Filesystem APIs

Problem

What becomes confusing, fragile, or impossible without understanding filesystem APIs? This lesson answers that through explanation, a worked example, two runnable exercises, and a reference solution. No teacher-supplied worksheet is required.

Node applied JavaScript’s event-driven model to servers and command-line programs, pairing a single process with nonblocking I/O.

Concept explanation

Filesystem APIs belongs to “Files, streams, and HTTP”. Node files, streams, HTTP, routing, and SQLite form one-process backend with explicit flow control.

For filesystem APIs, trace concrete input, state transition, output, and failure through a server-side runtime boundary involving process lifecycle, filesystem or network I/O, streams, and capacity.

One process owns an event loop, module graph, heap, handles, streams, signals, and explicit boundaries to the OS and network. Apply that model to supplied normal, boundary, and failure cases; each case below names its input and expected evidence.

Example bank

Compare normal, boundary, failure, and cross-layer cases. Predict each observation before revealing the explanation.

Worked example

Start from supplied server.mjs. Focus: Serve GET/POST notes backed by SQLite and stream export.

1. Run: node server.mjs > server.log 2>&1 & server_pid=$!; trap 'kill $server_pid' EXIT; sleep 1; curl -i http://127.0.0.1:3000/
2. Save baseline evidence. Use Node inspector, active handles, process signals, curl, CPU profiles, heap snapshots, and OS process tools.
3. Boundary case: Upload body larger than one chunk and apply backpressure.
4. Failure case: Send malformed JSON and failed query; return useful status without process crash.

RESULT
curl trace proves routes, persistence, streaming, validation, and error mapping. Starter-level baseline: Server prints its URL; curl receives 200, JSON content type, correct byte length, and a body containing topic and GET method.

Starter material

Create server.mjs, paste this exact content, then run the command below.

import { createServer } from "node:http";

const server = createServer((request, response) => {
  const body = JSON.stringify({ topic: "filesystem APIs", method: request.method });
  response.writeHead(200, { "content-type": "application/json", "content-length": Buffer.byteLength(body) });
  response.end(body);
});

server.listen(3000, "127.0.0.1", () => console.log("http://127.0.0.1:3000"));

STOP / CLEANUPSupplied command traps shell exit and stops server. If running server alone, press Ctrl+C.

Independent exercise

Find the boundary: filesystem APIs

1. Create second case from blank file: Upload body larger than one chunk and apply backpressure.
2. Then create controlled failure: Send malformed JSON and failed query; return useful status without process crash.
3. Use Node inspector · curl · SQLite CLI · process tools to prove behavior, then repair controlled failure.
4. Compare result against supplied acceptance checks and reference approach before marking complete.

Expected result

• curl trace proves routes, persistence, streaming, validation, and error mapping.
• Server prints its URL; curl receives 200, JSON content type, correct byte length, and a body containing topic and GET method.
• Controlled filesystem APIs failure produces captured evidence; repair restores stated invariant without hiding error.

Hints

Solution

Attempt both exercises before opening reference approach.