocolUrlWithEmptyPath() throws IOException {
+        assertNull(null, MediaUtils.urlToProtocolUrl(null));
+        assertEquals("", MediaUtils.urlToProtocolUrl(""));
+    }
+
+    @Test
+    @DisplayName("Should return source path with invalid path")
+    void testUrlToProtocolUrlWithInvalidPath() throws IOException {
+        String path = "/path/to/file/<:|/\\>\u0000\b\n\t\0.txt";
+        assertEquals(path, MediaUtils.urlToProtocolUrl(path));
+    }
+
     @Test
     @DisplayName("To file protocol url with file path")
     void testToFileProtocolUrlWithFile() throws IOException {