Update Gmp selection class

CHANGELOG.md

@@ -1,9 +1,22 @@
 # Changelog
+
 All notable changes to this project will be documented in this file.
 
 The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/),
 and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 
+## [Unreleased]
+
+### Added
+* Added DEFAULT_SSH_PORT and DEFAULT_HOSTNAME constants to `gmp.connection` [#185](https://github.com/greenbone/python-gvm/pull/185)
+* Added `determine_remote_gmp_version` and `determine_supported_gmp` methods to
+  `gmp.protocols.gmp` module [#186](https://github.com/greenbone/python-gvm/pull/186)
+
+### Changed
+### Fixed
+
+[Unreleased]: https://github.com/greenbone/python-gvm/compare/v1.1.0...master
+
 ## [1.1.0] - 2019-11-22
 
 ### Added

gvm/protocols/gmp.py

@@ -19,7 +19,7 @@
 """
 Module for communication with gvmd
 """
-from typing import Any, Optional, Callable
+from typing import Any, Optional, Callable, Union
 
 from gvm.errors import GvmError
 
@@ -33,6 +33,8 @@
 
 from gvm.xml import XmlCommand
 
+SupportedGmpVersion = Union[Gmpv7, Gmpv8, Gmpv9]
+
 
 class Gmp(GvmProtocol):
     """Dynamically select supported GMP protocol of the remote manager daemon.
@@ -75,7 +77,9 @@ def __init__(
         super().__init__(connection, transform=EtreeCheckCommandTransform())
         self._gmp_transform = transform
 
-    def __enter__(self):
+    def determine_remote_gmp_version(self) -> str:
+        """ Determine the supported GMP version of the remote deamon
+        """
         self.connect()
         resp = self._send_xml_command(XmlCommand("get_version"))
         self.disconnect()
@@ -87,9 +91,14 @@ def __enter__(self):
                 'version information.'
             )
 
-        version = version_el.text
-        major_version = int(version[0])
+        return version_el.text
 
+    def determine_supported_gmp(self) -> SupportedGmpVersion:
+        """ Determine supported GMP version of the remote deamon and return a
+            corresponding Gmp class instance
+        """
+        version = self.determine_remote_gmp_version()
+        major_version = int(version[0])
         if major_version == 7:
             gmp_class = Gmpv7
         elif major_version == 8:
@@ -102,7 +111,11 @@ def __enter__(self):
                 'The GMP version was {}.'.format(version)
             )
 
-        gmp = gmp_class(self._connection, transform=self._gmp_transform)
+        return gmp_class(self._connection, transform=self._gmp_transform)
+
+    def __enter__(self):
+        gmp = self.determine_supported_gmp()
+
         gmp.connect()
 
         return gmp