--- a/mercurial/debugcommands.py Tue Mar 13 11:20:07 2018 -0700
+++ b/mercurial/debugcommands.py Tue Mar 13 10:34:36 2018 -0700
@@ -2846,6 +2846,12 @@
if ui.debugflag:
openerargs[r'loggingopts'][r'logdataapis'] = True
+ # Don't send default headers when in raw mode. This allows us to
+ # bypass most of the behavior of our URL handling code so we can
+ # have near complete control over what's sent on the wire.
+ if opts['peer'] == 'raw':
+ openerargs[r'sendaccept'] = False
+
opener = urlmod.opener(ui, authinfo, **openerargs)
if opts['peer'] == 'raw':