Why my Go net.Conn is not cast to custom interface when using httpTrace.ClientTrace{GotConn}

huangapple
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英文:

Why my Go net.Conn is not cast to custom interface when using httpTrace.ClientTrace{GotConn}

问题

为了跟踪连接（在这种情况下，我想给我的连接一个名称），我用一个名为TrackedConn的结构体对其进行了封装。这个TrackedConn实现了HasId接口，并且在调用时应该返回一个标识符。

然而，当我尝试将其转换为HasId接口时，放在httptrace.ClientTrace{}的GotConn中，它是无效的。我想知道为什么会这样？

wrappedAddr只是为了向您展示它的工作原理。

  1. type HasId interface {
  2. 	Id() string
  3. }
  5. func main() {
  6. 	client := &http.Client{
  7. 		Transport: &http.Transport{
  8. 			DialContext: wrapDialContext(&net.Dialer{}),
  9. 		},
  10. 	}
  12. 	trace := &httptrace.ClientTrace{
  13. 		GotConn: func(info httptrace.GotConnInfo) {
  15. 			// 这个按预期进行了转换
  16. 			if c, ok := (info.Conn.RemoteAddr()).(HasId); ok {
  17. 				fmt.Printf("info.Conn.RemoteAddr() HasId: %s\n", c.Id())
  18. 			}
  20. 			// 为什么这个没有转换？
  21. 			if c, ok := (info.Conn).(HasId); ok {
  22. 				fmt.Printf("info.Conn HasId: %s\n", c.Id())
  23. 			}
  24. 		},
  25. 	}
  27. 	req, err := http.NewRequest("GET", "https://gobyexample.com", nil)
  28. 	req = req.WithContext(httptrace.WithClientTrace(req.Context(), trace))
  29. 	...
  30. 	resp, err := client.Do(req)
  31. 	...
  33. }
  35. func wrapDialContext(dialer *net.Dialer) func(ctx context.Context, network, address string) (net.Conn, error) {
  36. 	return func(ctx context.Context, network, address string) (net.Conn, error) {
  37. 		conn, err := dialer.DialContext(ctx, network, address)
  38. 		wrappedConn := TrackedConn{
  39. 			conn,
  40. 			"wrappedConn id",
  41. 		}
  42. 		return wrappedConn, err
  43. 	}
  44. }
  46. type wrappedAddr struct {
  47. 	net.Addr
  48. 	ident string
  49. }
  51. func (ta wrappedAddr) Id() string {
  52. 	return "wrappedAddr id"
  53. }
  55. type TrackedConn struct {
  56. 	conn net.Conn
  57. 	id   string
  58. }
  60. func (c TrackedConn) Id() string {
  61. 	return "TrackedConn id"
  62. }
  64. func (c TrackedConn) RemoteAddr() net.Addr {
  65. 	return wrappedAddr{
  66. 		Addr:  c.conn.RemoteAddr(),
  67. 		ident: c.id,
  68. 	}
  69. }
  71. // 其他方法来满足`net.Conn`接口。可以忽略它们。
  72. ....

执行它们的结果是

  1. info.Conn.RemoteAddr() HasId: wrappedAddr id

我期望也能看到info.Conn HasId: wrappedConn id。

完整代码在这里：https://play.golang.org/p/05qx45Ub8DH（由于HTTP请求的原因，Playground将无法工作）

英文:

To track connection (in this case, I want to give my connection a name), I wrapped it with a struct TrackedConn. This TrackedConn implements HasId interface and it's expected to return an identifier when call.

However, when I try to cast it to HasId interface inside httptrace.ClientTrace{} GotConn, it wasn't valid. I wonder why is that ?

wrappedAddr is just to show you that it works.

  1. type HasId interface {
  2. 	Id() string
  3. }
  5. func main() {
  6. 	client := &http.Client{
  7. 		Transport: &http.Transport{
  8. 			DialContext: wrapDialContext(&net.Dialer{}),
  9. 		},
  10. 	}
  12. 	trace := &httptrace.ClientTrace{
  13. 		GotConn: func(info httptrace.GotConnInfo) {
  15. 			// this is cast as expected
  16. 			if c, ok := (info.Conn.RemoteAddr()).(HasId); ok {
  17. 				fmt.Printf("info.Conn.RemoteAddr() HasId: %s\n", c.Id())
  18. 			}
  20. 			// why is this not cast ?
  21. 			if c, ok := (info.Conn).(HasId); ok {
  22. 				fmt.Printf("info.Conn HasId: %s\n", c.Id())
  23. 			}
  24. 		},
  25. 	}
  27. 	req, err := http.NewRequest("GET", "https://gobyexample.com", nil)
  28. 	req = req.WithContext(httptrace.WithClientTrace(req.Context(), trace))
  29. 	...
  30. 	resp, err := client.Do(req)
  31. 	...
  33. }
  35. func wrapDialContext(dialer *net.Dialer) func(ctx context.Context, network, address string) (net.Conn, error) {
  36. 	return func(ctx context.Context, network, address string) (net.Conn, error) {
  37. 		conn, err := dialer.DialContext(ctx, network, address)
  38. 		wrappedConn := TrackedConn{
  39. 			conn,
  40. 			"wrappedConn id",
  41. 		}
  42. 		return wrappedConn, err
  43. 	}
  44. }
  46. type wrappedAddr struct {
  47. 	net.Addr
  48. 	ident string
  49. }
  51. func (ta wrappedAddr) Id() string {
  52. 	return "wrappedAddr id"
  53. }
  55. type TrackedConn struct {
  56. 	conn net.Conn
  57. 	id   string
  58. }
  60. func (c TrackedConn) Id() string {
  61. 	return "TrackedConn id"
  62. }
  64. func (c TrackedConn) RemoteAddr() net.Addr {
  65. 	return wrappedAddr{
  66. 		Addr:  c.conn.RemoteAddr(),
  67. 		ident: c.id,
  68. 	}
  69. }
  71. // Other methods to fulfil `net.Conn` interface. It's ok to ignore them.
  72. ....

Executing them results in

  1. info.Conn.RemoteAddr() HasId: wrappedAddr id

I expected to see info.Conn HasId: wrappedConn id" as well

Full code here : https://play.golang.org/p/05qx45Ub8DH
(Playground is not going to work because of HTTP request)

答案1

得分: 2

为了调试您的问题，请查看info.Conn的类型：

  1. fmt.Printf("conn type: %T", info.Conn)

您正在联系一个https服务器，所以您得到的类型是：*tls.Conn。

您需要插入到您的Transport.DialTLSContext()方法中。

英文:

To debug your issue, look at the type of info.Conn :

  1. fmt.Printf("conn type: %T", info.Conn)

You are contacting an https server, so the type you get is : *tls.Conn.

You need to plug into your Transport.DialTLSContext() method.

huangapple
  • 本文由 发表于 2021年10月5日 21:09:16
  • 转载请务必保留本文链接：https://go.coder-hub.com/69451093.html
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