run-dev: Add streamlined option.

For basic testing (either manual or automated), we
generally only need the server and tornado running.

Obviously, it's nice to test the complete system,
but if you're on a slow PC, the overhead can be
annoying.

Note that we don't launch any of these processes
in `--streamlined` mode:

    process_queue
    process_fts_updates
    deliver_scheduled_messages
    thumbor

And then by not launching process_queue, we avoid
several child processes.

Basic functionality like sending messages will
still work here.

The streamlined mode may be helpful in debugging
our generally slow server startup time.  Obviously,
some of the problem with startup is the auxiliary
processes here, but removing them as a variable
could help us focus on getting the core stuff fast.

Note that we still have the webpack watcher running
in streamlined mode.

For the particular case of thumbor, note that we
modify the proxy server to explicitly print and
return an error if we get a `/thumbor/*` request.

tools/run-dev.py

@@ -59,6 +59,9 @@ parser.add_argument('--interface',
 parser.add_argument('--no-clear-memcached',
                     action='store_false', dest='clear_memcached',
                     default=True, help='Do not clear memcached')
+parser.add_argument('--streamlined',
+                    action="store_true",
+                    default=False, help='Avoid thumbor, etc.')
 parser.add_argument('--force',
                     action="store_true",
                     default=False, help='Run command despite possible problems.')
@@ -100,7 +103,7 @@ os.environ['DJANGO_SETTINGS_MODULE'] = settings_module
 
 sys.path.append(os.path.join(os.path.dirname(__file__), '..'))
 
-from scripts.lib.zulip_tools import CYAN, WARNING, ENDC
+from scripts.lib.zulip_tools import CYAN, WARNING, FAIL, ENDC
 
 proxy_port = base_port
 django_port = base_port + 1
@@ -142,6 +145,14 @@ def server_processes() -> List[List[str]]:
         manage_args + runserver_args + ['127.0.0.1:%d' % (django_port,)],
         ['env', 'PYTHONUNBUFFERED=1', './manage.py', 'runtornado'] +
         manage_args + ['127.0.0.1:%d' % (tornado_port,)],
+    ]
+
+    if options.streamlined:
+        # The streamlined operation allows us to do many
+        # things, but search/thumbor/etc. features won't work.
+        return main_cmds
+
+    other_cmds = [
         ['./manage.py', 'process_queue', '--all'] + manage_args,
         ['env', 'PGHOST=127.0.0.1',  # Force password authentication using .pgpass
          './puppet/zulip/files/postgresql/process_fts_updates'],
@@ -150,7 +161,8 @@ def server_processes() -> List[List[str]]:
          '-p', '%s' % (thumbor_port,)],
     ]
 
-    return main_cmds
+    # NORMAL (but slower) operation:
+    return main_cmds + other_cmds
 
 def do_one_time_webpack_compile() -> None:
     # We just need to compile webpack assets once at startup, not run a daemon,
@@ -299,13 +311,24 @@ class ThumborHandler(BaseHandler):
     target_port = thumbor_port
 
 
+class ErrorHandler(BaseHandler):
+    @web.asynchronous
+    def prepare(self) -> None:
+        print(FAIL + 'Unexpected request: ' + ENDC, self.request.path)
+        self.set_status(500)
+        self.write('path not supported')
+        self.finish()
+
+def using_thumbor() -> bool:
+    return not options.streamlined
+
 class Application(web.Application):
     def __init__(self, enable_logging: bool = False) -> None:
         handlers = [
             (r"/json/events.*", TornadoHandler),
             (r"/api/v1/events.*", TornadoHandler),
             (r"/webpack.*", WebPackHandler),
-            (r"/thumbor.*", ThumborHandler),
+            (r"/thumbor.*", ThumborHandler if using_thumbor() else ErrorHandler),
             (r"/.*", DjangoHandler)
         ]
         super().__init__(handlers, enable_logging=enable_logging)
@@ -337,7 +360,8 @@ def print_listeners() -> None:
     if not options.test:
         ports.append((webpack_port, 'webpack'))
 
-    ports.append((thumbor_port, 'Thumbor'))
+    if using_thumbor():
+        ports.append((thumbor_port, 'Thumbor'))
 
     for port, label in ports:
         print(f'   {port}: {label}')