moo.go

func aggregate(baseCtx context.Context) {
	ctx, cancel := context.WithTimeout(baseCtx, 5*time.Second)
	defer cancel()
	ch := make(chan *http.Response)
	var wg *sync.WaitGroup
	var sources []string
	for _, src := range sources {
		wg.Add(1)
		go func(ctx context.Context, source string) {
			defer wg.Done()
			resp, err := makeRequest(ctx, source)
			if err != nil {
				// log error
			}
			ch <- resp

		}(ctx, src)
	}
	go func(wg *sync.WaitGroup) {
		wg.Wait()
		close(ch)
	}(wg)
	results := make([]*http.Response, 0, len(sources))
	for {
		select {
		case resp := <-ch:
			results = append(results, resp)
		case <-ctx.Done():
			break
		}
	}

	// use results
}

i see 2 issues here:

1. results := make([]*http.Response, 0, len(sources)) and the for is appending into this, which means len(sources) number of elements in this slice will be nil pointers forever and actual response will be added after that.
2. consider that all goroutines finish and write response to ch. the for loop is collecting it and adding it to the results. But problem is, it will keep on doing this (even after close(ch) since reading from a closed channel returns zero-value) until ctx.Done() returns ..

func aggregate(baseCtx context.Context) {
	ctx, cancel := context.WithTimeout(baseCtx, 5*time.Second)
	defer cancel()
	ch := make(chan *http.Response)
	var wg *sync.WaitGroup
	var sources []string
	for _, src := range sources {
		wg.Add(1)
		go func(ctx context.Context, source string) {
			defer wg.Done()
			resp, err := makeRequest(ctx, source)
			if err != nil {
				// log error
			}
			ch <- resp

		}(ctx, src)
	}
	go func(wg *sync.WaitGroup) {
		wg.Wait()
		close(ch)
	}(wg)
	var results []*http.Response
	for {
		select {
		case resp, ok := <-ch:
                        if !ok {
                              break
                        }
			results = append(results, resp)
		case <-ctx.Done():
			break
		}
	}

	// use results
}