DEV Community: Odinaka Robert Nnamani

If-Match: two curls, one 412

Odinaka Robert Nnamani — Fri, 28 Aug 2026 13:47:14 +0000

Two tabs save the same note. Last write wins. The first tab's words vanish.

Two terminals on your laptop are two tabs. You GET. You type. You PUT.

Save this as if-match-server.mjs. Run node if-match-server.mjs.

import http from "node:http";

let note = { text: "hello" };
let etag = "1";

http.createServer((req, res) => {
  const reply = (status, body) => {
    const json = JSON.stringify(body);
    res.writeHead(status, {
      "Content-Type": "application/json",
      ETag: `"${etag}"`,
      "Content-Length": Buffer.byteLength(json),
    });
    res.end(json);
  };

  if (req.url !== "/note") return reply(404, { error: "not found" });
  if (req.method === "GET") return reply(200, { text: note.text, etag });
  if (req.method !== "PUT") return reply(405, { error: "method not allowed" });

  let raw = "";
  req.on("data", (c) => (raw += c));
  req.on("end", () => {
    const ifMatch = req.headers["if-match"];
    if (ifMatch && ifMatch !== `"${etag}"`) {
      return reply(412, { error: "Precondition Failed" });
    }
    const body = JSON.parse(raw || "{}");
    note = { text: body.text ?? note.text };
    etag = String(Number(etag) + 1);
    reply(200, { text: note.text, etag });
  });
}).listen(3456, "127.0.0.1", () => {
  console.log("http://127.0.0.1:3456/note");
});

The server holds one note at /note. GET returns the JSON and an ETag header. PUT with no extra header always overwrites. That overwrite is the mistake.

Last write wins

Fetch the note.

curl -i http://127.0.0.1:3456/note

I ran that. This came back:

HTTP/1.1 200 OK
Content-Type: application/json
ETag: "1"
Content-Length: 27

{"text":"hello","etag":"1"}

That is tab one. It still has hello and ETag "1". Tab one starts editing. It does not send the ETag back yet.

Tab two saves a different sentence. No extra header. This is the second tab hitting save.

curl -i -X PUT http://127.0.0.1:3456/note \
  -H 'Content-Type: application/json' \
  -d '{"text":"from tab two"}'

HTTP/1.1 200 OK
Content-Type: application/json
ETag: "2"
Content-Length: 34

{"text":"from tab two","etag":"2"}

GET the note again.

curl -i http://127.0.0.1:3456/note

HTTP/1.1 200 OK
Content-Type: application/json
ETag: "2"
Content-Length: 34

{"text":"from tab two","etag":"2"}

hello is gone. Tab two wrote last, so tab two won. Tab one still shows hello on screen. The server does not. If tab one saves now with no extra header, it will wipe tab two the same way.

Send If-Match

Tab one still holds ETag "1". Send that token on the PUT. Do not write without it.

curl -i -X PUT http://127.0.0.1:3456/note \
  -H 'Content-Type: application/json' \
  -H 'If-Match: "1"' \
  -d '{"text":"from tab one"}'

I ran that. This came back:

HTTP/1.1 412 Precondition Failed
Content-Type: application/json
ETag: "2"
Content-Length: 31

{"error":"Precondition Failed"}

GET the note.

curl -i http://127.0.0.1:3456/note

HTTP/1.1 200 OK
Content-Type: application/json
ETag: "2"
Content-Length: 34

{"text":"from tab two","etag":"2"}

The stale write stopped. The stored text did not change. from tab one is not on the server.

Now send the ETag the last GET returned.

curl -i -X PUT http://127.0.0.1:3456/note \
  -H 'Content-Type: application/json' \
  -H 'If-Match: "2"' \
  -d '{"text":"from tab two, edited"}'

HTTP/1.1 200 OK
Content-Type: application/json
ETag: "3"
Content-Length: 42

{"text":"from tab two, edited","etag":"3"}

The write went through. The ETag bumped to "3".

If-Match means only do this if the resource still matches this ETag. ETag is the version token the server sent on GET. If-Match is a request header. Comparison is strong, byte-for-byte. A weak tag like W/"1" never matches it. This is not If-None-Match. If-None-Match is the cache shortcut that returns 304.

No header: last write wins.
A stale header returns 412 Precondition Failed.
The body stays put.
A current header returns 200, and the version moves.

GET, then PUT with that ETag. That is the pair. If someone else wrote in between, you get 412 instead of a silent overwrite.

Check

Change the note. Replay an old If-Match. Confirm 412. Confirm the body did not revert.

I replayed If-Match: "2" after the ETag was already "3".

curl -i -X PUT http://127.0.0.1:3456/note \
  -H 'Content-Type: application/json' \
  -H 'If-Match: "2"' \
  -d '{"text":"should not land"}'

HTTP/1.1 412 Precondition Failed
Content-Type: application/json
ETag: "3"
Content-Length: 31

{"error":"Precondition Failed"}

GET:

curl -i http://127.0.0.1:3456/note

HTTP/1.1 200 OK
Content-Type: application/json
ETag: "3"
Content-Length: 42

{"text":"from tab two, edited","etag":"3"}

should not land is not in the body. The old token did not rewind the note.

If this server is already at ETag "3", stop it and run node if-match-server.mjs again.
GET. PUT with the current ETag. Then replay the previous one.
You should see 412 again. The text should stay on the current sentence.

After the first 412, is the note still from tab two?

Project Blog : Intelligent Writing Assistant

Odinaka Robert Nnamani — Wed, 06 Nov 2024 15:59:28 +0000

Intelligent Writing Assistant:

The intelligent writing assistant aims to help brainstorm and craft excellent writing material for personal fun, stories, or a business proposal. The use of writing is endless and can’t be overemphasized. I worked on this project alone, both the web app’s backend and frontend sides. I executed every feature in the app—the user sign-in/login experience, user authentication and document creation, and everything in between—and made sure to structure how it works.

As an engineering problem, I sourced the Gemini API in the backend program so that users can be offered a wide range of writing inputs, auto-generation, corrections, and whatever writing challenge they might want to try out

I’ve had two different ideas for this portfolio project. Each one is as ambitious as the others. Each one fails just as much as the other. This writing assistant is the third idea I’ve come up with. Honestly, at first, I was blank after the code compiler I was working on had a segmentation fault,’ and I was running out of time to debug so I could present something as a portfolio project. Then came the 2D game idea: Maze Runner. The same thing happened. I had a segmentation fault, and the worst was that even the tutorials had segmentation faults when I tried compiling them verbatim on my system. Finally, the Gemini API competition came, and I didn’t know what to do. Yes, I’ve always liked writing stories, but everything has been new to me in this coding work, so I didn’t know what to do with the API. This project sums up the feeling of never stopping and reinforces that I enjoy doing anything. Above all, I’m doing something I’ve always wanted to learn, and I can follow through structurally with the logic of the code. It’s exciting and encourages me to keep going despite bugs or errors. I made this app, and I’m proud of it. I have many life lessons to incorporate into my daily life from now on! It was nice!

structure of the writing_assistant Directory

intelligent-writing-assistant/
├── backend/
│ ├── alembic/
│ │ ├── versions/
│ │ └── env.py
│ │ └── script.py.mako
│ ├── app/
│ │ ├── init.py
│ │ ├── main.py
│ │ ├── models.py
│ │ ├── schemas.py
│ │ ├── database.py
│ │ ├── services/
│ │ │ ├── init.py
│ │ │ ├── writing_service.py
│ │ ├── routers/
│ │ │ ├── init.py
│ │ │ ├── auth.py
│ │ │ ├── writing.py
│ │ ├── utils/
│ │ ├── init.py
│ │ ├── security.py
│ ├── .env.local
│ ├── requirements.txt
│ ├── Dockerfile
│ ├── docker-compose.yml
│ └── alembic.ini
├── frontend/
│ ├── public/
│ │ ├── index.html
│ ├── src/
│ │ ├── components/
│ │ │ ├── Navbar.js
│ │ │ ├── Footer.js
│ │ │ ├── TextEditor.js
│ │ │ ├── SuggestionsList.js
│ │ ├── pages/
│ │ │ ├── Home.js
│ │ │ ├── Dashboard.js
│ │ │ ├── Editor.js
│ │ │ ├── Login.js
│ │ │ ├── Signup.js
│ │ ├── redux/
│ │ │ ├── store.js
│ │ │ ├── actions.js
│ │ │ ├── reducers.js
│ │ ├── services/
│ │ │ ├── api.js
│ │ ├── App.js
│ │ ├── index.js
│ ├── .env
│ ├── package.json
│ ├── Dockerfile
│ ├── docker-compose.yml
├── .gitignore
└── README.md

Backend (Python with FastAPI)

Frameworks and Libraries:

FastAPI: For building the API endpoints.
SQLAlchemy: For ORM (Object-Relational Mapping) with PostgreSQL.
Alembic: For database migrations.
Pydantic: For data validation.
JWT (PyJWT): For authentication.
Uvicorn: For serving the FastAPI application.
HTTPX: This is for making external API requests to the Gemini API.

Frontend (JavaScript with React.js)

Frameworks and Libraries:

React.js: For building the user interface.
Axios: For making HTTP requests to the backend.
React Router: This is used to handle navigation within the application.
Redux: For state management, if the application grows in complexity.
Formik: For form handling.
Yup, For form validation.
Quill.js: For the rich text editor component.

Features already implemented:

User authentication and authorization:
• Functionality: Registers a new user, hashes the password, and stores the user details in the database.

Document Creation and Retrieval:
• Functionality: Creates a new document with the provided title and content, associating it with the authenticated user.

Retrieves the document by ID if it exists and belongs to the authenticated user.

Unicorn is simple to use if you get the way it works. It happened that PostgreSQL interacts with Uvicorn to start up our app based on my file integration and structure. I haven’t used PostgreSQL before, so I went in to figure it out. It’s mainly like MySQL (looking back now). Even though I had an excellent Puhton script that integrated all parts of the code correctly, I didn’t install PostgreSQL and kept trying to start my web app. Errors and errors later, I figured it out and installed it; next was no database error, then no user error and password. It took time, but I finally configured the database, and now it connects seamlessly to the default port. Using Cors, the unicorn can share resources across PostgreSQL and ensure my web app loads up with the proper data setup.

Working on this project, I realized having some personal conviction and resolve to summon the tough stuff is essential. I struggle with concepts and understanding libraries and frameworks and what to use and when to use each. They’re all jumbled up in my head. It’s expected of a learner, but it’s frustrating not to realize simple bugs and solutions. But it’s something time will show me as I code more projects that are valuable to me.

Technically speaking, bugs are the only way you see things differently and ultimately grow, even though they can be very annoying and energy-draining for the most part. I wouldn’t do anything different except push myself to sit through the tough, unpredictable moments no matter what and keep trying to get through it all until it makes sense.

This project has reaffirmed my belief that coding, like writing, is a challenging yet profoundly satisfying endeavor. The process of meticulously structuring and refining each component of the project has been a joy. These moments remind me why I’m a tech enthusiast and why I'm committed to this path despite its challenges.

I’m a tech enthusiast, and I enjoy coding and writing as well. It’s a very specific niche that has always felt right. I know there’s a lot to come if I keep this path despite its challenges and setbacks.

Github: https://github.com/Robertpaschal/Portfolio_Project.git

LinkedIn: (31) Odinaka (Robert) Nnamani | LinkedIn