HTTP server

Problem

What becomes confusing, fragile, or impossible without understanding HTTP server? 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

HTTP server belongs to “Files, streams, and HTTP”. HTTP server must be connected to layer below by tracing representation, ownership, control, and failure. Node files, streams, HTTP, routing, and SQLite form one-process backend with explicit flow control.

For HTTP server, 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: Trace HTTP server end-to-end while running: 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: At every HTTP server boundary, label owner and representation during: Upload body larger than one chunk and apply backpressure.
4. Failure case: Locate first layer where evidence diverges during: Send malformed JSON and failed query; return useful status without process crash.

RESULT
Trace explains curl trace proves routes, persistence, streaming, validation, and error mapping. without skipping any conversion, queue, process, protocol, or storage boundary. 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: "HTTP server", 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

Remove one abstraction: HTTP server

1. Create second case from blank file: At every HTTP server boundary, label owner and representation during: Upload body larger than one chunk and apply backpressure.
2. Then create controlled failure: Locate first layer where evidence diverges during: 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

• Trace explains curl trace proves routes, persistence, streaming, validation, and error mapping. without skipping any conversion, queue, process, protocol, or storage boundary.
• Server prints its URL; curl receives 200, JSON content type, correct byte length, and a body containing topic and GET method.
• Controlled HTTP server failure produces captured evidence; repair restores stated invariant without hiding error.

Hints

Solution

Attempt both exercises before opening reference approach.