SCP sink implementation in GO - go

Question

I'm trying to implement SSH server which acts as SCP sink (without calling external scp command) in GO.
I've ended up in partially working code:
https://gist.github.com/Seitanas/ad02158e8d5d2acedd9e7973ae44c77c.
The problem is that when I try to scp file to this service, local scp client copies data correctly but returns 1.
I think something happens at channel close. Maybe I'm missing something inside SCP protocol?
I'm guessing that ssh returns -1 and then scp exits with 1
Testing results:
echo "contents"> test.txt
scp -v -P2222 test.txt foo#127.0.0.1:/
Executing: program /usr/bin/ssh host 127.0.0.1, user foo, command scp -v -t /
...
debug1: SSH2_MSG_SERVICE_ACCEPT received
debug1: Authentications that can continue: password
debug1: Next authentication method: password
foo#127.0.0.1's password:
debug1: Authentication succeeded (password).
Authenticated to 127.0.0.1 ([127.0.0.1]:2222).
debug1: channel 0: new [client-session]
debug1: Requesting no-more-sessions#openssh.com
debug1: Entering interactive session.
debug1: pledge: network
debug1: Sending environment.
debug1: Sending env LC_TERMINAL_VERSION = 3.4.12
debug1: Sending env LC_CTYPE = en_US.UTF-8
debug1: Sending env LC_TERMINAL = iTerm2
debug1: Sending command: scp -v -t /
Sending file modes: C0644 9 test.txt
test.txt 0% 0 0.0KB/s --:-- ETAdebug1: channel 0: free: client-session, nchannels 1
test.txt 100% 9 21.4KB/s 00:00
debug1: fd 0 clearing O_NONBLOCK
Transferred: sent 2032, received 1116 bytes, in 0.0 seconds
Bytes per second: sent 1245098.0, received 683823.5
debug1: Exit status -1
echo $?
1
Output from go code:
go run test.go
2022/02/15 17:17:21 Command: C
2022/02/15 17:17:21 File info: 0644 9 test.txt
2022/02/15 17:17:21 File size: 9
2022/02/15 17:17:21 Content: contents
Thank you for any ideas.

Answer 1

Right, I've found what the problem is.
I've forgot that I'm simulating SCP binary ant server side, so i need to simulate its exit code also.
So I've added additional line at the end:
channel.SendRequest("exit-status", false, []byte{0, 0, 0, 0})
This will send exit 0 status via channel.
Without it SCP at client side was waiting for remote transfer to finish, but socket was closing right after transfer without exit code.
Now everything works as expected:
debug1: Sending command: scp -v -t /
Sending file modes: C0644 9 test.txt
test.txt 0% 0 0.0KB/s --:-- ETAdebug1: client_input_channel_req: channel 0 rtype exit-status reply 0
debug1: channel 0: free: client-session, nchannels 1
test.txt 100% 9 14.1KB/s 00:00
debug1: fd 0 clearing O_NONBLOCK
Transferred: sent 2152, received 1172 bytes, in 0.0 seconds
Bytes per second: sent 1391979.3, received 758085.4
debug1: Exit status 0