Smart mode for sftp+scp (#17813)

If the sftp fails, roll over to scp by default. This saves users
from having to know about the scp_if_ssh method when sftp is broken
on the remote host.

examples/ansible.cfg

@@ -306,9 +306,11 @@
 #
 #pipelining = False
 
-# if True, make ansible use scp if the connection type is ssh
-# (default is sftp)
-#scp_if_ssh = True
+# Control the mechanism for transfering files
+#   * smart = try sftp and then try scp [default]
+#   * True = use scp only
+#   * False = use sftp only
+#scp_if_ssh = smart
 
 # if False, sftp will not use batch mode to transfer files. This may cause some
 # types of file transfer failures impossible to catch however, and should

lib/ansible/constants.py

@@ -172,7 +172,7 @@ DEFAULT_REMOTE_PORT       = get_config(p, DEFAULTS, 'remote_port',      'ANSIBLE
 DEFAULT_ASK_VAULT_PASS    = get_config(p, DEFAULTS, 'ask_vault_pass',    'ANSIBLE_ASK_VAULT_PASS',    False, boolean=True)
 DEFAULT_VAULT_PASSWORD_FILE = get_config(p, DEFAULTS, 'vault_password_file', 'ANSIBLE_VAULT_PASSWORD_FILE', None, ispath=True)
 DEFAULT_TRANSPORT         = get_config(p, DEFAULTS, 'transport',        'ANSIBLE_TRANSPORT',        'smart')
-DEFAULT_SCP_IF_SSH        = get_config(p, 'ssh_connection', 'scp_if_ssh',       'ANSIBLE_SCP_IF_SSH',       False, boolean=True)
+DEFAULT_SCP_IF_SSH        = get_config(p, 'ssh_connection', 'scp_if_ssh',       'ANSIBLE_SCP_IF_SSH',       'smart')
 DEFAULT_SFTP_BATCH_MODE   = get_config(p, 'ssh_connection', 'sftp_batch_mode', 'ANSIBLE_SFTP_BATCH_MODE', True, boolean=True)
 DEFAULT_MANAGED_STR       = get_config(p, DEFAULTS, 'ansible_managed',  None,           'Ansible managed: {file} modified on %Y-%m-%d %H:%M:%S by {uid} on {host}')
 DEFAULT_SYSLOG_FACILITY   = get_config(p, DEFAULTS, 'syslog_facility',  'ANSIBLE_SYSLOG_FACILITY', 'LOG_USER')

lib/ansible/plugins/connection/ssh.py

@@ -31,10 +31,14 @@ import time
 from ansible import constants as C
 from ansible.compat.six import text_type, binary_type
 from ansible.errors import AnsibleError, AnsibleConnectionFailure, AnsibleFileNotFound
+from ansible.errors import AnsibleOptionsError
+from ansible.module_utils.basic import BOOLEANS
 from ansible.module_utils._text import to_bytes, to_native, to_text
 from ansible.plugins.connection import ConnectionBase
+from ansible.utils.boolean import boolean
 from ansible.utils.path import unfrackpath, makedirs_safe
 
+
 try:
     from __main__ import display
 except ImportError:
@@ -309,7 +313,7 @@ class Connection(ConnectionBase):
 
         return b''.join(output), remainder
 
-    def _run(self, cmd, in_data, sudoable=True):
+    def _run(self, cmd, in_data, sudoable=True, checkrc=True):
         '''
         Starts the command and communicates with it until it ends.
         '''
@@ -551,7 +555,7 @@ class Connection(ConnectionBase):
         if p.returncode != 0 and controlpersisterror:
             raise AnsibleError('using -c ssh on certain older ssh versions may not support ControlPersist, set ANSIBLE_SSH_ARGS="" (or ssh_args in [ssh_connection] section of the config file) before running again')
 
-        if p.returncode == 255 and in_data:
+        if p.returncode == 255 and in_data and checkrc:
             raise AnsibleConnectionFailure('SSH Error: data could not be sent to the remote host. Make sure this host can be reached over ssh')
 
         return (p.returncode, b_stdout, b_stderr)
@@ -641,18 +645,49 @@ class Connection(ConnectionBase):
         # accept them for hostnames and IPv4 addresses too.
         host = '[%s]' % self.host
 
-        if C.DEFAULT_SCP_IF_SSH:
-            cmd = self._build_command('scp', in_path, u'{0}:{1}'.format(host, pipes.quote(out_path)))
-            in_data = None
-        else:
-            cmd = self._build_command('sftp', to_bytes(host))
-            in_data = u"put {0} {1}\n".format(pipes.quote(in_path), pipes.quote(out_path))
+        # since this can be a non-bool now, we need to handle it correctly
+        scp_if_ssh = C.DEFAULT_SCP_IF_SSH
+        if not isinstance(scp_if_ssh, bool):
+            scp_if_ssh = scp_if_ssh.lower()
+            if scp_if_ssh in BOOLEANS:
+                scp_if_ssh = boolean(scp_if_ssh)
+            elif scp_if_ssh != 'smart':
+                raise AnsibleOptionsError('scp_if_ssh needs to be one of [smart|True|False]')
 
-        in_data = to_bytes(in_data, nonstring='passthru')
-        (returncode, stdout, stderr) = self._run(cmd, in_data)
+        # create a list of commands to use based on config options
+        methods = ['sftp']
+        if scp_if_ssh == 'smart':
+            methods.append('scp')
+        elif scp_if_ssh:
+            methods = ['scp']
 
-        if returncode != 0:
-            raise AnsibleError("failed to transfer file to {0}:\n{1}\n{2}".format(to_native(out_path), to_native(stdout), to_native(stderr)))
+        success = False
+        res = None
+        for method in methods:
+            if method == 'sftp':
+                cmd = self._build_command('sftp', to_bytes(host))
+                in_data = u"put {0} {1}\n".format(pipes.quote(in_path), pipes.quote(out_path))
+            elif method == 'scp':
+                cmd = self._build_command('scp', in_path, u'{0}:{1}'.format(host, pipes.quote(out_path)))
+                in_data = None
+
+            in_data = to_bytes(in_data, nonstring='passthru')
+            (returncode, stdout, stderr) = self._run(cmd, in_data, checkrc=False)
+            # Check the return code and rollover to next method if failed
+            if returncode == 0:
+                success = True
+                break
+            else:
+                # If not in smart mode, the data will be printed by the raise below 
+                if scp_if_ssh == 'smart':
+                    display.warning(msg='%s transfer mechanism failed on %s. Use ANSIBLE_DEBUG=1 to see detailed information' % (method, host))
+                    display.debug(msg='%s' % to_native(stdout))
+                    display.debug(msg='%s' % to_native(stderr))
+                res = (returncode, stdout, stderr)
+
+        if not success:
+            raise AnsibleError("failed to transfer file to {0}:\n{1}\n{2}"\
+                    .format(to_native(out_path), to_native(res[1]), to_native(res[2])))
 
     def fetch_file(self, in_path, out_path):
         ''' fetch a file from remote to local '''

test/units/plugins/connections/test_connection_ssh.py

@@ -311,22 +311,22 @@ class TestConnectionBaseClass(unittest.TestCase):
         # test with C.DEFAULT_SCP_IF_SSH enabled
         C.DEFAULT_SCP_IF_SSH = True
         conn.put_file('/path/to/in/file', '/path/to/dest/file')
-        conn._run.assert_called_with('some command to run', None)
+        conn._run.assert_called_with('some command to run', None, checkrc=False)
 
         conn.put_file(u'/path/to/in/file/with/unicode-fö〩', u'/path/to/dest/file/with/unicode-fö〩')
-        conn._run.assert_called_with('some command to run', None)
+        conn._run.assert_called_with('some command to run', None, checkrc=False)
 
         # test with C.DEFAULT_SCP_IF_SSH disabled
         C.DEFAULT_SCP_IF_SSH = False
         expected_in_data = b' '.join((b'put', to_bytes(pipes.quote('/path/to/in/file')), to_bytes(pipes.quote('/path/to/dest/file')))) + b'\n'
         conn.put_file('/path/to/in/file', '/path/to/dest/file')
-        conn._run.assert_called_with('some command to run', expected_in_data)
+        conn._run.assert_called_with('some command to run', expected_in_data, checkrc=False)
 
         expected_in_data = b' '.join((b'put',
             to_bytes(pipes.quote('/path/to/in/file/with/unicode-fö〩')),
             to_bytes(pipes.quote('/path/to/dest/file/with/unicode-fö〩')))) + b'\n'
         conn.put_file(u'/path/to/in/file/with/unicode-fö〩', u'/path/to/dest/file/with/unicode-fö〩')
-        conn._run.assert_called_with('some command to run', expected_in_data)
+        conn._run.assert_called_with('some command to run', expected_in_data, checkrc=False)
 
         # test that a non-zero rc raises an error
         conn._run.return_value = (1, 'stdout', 'some errors')