Massively speed up low-level SFTP read/write

This doesn't impact most users who perform reads/writes using
SFTPClient.get(fo)/put(fo) as those naturally perform chunking. However,
users accessing the raw SFTPFile objects via SFTPClient.open() and then
reading/writing large (more than a few MB) files, may experience severe
slowdown due to inefficient slicing of the file being read/written.

This change replaces the naive "slice a list of bytes" code with
bytearray and memoryview, which are significantly more performant in
these use cases, while remaining backwards compatible.

Patch courtesy of Sevastian Tchernov.

1 files changed, 10 insertions, 0 deletions

diff --git a/sites/www/changelog.rst b/sites/www/changelog.rst
index 48119f00..9387aabf 100644
--- a/sites/www/changelog.rst
+++ b/sites/www/changelog.rst
@@ -2,6 +2,16 @@
 Changelog
 =========
 
+- :bug:`892 major` Significantly speed up low-level read/write actions on
+  `~paramiko.sftp_file.SFTPFile` objects by using `bytearray`/`memoryview`.
+  This is unlikely to change anything for users of the higher level methods
+  like ``SFTPClient.get`` or ``SFTPClient.getfo``, but users of
+  `SFTPClient.open <paramiko.sftp_client.SFTPClient.open>` will likely see
+  orders of magnitude improvements for files larger than a few megabytes in
+  size.
+
+  Thanks to ``@jkji`` for the original report and to Sevastian Tchernov for the
+  patch.
 - :support:`1985` Add ``six`` explicitly to install-requires; it snuck into
   active use at some point but has only been indicated by transitive dependency
   on ``bcrypt`` until they somewhat-recently dropped it. This will be