SKILL.md
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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 &#x26; 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 &#x26; 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 &#x26; 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-concurrencyskill for goroutine cancellation patterns using context
- → See the
samber/cc-skills-golang@golang-databaseskill for context-aware database operations (QueryContext, ExecContext)
- → See the
samber/cc-skills-golang@golang-observabilityskill for trace context propagation with OpenTelemetry
- → See the
samber/cc-skills-golang@golang-design-patternsskill 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-lint skill for configuration and usage.