feat: add artifacts logic (#8)

backend/src/gateway/routers/artifacts.py

@@ -0,0 +1,75 @@
+import os
+from pathlib import Path
+
+from fastapi import APIRouter, HTTPException
+from fastapi.responses import FileResponse
+
+# Base directory for thread data (relative to backend/)
+THREAD_DATA_BASE_DIR = ".deer-flow/threads"
+
+# Virtual path prefix used in sandbox environments (without leading slash for URL path matching)
+VIRTUAL_PATH_PREFIX = "mnt/user-data"
+
+router = APIRouter(prefix="/api", tags=["artifacts"])
+
+
+def _resolve_artifact_path(thread_id: str, artifact_path: str) -> Path:
+    """Resolve a virtual artifact path to the actual filesystem path.
+
+    Args:
+        thread_id: The thread ID.
+        artifact_path: The virtual path (e.g., mnt/user-data/outputs/file.txt).
+
+    Returns:
+        The resolved filesystem path.
+
+    Raises:
+        HTTPException: If the path is invalid or outside allowed directories.
+    """
+    # Validate and remove virtual path prefix
+    if not artifact_path.startswith(VIRTUAL_PATH_PREFIX):
+        raise HTTPException(status_code=400, detail=f"Path must start with /{VIRTUAL_PATH_PREFIX}")
+    relative_path = artifact_path[len(VIRTUAL_PATH_PREFIX) :].lstrip("/")
+
+    # Build the actual path
+    base_dir = Path(os.getcwd()) / THREAD_DATA_BASE_DIR / thread_id / "user-data"
+    actual_path = base_dir / relative_path
+
+    # Security check: ensure the path is within the thread's user-data directory
+    try:
+        actual_path = actual_path.resolve()
+        base_dir = base_dir.resolve()
+        if not str(actual_path).startswith(str(base_dir)):
+            raise HTTPException(status_code=403, detail="Access denied: path traversal detected")
+    except (ValueError, RuntimeError):
+        raise HTTPException(status_code=400, detail="Invalid path")
+
+    return actual_path
+
+
+@router.get("/threads/{thread_id}/artifacts/{path:path}")
+async def get_artifact(thread_id: str, path: str) -> FileResponse:
+    """Get an artifact file by its path.
+
+    Args:
+        thread_id: The thread ID.
+        path: The artifact path with virtual prefix (e.g., mnt/user-data/outputs/file.txt).
+
+    Returns:
+        The file content as a FileResponse.
+
+    Raises:
+        HTTPException: 404 if file not found, 403 if access denied.
+    """
+    actual_path = _resolve_artifact_path(thread_id, path)
+
+    if not actual_path.exists():
+        raise HTTPException(status_code=404, detail=f"Artifact not found: {path}")
+
+    if not actual_path.is_file():
+        raise HTTPException(status_code=400, detail=f"Path is not a file: {path}")
+
+    return FileResponse(
+        path=actual_path,
+        filename=actual_path.name,
+    )