Errgroup Context Cancellation HTTP

package main

import (
	"context"
	"fmt"
	"net/http"

	"golang.org/x/sync/errgroup"
)

type Result struct {
	URL  string
	Code int
}

func fetchAll(ctx context.Context, urls []string) ([]Result, error) {
	g, ctx := errgroup.WithContext(ctx)
	results := make([]Result, len(urls))

	for i, url := range urls {
		i, url := i, url // 捕获循环变量（Go 1.22 前必需）
		g.Go(func() error {
			req, err := http.NewRequestWithContext(ctx, http.MethodGet, url, nil)
			if err != nil {
				return fmt.Errorf("build request %s: %w", url, err)
			}
			resp, err := http.DefaultClient.Do(req)
			if err != nil {
				return fmt.Errorf("fetch %s: %w", url, err)
			}
			defer resp.Body.Close()
			results[i] = Result{URL: url, Code: resp.StatusCode}
			return nil
		})
	}

	if err := g.Wait(); err != nil {
		return nil, err // ctx 已取消，其余 goroutine 全部提前退出
	}
	return results, nil
}

func main() {
	rs, err := fetchAll(
		context.Background(),
		[]string{"https://example.com/a", "https://example.com/b"},
	)
	fmt.Println(len(rs), err)
}