Subscription Service

Small gRPC service for managing email subscriptions. This repo is used in a face‑to‑face interview. Keep it simple, ask clarifying questions, and implement the core tasks.

Quick Start

• cd subscription
• Optional env vars: DATABASE_URL (default sqlite://interview.db), PORT (default 50051), RUST_LOG (e.g., info)
• Run the server: cargo run
• Optional ping: grpcurl -plaintext -d '{"message":"hello"}' localhost:50051 subscription.SubscriptionService/Ping
• Optional tests: cargo test (there’s a skeleton in subscription/tests/assignment.rs)

Requirements: Rust + Cargo; SQLite 3 available on your system.

Your Tasks (≈30 min)

• List subscriptions

  • Implement list_subscriptions to return emails.
  • Extend the proto to support an optional email filter and pagination.

• Subscribe hardening

  • Validate email; map invalid input to InvalidArgument.
  • Make duplicate subscribe clearly idempotent (document behavior or return AlreadyExists).

• Unsubscribe

  • Remove by email; return NotFound if missing. Be explicit about case sensitivity.

Optional add‑ons (pick one if time allows):

• Domain stats RPC (counts grouped by domain)
• Server‑streaming export RPC
• Idempotency‑Key on Subscribe
• Simple rate‑limiting or request tracing interceptor

Clarify With Us

• Pagination: offset vs cursor token; expected stability across writes.
• Sorting: default order; deterministic tie‑breakers.
• Filtering: substring vs prefix; case sensitivity; normalization.
• Validation: how strict should email checks be; max lengths.
• Idempotency: duplicate subscribe/unsubscribe semantics and status codes.
• Page size: defaults and maximum caps.
• Error semantics: mapping DB and validation errors to gRPC codes; how much detail to expose.
• Observability: what to log (and not log), request IDs/tracing.

Paths You’ll Touch

• Proto: subscription/proto/api.proto
• Handler: subscription/src/handlers/api.rs
• Entrypoint: subscription/src/main.rs
• Descriptor (optional for Postman): subscription/src/api/gen/description.bin

AI tools are allowed. Aim for small, clean changes and sensible defaults.