http: Add error handling for the repo-locked exception. Part of #4237

Previously the repo locekd exception was raised on return
of the call to the hooks daemon and propagates all the
way up to the WSGI server (e.g. waitress). In case of
locked repos we want to return a custom response which
contains an explanation for the user that the repo is
locked and who has locked it.

vcsserver/exceptions.py

@@ -25,6 +25,7 b' different error conditions.'
 """
 
 import functools
+from pyramid.httpexceptions import HTTPLocked
 
 
 def _make_exception(kind, *args):
@@ -54,3 +55,14 b' RequirementException = functools.partial'
 UnhandledException = functools.partial(_make_exception, 'unhandled')
 
 URLError = functools.partial(_make_exception, 'url_error')
+
+
+class HTTPRepoLocked(HTTPLocked):
+    """
+    Subclass of HTTPLocked response that allows to set the title and status
+    code via constructor arguments.
+    """
+    def __init__(self, title, status_code=None, **kwargs):
+        self.code = status_code or HTTPLocked.code
+        self.title = title
+        super(HTTPRepoLocked, self).__init__(**kwargs)

vcsserver/http_main.py

@@ -31,6 +31,7 b' from pyramid.wsgi import wsgiapp'
 from vcsserver import remote_wsgi, scm_app, settings, hgpatches
 from vcsserver.echo_stub import remote_wsgi as remote_wsgi_stub
 from vcsserver.echo_stub.echo_app import EchoApp
+from vcsserver.exceptions import HTTPRepoLocked
 from vcsserver.server import VcsServer
 
 try:
@@ -197,6 +198,9 b' class HTTPApplication(object):'
 
         self.config.add_view(self.hg_stream(), route_name='stream_hg')
         self.config.add_view(self.git_stream(), route_name='stream_git')
+        self.config.add_view(
+            self.handle_vcs_exception, context=Exception,
+            custom_predicates=[self.is_vcs_exception])
 
     def wsgi_app(self):
         return self.config.make_wsgi_app()
@@ -317,6 +321,23 b' class HTTPApplication(object):'
                 return app(environ, start_response)
             return _git_stream
 
+    def is_vcs_exception(self, context, request):
+        """
+        View predicate that returns true if the context object is a VCS
+        exception.
+        """
+        return hasattr(context, '_vcs_kind')
+
+    def handle_vcs_exception(self, exception, request):
+        if exception._vcs_kind == 'repo_locked':
+            # Get custom repo-locked status code if present.
+            status_code = request.headers.get('X-RC-Locked-Status-Code')
+            return HTTPRepoLocked(
+                title=exception.message, status_code=status_code)
+
+        # Re-raise exception if we can not handle it.
+        raise exception
+
 
 class ResponseFilter(object):