Re: [go-nuts] http.Client returning "http2: no cached connection was available"

['Ingo Oeser' via golang-nuts]

Could you document your workaround here? 

It might be needed by others for the next 6 months because the bug has been 
classified as Go 1.8 work.

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Re: [go-nuts] http.Client returning "http2: no cached connection was available"

['Russ Amos' via golang-nuts]

Thanks for the extremely quick triage, Brad. I'll work around it in my
program, for now.

On Tue, Aug 2, 2016 at 10:08 PM Brad Fitzpatrick 
wrote:

> Oh, sorry, I read that as GODEBUG=http2debug=1.
>
> Okay, I'll follow up in https://golang.org/issues/16582
>
> On Tue, Aug 2, 2016 at 7:00 PM, Russ Amos  wrote:
>
>> Those messages aren't GODEBUG output, it's the errors printed by the
>> program as received from http.Client.Get. I'll file a bug.
>>
>> On Tue, Aug 2, 2016 at 9:51 PM Brad Fitzpatrick 
>> wrote:
>>
>>> Sorry, I don't read all of golang-nuts@ and never saw that. You
>>> could've escalated, though. There are at least two bug trackers available
>>> to you:
>>>
>>> http://b/
>>> https://github.com/golang/go/issues  (the one I prefer)
>>>
>>> But I think your interpretation of the the HTTP/2 client is wrong.
>>>
>>> If you're a video person, there's a talk on Go's HTTP client and its
>>> HTTP/2<->HTTP/1<->HTTP/2 dialing sandwich...
>>> https://www.youtube.com/watch?v=FARQMJndUn0
>>> If you're not a video person, the slides are linked from youtube.
>>>
>>> Your output in this email from your program (
>>> https://play.golang.org/p/zKthX7Y9RW) doesn't include any error output.
>>> You can ignore the GODEBUG output. If it says there's no cached connection,
>>> that means http2 has no cached connection it needs to dial (which http1
>>> will do). Then http1 works as normal, unless it decides that it negotiated
>>> http2, and then it goes back to http2.
>>>
>>> But any rate-limiting you refer to is unchanged from before, since
>>> HTTP/1 still dials as normal. There's an open bug to optimize it (to only
>>> start 1 or 2 TCP connections until we know the negotiated protocol, and
>>> then settle on 6 or 1 max connections, etc), but it's no different today
>>> than Go 1.5 and earlier.
>>>
>>> In any case, if you have a reproducible bug, let's move this to a bug
>>> tracker.
>>>
>>>
>>>
>>>
>>>
>>>
>>>
>>>
>>>
>>>
>>>
>>>
>>> On Tue, Aug 2, 2016 at 6:36 PM, 'Russ Amos' via golang-nuts <
>>> golang-nuts@googlegroups.com> wrote:
>>>
 I'm seeing "http2: no cached connection was available" failures from
 http.Client when I start many (~hundreds) requests at once. (This issue was
 also posted to golang-nuts@ in April
 ,
 with no response)

 I may not understand correctly, but I thought this kind of usage was
 fine with HTTP 1.1 and net/http, because the spec mandates a max number of
 outgoing connections to any given host, so http.Client throttles open
 connections and effectively queues requests past that. The http2 package
 seems not to do the same. That might be correct according to the spec (I
 don't know), but makes using http.Client weird -- I need to rate limit its
 usage if the server is HTTP 2, but it does rate limiting for me if the
 server is HTTP 1.1.

 Is my understanding correct? Is this a bug? Is the expectation that my
 app should be rate limiting, regardless of server version?

 Also, It seems the error being returned is exported
  in the http2
 package, but is not exported in the bundled version
  in net/http. If
 it was exported, I think I could at least retry on my own, but perhaps
 that's not the intended usage anyway.

 I wrote this program  hitting
 https://www.google.com/ to demonstrate -- here are a few run results:

 $ GODEBUG=http2client=0 go run /tmp/foo.go
 $ GODEBUG=http2client=0 go run /tmp/foo.go
 $ GODEBUG=http2client=0 go run /tmp/foo.go
 $ GODEBUG=http2client=0 go run /tmp/foo.go
 $ GODEBUG=http2client=0 go run /tmp/foo.go

 $ GODEBUG=http2client=1 go run /tmp/foo.go
 Get https://www.google.com/: http2: no cached connection was available
 Get https://www.google.com/: http2: no cached connection was available
 Get https://www.google.com/: http2: no cached connection was available
 ...
 $ GODEBUG=http2client=1 go run /tmp/foo.go
 Get https://www.google.com/: http2: no cached connection was available
 $ GODEBUG=http2client=1 go run /tmp/foo.go
 $ GODEBUG=http2client=1 go run /tmp/foo.go
 Get https://www.google.com/: http2: no cached connection was available
 Get https://www.google.com/: http2: no cached connection was available
 Get https://www.google.com/: http2: no cached connection was available
 ...
 $ GODEBUG=http2client=1 go run /tmp/foo.go
 Get https://www.google.com/: http2: no cached connection was available
 Get https://www.google.com/: http2: no cached connection was available
 Get https://www.google.com/: http2: no cached connection was available
 ...

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Re: [go-nuts] http.Client returning "http2: no cached connection was available"

[Brad Fitzpatrick]

Oh, sorry, I read that as GODEBUG=http2debug=1.

Okay, I'll follow up in https://golang.org/issues/16582

On Tue, Aug 2, 2016 at 7:00 PM, Russ Amos  wrote:

> Those messages aren't GODEBUG output, it's the errors printed by the
> program as received from http.Client.Get. I'll file a bug.
>
> On Tue, Aug 2, 2016 at 9:51 PM Brad Fitzpatrick 
> wrote:
>
>> Sorry, I don't read all of golang-nuts@ and never saw that. You could've
>> escalated, though. There are at least two bug trackers available to you:
>>
>> http://b/
>> https://github.com/golang/go/issues  (the one I prefer)
>>
>> But I think your interpretation of the the HTTP/2 client is wrong.
>>
>> If you're a video person, there's a talk on Go's HTTP client and its
>> HTTP/2<->HTTP/1<->HTTP/2 dialing sandwich...
>> https://www.youtube.com/watch?v=FARQMJndUn0
>> If you're not a video person, the slides are linked from youtube.
>>
>> Your output in this email from your program (
>> https://play.golang.org/p/zKthX7Y9RW) doesn't include any error output.
>> You can ignore the GODEBUG output. If it says there's no cached connection,
>> that means http2 has no cached connection it needs to dial (which http1
>> will do). Then http1 works as normal, unless it decides that it negotiated
>> http2, and then it goes back to http2.
>>
>> But any rate-limiting you refer to is unchanged from before, since HTTP/1
>> still dials as normal. There's an open bug to optimize it (to only start 1
>> or 2 TCP connections until we know the negotiated protocol, and then settle
>> on 6 or 1 max connections, etc), but it's no different today than Go 1.5
>> and earlier.
>>
>> In any case, if you have a reproducible bug, let's move this to a bug
>> tracker.
>>
>>
>>
>>
>>
>>
>>
>>
>>
>>
>>
>>
>> On Tue, Aug 2, 2016 at 6:36 PM, 'Russ Amos' via golang-nuts <
>> golang-nuts@googlegroups.com> wrote:
>>
>>> I'm seeing "http2: no cached connection was available" failures from
>>> http.Client when I start many (~hundreds) requests at once. (This issue was
>>> also posted to golang-nuts@ in April
>>> ,
>>> with no response)
>>>
>>> I may not understand correctly, but I thought this kind of usage was
>>> fine with HTTP 1.1 and net/http, because the spec mandates a max number of
>>> outgoing connections to any given host, so http.Client throttles open
>>> connections and effectively queues requests past that. The http2 package
>>> seems not to do the same. That might be correct according to the spec (I
>>> don't know), but makes using http.Client weird -- I need to rate limit its
>>> usage if the server is HTTP 2, but it does rate limiting for me if the
>>> server is HTTP 1.1.
>>>
>>> Is my understanding correct? Is this a bug? Is the expectation that my
>>> app should be rate limiting, regardless of server version?
>>>
>>> Also, It seems the error being returned is exported
>>>  in the http2
>>> package, but is not exported in the bundled version
>>>  in net/http. If it
>>> was exported, I think I could at least retry on my own, but perhaps that's
>>> not the intended usage anyway.
>>>
>>> I wrote this program  hitting
>>> https://www.google.com/ to demonstrate -- here are a few run results:
>>>
>>> $ GODEBUG=http2client=0 go run /tmp/foo.go
>>> $ GODEBUG=http2client=0 go run /tmp/foo.go
>>> $ GODEBUG=http2client=0 go run /tmp/foo.go
>>> $ GODEBUG=http2client=0 go run /tmp/foo.go
>>> $ GODEBUG=http2client=0 go run /tmp/foo.go
>>>
>>> $ GODEBUG=http2client=1 go run /tmp/foo.go
>>> Get https://www.google.com/: http2: no cached connection was available
>>> Get https://www.google.com/: http2: no cached connection was available
>>> Get https://www.google.com/: http2: no cached connection was available
>>> ...
>>> $ GODEBUG=http2client=1 go run /tmp/foo.go
>>> Get https://www.google.com/: http2: no cached connection was available
>>> $ GODEBUG=http2client=1 go run /tmp/foo.go
>>> $ GODEBUG=http2client=1 go run /tmp/foo.go
>>> Get https://www.google.com/: http2: no cached connection was available
>>> Get https://www.google.com/: http2: no cached connection was available
>>> Get https://www.google.com/: http2: no cached connection was available
>>> ...
>>> $ GODEBUG=http2client=1 go run /tmp/foo.go
>>> Get https://www.google.com/: http2: no cached connection was available
>>> Get https://www.google.com/: http2: no cached connection was available
>>> Get https://www.google.com/: http2: no cached connection was available
>>> ...
>>>
>>> --
>>> You received this message because you are subscribed to the Google
>>> Groups "golang-nuts" group.
>>> To unsubscribe from this group and stop receiving emails from it, send
>>> an email to golang-nuts+unsubscr...@googlegroups.com.
>>> For more options, visit https://groups.google.com/d/optout.
>>>
>>

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Re: [go-nuts] http.Client returning "http2: no cached connection was available"

['Russ Amos' via golang-nuts]

http://golang.org/issues/16582

On Tue, Aug 2, 2016 at 10:00 PM Russ Amos  wrote:

> Those messages aren't GODEBUG output, it's the errors printed by the
> program as received from http.Client.Get. I'll file a bug.
>
> On Tue, Aug 2, 2016 at 9:51 PM Brad Fitzpatrick 
> wrote:
>
>> Sorry, I don't read all of golang-nuts@ and never saw that. You could've
>> escalated, though. There are at least two bug trackers available to you:
>>
>> http://b/
>> https://github.com/golang/go/issues  (the one I prefer)
>>
>> But I think your interpretation of the the HTTP/2 client is wrong.
>>
>> If you're a video person, there's a talk on Go's HTTP client and its
>> HTTP/2<->HTTP/1<->HTTP/2 dialing sandwich...
>> https://www.youtube.com/watch?v=FARQMJndUn0
>> If you're not a video person, the slides are linked from youtube.
>>
>> Your output in this email from your program (
>> https://play.golang.org/p/zKthX7Y9RW) doesn't include any error output.
>> You can ignore the GODEBUG output. If it says there's no cached connection,
>> that means http2 has no cached connection it needs to dial (which http1
>> will do). Then http1 works as normal, unless it decides that it negotiated
>> http2, and then it goes back to http2.
>>
>> But any rate-limiting you refer to is unchanged from before, since HTTP/1
>> still dials as normal. There's an open bug to optimize it (to only start 1
>> or 2 TCP connections until we know the negotiated protocol, and then settle
>> on 6 or 1 max connections, etc), but it's no different today than Go 1.5
>> and earlier.
>>
>> In any case, if you have a reproducible bug, let's move this to a bug
>> tracker.
>>
>>
>>
>>
>>
>>
>>
>>
>>
>>
>>
>>
>> On Tue, Aug 2, 2016 at 6:36 PM, 'Russ Amos' via golang-nuts <
>> golang-nuts@googlegroups.com> wrote:
>>
>>> I'm seeing "http2: no cached connection was available" failures from
>>> http.Client when I start many (~hundreds) requests at once. (This issue was
>>> also posted to golang-nuts@ in April
>>> ,
>>> with no response)
>>>
>>> I may not understand correctly, but I thought this kind of usage was
>>> fine with HTTP 1.1 and net/http, because the spec mandates a max number of
>>> outgoing connections to any given host, so http.Client throttles open
>>> connections and effectively queues requests past that. The http2 package
>>> seems not to do the same. That might be correct according to the spec (I
>>> don't know), but makes using http.Client weird -- I need to rate limit its
>>> usage if the server is HTTP 2, but it does rate limiting for me if the
>>> server is HTTP 1.1.
>>>
>>> Is my understanding correct? Is this a bug? Is the expectation that my
>>> app should be rate limiting, regardless of server version?
>>>
>>> Also, It seems the error being returned is exported
>>>  in the http2
>>> package, but is not exported in the bundled version
>>>  in net/http. If it
>>> was exported, I think I could at least retry on my own, but perhaps that's
>>> not the intended usage anyway.
>>>
>>> I wrote this program  hitting
>>> https://www.google.com/ to demonstrate -- here are a few run results:
>>>
>>> $ GODEBUG=http2client=0 go run /tmp/foo.go
>>> $ GODEBUG=http2client=0 go run /tmp/foo.go
>>> $ GODEBUG=http2client=0 go run /tmp/foo.go
>>> $ GODEBUG=http2client=0 go run /tmp/foo.go
>>> $ GODEBUG=http2client=0 go run /tmp/foo.go
>>>
>>> $ GODEBUG=http2client=1 go run /tmp/foo.go
>>> Get https://www.google.com/: http2: no cached connection was available
>>> Get https://www.google.com/: http2: no cached connection was available
>>> Get https://www.google.com/: http2: no cached connection was available
>>> ...
>>> $ GODEBUG=http2client=1 go run /tmp/foo.go
>>> Get https://www.google.com/: http2: no cached connection was available
>>> $ GODEBUG=http2client=1 go run /tmp/foo.go
>>> $ GODEBUG=http2client=1 go run /tmp/foo.go
>>> Get https://www.google.com/: http2: no cached connection was available
>>> Get https://www.google.com/: http2: no cached connection was available
>>> Get https://www.google.com/: http2: no cached connection was available
>>> ...
>>> $ GODEBUG=http2client=1 go run /tmp/foo.go
>>> Get https://www.google.com/: http2: no cached connection was available
>>> Get https://www.google.com/: http2: no cached connection was available
>>> Get https://www.google.com/: http2: no cached connection was available
>>> ...
>>>
>>> --
>>> You received this message because you are subscribed to the Google
>>> Groups "golang-nuts" group.
>>> To unsubscribe from this group and stop receiving emails from it, send
>>> an email to golang-nuts+unsubscr...@googlegroups.com.
>>> For more options, visit https://groups.google.com/d/optout.
>>>
>>

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Re: [go-nuts] http.Client returning "http2: no cached connection was available"

['Russ Amos' via golang-nuts]

Those messages aren't GODEBUG output, it's the errors printed by the
program as received from http.Client.Get. I'll file a bug.

On Tue, Aug 2, 2016 at 9:51 PM Brad Fitzpatrick  wrote:

> Sorry, I don't read all of golang-nuts@ and never saw that. You could've
> escalated, though. There are at least two bug trackers available to you:
>
> http://b/
> https://github.com/golang/go/issues  (the one I prefer)
>
> But I think your interpretation of the the HTTP/2 client is wrong.
>
> If you're a video person, there's a talk on Go's HTTP client and its
> HTTP/2<->HTTP/1<->HTTP/2 dialing sandwich...
> https://www.youtube.com/watch?v=FARQMJndUn0
> If you're not a video person, the slides are linked from youtube.
>
> Your output in this email from your program (
> https://play.golang.org/p/zKthX7Y9RW) doesn't include any error output.
> You can ignore the GODEBUG output. If it says there's no cached connection,
> that means http2 has no cached connection it needs to dial (which http1
> will do). Then http1 works as normal, unless it decides that it negotiated
> http2, and then it goes back to http2.
>
> But any rate-limiting you refer to is unchanged from before, since HTTP/1
> still dials as normal. There's an open bug to optimize it (to only start 1
> or 2 TCP connections until we know the negotiated protocol, and then settle
> on 6 or 1 max connections, etc), but it's no different today than Go 1.5
> and earlier.
>
> In any case, if you have a reproducible bug, let's move this to a bug
> tracker.
>
>
>
>
>
>
>
>
>
>
>
>
> On Tue, Aug 2, 2016 at 6:36 PM, 'Russ Amos' via golang-nuts <
> golang-nuts@googlegroups.com> wrote:
>
>> I'm seeing "http2: no cached connection was available" failures from
>> http.Client when I start many (~hundreds) requests at once. (This issue was
>> also posted to golang-nuts@ in April
>> ,
>> with no response)
>>
>> I may not understand correctly, but I thought this kind of usage was fine
>> with HTTP 1.1 and net/http, because the spec mandates a max number of
>> outgoing connections to any given host, so http.Client throttles open
>> connections and effectively queues requests past that. The http2 package
>> seems not to do the same. That might be correct according to the spec (I
>> don't know), but makes using http.Client weird -- I need to rate limit its
>> usage if the server is HTTP 2, but it does rate limiting for me if the
>> server is HTTP 1.1.
>>
>> Is my understanding correct? Is this a bug? Is the expectation that my
>> app should be rate limiting, regardless of server version?
>>
>> Also, It seems the error being returned is exported
>>  in the http2
>> package, but is not exported in the bundled version
>>  in net/http. If it
>> was exported, I think I could at least retry on my own, but perhaps that's
>> not the intended usage anyway.
>>
>> I wrote this program  hitting
>> https://www.google.com/ to demonstrate -- here are a few run results:
>>
>> $ GODEBUG=http2client=0 go run /tmp/foo.go
>> $ GODEBUG=http2client=0 go run /tmp/foo.go
>> $ GODEBUG=http2client=0 go run /tmp/foo.go
>> $ GODEBUG=http2client=0 go run /tmp/foo.go
>> $ GODEBUG=http2client=0 go run /tmp/foo.go
>>
>> $ GODEBUG=http2client=1 go run /tmp/foo.go
>> Get https://www.google.com/: http2: no cached connection was available
>> Get https://www.google.com/: http2: no cached connection was available
>> Get https://www.google.com/: http2: no cached connection was available
>> ...
>> $ GODEBUG=http2client=1 go run /tmp/foo.go
>> Get https://www.google.com/: http2: no cached connection was available
>> $ GODEBUG=http2client=1 go run /tmp/foo.go
>> $ GODEBUG=http2client=1 go run /tmp/foo.go
>> Get https://www.google.com/: http2: no cached connection was available
>> Get https://www.google.com/: http2: no cached connection was available
>> Get https://www.google.com/: http2: no cached connection was available
>> ...
>> $ GODEBUG=http2client=1 go run /tmp/foo.go
>> Get https://www.google.com/: http2: no cached connection was available
>> Get https://www.google.com/: http2: no cached connection was available
>> Get https://www.google.com/: http2: no cached connection was available
>> ...
>>
>> --
>> You received this message because you are subscribed to the Google Groups
>> "golang-nuts" group.
>> To unsubscribe from this group and stop receiving emails from it, send an
>> email to golang-nuts+unsubscr...@googlegroups.com.
>> For more options, visit https://groups.google.com/d/optout.
>>
>

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Re: [go-nuts] http.Client returning "http2: no cached connection was available"

[Brad Fitzpatrick]

Sorry, I don't read all of golang-nuts@ and never saw that. You could've
escalated, though. There are at least two bug trackers available to you:

http://b/
https://github.com/golang/go/issues  (the one I prefer)

But I think your interpretation of the the HTTP/2 client is wrong.

If you're a video person, there's a talk on Go's HTTP client and its
HTTP/2<->HTTP/1<->HTTP/2 dialing sandwich...
https://www.youtube.com/watch?v=FARQMJndUn0
If you're not a video person, the slides are linked from youtube.

Your output in this email from your program (
https://play.golang.org/p/zKthX7Y9RW) doesn't include any error output. You
can ignore the GODEBUG output. If it says there's no cached connection,
that means http2 has no cached connection it needs to dial (which http1
will do). Then http1 works as normal, unless it decides that it negotiated
http2, and then it goes back to http2.

But any rate-limiting you refer to is unchanged from before, since HTTP/1
still dials as normal. There's an open bug to optimize it (to only start 1
or 2 TCP connections until we know the negotiated protocol, and then settle
on 6 or 1 max connections, etc), but it's no different today than Go 1.5
and earlier.

In any case, if you have a reproducible bug, let's move this to a bug
tracker.












On Tue, Aug 2, 2016 at 6:36 PM, 'Russ Amos' via golang-nuts <
golang-nuts@googlegroups.com> wrote:

> I'm seeing "http2: no cached connection was available" failures from
> http.Client when I start many (~hundreds) requests at once. (This issue was
> also posted to golang-nuts@ in April
> ,
> with no response)
>
> I may not understand correctly, but I thought this kind of usage was fine
> with HTTP 1.1 and net/http, because the spec mandates a max number of
> outgoing connections to any given host, so http.Client throttles open
> connections and effectively queues requests past that. The http2 package
> seems not to do the same. That might be correct according to the spec (I
> don't know), but makes using http.Client weird -- I need to rate limit its
> usage if the server is HTTP 2, but it does rate limiting for me if the
> server is HTTP 1.1.
>
> Is my understanding correct? Is this a bug? Is the expectation that my app
> should be rate limiting, regardless of server version?
>
> Also, It seems the error being returned is exported
>  in the http2
> package, but is not exported in the bundled version
>  in net/http. If it
> was exported, I think I could at least retry on my own, but perhaps that's
> not the intended usage anyway.
>
> I wrote this program  hitting
> https://www.google.com/ to demonstrate -- here are a few run results:
>
> $ GODEBUG=http2client=0 go run /tmp/foo.go
> $ GODEBUG=http2client=0 go run /tmp/foo.go
> $ GODEBUG=http2client=0 go run /tmp/foo.go
> $ GODEBUG=http2client=0 go run /tmp/foo.go
> $ GODEBUG=http2client=0 go run /tmp/foo.go
>
> $ GODEBUG=http2client=1 go run /tmp/foo.go
> Get https://www.google.com/: http2: no cached connection was available
> Get https://www.google.com/: http2: no cached connection was available
> Get https://www.google.com/: http2: no cached connection was available
> ...
> $ GODEBUG=http2client=1 go run /tmp/foo.go
> Get https://www.google.com/: http2: no cached connection was available
> $ GODEBUG=http2client=1 go run /tmp/foo.go
> $ GODEBUG=http2client=1 go run /tmp/foo.go
> Get https://www.google.com/: http2: no cached connection was available
> Get https://www.google.com/: http2: no cached connection was available
> Get https://www.google.com/: http2: no cached connection was available
> ...
> $ GODEBUG=http2client=1 go run /tmp/foo.go
> Get https://www.google.com/: http2: no cached connection was available
> Get https://www.google.com/: http2: no cached connection was available
> Get https://www.google.com/: http2: no cached connection was available
> ...
>
> --
> You received this message because you are subscribed to the Google Groups
> "golang-nuts" group.
> To unsubscribe from this group and stop receiving emails from it, send an
> email to golang-nuts+unsubscr...@googlegroups.com.
> For more options, visit https://groups.google.com/d/optout.
>

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[go-nuts] http.Client returning "http2: no cached connection was available"

['Russ Amos' via golang-nuts]

I'm seeing "http2: no cached connection was available" failures from
http.Client when I start many (~hundreds) requests at once. (This issue was
also posted to golang-nuts@ in April
,
with no response)

I may not understand correctly, but I thought this kind of usage was fine
with HTTP 1.1 and net/http, because the spec mandates a max number of
outgoing connections to any given host, so http.Client throttles open
connections and effectively queues requests past that. The http2 package
seems not to do the same. That might be correct according to the spec (I
don't know), but makes using http.Client weird -- I need to rate limit its
usage if the server is HTTP 2, but it does rate limiting for me if the
server is HTTP 1.1.

Is my understanding correct? Is this a bug? Is the expectation that my app
should be rate limiting, regardless of server version?

Also, It seems the error being returned is exported
 in the http2
package, but is not exported in the bundled version
 in net/http. If it was
exported, I think I could at least retry on my own, but perhaps that's not
the intended usage anyway.

I wrote this program  hitting
https://www.google.com/ to demonstrate -- here are a few run results:

$ GODEBUG=http2client=0 go run /tmp/foo.go
$ GODEBUG=http2client=0 go run /tmp/foo.go
$ GODEBUG=http2client=0 go run /tmp/foo.go
$ GODEBUG=http2client=0 go run /tmp/foo.go
$ GODEBUG=http2client=0 go run /tmp/foo.go

$ GODEBUG=http2client=1 go run /tmp/foo.go
Get https://www.google.com/: http2: no cached connection was available
Get https://www.google.com/: http2: no cached connection was available
Get https://www.google.com/: http2: no cached connection was available
...
$ GODEBUG=http2client=1 go run /tmp/foo.go
Get https://www.google.com/: http2: no cached connection was available
$ GODEBUG=http2client=1 go run /tmp/foo.go
$ GODEBUG=http2client=1 go run /tmp/foo.go
Get https://www.google.com/: http2: no cached connection was available
Get https://www.google.com/: http2: no cached connection was available
Get https://www.google.com/: http2: no cached connection was available
...
$ GODEBUG=http2client=1 go run /tmp/foo.go
Get https://www.google.com/: http2: no cached connection was available
Get https://www.google.com/: http2: no cached connection was available
Get https://www.google.com/: http2: no cached connection was available
...

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