500 Internal Server Error when POSTing to /api/auth/register

[149189]

Description

POST requests to the /api/auth/register endpoint return 500 Internal Server Error during registration. Server starts up fine and connects to MongoDB, but the register route fails at runtime. The error is not currently showing a full traceback in the response — we need the root cause (duplicate key, hashing error, JWT misconfiguration, etc.).

Reproduction Steps

1. Start the backend:

(venv) C:\Users\kaust\OneDrive\Documents\GitHub\Singularity\backend> py run.py

2. Send a registration request:

curl -v -X POST http://127.0.0.1:8000/api/auth/register \
  -H "Content-Type: application/json" \
  -d '{"email":"test@example.com","password":"Pass1234"}'

Observed Behavior

• The server prints startup logs and connects to MongoDB, then:

INFO:     127.0.0.1:62275 - "OPTIONS /api/auth/register HTTP/1.1" 200 OK
Registration error:
INFO:     127.0.0.1:62275 - "POST /api/auth/register HTTP/1.1" 500 Internal Server Error

• The client receives HTTP 500; no detailed traceback is currently visible in logs posted here.

Expected Behavior

• Successful registration returns 201 or 200 with created user id / token.
• If the request is invalid (e.g., duplicate email), return 400 with a helpful error message (e.g., "Email already registered").
• Full traceback logged to server console (in dev) for easier debugging.

Environment

• OS: Windows (logs from C:\Users\kaust\OneDrive\...)
• Python: running py run.py from venv
• Server: Uvicorn (auto reload)
• Database: MongoDB (connected; DB name: singularity)
• Stack: FastAPI + Mongo driver (Motor )

Logs

(venv) C:\Users\kaust\OneDrive\Documents\GitHub\Singularity\backend>py run.py
INFO:     Will watch for changes in these directories: ['C:\\Users\\kaust\\OneDrive\\Documents\\GitHub\\Singularity\\backend']
INFO:     Uvicorn running on http://0.0.0.0:8000 (Press CTRL+C to quit)
INFO:     Started reloader process [31464] using StatReload
INFO:     Started server process [22052]
INFO:     Waiting for application startup.
✅ Connected to MongoDB: singularity
📊 Database indexes created
INFO:     Application startup complete.
INFO:     127.0.0.1:62275 - "OPTIONS /api/auth/register HTTP/1.1" 200 OK
Registration error:
INFO:     127.0.0.1:62275 - "POST /api/auth/register HTTP/1.1" 500 Internal Server Error

Possible Root Causes (prioritized)

• Duplicate key error on insert (unique index on email) → should be handled and returned as 400.
• Missing / incorrectly loaded environment variables (e.g., JWT_SECRET) causing JWT encoding to fail.
• Password hashing error (wrong type passed to bcrypt/passlib).
• BSON / ObjectId conversion errors when creating/reading IDs.
• Unhandled exceptions from DB driver (Motor / PyMongo network or schema errors).
• Any other unhandled runtime exception in the register handler.

Suggested Immediate Debugging Steps

1. Enable detailed exceptions in dev
   Set FastAPI debug for local debugging:

   app = FastAPI(debug=True)

2. Enable uvicorn debug logging when launching:

   uvicorn run:app --reload --log-level debug

   (Or ensure py run.py passes log_level="debug" to uvicorn.run.)

3. Add exception logging to the register route to capture full traceback:

import logging, traceback
logger = logging.getLogger("uvicorn.error")

try:
    # handler logic...
except Exception:
    logger.exception("Unhandled exception during registration")
    traceback.print_exc()
    raise HTTPException(status_code=500, detail="Internal Server Error")

4. Test with a unique email to rule out DuplicateKeyError. If failure only occurs for certain emails, inspect the unique index:

   • Run db.users.getIndexes() in Mongo shell or check via MongoDB Compass.

5. Verify environment variables like JWT_SECRET are set and not None. Add an early runtime check:

import os
if not os.environ.get("JWT_SECRET"):
    raise RuntimeError("JWT_SECRET not set")

Quick Fix Examples (to handle common errors)

• Catch duplicate key:

from pymongo.errors import DuplicateKeyError

try:
    await db.users.insert_one(user_doc)
except DuplicateKeyError:
    raise HTTPException(status_code=400, detail="Email already registered")

• Ensure password hashing receives bytes and returns a string:

hashed = bcrypt.hashpw(password.encode('utf-8'), bcrypt.gensalt())
user_doc['password'] = hashed.decode('utf-8')

• Validate jwt.encode uses a valid secret:

import os
SECRET_KEY = os.environ.get('JWT_SECRET')
if not SECRET_KEY:
    raise RuntimeError("JWT_SECRET not set")
token = jwt.encode({"user_id": user_id}, SECRET_KEY, algorithm="HS256")

Acceptance Criteria (for closing this issue)

• The register endpoint returns 200/201 for valid new registrations.
• Duplicate registration returns 400 with a descriptive message.
• Any server exceptions are logged with full traceback during development.
• Add a unit/integration test covering registration success and duplicate-email case.