[PATCH v6 06/10] dts: add ssh session module

["Juraj Linkeš" <juraj.linkes@pantheon.tech>]

The module uses the pexpect python library and implements connection to
a node and two ways to interact with the node:
1. Send a string with specified prompt which will be matched after
   the string has been sent to the node.
2. Send a command to be executed. No prompt is specified here.

Signed-off-by: Owen Hilyard <ohilyard@iol.unh.edu>
Signed-off-by: Juraj Linkeš <juraj.linkes@pantheon.tech>
---
 dts/framework/exception.py                    |  57 ++++++
 dts/framework/remote_session/__init__.py      |  10 +
 .../remote_session/remote_session.py          |  40 ++--
 dts/framework/remote_session/ssh_session.py   | 185 ++++++++++++++++++
 dts/framework/utils.py                        |  13 ++
 5 files changed, 285 insertions(+), 20 deletions(-)
 create mode 100644 dts/framework/exception.py
 create mode 100644 dts/framework/remote_session/ssh_session.py
 create mode 100644 dts/framework/utils.py

diff --git a/dts/framework/exception.py b/dts/framework/exception.py
new file mode 100644
index 0000000000..8bff9cf9f6
--- /dev/null
+++ b/dts/framework/exception.py
@@ -0,0 +1,57 @@
+# SPDX-License-Identifier: BSD-3-Clause
+# Copyright(c) 2010-2014 Intel Corporation
+# Copyright(c) 2022 PANTHEON.tech s.r.o.
+# Copyright(c) 2022 University of New Hampshire
+#
+
+"""
+User-defined exceptions used across the framework.
+"""
+
+
+class SSHTimeoutError(Exception):
+    """
+    Command execution timeout.
+    """
+
+    command: str
+    output: str
+
+    def __init__(self, command: str, output: str):
+        self.command = command
+        self.output = output
+
+    def __str__(self) -> str:
+        return f"TIMEOUT on {self.command}"
+
+    def get_output(self) -> str:
+        return self.output
+
+
+class SSHConnectionError(Exception):
+    """
+    SSH connection error.
+    """
+
+    host: str
+
+    def __init__(self, host: str):
+        self.host = host
+
+    def __str__(self) -> str:
+        return f"Error trying to connect with {self.host}"
+
+
+class SSHSessionDeadError(Exception):
+    """
+    SSH session is not alive.
+    It can no longer be used.
+    """
+
+    host: str
+
+    def __init__(self, host: str):
+        self.host = host
+
+    def __str__(self) -> str:
+        return f"SSH session with {self.host} has died"
diff --git a/dts/framework/remote_session/__init__.py b/dts/framework/remote_session/__init__.py
index d924d8aaa9..d7478e6800 100644
--- a/dts/framework/remote_session/__init__.py
+++ b/dts/framework/remote_session/__init__.py
@@ -2,4 +2,14 @@
 # Copyright(c) 2022 PANTHEON.tech s.r.o.
 #
 
+from framework.config import NodeConfiguration
+from framework.logger import DTSLOG
+
 from .remote_session import RemoteSession
+from .ssh_session import SSHSession
+
+
+def create_remote_session(
+    node_config: NodeConfiguration, name: str, logger: DTSLOG
+) -> RemoteSession:
+    return SSHSession(node_config, name, logger)
diff --git a/dts/framework/remote_session/remote_session.py b/dts/framework/remote_session/remote_session.py
index 7c499c32e3..eaa4fa7a42 100644
--- a/dts/framework/remote_session/remote_session.py
+++ b/dts/framework/remote_session/remote_session.py
@@ -55,6 +55,13 @@ def __init__(
         self._connect()
         self.logger.info(f"Connection to {self.username}@{self.hostname} successful.")
 
+    @abstractmethod
+    def _connect(self) -> None:
+        """
+        Create connection to assigned node.
+        """
+        pass
+
     def send_command(self, command: str, timeout: float = SETTINGS.timeout) -> str:
         self.logger.info(f"Sending: {command}")
         out = self._send_command(command, timeout)
@@ -62,39 +69,32 @@ def send_command(self, command: str, timeout: float = SETTINGS.timeout) -> str:
         self._history_add(command=command, output=out)
         return out
 
-    def close(self, force: bool = False) -> None:
-        self.logger.logger_exit()
-        self._close(force)
+    @abstractmethod
+    def _send_command(self, command: str, timeout: float) -> str:
+        """
+        Send a command and return the output.
+        """
+        pass
 
     def _history_add(self, command: str, output: str) -> None:
         self.history.append(
             HistoryRecord(name=self.name, command=command, output=output)
         )
 
-    @abstractmethod
-    def is_alive(self) -> bool:
-        """
-        Check whether the session is still responding.
-        """
-        pass
-
-    @abstractmethod
-    def _connect(self) -> None:
-        """
-        Create connection to assigned node.
-        """
-        pass
+    def close(self, force: bool = False) -> None:
+        self.logger.logger_exit()
+        self._close(force)
 
     @abstractmethod
-    def _send_command(self, command: str, timeout: float) -> str:
+    def _close(self, force: bool = False) -> None:
         """
-        Send a command and return the output.
+        Close the remote session, freeing all used resources.
         """
         pass
 
     @abstractmethod
-    def _close(self, force: bool = False) -> None:
+    def is_alive(self) -> bool:
         """
-        Close the remote session, freeing all used resources.
+        Check whether the session is still responding.
         """
         pass
diff --git a/dts/framework/remote_session/ssh_session.py b/dts/framework/remote_session/ssh_session.py
new file mode 100644
index 0000000000..f71acfb1ca
--- /dev/null
+++ b/dts/framework/remote_session/ssh_session.py
@@ -0,0 +1,185 @@
+# SPDX-License-Identifier: BSD-3-Clause
+# Copyright(c) 2010-2014 Intel Corporation
+# Copyright(c) 2022 PANTHEON.tech s.r.o.
+# Copyright(c) 2022 University of New Hampshire
+#
+
+import time
+
+from pexpect import pxssh
+
+from framework.config import NodeConfiguration
+from framework.exception import SSHConnectionError, SSHSessionDeadError, SSHTimeoutError
+from framework.logger import DTSLOG
+from framework.utils import GREEN, RED
+
+from .remote_session import RemoteSession
+
+
+class SSHSession(RemoteSession):
+    """
+    Module for creating Pexpect SSH sessions to a node.
+    """
+
+    session: pxssh.pxssh
+    magic_prompt: str
+
+    def __init__(
+        self,
+        node_config: NodeConfiguration,
+        session_name: str,
+        logger: DTSLOG,
+    ):
+        self.magic_prompt = "MAGIC PROMPT"
+        super(SSHSession, self).__init__(node_config, session_name, logger)
+
+    def _connect(self) -> None:
+        """
+        Create connection to assigned node.
+        """
+        retry_attempts = 10
+        login_timeout = 20 if self.port else 10
+        password_regex = (
+            r"(?i)(?:password:)|(?:passphrase for key)|(?i)(password for .+:)"
+        )
+        try:
+            for retry_attempt in range(retry_attempts):
+                self.session = pxssh.pxssh(encoding="utf-8")
+                try:
+                    self.session.login(
+                        self.ip,
+                        self.username,
+                        self.password,
+                        original_prompt="[$#>]",
+                        port=self.port,
+                        login_timeout=login_timeout,
+                        password_regex=password_regex,
+                    )
+                    break
+                except Exception as e:
+                    self.logger.warning(e)
+                    time.sleep(2)
+                    self.logger.info(
+                        f"Retrying connection: retry number {retry_attempt + 1}."
+                    )
+            else:
+                raise Exception(f"Connection to {self.hostname} failed")
+
+            self.send_expect("stty -echo", "#")
+            self.send_expect("stty columns 1000", "#")
+        except Exception as e:
+            self.logger.error(RED(str(e)))
+            if getattr(self, "port", None):
+                suggestion = (
+                    f"\nSuggestion: Check if the firewall on {self.hostname} is "
+                    f"stopped.\n"
+                )
+                self.logger.info(GREEN(suggestion))
+
+            raise SSHConnectionError(self.hostname)
+
+    def send_expect(
+        self, command: str, prompt: str, timeout: float = 15, verify: bool = False
+    ) -> str | int:
+        try:
+            ret = self.send_expect_base(command, prompt, timeout)
+            if verify:
+                ret_status = self.send_expect_base("echo $?", prompt, timeout)
+                try:
+                    retval = int(ret_status)
+                    if retval:
+                        self.logger.error(f"Command: {command} failure!")
+                        self.logger.error(ret)
+                        return retval
+                    else:
+                        return ret
+                except ValueError:
+                    return ret
+            else:
+                return ret
+        except Exception as e:
+            self.logger.error(
+                f"Exception happened in [{command}] and output is "
+                f"[{self._get_output()}]"
+            )
+            raise e
+
+    def send_expect_base(self, command: str, prompt: str, timeout: float) -> str:
+        self._clean_session()
+        original_prompt = self.session.PROMPT
+        self.session.PROMPT = prompt
+        self._send_line(command)
+        self._prompt(command, timeout)
+
+        before = self._get_output()
+        self.session.PROMPT = original_prompt
+        return before
+
+    def _clean_session(self) -> None:
+        self.get_output(timeout=0.01)
+
+    def _send_line(self, command: str) -> None:
+        if not self.is_alive():
+            raise SSHSessionDeadError(self.hostname)
+        if len(command) == 2 and command.startswith("^"):
+            self.session.sendcontrol(command[1])
+        else:
+            self.session.sendline(command)
+
+    def _prompt(self, command: str, timeout: float) -> None:
+        if not self.session.prompt(timeout):
+            raise SSHTimeoutError(command, self._get_output()) from None
+
+    def get_output(self, timeout: float = 15) -> str:
+        """
+        Get all output before timeout
+        """
+        self.session.PROMPT = self.magic_prompt
+        try:
+            self.session.prompt(timeout)
+        except Exception:
+            pass
+
+        before = self._get_output()
+        self._flush()
+
+        self.logger.debug(before)
+        return before
+
+    def _get_output(self) -> str:
+        if not self.is_alive():
+            raise SSHSessionDeadError(self.hostname)
+        before = self.session.before.rsplit("\r\n", 1)[0]
+        if before == "[PEXPECT]":
+            return ""
+        return before
+
+    def _flush(self) -> None:
+        """
+        Clear all session buffer
+        """
+        self.session.buffer = ""
+        self.session.before = ""
+
+    def is_alive(self) -> bool:
+        return self.session.isalive()
+
+    def _send_command(self, command: str, timeout: float) -> str:
+        try:
+            self._clean_session()
+            self._send_line(command)
+        except Exception as e:
+            raise e
+
+        output = self.get_output(timeout=timeout)
+        self.session.PROMPT = self.session.UNIQUE_PROMPT
+        self.session.prompt(0.1)
+
+        return output
+
+    def _close(self, force: bool = False) -> None:
+        if force is True:
+            self.session.close()
+        else:
+            if self.is_alive():
+                self.session.logout()
diff --git a/dts/framework/utils.py b/dts/framework/utils.py
new file mode 100644
index 0000000000..fe13ae5e77
--- /dev/null
+++ b/dts/framework/utils.py
@@ -0,0 +1,13 @@
+# SPDX-License-Identifier: BSD-3-Clause
+# Copyright(c) 2010-2014 Intel Corporation
+# Copyright(c) 2022 PANTHEON.tech s.r.o.
+# Copyright(c) 2022 University of New Hampshire
+#
+
+
+def GREEN(text: str) -> str:
+    return f"\u001B[32;1m{str(text)}\u001B[0m"
+
+
+def RED(text: str) -> str:
+    return f"\u001B[31;1m{str(text)}\u001B[0m"
-- 
2.30.2