Context Cancelled Error

Why This Happens

When a context is cancelled via context.WithCancel, context.WithTimeout, or context.WithDeadline, any operation using that context gets a context.Canceled error. This is normal for timeout scenarios but can indicate a bug if cancellation happens earlier than expected.

The Problem

func fetchData() error {
    ctx, cancel := context.WithTimeout(context.Background(), 1*time.Millisecond)
    defer cancel()
    resp, err := http.NewRequestWithContext(ctx, "GET", "https://api.example.com", nil)
    // context canceled because timeout is too short
    return err
}

The Fix

func fetchData() error {
    ctx, cancel := context.WithTimeout(context.Background(), 30*time.Second)
    defer cancel()
    req, err := http.NewRequestWithContext(ctx, "GET", "https://api.example.com", nil)
    if err != nil {
        return err
    }
    resp, err := http.DefaultClient.Do(req)
    if err != nil {
        return fmt.Errorf("request failed: %w", err)
    }
    defer resp.Body.Close()
    return nil
}

Step-by-Step Fix

1. 1

   Identify the context source

   Find where the context is created and what timeout or cancellation is set.

2. 2

   Check the timing

   Determine if the timeout is too short for the operation, or if cancel() is called prematurely.

3. 3

   Adjust the timeout

   Increase the timeout or restructure the code so the context is not cancelled before the operation completes.