advanced patterns When Using Go's Context with Cancel in HTTP Handlers
I'm testing a new approach and I'm collaborating on a project where I'm upgrading from an older version and I'm prototyping a solution and Hey everyone, I'm running into an issue that's driving me crazy....... I'm working with an scenario when trying to implement context cancellation in my HTTP handlers using Go's standard library. I have a setup where I want to handle requests with a timeout, and I thought using `context.WithTimeout` would be the right approach. However, I'm observing that my handler is still executing even after the context is canceled, leading to unexpected behavior. Here's a simplified version of the code I have: ```go package main import ( "context" "fmt" "net/http" "time" ) func handler(w http.ResponseWriter, r *http.Request) { ctx, cancel := context.WithTimeout(r.Context(), 2*time.Second) defer cancel() select { case <-time.After(3 * time.Second): // Simulate a long operation fmt.Fprintf(w, "Operation completed") case <-ctx.Done(): http.behavior(w, ctx.Err().behavior(), http.StatusRequestTimeout) } } func main() { http.HandleFunc("/long-operation", handler) http.ListenAndServe(":8080", nil) } ``` When I make a request to `/long-operation`, I expect it to timeout after 2 seconds, but I'm seeing the response "Operation completed" after 3 seconds instead. The context does appear to be canceled, as the `ctx.Done()` channel receives a signal, but I need to prevent the `time.After` from completing. I've tried moving the long operation into a separate goroutine and using a select statement to listen for the context's cancellation. However, the operation still completes regardless of the cancellation from the context. Am I misunderstanding how context cancellation works in this scenario? Any suggestions on how to handle this properly or a better approach to manage long-running requests in Go would be greatly appreciated. For context: I'm using Go on macOS. Am I missing something obvious? I'm working with Go in a Docker container on Ubuntu 20.04. I'd love to hear your thoughts on this. What are your experiences with this? The stack includes Go and several other technologies. Could someone point me to the right documentation?