Support go1.21.0

[Rui Chen]

👋 Right now go1.19 is already EOL, and this go1.20 support commit did not get released, any chance of releasing it first and then move on to support go 1.21.0? Thanks!

build failure with go 1.21.0

# github.com/quic-go/quic-go/internal/qtls
/Users/rui/Library/Caches/Homebrew/go_mod_cache/pkg/mod/github.com/quic-go/quic-go@v0.32.0/internal/qtls/go121.go:5:13: cannot use "The version of quic-go you're using can't be built on Go 1.21 yet. For more details, please see https://github.com/quic-go/quic-go/wiki/quic-go-and-Go-versions." (untyped string constant "The version of quic-go you're using can't be built on Go 1.21 yet. F...) as int value in variable declaration

relates to Homebrew/homebrew-core#139431

[Vangelis66]

With respect 😉 , is it absolutely mandatory to chase after the latest quic-go version? Most sadly, because of this, latest quic-go (now at version 0.38.1) will only build under go1.20 and go1.21 😢 ...
But, this is not all; OP is a MacOS user, but on the Windows OS side of things 😉 , go1.21 cuts support for anything below Win10 😡 ; lots of people, me included, still use systems with < Win10 (yes, the "vendor" has stopped Extended Support, but, what the heck, people in China still use XP/7), so building on go1.21+ will leave such users stranded 😭 ...

go1.20 was recently updated with sec fixes to v1.20.8; would the gost developers consider extending support for go1.20 for the benefit of lots of Windows users still on NT 6.1/6.2/6.3 ? FWIW, even NT 6.0 is still (inadvertently 😄 ) supported, if the subsystem PE header of the go1.20 produced executables is "lowered" to 6.0...

Kind regards 😄 ...

[Vangelis66]

... Pending PR #983 is supposed to "fix" this issue here; due to my needs to keep support for Windows NT < 10.0 (that go1.21+ now excludes 😞 ), I explored the possibility of compiling the PR983 source code on latest go1.20, i.e. v1.20.8...

Well, of all the go modules updated inside that PR, it appears that the only one incompatible with go1.20 is kcp-go\v5 v5.6.3 (reason being this commit); so, I downgraded to its previous v5.6.2 (and, along the way, I updated go module quic-go to latest v0.38.1 - still go1.20 compatible) and thus I was able to compile the code with go1.20.8 in my older Win7 SP1 32-bit laptop:

file ./go.mod:

L3
-go 1.21
+go 1.20

L20
-	github.com/quic-go/quic-go v0.38.0
+	github.com/quic-go/quic-go v0.38.1

L25
-	github.com/xtaci/kcp-go/v5 v5.6.3
+	github.com/xtaci/kcp-go/v5 v5.6.2

file ./go.sum:

L90-L91
-github.com/quic-go/quic-go v0.38.0 h1:T45lASr5q/TrVwt+jrVccmqHhPL2XuSyoCLVCpfOSLc=
-github.com/quic-go/quic-go v0.38.0/go.mod h1:MPCuRq7KBK2hNcfKj/1iD1BGuN3eAYMeNxp3T42LRUg=
+github.com/quic-go/quic-go v0.38.1 h1:M36YWA5dEhEeT+slOu/SwMEucbYd0YFidxG3KlGPZaE=
+github.com/quic-go/quic-go v0.38.1/go.mod h1:ijnZM7JsFIkp4cRyjxJNIzdSfCLmUMg9wdyhGmg+SN4=

L107-L108
-github.com/xtaci/kcp-go/v5 v5.6.3 h1:yd59SKXdJ0PBxeMBy3apalxFCEmBLGgQmL6nP46tU0g=
-github.com/xtaci/kcp-go/v5 v5.6.3/go.mod h1:uIuw2KEg3FcmEdS4PeXHaGty9Ui7NYb1WKIrSDwpMg4=
+github.com/xtaci/kcp-go/v5 v5.6.2 h1:pSXMa5MOsb+EIZKe4sDBqlTExu2A/2Z+DFhoX2qtt2A=
+github.com/xtaci/kcp-go/v5 v5.6.2/go.mod h1:LsinWoru+lWWJHb+EM9HeuqYxV6bb9rNcK12v67jYzQ=

... and then compilation of binary gost-windows-386.exe was possible on go1.20:

gost-windows-386 -V => 

gost 2.12.0 (go1.20.8 windows/386)

Hope it's helpful to others 😜 ...