[go-nuts] Re: net/http and errors.

[mb . dhananjay]

> if err, ok := err.(*url.Error); ok {
> if err, ok := err.Err.(*net.OpError); ok {
> if err, ok := err.Err.(*net.DNSError); ok {
> fmt.Println("DNS ERROR:", err)
> }
> }
> }
>

This works as expected. :-)

On Monday, November 28, 2016 at 9:32:55 PM UTC+1, Dave Cheney wrote:
>
> Indeed. Does your program differentiate between a URL not resolving, the 
> webserver at the other end being down or refusing to connect, or it 
> returnining a non temporary fatal error, 4xx? 


Yes, it tries to be verbose about failure reasons. DNS / Server not 
listening / HTTP Status codes if present.. 

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[go-nuts] Re: net/http and errors.

[Dave Cheney]

Indeed. Does your program differentiate between a URL not resolving, the 
webserver at the other end being down or refusing to connect, or it returnining 
a non temporary fatal error, 4xx? 

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[go-nuts] Re: net/http and errors.

[James Bardin]

If you want to assert your way down to the original error, the order of the 
structures returned from http.Get is:

if err, ok := err.(*url.Error); ok {
if err, ok := err.Err.(*net.OpError); ok {
if err, ok := err.Err.(*net.DNSError); ok {
fmt.Println("DNS ERROR:", err)
}
}
}

Again though, the action (http.Get) failed regardless of the reason, so you 
would usually the errors all in the same manner. You can't necessarily 
count on a DNS error being permanent either, just look at what happened a 
few weeks ago, when a huge number of major sites couldn't be resolved. 





On Monday, November 28, 2016 at 12:01:18 PM UTC-5, mb.dha...@gmail.com 
wrote:
>
> I'm downloading a large number of urls and the result is expected to have 
> failure reasons, DNS lookup failed being one.
>
> calling lookup manually would solve my issue, I suppose. Just wanted to 
> make sure that I'm not missing any obvious solutions.
>
> 1. lookup DNS and if it succeeds, 
> 2. try http.Get - which calles Lookup again (also maybe DNS server went 
> down now - improbable but not impossible?)
>
>
> On Monday, November 28, 2016 at 1:05:25 PM UTC+1, Dave Cheney wrote:
>>
>> What specifically do you want to handle about DNS errors ?
>>
>> If you have a set of possible dns names and you don't know if some of 
>> them are valid, you could use net.LookupHost to check which ones are valid 
>> before calling http.Get.
>>
>> On Monday, 28 November 2016 22:44:37 UTC+11, mb.dha...@gmail.com wrote:
>>>
>>> But AFIU, err.Temporary() could be true for other kind of errors that 
>>> might happen, isn't that a problem if I only want to handle DNS errors?
>>>
>>>
>>> On Friday, November 25, 2016 at 6:35:59 PM UTC+1, Victor Vrantchan wrote:

 In Go, you can check if a type satisfies a particular behavior by 
 declaring an interface, and then checking if the type satisfies that 
 interface. 
 In your case, you can check if the error is `Temporrary()` or not. 

 See this snippet as an example: https://I don't 
 thinplay.golang.org/p/Ffyg61iDpB 

 I recommend 
 https://dave.cheney.net/2016/04/27/dont-just-check-errors-handle-them-gracefully
  
 and.or the GopherCon talk https://www.youtube.com/watch?v=lsBF58Q-DnY 
 by Dave Cheney for a more in-depth presentation of this idea. 

 On Friday, November 25, 2016 at 12:00:06 PM UTC-5, mb.dha...@gmail.com 
 wrote:
>
> This is a question about the net/http API, Googling was not very 
> helpful.
>
> _, err := http.Get("https://random_non_existing_domain.com;)
>
>
> Following code will obviously fail, but how can I check if it failed 
> because of DNS error not because a billion other things that might have 
> gone wrong?
>
> I tried this, (mostly as a shot in the dark)
>
> if e, ok := err.(net.Error); ok {
> fmt.Println("dial error", e.Temporary())
> }
> if e, ok := err.(*net.AddrError); ok {
> fmt.Println("addr rror", e.Temporary())
> }
> if e, ok := err.(*net.DNSError); ok {
> fmt.Println(e)
>
> and it seems to print 
>
>dial error false
>
> Is there any easy way to do what I'm trying to achieve?
>
> -
> dbalan
> @notmycommit
>
>
>

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[go-nuts] Re: net/http and errors.

[mb . dhananjay]

I'm downloading a large number of urls and the result is expected to have 
failure reasons, DNS lookup failed being one.

calling lookup manually would solve my issue, I suppose. Just wanted to 
make sure that I'm not missing any obvious solutions.

1. lookup DNS and if it succeeds, 
2. try http.Get - which calles Lookup again (also maybe DNS server went 
down now - improbable but not impossible?)


On Monday, November 28, 2016 at 1:05:25 PM UTC+1, Dave Cheney wrote:
>
> What specifically do you want to handle about DNS errors ?
>
> If you have a set of possible dns names and you don't know if some of them 
> are valid, you could use net.LookupHost to check which ones are valid 
> before calling http.Get.
>
> On Monday, 28 November 2016 22:44:37 UTC+11, mb.dha...@gmail.com wrote:
>>
>> But AFIU, err.Temporary() could be true for other kind of errors that 
>> might happen, isn't that a problem if I only want to handle DNS errors?
>>
>>
>> On Friday, November 25, 2016 at 6:35:59 PM UTC+1, Victor Vrantchan wrote:
>>>
>>> In Go, you can check if a type satisfies a particular behavior by 
>>> declaring an interface, and then checking if the type satisfies that 
>>> interface. 
>>> In your case, you can check if the error is `Temporrary()` or not. 
>>>
>>> See this snippet as an example: https://I don't 
>>> thinplay.golang.org/p/Ffyg61iDpB 
>>>
>>> I recommend 
>>> https://dave.cheney.net/2016/04/27/dont-just-check-errors-handle-them-gracefully
>>>  
>>> and.or the GopherCon talk https://www.youtube.com/watch?v=lsBF58Q-DnY 
>>> by Dave Cheney for a more in-depth presentation of this idea. 
>>>
>>> On Friday, November 25, 2016 at 12:00:06 PM UTC-5, mb.dha...@gmail.com 
>>> wrote:

 This is a question about the net/http API, Googling was not very 
 helpful.

 _, err := http.Get("https://random_non_existing_domain.com;)


 Following code will obviously fail, but how can I check if it failed 
 because of DNS error not because a billion other things that might have 
 gone wrong?

 I tried this, (mostly as a shot in the dark)

 if e, ok := err.(net.Error); ok {
 fmt.Println("dial error", e.Temporary())
 }
 if e, ok := err.(*net.AddrError); ok {
 fmt.Println("addr rror", e.Temporary())
 }
 if e, ok := err.(*net.DNSError); ok {
 fmt.Println(e)

 and it seems to print 

dial error false

 Is there any easy way to do what I'm trying to achieve?

 -
 dbalan
 @notmycommit




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[go-nuts] Re: net/http and errors.

[Dave Cheney]

What specifically do you want to handle about DNS errors ?

If you have a set of possible dns names and you don't know if some of them 
are valid, you could use net.LookupHost to check which ones are valid 
before calling http.Get.

On Monday, 28 November 2016 22:44:37 UTC+11, mb.dha...@gmail.com wrote:
>
> But AFIU, err.Temporary() could be true for other kind of errors that 
> might happen, isn't that a problem if I only want to handle DNS errors?
>
>
> On Friday, November 25, 2016 at 6:35:59 PM UTC+1, Victor Vrantchan wrote:
>>
>> In Go, you can check if a type satisfies a particular behavior by 
>> declaring an interface, and then checking if the type satisfies that 
>> interface. 
>> In your case, you can check if the error is `Temporrary()` or not. 
>>
>> See this snippet as an example: https://I don't 
>> thinplay.golang.org/p/Ffyg61iDpB 
>>
>> I recommend 
>> https://dave.cheney.net/2016/04/27/dont-just-check-errors-handle-them-gracefully
>>  
>> and.or the GopherCon talk https://www.youtube.com/watch?v=lsBF58Q-DnY by 
>> Dave Cheney for a more in-depth presentation of this idea. 
>>
>> On Friday, November 25, 2016 at 12:00:06 PM UTC-5, mb.dha...@gmail.com 
>> wrote:
>>>
>>> This is a question about the net/http API, Googling was not very helpful.
>>>
>>> _, err := http.Get("https://random_non_existing_domain.com;)
>>>
>>>
>>> Following code will obviously fail, but how can I check if it failed 
>>> because of DNS error not because a billion other things that might have 
>>> gone wrong?
>>>
>>> I tried this, (mostly as a shot in the dark)
>>>
>>> if e, ok := err.(net.Error); ok {
>>> fmt.Println("dial error", e.Temporary())
>>> }
>>> if e, ok := err.(*net.AddrError); ok {
>>> fmt.Println("addr rror", e.Temporary())
>>> }
>>> if e, ok := err.(*net.DNSError); ok {
>>> fmt.Println(e)
>>>
>>> and it seems to print 
>>>
>>>dial error false
>>>
>>> Is there any easy way to do what I'm trying to achieve?
>>>
>>> -
>>> dbalan
>>> @notmycommit
>>>
>>>
>>>

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[go-nuts] Re: net/http and errors.

[mb . dhananjay]

But AFIU, err.Temporary() could be true for other kind of errors that might 
happen, isn't that a problem if I only want to handle DNS errors?


On Friday, November 25, 2016 at 6:35:59 PM UTC+1, Victor Vrantchan wrote:
>
> In Go, you can check if a type satisfies a particular behavior by 
> declaring an interface, and then checking if the type satisfies that 
> interface. 
> In your case, you can check if the error is `Temporrary()` or not. 
>
> See this snippet as an example: https://I don't 
> thinplay.golang.org/p/Ffyg61iDpB 
>
> I recommend 
> https://dave.cheney.net/2016/04/27/dont-just-check-errors-handle-them-gracefully
>  
> and.or the GopherCon talk https://www.youtube.com/watch?v=lsBF58Q-DnY by 
> Dave Cheney for a more in-depth presentation of this idea. 
>
> On Friday, November 25, 2016 at 12:00:06 PM UTC-5, mb.dha...@gmail.com 
> wrote:
>>
>> This is a question about the net/http API, Googling was not very helpful.
>>
>> _, err := http.Get("https://random_non_existing_domain.com;)
>>
>>
>> Following code will obviously fail, but how can I check if it failed 
>> because of DNS error not because a billion other things that might have 
>> gone wrong?
>>
>> I tried this, (mostly as a shot in the dark)
>>
>> if e, ok := err.(net.Error); ok {
>> fmt.Println("dial error", e.Temporary())
>> }
>> if e, ok := err.(*net.AddrError); ok {
>> fmt.Println("addr rror", e.Temporary())
>> }
>> if e, ok := err.(*net.DNSError); ok {
>> fmt.Println(e)
>>
>> and it seems to print 
>>
>>dial error false
>>
>> Is there any easy way to do what I'm trying to achieve?
>>
>> -
>> dbalan
>> @notmycommit
>>
>>
>>

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[go-nuts] Re: net/http and errors.

[Victor Vrantchan]

In Go, you can check if a type satisfies a particular behavior by declaring 
an interface, and then checking if the type satisfies that interface. 
In your case, you can check if the error is `Temporrary()` or not. 

See this snippet as an example: https://play.golang.org/p/Ffyg61iDpB

I 
recommend 
https://dave.cheney.net/2016/04/27/dont-just-check-errors-handle-them-gracefully
 
and.or the GopherCon talk https://www.youtube.com/watch?v=lsBF58Q-DnY by 
Dave Cheney for a more in-depth presentation of this idea. 

On Friday, November 25, 2016 at 12:00:06 PM UTC-5, mb.dha...@gmail.com 
wrote:
>
> This is a question about the net/http API, Googling was not very helpful.
>
> _, err := http.Get("https://random_non_existing_domain.com;)
>
>
> Following code will obviously fail, but how can I check if it failed 
> because of DNS error not because a billion other things that might have 
> gone wrong?
>
> I tried this, (mostly as a shot in the dark)
>
> if e, ok := err.(net.Error); ok {
> fmt.Println("dial error", e.Temporary())
> }
> if e, ok := err.(*net.AddrError); ok {
> fmt.Println("addr rror", e.Temporary())
> }
> if e, ok := err.(*net.DNSError); ok {
> fmt.Println(e)
>
> and it seems to print 
>
>dial error false
>
> Is there any easy way to do what I'm trying to achieve?
>
> -
> dbalan
> @notmycommit
>
>
>

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