Context and Request Lifecycle Management

Learn context and request lifecycle management through an executable example, then connect the small demonstration to production code.

Every HTTP request has a Context. Pass r.Context() to downstream operations so cancellations and deadlines can interrupt slow work when appropriate. Do not store contexts on long-lived structs as ordinary configuration.

The example cancels a request-derived context and checks its error deterministically.

Follow this diagram before executing the example. Check where a value or decision changes what runs next.

For example, db.QueryContext(r.Context(), query) ties database work to the request lifetime. A driver must support cancellation for the desired behavior.

This example is a complete program. Save it as main.go or paste it into the Go Playground.

Go code

package main

import (
	"context"
	"fmt"
	"net/http/httptest"
)

func main() {
	request := httptest.NewRequest("GET", "/tasks", nil)
	ctx, cancel := context.WithCancel(request.Context())
	request = request.WithContext(ctx)
	cancel()
	fmt.Println("Cancelled:", request.Context().Err() == context.Canceled)
}

Output

Cancelled: true

The request inherits a new cancelable context. Calling cancel marks that context canceled; the next check compares its error to context.Canceled.

• Always invoke returned cancellation functions, normally with defer, when their scope ends.
• Context cancellation does not undo a database transaction already committed.

Use context.WithTimeout in a helper function and defer cancel; explain how a DB query would receive the context.

Tip: Edit the example above, predict the output, and run the modified code to test your reasoning.

You have practiced Context and Request Lifecycle Management in a small, self-contained program. The important habit is to predict what runs, inspect the actual output and distinguish the language rule from the particular example.

Before continuing, make sure you can explain the program to someone who has not seen it, including the line that changes its result.