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Go context.Context Best Practices

context.Context is Go's mechanism for propagating cancellation signals, deadlines, and request-scoped values across API boundaries and between goroutines. Think of it as the "session" of a request — it ties together every operation that belongs to the same unit of work.

Best Practices Summary

1. The same context MUST be propagated through the entire request lifecycle: HTTP handler → service → DB → external APIs
2. ctx MUST be the first parameter, named ctx context.Context
3. NEVER store context in a struct — pass explicitly through function parameters
4. NEVER pass nil context — use context.TODO() if unsure
5. cancel() MUST always be deferred immediately after WithCancel/WithTimeout/WithDeadline
6. context.Background() MUST only be used at the top level (main, init, tests)
7. Use context.TODO() as a placeholder when you know a context is needed but don't have one yet
8. NEVER create a new context.Background() in the middle of a request path
9. Context value keys MUST be unexported types to prevent collisions
10. Context values MUST only carry request-scoped metadata — NEVER function parameters
11. Use context.WithoutCancel (Go 1.21+) when spawning background work that must outlive the parent request