[client] Handle invalid proxy settings

If `HTTP_PROXY` / `HTTPS_PROXY` environment variables are set and the
URL is invalid (e.g.: it doesn't contains a schema like localhost:8001)
the client will throw the following exception:
```
'NoneType' object has no attribute 'rfind'
  File "/codechecker/build/CodeChecker/cc_bin/CodeChecker.py", line 174, in <module>
    main(commands)
  File "/codechecker/build/CodeChecker/cc_bin/CodeChecker.py", line 141, in main
    sys.exit(args.func(args))
  File "//codechecker/build/CodeChecker/lib/python3/codechecker_client/cmd/store.py", line 856, in main
    traceback.print_stack()
```
From this error message it is hard to understand the real problem.

Unfortunately Thrift does not handle the use case when invalid proxy format
is used (e.g.: no schema is specified). For this reason we need to verify
the proxy format in our side.

web/client/codechecker_client/thrift_call.py

@@ -21,6 +21,37 @@
 
 LOG = get_logger('system')
 
+PROXY_VALIDATION_NEEDED = True
+
+
+def proxy_settings_are_valid(transport):
+    """
+    Return True if no proxy settings are used or the proxy format it valid.
+    """
+    if not transport.using_proxy():
+        return True
+
+    return transport.host and isinstance(transport.port, int)
+
+
+def validate_proxy_format(transport):
+    """
+    It will check the proxy settings once and validate the proxy settings.
+    If the proxy settings are invalid, it will print an error message and
+    stop the program.
+    """
+    global PROXY_VALIDATION_NEEDED
+
+    if PROXY_VALIDATION_NEEDED:
+        if not proxy_settings_are_valid(transport):
+            LOG.error("Invalid proxy format! Check your "
+                      "HTTP_PROXY/HTTPS_PROXY environment variables if "
+                      "these are in the right format:"
+                      "'http[s]://host:port'.")
+            sys.exit(1)
+
+        PROXY_VALIDATION_NEEDED = False
+
 
 def truncate_arg(arg, max_len=100):
     """ Truncate the given argument if the length is too large. """
@@ -38,6 +69,11 @@ def ThriftClientCall(function):
     funcName = function.__name__
 
     def wrapper(self, *args, **kwargs):
+        # Thrift do not handle the use case when invalid proxy format is used
+        # (e.g.: no schema is specified). For this reason we need to verify
+        # the proxy format in our side.
+        validate_proxy_format(self.transport)
+
         self.transport.open()
         func = getattr(self.client, funcName)
         try:

web/tests/functional/cmdline/test_cmdline.py

@@ -47,9 +47,9 @@ def setUp(self):
         test_class = self.__class__.__name__
         print('Running ' + test_class + ' tests in ' + test_workspace)
 
-        codechecker_cfg = env.import_test_cfg(test_workspace)[
+        self.codechecker_cfg = env.import_test_cfg(test_workspace)[
             'codechecker_cfg']
-        self.server_url = env.parts_to_url(codechecker_cfg)
+        self.server_url = env.parts_to_url(self.codechecker_cfg)
 
         # Get the test project configuration from the prepared test workspace.
         self._testproject_data = env.setup_test_proj_cfg(test_workspace)
@@ -123,6 +123,28 @@ def test_runs_filter(self):
         self.assertEqual(0, ret)
         self.assertEqual(1, len(json.loads(res)))
 
+    def test_proxy_settings(self):
+        """ Test proxy settings validation. """
+        server_url = f"{self.codechecker_cfg['viewer_host']}:" \
+                     f"{str(self.codechecker_cfg['viewer_port'])}"
+
+        env = self.codechecker_cfg['check_env'].copy()
+        env['HTTP_PROXY'] = server_url
+
+        res_cmd = [self._codechecker_cmd, 'cmd', 'runs',
+                   '--url', str(self.server_url)]
+        ret, _, err = run_cmd(res_cmd, env=env)
+        self.assertEqual(1, ret)
+        self.assertIn("Invalid proxy format", err)
+
+        env['HTTP_PROXY'] = f"http://{server_url}"
+        _, _, err = run_cmd(res_cmd, env=env)
+
+        # We can't check the return code here, because on host machine it will
+        # be zero, but on the GitHub action's job it will be 1 with "Failed to
+        # connect to the server" error message.
+        self.assertNotIn("Invalid proxy format", err)
+
     def test_runs_row(self):
         """ Test cmd row output type. """
         env = self._test_config['codechecker_cfg']['check_env']