Add Windows support

[jawnsy]

I'm opening this issue to discuss the best way to add Windows support, along with what I've found so far. I'd be happy to contribute a Windows implementation, including tests, but will require your guidance in order to do so effectively.

The current implementation of localexec_windows.go is an empty stub. By copying the implementation from localexec_unix.go and removing the non-portable Linux-specific parts (syscall, UID/GID), I was able to get a partial implementation running on Windows 10 under MinGW (Git Bash). I don't know if this is one of your near-term goals, but I thought you might be interested nonetheless.

Some caveats of the example I hacked together:

• I didn't implement TTY support or Resize
• A bunch of the integration tests are still failing
• This required a modification to ./dev/client/main.go to remove the build tag and comment out the SIGWINCH signals

Here's what I have working so far:

$ go version
go version go1.15.5 windows/amd64
$ go run ./dev/client notty ls
browser
ci
client.go
client_test.go
dev
doc.go
exec.go
go.mod
go.sum
internal
LICENSE.txt
localexec.go
localexec_test.go
localexec_unix.go
localexec_windows.go
README.md
server.go
tty_test.go
$ go run ./dev/client notty ps ux
      PID    PPID    PGID     WINPID   TTY         UID    STIME COMMAND
      716       1     716      10016  cons0    1051769 11:33:25 /usr/bin/bash
      810     716     810        252  cons0    1051769 11:35:48 /c/Program Files/Go/bin/go
      760       1     760      23620  cons1    1051769 11:33:42 /usr/bin/bash
      814     760     814      12756  cons1    1051769 11:37:38 /c/Program Files/Go/bin/go
      815       1     815       8208  ?        1051769 11:37:50 /usr/bin/ps

If I use the Command Prompt to start the server, then the results aren't as nice, however:

C:\projects\wsep>go run ./dev/server
2020-11-29 12:04:17 ERROR       failed to serve execer: start command: exec: "dir": executable file not found in %PATH%
2020/11/29 12:04:17 websocket: failed to marshal close frame: status code StatusAbnormalClosure cannot be set
exit status 2

A similar issue for PowerShell, too:

PS C:\projects\wsep> go run ./dev/server
2020-11-29 12:02:31 ERROR       failed to serve execer: start command: exec: "ls": executable file not found in %PATH%
2020/11/29 12:02:31 websocket: failed to marshal close frame: status code StatusAbnormalClosure cannot be set
2020-11-29 12:02:45 ERROR       failed to serve execer: start command: exec: "dir": executable file not found in %PATH%
2020/11/29 12:02:45 websocket: failed to marshal close frame: status code StatusAbnormalClosure cannot be set
exit status 2
PS C:\projects\wsep> dir

Mode                 LastWriteTime         Length Name
----                 -------------         ------ ----
d-----        11/29/2020     11:22                .github
d-----        11/29/2020     11:22                browser
d-----        11/29/2020     11:22                ci
d-----        11/29/2020     11:22                dev
d-----        11/29/2020     11:22                internal
-a----        11/29/2020     11:22              7 .gitignore
-a----        11/29/2020     11:22           5276 client.go
-a----        11/29/2020     11:22           3552 client_test.go
-a----        11/29/2020     11:22            223 doc.go
-a----        11/29/2020     11:22           1813 exec.go
-a----        11/29/2020     11:22            432 go.mod
-a----        11/29/2020     11:22          28298 go.sum
-a----        11/29/2020     11:22           1083 LICENSE.txt
-a----        11/29/2020     11:22           1022 localexec.go
-a----        11/29/2020     11:22           3415 localexec_test.go
-a----        11/29/2020     11:22           2279 localexec_unix.go
-a----        11/29/2020     11:35           1381 localexec_windows.go
-a----        11/29/2020     11:22           2360 README.md
-a----        11/29/2020     11:22           3732 server.go
-a----        11/29/2020     11:22           1283 tty_test.go

[jawnsy]

Ah, upon a closer look, this seems like full support will depend on creack/pty#109 or another one of the solutions discussed in this issue: creack/pty#95

[jawnsy]

Ah, I also see there's a branch for Windows support using the WinPTY approach, and thus requires shipping a DLL