# HG changeset patch
# User Augie Fackler <augie@google.com>
# Date 1537843532 14400
# Node ID 1cf1680b05546b9c8df1a899792d2da0e3a37813
# Parent  d3d333ab167a5f0c23bd42a822732683d9afa221
keepalive: be more careful about self._rbuf when calling super impls

In Python 3, HTTPResponse implements read() in terms of readinto(),
which was calling back into our readinto(), which duplicates
self._rbuf if it's not empty. Before calling into super's read(),
ensure self._rbuf is empty.

Inheritance is bad, and undocumented self-use of your public API is
one of many reasons.

Differential Revision: https://phab.mercurial-scm.org/D4728

diff -r d3d333ab167a -r 1cf1680b0554 mercurial/keepalive.py
--- a/mercurial/keepalive.py	Mon Sep 17 11:50:59 2018 -0700
+++ b/mercurial/keepalive.py	Mon Sep 24 22:45:32 2018 -0400
@@ -417,9 +417,12 @@
                 s = self._rbuf[:amt]
                 self._rbuf = self._rbuf[amt:]
                 return s
-
-        s = self._rbuf + self._raw_read(amt)
+        # Careful! http.client.HTTPResponse.read() on Python 3 is
+        # implemented using readinto(), which can duplicate self._rbuf
+        # if it's not empty.
+        s = self._rbuf
         self._rbuf = ''
+        s += self._raw_read(amt)
         return s
 
     # stolen from Python SVN #68532 to fix issue1088