Read a file only if it's inside the roots
You built is_path_allowed() in the last exercise — now put it to work. A read_file tool should never hand back a file the user didn't grant access to, so it has to check the path against the client's roots before reading anything.
FastMCP, Context, and Path are imported and the server mcp is created. Your is_path_allowed() is provided. run_tool(path) calls your tool through a real MCP client–server session: the connected client grants /tmp/mcp_allowed_root (holding notes.txt), and mcp_secret.txt sits outside it.
この演習はコースの一部です
Model Context Protocol: Advanced Topics
演習の手順
- Guard the read: call
is_path_allowed()with the requestedPathandctx, so the tool refuses when it returnsFalse. - When the path is allowed, read the file with
Path.read_text()and return its contents.
実践的なインタラクティブ演習
このサンプルコードを完成させて、この演習に挑戦してみましょう。
@mcp.tool()
async def read_file(path: str, ctx: Context) -> str:
requested = Path(path)
# Refuse paths outside the roots
if not await is_path_allowed(____, ctx):
return "Access denied: that path is outside the allowed roots."
# Read and return the file
return requested.____()
# Try a file inside the allowed root, and one outside it
inside = run_tool("/tmp/mcp_allowed_root/notes.txt")
outside = run_tool("/tmp/mcp_secret.txt")
print(inside)
print(outside)