Context In Golang

What is context.Context?

context.Context is a standard Go interface used to:

• Control cancellation of operations (e.g., HTTP requests, DB queries, goroutines)
• Set timeouts and deadlines
• Pass request-scoped values (like request ID or user ID) safely

It helps manage long-running processes, especially in concurrent or distributed systems.

The context.Context Interface

type Context interface {
    Deadline() (deadline time.Time, ok bool)
    Done() <-chan struct{}
    Err() error
    Value(key any) any
}

Why is context important?

• Prevents resource leaks
• Helps build cancellable, timeout-aware services
• Standardizes request metadata propagation
• Critical in HTTP servers, databases, microservices, etc.

Common Context Functions

Function	Description
context.Background()	Root context (default starting point)
context.TODO()	Placeholder for future context logic
context.WithCancel(ctx)	Adds cancel capability
context.WithTimeout(ctx, d)	Cancels after timeout duration
context.WithDeadline(ctx, t)	Cancels at specific time
context.WithValue(ctx, key, val)	Adds value to context

Use Cases

• Timeout for HTTP/DB calls
• Cancel goroutines cleanly
• Propagate request metadata (e.g., requestID)
• Graceful shutdowns (HTTP servers, background jobs)

Examples

• database operation
• canceling goroutines
• timeouts http request
• broken propagation
• chain propagation

What NOT to do

Bad Practice	Why it's bad
Creating context.Background() in services	Breaks cancellation chain
Passing nil context	Can panic, unclear behavior
Storing context in struct fields	Misuse — context should flow by function

Best Practices

• Always pass context as the first argument: func(ctx context.Context, ...)
• Use defer cancel() after WithCancel, WithTimeout, or WithDeadline
• Don’t abuse WithValue — use for control data, not app logic