⚙️ Backend Dev

How does Socket.IO handle WebSocket failures with fallbacks?

Transports are communication protocols, WebSocket is primary, long-polling is fallback, client auto-detects and downgrades.

How do Socket.IO rooms organize client communication?

Rooms group sockets for targeted broadcasting, socket can join multiple rooms, emit to room broadcasts to all members.

easy1 min read

How to add Socket.IO to an Express application?

Create HTTP server with express(), attach Socket.IO to it, listen on server not app, define event handlers.

easy1 min read

Socket.IO emit methods: socket, io, broadcast differences?

Socket.emit() sends to one client, broadcast.emit() to all except sender, io.emit() to all.

easy1 min read

HTTP request-response versus WebSocket connections?

HTTP is request-initiated, pull-based, client waits for response. WebSocket is persistent, bidirectional, either side sends data anytime.

How do you handle errors across piped streams safely?

Pipe connects streams but errors don't auto-propagate, must listen on each stream. Use pipeline() helper for auto-cleanup.

postMessage vs SharedArrayBuffer in worker_threads tradeoffs?

Structured cloning copies data, SharedArrayBuffer shares memory.

How does Node.js cluster module enable zero-downtime restarts?

Master-worker architecture, graceful shutdown of old workers, routing new requests to new workers.

Choosing Uvicorn worker count in production

Workers exist to use multiple CPU cores past the GIL; a common starting point ties count to cores, then you tune by load testing, balancing CPU and memory (each worker is a full copy) against connection-pool…

Reading the full response body in middleware

Responses stream as multiple body messages and headers go first, so you cannot add a header after seeing the body; you must buffer all chunks, compute the hash, set the header, then resend.

OAuth2 social login with your own JWT

A login endpoint redirects to the provider with a state param, a callback exchanges the code for the provider token, you fetch the user profile, upsert the local user, then mint your own JWT.

selectinload vs joinedload for eager loading

Use eager loading options to avoid lazy N+1; joinedload uses a single JOIN (good for many-to-one) but can fan out rows on collections; selectinload issues a second IN query (better for one-to-many).

Feature-based vs layer-based project structure

Layer-based groups by technical role and is simple early but scatters a feature across folders; feature-based groups by domain, improving cohesion and ownership at the cost of some duplication and…

Streaming large file downloads efficiently

Use StreamingResponse with a generator that yields chunks (or FileResponse for an on-disk file), set media_type and a Content-Disposition header, so memory stays flat regardless of file size.

Pydantic computed fields in response models

A @computed_field decorated property is excluded from input and validation but included in serialization and the OpenAPI schema, ideal for values like full_name derived from other fields.

Mapping camelCase JSON to snake_case Pydantic fields

Set an alias_generator (to_camel) plus populate_by_name in model config, accept aliases on input, and serialize with by_alias=True so responses come out camelCase.

Pydantic BaseModel vs dataclasses in FastAPI

BaseModel validates and coerces data at runtime, parses and serializes JSON, integrates with OpenAPI schema generation, and supports rich validators; dataclasses only store data with no validation.

Testing a DB endpoint via dependency override

Use app.dependency_overrides to swap the real get_db for one yielding a test database session, run against a disposable SQLite or test Postgres, and assert through TestClient.

Secure refresh token flow for access renewal

Short-lived access token, longer-lived refresh token stored server-side, a refresh endpoint that validates and rotates the refresh token issuing a new pair.