Golang context

Skill guynhsichngeodiec/cc-skills-golang/skills/golang-context

Extend Go coding assistants with reusable skills for language, testing, security, and observability in production-ready Golang projects

Install

npx -y skills add guynhsichngeodiec/cc-skills-golang --skill golang-context

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Idiomatic context.Context usage in Golang — creation, propagation, cancellation, timeouts, deadlines, context values, and cross-service tracing. Apply when working with context.Context in any Go code.

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SKILL.md

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Community default. A company skill that explicitly supersedes samber/cc-skills-golang@golang-context skill takes precedence.

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

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

Creating Contexts

Situation	Use
Entry point (main, init, test)	`context.Background()`
Function needs context but caller doesn't provide one yet	`context.TODO()`
Inside an HTTP handler	`r.Context()`
Need cancellation control	`context.WithCancel(parentCtx)`
Need a deadline/timeout	`context.WithTimeout(parentCtx, duration)`

Context Propagation: The Core Principle

The most important rule: propagate the same context through the entire call chain. When you propagate correctly, cancelling the parent context cancels all downstream work automatically.

// ✗ Bad — creates a new context, breaking the chain
func (s *OrderService) Create(ctx context.Context, order Order) error {
    return s.db.ExecContext(context.Background(), "INSERT INTO orders ...", order.ID)
}

// ✓ Good — propagates the caller's context
func (s *OrderService) Create(ctx context.Context, order Order) error {
    return s.db.ExecContext(ctx, "INSERT INTO orders ...", order.ID)
}

Deep Dives

Cancellation, Timeouts & Deadlines — How cancellation propagates: WithCancel for manual cancellation, WithTimeout for automatic cancellation after a duration, WithDeadline for absolute time deadlines. Patterns for listening (<-ctx.Done()) in concurrent code, AfterFunc callbacks, and WithoutCancel for operations that must outlive their parent request (e.g., audit logs).
Context Values & Cross-Service Tracing — Safe context value patterns: unexported key types to prevent namespace collisions, when to use context values (request ID, user ID) vs function parameters. Trace context propagation: OpenTelemetry trace headers, correlation IDs for log aggregation, and marshaling/unmarshaling context across service boundaries.
Context in HTTP Servers & Service Calls — HTTP handler context: r.Context() for request-scoped cancellation, middleware integration, and propagating to services. HTTP client patterns: NewRequestWithContext, client timeouts, and retries with context awareness. Database operations: always use *Context variants (QueryContext, ExecContext) to respect deadlines.

Cross-References

→ See the samber/cc-skills-golang@golang-concurrency skill for goroutine cancellation patterns using context
→ See the samber/cc-skills-golang@golang-database skill for context-aware database operations (QueryContext, ExecContext)
→ See the samber/cc-skills-golang@golang-observability skill for trace context propagation with OpenTelemetry
→ See the samber/cc-skills-golang@golang-design-patterns skill for timeout and resilience patterns

Enforce with Linters

Many context pitfalls are caught automatically by linters: govet, staticcheck. → See the samber/cc-skills-golang@golang-linter skill for configuration and usage.