Practical Go

4.1 §

重定向 §

默认的 HTTP 客户端会自动且静默地跟踪重定向最多 10 次，之后它会终止。

The custom function to implement the redirect policy must satisfy the following signature:

func (req *http.Request, via []*http.Request) error

The first argument, req, is the request to follow the redirect response that it got back from the server; the slice, via, contains the requests that have been made so far, with the oldest request (your original request) the first element of this slice.

函数返回nil则追踪重定向（client重发请求），返回error则终止重定向。

比如要终止重定向：

func redirectPolicyFunc(req *http.Request, via []*http.Request) error {
  if len(via)>= 1 {
    return errors.New("stopped after 1 redirect")
  }
  return nil
}
 
func createHTTPClientWithTimeout(d time.Duration) *http.Client {
  return &http.Client{
    Timeout: d, 
		CheckRedirect: redirectPolicyFunc
  }
}

5 §

在context中保存键值对，要确保：

• 键不应是基本类型之一，如 string

• 应定义自己的未导出类型作为键，如

  type requestContextKey struct{}
  type requestContextValue struct {
    requestID string
  }