Add remoteid extension (prints FQDN of remote host during remote session)

Summary:
Wrap the capabilities wire protocol command to print the hostname to stderr.

This commit contains the implementation of the extension but not code to register it on a particular repo.

Test Plan: `rt`

Reviewers: #sourcecontrol, rmcelroy

Reviewed By: rmcelroy

Subscribers: durham, wez, stash, simonfar, mjpieters

Differential Revision: https://phabricator.intern.facebook.com/D5087634

Tasks: 16758829

Signature: t1:5087634:1495498748:213a32c5c474145371bbbc43b0463dee31868a9a

remoteid.py

@@ -0,0 +1,16 @@
+# Copyright 2016-present Facebook. All Rights Reserved.
+#
+# print server fqdn during a remote session
+
+import socket
+
+from mercurial import wireproto
+from mercurial.extensions import wrapfunction
+from mercurial.i18n import _
+
+def extsetup(ui):
+    def printhostname(orig, *args, **kwargs):
+        ui.warn(_('hostname') + ': ' + socket.getfqdn())
+        return orig(*args, **kwargs)
+
+    wrapfunction(wireproto, '_capabilities', printhostname)

tests/test-remoteid-print.t

@@ -0,0 +1,37 @@
+  $ PYTHONPATH=$TESTDIR/..:$PYTHONPATH
+  $ export PYTHONPATH
+
+  $ . "$TESTDIR/library.sh"
+
+# create a repo to behave as the server
+
+  $ hginit server
+  $ cd server
+  $ echo x > x
+  $ hg commit -qAm x
+
+# enable the remoteid extension
+
+  $ fb_hgext_dir=`realpath $TESTDIR/..`
+  $ cat >> .hg/hgrc <<EOF
+  > [extensions]
+  > remoteid=$fb_hgext_dir/remoteid.py
+  > 
+  > [remotefilelog]
+  > server=True
+  > EOF
+
+# clone the server repo - should display "hostname: ..."
+
+  $ cd ..
+  $ hgcloneshallow ssh://user@dummy/server client
+  remote: hostname: * (glob)
+  streaming all changes
+  2 files to transfer, 227 bytes of data
+  transferred 227 bytes in * seconds (*/sec) (glob)
+  searching for changes
+  no changes found
+  updating to branch default
+  remote: hostname: * (glob)
+  1 files updated, 0 files merged, 0 files removed, 0 files unresolved
+  1 files fetched over 1 fetches - (1 misses, 0.00% hit ratio) over *s (glob)