core: dump some debug info in /data/environment

Summary:
In #4751, we implemented `data_location` support for RustBoard, which
means that the location no longer includes the gRPC address. But while
this is an improvement for users, the address was convenient for
development, and there’s no other way to get it from the UI. This patch
augments `/data/environment` to dump some basic debug info: the
TensorBoard version, the data provider, and the command-line flags.

This behavior can be turned off. It’s enabled in `tensorboard(1)`, but
disabled by default on the `CorePlugin` and `CorePluginLoader` APIs.
Thus, users who build their own TensorBoards will not find themselves
unexpectedly leaking information about their setup. For normal users of
`tensorboard(1)`, the flags are fine to render; the only potentially
sensitive thing is the logdir path, which is of course already
prominent.

Sample response, passed through `jq .`:

```
{
  "data_location": "logs/mnist/",
  "window_title": "",
  "debug": {
    "version": "2.5.0a0",
    "data_provider": "GrpcDataProvider(addr='localhost:42127')",
    "flags": {
      "logdir": "logs/mnist/",
      "logdir_spec": "",
      "host": null,
      "bind_all": true,
      "port": null,
      "reuse_port": false,
      "load_fast": true,
      "grpc_creds_type": "local",
      "grpc_data_provider": "",
      "purge_orphaned_data": true,
      "db": "",
      "db_import": false,
      "inspect": false,
      "version_tb": false,
      "tag": "",
      "event_file": "",
      "path_prefix": "",
      "window_title": "",
      "max_reload_threads": 1,
      "reload_interval": 5,
      "reload_task": "auto",
      "reload_multifile": null,
      "reload_multifile_inactive_secs": 86400,
      "generic_data": "auto",
      "samples_per_plugin": {
        "scalars": 0,
        "images": 0
      },
      "custom_predict_fn": "",
      "wit_data_dir": "",
      "__tensorboard_subcommand": "serve"
    }
  }
}
```

Test Plan:
Manually navigated to `/data/environment` and verified that the flags
render and the data provider appears for both `--load_fast` and the
legacy multiplexer. Checked that when the change to `default.py` is
reverted, no debug data shows up.

wchargin-branch: environment-debug-info
wchargin-source: 772a3783d6f19e4060b37fe43076b963cfd8d96e

Author: wchargin

tensorboard/backend/event_processing/data_provider.py

@@ -41,6 +41,9 @@ def __init__(self, multiplexer, logdir):
         self._multiplexer = multiplexer
         self._logdir = logdir
 
+    def __str__(self):
+        return "MultiplexerDataProvider(logdir=%r)" % self._logdir
+
     def _validate_context(self, ctx):
         if type(ctx).__name__ != "RequestContext":
             raise TypeError("ctx must be a RequestContext; got: %r" % (ctx,))

tensorboard/data/grpc_provider.py

@@ -46,6 +46,9 @@ def __init__(self, addr, stub):
         self._addr = addr
         self._stub = stub
 
+    def __str__(self):
+        return "GrpcDataProvider(addr=%r)" % self._addr
+
     def data_location(self, ctx, *, experiment_id):
         req = data_provider_pb2.GetExperimentRequest()
         req.experiment_id = experiment_id

tensorboard/default.py

@@ -71,7 +71,7 @@ class ExperimentalNpmiPlugin(
 # Ordering matters. The order in which these lines appear determines the
 # ordering of tabs in TensorBoard's GUI.
 _PLUGINS = [
-    core_plugin.CorePluginLoader,
+    core_plugin.CorePluginLoader(include_debug_info=True),
     scalars_plugin.ScalarsPlugin,
     custom_scalars_plugin.CustomScalarsPlugin,
     images_plugin.ImagesPlugin,

tensorboard/plugins/core/BUILD

@@ -15,6 +15,7 @@ py_library(
         "//tensorboard/plugins:base_plugin",
         "//tensorboard/util:grpc_util",
         "//tensorboard/util:tb_logging",
+        "//tensorboard:version",
         "@org_pocoo_werkzeug",
     ],
 )

tensorboard/plugins/core/core_plugin.py

@@ -31,6 +31,7 @@
 from tensorboard.plugins import base_plugin
 from tensorboard.util import grpc_util
 from tensorboard.util import tb_logging
+from tensorboard import version
 
 logger = tb_logging.get_logger()
 
@@ -50,18 +51,24 @@ class CorePlugin(base_plugin.TBPlugin):
 
     plugin_name = "core"
 
-    def __init__(self, context):
+    def __init__(self, context, include_debug_info=None):
         """Instantiates CorePlugin.
 
         Args:
           context: A base_plugin.TBContext instance.
+          include_debug_info: If true, `/data/environment` will include some
+            basic information like the TensorBoard server version. Disabled by
+            default to prevent surprising information leaks in custom builds of
+            TensorBoard.
         """
+        self._flags = context.flags
         logdir_spec = context.flags.logdir_spec if context.flags else ""
         self._logdir = context.logdir or logdir_spec
         self._window_title = context.window_title
         self._path_prefix = context.flags.path_prefix if context.flags else None
         self._assets_zip_provider = context.assets_zip_provider
         self._data_provider = context.data_provider
+        self._include_debug_info = bool(include_debug_info)
 
     def is_active(self):
         return True
@@ -165,13 +172,7 @@ def _serve_index(self, index_asset_bytes, request):
 
     @wrappers.Request.application
     def _serve_environment(self, request):
-        """Serve a JSON object containing some base properties used by the
-        frontend.
-
-        * data_location is either a path to a directory or an address to a
-          database (depending on which mode TensorBoard is running in).
-        * window_title is the title of the TensorBoard web page.
-        """
+        """Serve a JSON object describing the TensorBoard parameters."""
         ctx = plugin_util.context(request.environ)
         experiment = plugin_util.experiment_id(request.environ)
         data_location = self._data_provider.data_location(
@@ -193,12 +194,38 @@ def _serve_environment(self, request):
                     "creation_time": experiment_metadata.creation_time,
                 }
             )
+        if self._include_debug_info:
+            environment["debug"] = {
+                "version": version.VERSION,
+                "data_provider": str(self._data_provider),
+                "flags": self._render_flags(),
+            }
         return http_util.Respond(
             request,
             environment,
             "application/json",
         )
 
+    def _render_flags(self):
+        """Return a JSON-and-human-friendly version of `self._flags`.
+
+        Like `json.loads(json.dumps(self._flags, default=str))` but
+        without the wasteful serialization overhead.
+        """
+        if self._flags is None:
+            return None
+
+        def go(x):
+            if isinstance(x, (type(None), str, int, float)):
+                return x
+            if isinstance(x, (list, tuple)):
+                return [go(v) for v in x]
+            if isinstance(x, dict):
+                return {str(k): go(v) for (k, v) in x.items()}
+            return str(x)
+
+        return go(vars(self._flags))
+
     @wrappers.Request.application
     def _serve_logdir(self, request):
         """Respond with a JSON object containing this TensorBoard's logdir."""
@@ -270,6 +297,9 @@ def _serve_experiment_runs(self, request):
 class CorePluginLoader(base_plugin.TBLoader):
     """CorePlugin factory."""
 
+    def __init__(self, include_debug_info=None):
+        self._include_debug_info = include_debug_info
+
     def define_flags(self, parser):
         """Adds standard TensorBoard CLI flags to parser."""
         parser.add_argument(
@@ -640,7 +670,7 @@ def fix_flags(self, flags):
 
     def load(self, context):
         """Creates CorePlugin instance."""
-        return CorePlugin(context)
+        return CorePlugin(context, include_debug_info=self._include_debug_info)
 
 
 def _gzip(bytestring):

tensorboard/plugins/core/core_plugin_test.py

@@ -190,6 +190,27 @@ def testEnvironmentForLogdir(self):
         parsed_object = self._get_json(self.server, "/data/environment")
         self.assertEqual(parsed_object["data_location"], self.get_temp_dir())
 
+    def testEnvironmentDebugOffByDefault(self):
+        parsed_object = self._get_json(self.server, "/data/environment")
+        self.assertNotIn("debug", parsed_object)
+
+    def testEnvironmentDebugOnExplicitly(self):
+        multiplexer = event_multiplexer.EventMultiplexer()
+        logdir = self.get_temp_dir()
+        provider = data_provider.MultiplexerDataProvider(multiplexer, logdir)
+        context = base_plugin.TBContext(
+            assets_zip_provider=get_test_assets_zip_provider(),
+            logdir=logdir,
+            data_provider=provider,
+            window_title="title foo",
+        )
+        plugin = core_plugin.CorePlugin(context, include_debug_info=True)
+        app = application.TensorBoardWSGI([plugin])
+        server = werkzeug_test.Client(app, wrappers.BaseResponse)
+
+        parsed_object = self._get_json(server, "/data/environment")
+        self.assertIn("debug", parsed_object)
+
     def testLogdir(self):
         """Test the format of the data/logdir endpoint."""
         parsed_object = self._get_json(self.server, "/data/logdir")