ssh kitten: Allow using python instead of the shell on the server

docs/changelog.rst

@@ -13,6 +13,9 @@ To update |kitty|, :doc:`follow the instructions <binary>`.
 
 - diff kitten: Implement recursive diff over SSH (:iss:`3268`)
 
+- ssh kitten: Allow using python instead of the shell on the server, useful if
+  the shell used is a non-POSIX compliant one, such as fish (:iss:`3277`)
+
 - Add support for the color settings stack that XTerm copied from us without
   acknowledgement and decided to use incompatible escape codes for.
 

docs/faq.rst

@@ -54,7 +54,12 @@ type it each time::
     alias ssh="kitty +kitten ssh"
 
 If for some reason that does not work (typically because the server is using a
-non POSIX compliant shell), you can use the following one-liner instead (it
+non POSIX compliant shell), you can try using it with python instead::
+
+    kitty +kitten ssh use-python myserver
+
+If that also fails, perhaps because python is not installed on the remote
+server, use the following one-liner instead (it
 is slower as it needs to ssh into the server twice, but will work with most
 servers)::
 

kittens/ssh/main.py

@@ -46,6 +46,33 @@ exec -a "-$shell_name" "$0"
 '''
 
 
+PYTHON_SCRIPT = '''\
+#!/usr/bin/env python
+from __future__ import print_function
+from tempfile import NamedTemporaryFile
+import subprocess, os, sys, pwd, binascii, json
+
+# macOS ships with an ancient version of tic that cannot read from stdin, so we
+# create a temp file for it
+with NamedTemporaryFile() as tmp:
+    tmp.write(binascii.unhexlify('{terminfo}'))
+    p = subprocess.Popen(['tic', '-x', '-o', os.path.expanduser('~/.terminfo'), tmp.name], stdout=subprocess.PIPE, stderr=subprocess.PIPE)
+    stdout, stderr = p.communicate()
+    if p.wait() != 0:
+        getattr(sys.stderr, 'buffer', sys.stderr).write(stdout + stderr)
+        raise SystemExit('Failed to compile terminfo using tic')
+command_to_execute = json.loads(binascii.unhexlify('{command_to_execute}'))
+if command_to_execute:
+    os.execlp(command_to_execute[0], *command_to_execute)
+try:
+    shell_path = pwd.getpwuid(os.geteuid()).pw_shell or '/bin/sh'
+except KeyError:
+    shell_path = '/bin/sh'
+shell_name = '-' + os.path.basename(shell_path)
+os.execlp(shell_path, shell_name)
+'''
+
+
 def get_ssh_cli() -> Tuple[Set[str], Set[str]]:
     other_ssh_args: List[str] = []
     boolean_ssh_args: List[str] = []
@@ -150,12 +177,7 @@ def quote(x: str) -> str:
     return x
 
 
-def main(args: List[str]) -> NoReturn:
-    ssh_args, server_args, passthrough = parse_ssh_args(args[1:])
-    if passthrough:
-        cmd = ['ssh'] + ssh_args + server_args
-    else:
-        terminfo = subprocess.check_output(['infocmp']).decode('utf-8')
+def get_posix_cmd(terminfo: str, server_args: List[str]) -> List[str]:
     sh_script = SHELL_SCRIPT.replace('TERMINFO', terminfo, 1)
     if len(server_args) > 1:
         command_to_executeg = (quote(c) for c in server_args[1:])
@@ -163,7 +185,36 @@ def main(args: List[str]) -> NoReturn:
     else:
         command_to_execute = ''
     sh_script = sh_script.replace('EXEC_CMD', command_to_execute)
-        cmd = ['ssh'] + ssh_args + ['-t', server_args[0], sh_script] + server_args[1:]
+    return ['-t', server_args[0], sh_script] + server_args[1:]
+
+
+def get_python_cmd(terminfo: str, server_args: List[str]) -> List[str]:
+    import json
+    hostname = server_args[0]
+    command_to_execute = server_args[1:]
+    script = PYTHON_SCRIPT.format(
+        terminfo=terminfo.encode('utf-8').hex(),
+        command_to_execute=json.dumps(command_to_execute).encode('utf-8').hex()
+    )
+    return ['-t', hostname, f'python -c "{script}"']
+
+
+def main(args: List[str]) -> NoReturn:
+    args = args[1:]
+    use_posix = True
+    if args and args[0] == 'use-python':
+        args = args[1:]
+        use_posix = False
+    ssh_args, server_args, passthrough = parse_ssh_args(args)
+    if passthrough:
+        cmd = ['ssh'] + ssh_args + server_args
+    else:
+        terminfo = subprocess.check_output(['infocmp']).decode('utf-8')
+        cmd = ['ssh'] + ssh_args
+        if use_posix:
+            cmd += get_posix_cmd(terminfo, server_args)
+        else:
+            cmd += get_python_cmd(terminfo, server_args)
     os.execvp('ssh', cmd)