Bagaimanakah saya boleh menyemak dengan pasti ralat pembatalan permintaan dalam Go, walaupun ia telah dibalut oleh ralat lain?

package main

import (
    "context"
    "log"
    "net/http"
)

func main() {
    r, _ := http.NewRequest("GET", "http://example.com", nil)
    ctx, cancel := context.WithCancel(context.Background())
    r = r.WithContext(ctx)
    ch := make(chan bool)
    go func() {
        _, err := http.DefaultClient.Do(r)
        log.Println(err == context.Canceled)
        ch <- true
    }()
    cancel()
    <-ch
}

import (
    "context"
    "errors"
    "log"
    "net/http"
)

func main() {
    // Create a context that is already canceled
    ctx, cancel := context.WithCancel(context.Background())
    cancel()

    // Create the request with it
    r, _ := http.NewRequestWithContext(ctx, "GET", "http://example.com", nil)

    // Do it, it will immediately fail because the context is canceled.
    _, err := http.DefaultClient.Do(r)
    log.Println(err) // Get http://example.com: context canceled

    // This prints false, because the http client wraps the context.Canceled
    // error into another one with extra information.
    log.Println(err == context.Canceled)

    // This prints true, because errors.Is checks all the errors in the wrap chain,
    // and returns true if any of them matches.
    log.Println(errors.Is(err, context.Canceled))
}