clone: add a server-side option to disable full getbundles (pull-based clones)

For large enough repositories, pull-based clones take too long, and an attempt
to use them indicates some sort of configuration or other issue or maybe an
outdated Mercurial. Add a config option to disable them.

mercurial/help/config.txt

@@ -1660,6 +1660,12 b' Controls generic server settings.'
     When set, clients will try to use the uncompressed streaming
     protocol. (default: False)
 
+``disablefullbundle``
+    When set, servers will refuse attempts to do pull-based clones.
+    If this option is set, ``preferuncompressed`` and/or clone bundles
+    are highly recommended. Partial clones will still be allowed.
+    (default: False)
+
 ``validate``
     Whether to validate the completeness of pushed changesets by
     checking that all new file revisions specified in manifests are

mercurial/wireproto.py

@@ -16,6 +16,7 b' from .i18n import _'
 from .node import (
     bin,
     hex,
+    nullid,
 )
 
 from . import (
@@ -841,6 +842,17 b' def getbundle(repo, proto, others):'
                               hint=bundle2requiredhint)
 
     try:
+        if repo.ui.configbool('server', 'disablefullbundle', False):
+            # Check to see if this is a full clone.
+            clheads = set(repo.changelog.heads())
+            heads = set(opts.get('heads', set()))
+            common = set(opts.get('common', set()))
+            common.discard(nullid)
+            if not common and clheads == heads:
+                raise error.Abort(
+                    _('server has pull-based clones disabled'),
+                    hint=_('remove --pull if specified or upgrade Mercurial'))
+
         chunks = exchange.getbundlechunks(repo, 'serve', **opts)
     except error.Abort as exc:
         # cleanly forward Abort error to the client

tests/test-http-bundle1.t

@@ -365,3 +365,41 b' Check error reporting while pulling/clon'
   this is an exercise
   [255]
   $ cat error.log
+
+disable pull-based clones
+
+  $ hg -R test serve -p $HGPORT1 -d --pid-file=hg4.pid -E error.log --config server.disablefullbundle=True
+  $ cat hg4.pid >> $DAEMON_PIDS
+  $ hg clone http://localhost:$HGPORT1/ disable-pull-clone
+  requesting all changes
+  abort: remote error:
+  server has pull-based clones disabled
+  [255]
+
+... but keep stream clones working
+
+  $ hg clone --uncompressed --noupdate http://localhost:$HGPORT1/ test-stream-clone
+  streaming all changes
+  * files to transfer, * of data (glob)
+  transferred * in * seconds (* KB/sec) (glob)
+  searching for changes
+  no changes found
+
+... and also keep partial clones and pulls working
+  $ hg clone http://localhost:$HGPORT1 --rev 0 test-partial-clone
+  adding changesets
+  adding manifests
+  adding file changes
+  added 1 changesets with 4 changes to 4 files
+  updating to branch default
+  4 files updated, 0 files merged, 0 files removed, 0 files unresolved
+  $ hg pull -R test-partial-clone
+  pulling from http://localhost:$HGPORT1/
+  searching for changes
+  adding changesets
+  adding manifests
+  adding file changes
+  added 2 changesets with 3 changes to 3 files
+  (run 'hg update' to get a working copy)
+
+  $ cat error.log

tests/test-http.t

@@ -354,6 +354,44 b' check abort error reporting while pullin'
   [255]
   $ cat error.log
 
+disable pull-based clones
+
+  $ hg -R test serve -p $HGPORT1 -d --pid-file=hg4.pid -E error.log --config server.disablefullbundle=True
+  $ cat hg4.pid >> $DAEMON_PIDS
+  $ hg clone http://localhost:$HGPORT1/ disable-pull-clone
+  requesting all changes
+  remote: abort: server has pull-based clones disabled
+  abort: pull failed on remote
+  (remove --pull if specified or upgrade Mercurial)
+  [255]
+
+... but keep stream clones working
+
+  $ hg clone --uncompressed --noupdate http://localhost:$HGPORT1/ test-stream-clone
+  streaming all changes
+  * files to transfer, * of data (glob)
+  transferred * in * seconds (*/sec) (glob)
+  searching for changes
+  no changes found
+  $ cat error.log
+
+... and also keep partial clones and pulls working
+  $ hg clone http://localhost:$HGPORT1 --rev 0 test-partial-clone
+  adding changesets
+  adding manifests
+  adding file changes
+  added 1 changesets with 4 changes to 4 files
+  updating to branch default
+  4 files updated, 0 files merged, 0 files removed, 0 files unresolved
+  $ hg pull -R test-partial-clone
+  pulling from http://localhost:$HGPORT1/
+  searching for changes
+  adding changesets
+  adding manifests
+  adding file changes
+  added 2 changesets with 3 changes to 3 files
+  (run 'hg update' to get a working copy)
+
 corrupt cookies file should yield a warning
 
   $ cat > $TESTTMP/cookies.txt << EOF