Patch to enable SSH-based remote command executor for windows clients

This patch aims to fix a hanging Python sessions after the execution
of an SSH remote command call with no particular stdin input.

Interpretation from #68

    Without overriding stdin, the subprocess, i.e. ssh, and python share
    the same file pointer. It seems that stdin is configured in a way that
    unexpected by the interpreter and messes with python's way to read from
    sys.stdin.

This patch passes an explicit `b''` as `stdin` to the SSH client
execution process to effectively achieve a separate fiel descriptor for
that client process.

This patch should not interfere with the implementation of the `sshrun`
command in datalad-core. It uses a dedicated not-None value for any
execution. However, the compatibility and interference of this patch
should be subject to a thorough investigation and widespread testing
before this changeset is proposed for datalad-core.

Closes #68

datalad_ria/__init__.py

@@ -26,6 +26,9 @@
     ]
 )
 
+# patch datalad-core
+import datalad_ria.patches.enabled
+
 from ._version import get_versions
 __version__ = get_versions()['version']
 del get_versions

datalad_ria/patches/__init__.py

@@ -0,0 +1,3 @@
+import logging
+
+lgr = logging.getLogger('datalad.ext.ria.patches')

datalad_ria/patches/enabled.py

@@ -0,0 +1,3 @@
+from . import (
+    ssh_exec,
+)

datalad_ria/patches/ssh_exec.py

@@ -0,0 +1,57 @@
+"""
+
+With this patch ...
+"""
+
+import logging
+
+from datalad.support.sshconnector import (
+    StdOutErrCapture,
+    NoCapture,
+)
+
+from datalad_next.patches import apply_patch
+from datalad_next.utils import on_windows
+
+# use same logger as -core
+lgr = logging.getLogger('datalad.support.sshconnector')
+
+
+# This method interface/original implementation is taken from
+# datalad-core@58b8e06317fe1a03290aed80526bff1e2d5b7797
+# datalad/support/sshconnector.py:BaseSSHConnection
+def _exec_ssh(self, ssh_cmd, cmd, options=None, stdin=None, log_output=True):
+    cmd = self._adjust_cmd_for_bundle_execution(cmd)
+
+    for opt in options or []:
+        ssh_cmd.extend(["-o", opt])
+
+    # THIS IS THE PATCH
+    if on_windows and stdin is None:
+        # SSH on windows requires a special stdin handling. If we'd let
+        # stdin=None do its normal thing, the Python process would hang,
+        # because it looses touch with its own file descriptor.
+        # See https://github.com/datalad/datalad-ria/issues/68
+        stdin = b''
+
+    # build SSH call, feed remote command as a single last argument
+    # whatever it contains will go to the remote machine for execution
+    # we cannot perform any sort of escaping, because it will limit
+    # what we can do on the remote, e.g. concatenate commands with '&&'
+    ssh_cmd += [self.sshri.as_str()] + [cmd]
+
+    lgr.debug("%s is used to run %s", self, ssh_cmd)
+
+    # TODO: pass expect parameters from above?
+    # Hard to explain to toplevel users ... So for now, just set True
+    out = self.runner.run(
+        ssh_cmd,
+        protocol=StdOutErrCapture if log_output else NoCapture,
+        stdin=stdin)
+    return out['stdout'], out['stderr']
+
+
+apply_patch(
+    'datalad.support.sshconnector', 'BaseSSHConnection', '_exec_ssh',
+    _exec_ssh,
+)