ssl: set explicit symbol "!" to web.cacerts to disable SSL verification (BC)

The next patch will enable verification by using the system's CA store if
possible, which means we would have to distinguish None (=use default) from
'' (=--insecure). This smells bug-prone and provides no way to override
web.cacerts to forcibly use the system's store by --config argument.

This patch changes the meaning of web.cacerts as follows:

  value   behavior
  ------- ---------------------------------------
  None/'' use default
  '!'     never use CA certs (set by --insecure)
  <path>  verify by the specified CA certificates

Values other than <path> are for internal use and therefore undocumented.

mercurial/dispatch.py

@@ -826,7 +826,7 b' def _dispatch(req):'
 
     if cmdoptions.get('insecure', False):
         for ui_ in uis:
-            ui_.setconfig('web', 'cacerts', '', '--insecure')
+            ui_.setconfig('web', 'cacerts', '!', '--insecure')
 
     if options['version']:
         return commands.version_(ui)

mercurial/hg.py

@@ -672,7 +672,9 b' def remoteui(src, opts):'
         for key, val in src.configitems(sect):
             dst.setconfig(sect, key, val, 'copied')
     v = src.config('web', 'cacerts')
-    if v:
+    if v == '!':
+        dst.setconfig('web', 'cacerts', v, 'copied')
+    elif v:
         dst.setconfig('web', 'cacerts', util.expandpath(v), 'copied')
 
     return dst

mercurial/sslutil.py

@@ -134,7 +134,7 b' def _defaultcacerts():'
         dummycert = os.path.join(os.path.dirname(__file__), 'dummycert.pem')
         if os.path.exists(dummycert):
             return dummycert
-    return None
+    return '!'
 
 def sslkwargs(ui, host):
     kws = {}
@@ -142,17 +142,18 b' def sslkwargs(ui, host):'
     if hostfingerprint:
         return kws
     cacerts = ui.config('web', 'cacerts')
-    if cacerts:
+    if cacerts == '!':
+        pass
+    elif cacerts:
         cacerts = util.expandpath(cacerts)
         if not os.path.exists(cacerts):
             raise util.Abort(_('could not find web.cacerts: %s') % cacerts)
-    elif cacerts is None:
-        dummycert = _defaultcacerts()
-        if dummycert:
-            ui.debug('using %s to enable OS X system CA\n' % dummycert)
-            ui.setconfig('web', 'cacerts', dummycert, 'dummy')
-            cacerts = dummycert
-    if cacerts:
+    else:
+        cacerts = _defaultcacerts()
+        if cacerts and cacerts != '!':
+            ui.debug('using %s to enable OS X system CA\n' % cacerts)
+        ui.setconfig('web', 'cacerts', cacerts, 'defaultcacerts')
+    if cacerts != '!':
         kws.update({'ca_certs': cacerts,
                     'cert_reqs': CERT_REQUIRED,
                     })
@@ -201,7 +202,7 b' class validator(object):'
                                  hint=_('check hostfingerprint configuration'))
             self.ui.debug('%s certificate matched fingerprint %s\n' %
                           (host, nicefingerprint))
-        elif cacerts:
+        elif cacerts != '!':
             msg = _verifycert(peercert2, host)
             if msg:
                 raise util.Abort(_('%s certificate error: %s') % (host, msg),

tests/hghave.py

@@ -323,7 +323,7 b' def has_ssl():'
 @check("defaultcacerts", "can verify SSL certs by system's CA certs store")
 def has_defaultcacerts():
     from mercurial import sslutil
-    return sslutil._defaultcacerts()
+    return sslutil._defaultcacerts() != '!'
 
 @check("windows", "Windows")
 def has_windows():

tests/test-https.t

@@ -124,7 +124,7 b" Apple's OpenSSL. This trick do not work "
   abort: error: *certificate verify failed* (glob)
   [255]
 
-  $ DISABLEOSXDUMMYCERT="--config=web.cacerts="
+  $ DISABLEOSXDUMMYCERT="--config=web.cacerts=!"
 #endif
 
 clone via pull
@@ -240,7 +240,7 b' Fingerprints'
   $ echo "127.0.0.1 = 914f1aff87249c09b6859b88b1906d30756491ca" >> copy-pull/.hg/hgrc
 
 - works without cacerts
-  $ hg -R copy-pull id https://localhost:$HGPORT/ --config web.cacerts=
+  $ hg -R copy-pull id https://localhost:$HGPORT/ --config web.cacerts=!
   5fed3813f7f5
 
 - fails when cert doesn't match hostname (port is ignored)