fix(a2a-server): ensure task cancellation aborts execution loop (#28316)

packages/a2a-server/src/utils/path_utils.ts

@@ -0,0 +1,62 @@
+/**
+ * @license
+ * Copyright 2026 Google LLC
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+import * as fs from 'node:fs';
+import * as path from 'node:path';
+import { resolveToRealPath, isSubpath } from '@google/gemini-cli-core';
+
+/**
+ * Validates a workspace path to prevent path traversal attacks.
+ *
+ * @param workspacePath The path to validate.
+ * @param allowedRoot The root directory the path must be within. Defaults to CWD.
+ * @returns The resolved, safe path.
+ * @throws An error if the path is invalid or outside the allowed root.
+ */
+export async function validateWorkspacePath(
+  workspacePath?: string,
+  allowedRoot: string = process.cwd(),
+): Promise<string> {
+  const trimmedPath = workspacePath?.trim();
+  if (!trimmedPath) {
+    return resolveToRealPath(allowedRoot);
+  }
+
+  if (trimmedPath.includes('\0')) {
+    throw new Error('Security violation: Null byte detected in path.');
+  }
+
+  try {
+    const canonicalAllowedRoot = resolveToRealPath(allowedRoot);
+    const resolvedWorkspacePath = path.resolve(
+      canonicalAllowedRoot,
+      trimmedPath,
+    );
+    const canonicalWorkspacePath = resolveToRealPath(resolvedWorkspacePath);
+
+    // Check if the resolved path is within the allowed root directory
+    if (
+      canonicalWorkspacePath !== canonicalAllowedRoot &&
+      !isSubpath(canonicalAllowedRoot, canonicalWorkspacePath)
+    ) {
+      throw new Error(
+        `Security violation: The path "${trimmedPath}" is outside the allowed root directory.`,
+      );
+    }
+
+    const stats = await fs.promises.stat(canonicalWorkspacePath);
+    if (!stats.isDirectory()) {
+      throw new Error(`The path "${trimmedPath}" is not a directory.`);
+    }
+
+    return canonicalWorkspacePath;
+  } catch (e) {
+    if (e instanceof Error && 'code' in e && e.code === 'ENOENT') {
+      throw new Error(`The path "${trimmedPath}" does not exist.`);
+    }
+    throw e; // Re-throw other errors
+  }
+}