Fix check for paramiko version for 1.7.8...1.10.4

2 files changed, 39 insertions, 1 deletions

diff --git a/NEWS b/NEWS
index 2061b691..f8620c23 100644
--- a/NEWS
+++ b/NEWS
@@ -8,6 +8,18 @@ development, called `green-albatross`. It is **NOT** meant for real
 use. It is likely to change in incompatible ways without warning. Do
 not use it unless you're willing to lose your backup.
 
+Version 1.19.1, released UNRELEASED
+---------------------------------
+
+Bug fix:
+
+* The check for paramiko version turned out not to work with
+  versions 1.7.8 through 1.10.4, due to the
+  `paramiko.__version_info__` variable being missing. It's there in
+  earlier and later versions. Lars Wirzenius added code to make the
+  check work if the `paramiko.__version__` variable is there. Jan
+  Niggemann provided research and testing.
+
 Version 1.19, released 2016-01-15
 ---------------------------------
 
diff --git a/obnamlib/plugins/sftp_plugin.py b/obnamlib/plugins/sftp_plugin.py
index 47a3003c..ab87368f 100644
--- a/obnamlib/plugins/sftp_plugin.py
+++ b/obnamlib/plugins/sftp_plugin.py
@@ -80,6 +80,11 @@ class HardlinkError(obnamlib.ObnamError):
     '''
 
 
+class UnknownParamikoVersion(obnamlib.ObnamError):
+
+    msg = '''Cannot find out version of Paramiko.'''
+
+
 def ioerror_to_oserror(method):
     '''Decorator to convert an IOError exception to OSError.
 
@@ -574,12 +579,33 @@ class SftpFS(obnamlib.VirtualFileSystem):
 
         '''
 
-        if paramiko.__version_info__ < (1, 16):
+        version_info = self._get_paramiko_version_info()
+        if version_info < (1, 16):
             f.prefetch()
         else:
             file_size = self.lstat(pathname).st_size
             f.prefetch(file_size)
 
+    def _get_paramiko_version_info(self):
+        '''Get the __version_info__ tuple for paramiko.
+
+        Some versions of paramiko (1.7.8 to 1.10.4, according to
+        research by Jan Niggemann) have no __version_info__ tuple. We
+        need that tuple to do version comparisons.
+
+        This method constructs the tuple from paramiko.__version__, if
+        paramiko.__version_info__ is missing. If __version__ is also
+        missing, it raises an exception.
+
+        '''
+
+        if hasattr(paramiko, '__version_info__'):
+            return paramiko.__version_info__
+        elif hasattr(paramiko, '__version__'):
+            return tuple(int(x) for x in paramiko.__version__.split('.'))
+        else:
+            raise UnknownParamikoVersion()
+
     @ioerror_to_oserror
     def write_file(self, pathname, contents):
         mode = 'wbx'