Fix to work with old and new Paramiko prefetch

Found and reported by Kyle Manna.

2 files changed, 22 insertions, 1 deletions

diff --git a/NEWS b/NEWS
index dcb472eb..b38ec119 100644
--- a/NEWS
+++ b/NEWS
@@ -17,6 +17,12 @@ Bug fixes:
   won't keep trying to use it, forever. Instead, it crashes and
   terminates the backup.
 
+* The Paramiko SSH implementation, which Obnam uses, changed the
+  interface to the `prefetch` method in its 1.16 version. Obnam can
+  now deal with either variant of the method. Found and reported by
+  Kyle Manna, who provided a patch that Lars Wirzenius rewrote to be
+  backwards compatible to older versions of Paramiko.
+
 Improvements to the manual:
 
 * The manual now has an appendix listing all Obnam errors, with codes
diff --git a/obnamlib/plugins/sftp_plugin.py b/obnamlib/plugins/sftp_plugin.py
index c4d5c2f7..66aedf61 100644
--- a/obnamlib/plugins/sftp_plugin.py
+++ b/obnamlib/plugins/sftp_plugin.py
@@ -555,7 +555,7 @@ class SftpFS(obnamlib.VirtualFileSystem):
     def cat(self, pathname):
         self._delay()
         f = self.open(pathname, 'rb')
-        f.prefetch()
+        self._prefetch(f)
         chunks = []
         while True:
             chunk = f.read(self.chunk_size)
@@ -566,6 +566,20 @@ class SftpFS(obnamlib.VirtualFileSystem):
         f.close()
         return ''.join(chunks)
 
+    def _prefetch(self, f):
+        '''Call f.prefetch in the right way.
+
+        Up to paramiko version 1.15.1, prefetch accepts no arguments.
+        In 1.16 it requires one.
+
+        '''
+
+        if paramiko.__version_info__ < (1, 16):
+            f.prefetch()
+        else:
+            file_size = f.lstat().st_size
+            f.prefetch(file_size)
+
     @ioerror_to_oserror
     def write_file(self, pathname, contents):
         mode = 'wbx'
@@ -588,6 +602,7 @@ class SftpFS(obnamlib.VirtualFileSystem):
         f.close()
 
     def _tempfile(self, dirname):
+
         '''Create a new file with a random name, return handle and name.'''
 
         if dirname: