在使用Golang绑定库torrent时，如何转换为“alert”类型。

huangapple
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英文:

Casting an "alert" type in libtorrent, using Golang bindings

问题

我正在开发一个使用Golang的个人项目，使用libtorrent-go。

当我收到类型为"save_resume_data_alert"的警报时，我会捕获它，并且需要按照libtorrent文档中的写法进行类型转换。

  1. ...
  2. save_resume_data_alert const* rd = alert_cast<save_resume_data_alert>(a);
  3. ...

但是我真的不知道如何在Golang中进行类型转换！当前的代码如下：

  1. package main
  3. import (
  4. 	lt "github.com/steeve/libtorrent-go"
  6. 	"log"
  7. 	"time"
  8. )
  10. func main() {
  12. 	randomTorrent := lt.NewAdd_torrent_params()
  13. 	randomTorrent.SetUrl("PUT A MAGNET LINK HERE")
  14. 	randomTorrent.SetSave_path(".")
  16. 	ec := lt.NewError_code()
  17. 	torrentSession := lt.NewSession()
  18. 	torrentSession.Set_alert_mask(status_notification + storage_notification)
  19. 	torrentSession.Listen_on(lt.NewStd_pair_int_int(6900, 6999), ec)
  20. 	if ec.Value() != 0 {
  21. 		log.Println(ec.Message())
  22. 	}
  24. 	torrentHandle := torrentSession.Add_torrent(randomTorrent, ec)
  25. 	if ec.Value() != 0 {
  26. 		log.Println(ec.Message())
  27. 	}
  29. 	go func() {
  30. 		for {
  31. 			if torrentSession.Wait_for_alert(lt.Seconds(10)).Swigcptr() == 0 {
  32. 				log.Println("Alert timeout occurred!")
  33. 			}
  35. 			alert := torrentSession.Pop_alert()
  36. 			switch alert.What() {
  37. 			default:
  38. 				log.Printf("Alert: %#v", alert.What())
  39. 			case "metadata_received_alert":
  40. 				log.Println("Received Metadata!! finally!")
  41. 				torrentHandle.Save_resume_data()
  42. 			case "save_resume_data_alert":
  43. 				log.Println("Wrote Metadata!")
  44. 				// 需要实际写入resume_data :( 找不到如何写入
  45. 			case "save_resume_data_failed_alert":
  46. 				log.Println("Failed Metadata!")
  47. 			}
  48. 		}
  49. 	}()
  51. 	select {}
  52. }

请注意，我只会翻译代码部分，不会回答关于翻译的问题。

英文:

I am developing a personal project in Golang, using libtorrent-go

When I do receive an alert of type &quot;save_resume_data_alert&quot;, I pick it up and have to CAST it as written in libtorrent documentation

  1. ...
  2.         save_resume_data_alert const* rd = alert_cast&lt;save_resume_data_alert&gt;(a);
  3. ...

But i really have not idea how to cast it in golang! Current code:

  1. package main
  3. import (
  4. 	lt &quot;github.com/steeve/libtorrent-go&quot;
  6. 	&quot;log&quot;
  7. 	&quot;time&quot;
  8. )
  10. func main() {
  12. 	randomTorrent := lt.NewAdd_torrent_params()
  13. 	randomTorrent.SetUrl(&quot;PUT A MAGNET LINK HERE&quot;)
  14. 	randomTorrent.SetSave_path(&quot;.&quot;)
  16. 	ec := lt.NewError_code()
  17. 	torrentSession := lt.NewSession()
  18. 	torrentSession.Set_alert_mask(status_notification + storage_notification)
  19. 	torrentSession.Listen_on(lt.NewStd_pair_int_int(6900, 6999), ec)
  20. 	if ec.Value() != 0 {
  21. 		log.Println(ec.Message())
  22. 	}
  24. 	torrentHandle := torrentSession.Add_torrent(randomTorrent, ec)
  25. 	if ec.Value() != 0 {
  26. 		log.Println(ec.Message())
  27. 	}
  29. 	go func() {
  30. 		for {
  31. 			if torrentSession.Wait_for_alert(lt.Seconds(10)).Swigcptr() == 0 {
  32. 				log.Println(&quot;Alert timeout occurred!&quot;)
  33. 			}
  35. 			alert := torrentSession.Pop_alert()
  36. 			switch alert.What() {
  37. 			default:
  38. 				log.Printf(&quot;Alert: %#v&quot;, alert.What())
  39. 			case &quot;metadata_received_alert&quot;:
  40. 				log.Println(&quot;Received Metadata!! finally!&quot;)
  41. 				torrentHandle.Save_resume_data()
  42. 			case &quot;save_resume_data_alert&quot;:
  43. 				log.Println(&quot;Wrote Metadata!&quot;)
  44. 				// need to actually write the resume_data :( can&#39;t find how
  45. 			case &quot;save_resume_data_failed_alert&quot;:
  46. 				log.Println(&quot;Failed Metadata!&quot;)
  47. 			}
  48. 		}
  49. 	}()
  51. 	select {}
  52. }

答案1

得分: 1

如上所述，libtorrent-go的开发者回答了我，所以我将这个答案转发出来，以备后用。

使用SWIG库在Golang中进行C++结构的转换在SWIG-Golang文档中有详细说明。
特别是在以下语句中：

> 给定接口类型的值，Go代码可以通过调用Swigcptr方法来检索C++类型的指针。
> 这将返回一个SwigcptrClassName类型的值，它只是一个uintptr的别名。
> 可以使用Go类型转换将此值转换为不同的C++类型，但请注意，此转换不会进行类型检查，
> 并且本质上等同于reinterpret_cast。这只应该用于非常特殊的情况，例如C++中使用dynamic_cast的情况。

在我上面发布的那段代码中，为了使其工作，需要进行以下操作：

  1. case "save_resume_data_alert":
  2.   log.Println("Wrote Metadata!")
  3.   // 需要实际写入resume_data :( 找不到如何写入
  4.   SaveRDAlert := lt.SwigcptrSave_resume_data_alert(alert.Swigcptr())
  5.   log.Printf("Resume Data: %#v", SaveRDAlert.GetResume_data())
英文:

As stated above, libtorrent-go developer answered me, so I am forwarding the answer for posterity reasons.

Casting C++ structures in Golang using SWIG library is documented in SWIG-Golang documentation.
In particular in this statement:

> Given a value of the interface type, Go code can retrieve the pointer
> to the C++ type by calling the Swigcptr method. This will return a
> value of type SwigcptrClassName, which is just a name for uintptr. A
> Go type conversion can be used to convert this value to a different
> C++ type, but note that this conversion will not be type checked and
> is essentially equivalent to reinterpret_cast. This should only be
> used for very special cases, such as where C++ would use a
> dynamic_cast.

In that particular piece of code I posted above, the following was necessary to make it work:

  1. case &quot;save_resume_data_alert&quot;:
  2.   log.Println(&quot;Wrote Metadata!&quot;)
  3.   // need to actually write the resume_data :( can&#39;t find how
  4.   SaveRDAlert := lt.SwigcptrSave_resume_data_alert(alert.Swigcptr())
  5.   log.Printf(&quot;Resume Data: %#v&quot;, SaveRDAlert.GetResume_data())

huangapple
  • 本文由 发表于 2014年12月17日 19:35:54
  • 转载请务必保留本文链接：https://go.coder-hub.com/27524688.html
  • bittorrent
  • casting
  • go
  • libtorrent
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