Go で指定された時間制限の後にゴルーチンを正常にキャンセルするにはどうすればよいですか?

func attack(cfg AttackConfig) {
    // some code ...

    var ar attackResponse
    ch := make(chan uint8, 8)

    go func() {
        time.Sleep(cfg.Duration * time.Second)
        ch <- CALL_TIME_RAN_OUT
    }()

    for {
        if atomic.LoadInt32(&currConnections) < atomic.LoadInt32(&maxConnections) - 1 {
            go httpPost(cfg, &ar, ch)
        }

        switch <-ch {
        // some other cases ...
        case CALL_TIME_RAN_OUT:
            fmt.Printf("%d seconds have elapsed. Shutting down!", cfg.Duration)
            return
        }
    }
}

import (
    "context"
    "fmt"
    "golang.org/x/net/context"
    "time"
)

func attack(cfg AttackConfig) {
    // some code ...

    var ar attackResponse

    // Define a timeout context
    ctx, cancel := context.WithTimeout(context.Background(), cfg.Duration*time.Second)
    defer cancel()

    go func() {
        time.Sleep(cfg.Duration * time.Second)
        cancel()
    }()

    for {
        if atomic.LoadInt32(&currConnections) < atomic.LoadInt32(&maxConnections) - 1 {
            go httpPost(ctx, cfg, &ar)
        }

        select {
        // some other cases ...
        case <-ctx.Done():
            fmt.Printf("%d seconds have elapsed. Shutting down!", cfg.Duration)
            return
        }
    }
}

func httpPost(ctx context.Context, cfg AttackConfig, a *attackResponse) {
    // some code here to create HTTP client ...

    for {
        // some code to make HTTP call ...

        select {
        case <-ctx.Done():
            return
        default:
        }
    }
}