Make prefetching optional in get() and getfo()

In some cases prefetching can lead to problems when downloading larger files. The connection to the SFTP server is disconnected due to the query behavior.
Proprietary implementations in particular tend to behave that way. Switching off prefetching is a slow but resilient solution to this problem.

1 files changed, 9 insertions, 4 deletions

diff --git a/paramiko/sftp_client.py b/paramiko/sftp_client.py
index 93190d85..88e6eee0 100644
--- a/paramiko/sftp_client.py
+++ b/paramiko/sftp_client.py
@@ -758,7 +758,7 @@ class SFTPClient(BaseSFTP, ClosingContextManager):
         with open(localpath, "rb") as fl:
             return self.putfo(fl, remotepath, file_size, callback, confirm)
 
-    def getfo(self, remotepath, fl, callback=None):
+    def getfo(self, remotepath, fl, callback=None, prefetch=True):
         """
         Copy a remote file (``remotepath``) from the SFTP server and write to
         an open file or file-like object, ``fl``.  Any exception raised by
@@ -771,18 +771,21 @@ class SFTPClient(BaseSFTP, ClosingContextManager):
         :param callable callback:
             optional callback function (form: ``func(int, int)``) that accepts
             the bytes transferred so far and the total bytes to be transferred
+        :param bool prefetch:
+            option to deactivate prefetching
         :return: the `number <int>` of bytes written to the opened file object
 
         .. versionadded:: 1.10
         """
         file_size = self.stat(remotepath).st_size
         with self.open(remotepath, "rb") as fr:
-            fr.prefetch(file_size)
+            if prefetch:
+                fr.prefetch(file_size)
             return self._transfer_with_callback(
                 reader=fr, writer=fl, file_size=file_size, callback=callback
             )
 
-    def get(self, remotepath, localpath, callback=None):
+    def get(self, remotepath, localpath, callback=None, prefetch=True):
         """
         Copy a remote file (``remotepath``) from the SFTP server to the local
         host as ``localpath``.  Any exception raised by operations will be
@@ -793,13 +796,15 @@ class SFTPClient(BaseSFTP, ClosingContextManager):
         :param callable callback:
             optional callback function (form: ``func(int, int)``) that accepts
             the bytes transferred so far and the total bytes to be transferred
+        :param bool prefetch:
+            option to deactivate prefetching
 
         .. versionadded:: 1.4
         .. versionchanged:: 1.7.4
             Added the ``callback`` param
         """
         with open(localpath, "wb") as fl:
-            size = self.getfo(remotepath, fl, callback)
+            size = self.getfo(remotepath, fl, callback, prefetch)
         s = os.stat(localpath)
         if s.st_size != size:
             raise IOError(