This document is a guide on how to get started with Component Inspection depending on your needs:
I want to learn more about Inspect concepts
Read Getting Started with Inspect and the README.
I want to know how to use the iquery tool
Read the iquery manual. For detailed examples of usage, see Getting Started with Inspect.
This document provides a simplified example of iquery below.
I have an existing or new component, and I want to support inspection.
Continue reading this document.
See below for the quick start guide in your language of choice.
NOTE: If you need to support dynamic values, see Dynamic Value Support. If you are unsure, keep reading.
This section assumes you are writing an asynchronous component and that some part of your component (typically main.cc
) looks like this:
async::Loop loop(&kAsyncLoopConfigAttachToThread); auto component_context = sys::ComponentContext::Create(); // ... loop.Run();
This sets up an async loop, creates a ComponentContext
wrapping handles provided by the runtime, and then runs that loop following some other initialization work.
Change your initialization code to look like the following:
async::Loop loop(&kAsyncLoopConfigAttachToThread); auto component_context = sys::ComponentContext::Create(); auto inspector = inspect::ComponentInspector::Initialize(component_context.get()); inspect::Node& root_node = inspector->root_tree()->GetRoot(); // ... loop.Run();
Note: You will need to
#include <lib/inspect/component.h>
You are now using Inspect! To add some data and see it in action, try adding the following:
// Important: Make sure to hold on to hello_world_property and don't let it go out of scope. auto hello_world_property = root_node.CreateStringProperty("hello", "world");
See Viewing Inspect Data below to view what you are now exporting.
See Supported Data Types for a full list of data types you can try.
Want to test your Inspect integration? Include testing/inspect.h in your unit test for a full set of matchers. See this example of how it is used.
Read on to learn how Inspect is meant to be used in C++.
Certain features, such as LazyProperty, LazyMetric, and ChildrenCallback are deprecated, but a replacement is on the way (CF-761). If you determine that you need one of these data types, you may use the deprecated API by replacing the setup code with the following:
// Legacy work required to expose an inspect hierarchy over FIDL. auto root = component::ObjectDir::Make("root"); fidl::BindingSet<fuchsia::inspect::Inspect> inspect_bindings_; component_context->outgoing()->GetOrCreateDirectory("objects")->AddEntry( fuchsia::inspect::Inspect::Name_, std::make_unique<vfs::Service>( inspect_bindings_.GetHandler(root.object().get()))); auto root_node = inspect::Node(root);
Now that you have a root_node
you may start building your hierarchy. This section describes some important concepts and patterns to help you get started.
The code above gives you access to a single node named “root”. hello_world_property
is a Property that contains a string value (aptly called a StringProperty).
Class Node
has creator methods for every type of supported value. hello_world_property
was created using CreateStringProperty
. You could create a child under the root node by calling root_node.CreateChild("child name")
. Note that names must always be UTF-8 strings.
hello_world_property
owns the Property. When it is destroyed (goes out of scope) the underlying Property is deleted and no longer present in your component's Inspect output. This is true for Metrics and child Nodes as well.
Due to space limitations, the Inspect library may be unable to satisfy a Create
request. This error is not surfaced to your code: you will receive a Node/Metric/Property object for which the methods are no-ops.
It is useful to add an inspect::Node
argument to the constructors for your own classes. The parent object, which should own its own inspect::Node
, may then pass in the result of CreateChild(...)
to its children when they are constructed:
class Child { public: Child(inspect::Node my_node) : my_node_(std::move(my_node)) { // Create metrics and properties on my_node_. } private: inspect::Node my_node_; inspect::StringProperty some_property_; // ... more properties and metrics }; class Parent { public: // ... void AddChild() { // Note: inspect::UniqueName returns a globally unique name with the specified prefix. children_.emplace_back(my_node_.CreateChild(inspect::UniqueName("child-"))); } private: std::vector<Child> children_; inspect::Node my_node_; };
Rust support for inspect is currently in development.
TODO(crjohns,miguelfrde)
This example obtains and adds several data types and nested children to the root Inspect node.
BUILD.gn:
flutter_app("inspect_mod") { [...] deps = [ [...] "//topaz/public/dart/fuchsia_inspect", [...] ] [...]
root_intent_handler.dart:
import 'package:fuchsia_inspect/inspect.dart' as inspect; [...] class RootIntentHandler extends IntentHandler { @override void handleIntent(Intent intent) { var inspectNode = inspect.Inspect().root; runApp(InspectExampleApp(inspectNode)); } }
inspect_example_app.dart:
import 'package:fuchsia_inspect/inspect.dart' as inspect; class InspectExampleApp extends StatelessWidget { final inspect.Node _inspectNode; InspectExampleApp(this._inspectNode) { _inspectNode.stringProperty('greeting').setValue('Hello World'); _inspectNode.doubleProperty('double down')..setValue(1.23)..add(2); _inspectNode.intProperty('interesting')..setValue(123)..subtract(5); _inspectNode.byteDataProperty('bytes').setValue(ByteData(4)..setUint32(0, 0x01020304)); } @override Widget build(BuildContext context) { return MaterialApp( home: _InspectHomePage( inspectNode: _inspectNode.child('home-page')), [...] }
You can call delete()
on a Node or Property when you're done with it. Deleting a node deletes everything under it.
delete()
can also be triggered by a Future completing or broadcast Stream closing:
var answerFuture = _answerFinder.getTheAnswer(); var wait = _inspectNode.stringProperty('waiting')..setValue('for a hint'); answerFuture.whenComplete(wait.delete); stream.listen((_) {}, onDone: node.delete); // FIDL proxies contain a future that completes when the connection closes: final _proxy = my_fidl_import.MyServiceProxy(); _proxy.ctrl.whenClosed.whenComplete(node.delete);
You can use the iquery
tool to view the Inspect data you exported from your component by looking through the Hub.
This section assumes you have SSH access to your running Fuchsia system and that you started running your component. We will use the name my_component.cmx
as a placeholder for the name of your component.
Try the following:
# This prints all Inspect endpoints on the system. $ iquery --find /hub # This filters the above list to only print your component. $ iquery --find /hub | grep my_component.cmx
Under the listed directories you will see some paths including “system_objects.” This Inspect data is placed there by the Component Runtime itself.
Your component's endpoint will be listed as <path>/my_component.cmx/<id>/out/objects/root.inspect
.
Note: If you followed Dynamic Value Support above, “root.inspect” will be missing.
Navigate to the out/objects
directory that was printed above, and run:
$ iquery --recursive root.inspect # OR, if you used Dynamic Values: $ iquery --recursive .
This will print out the following if you followed the suggested steps above:
root: hello = world
Type | Description | Notes |
---|---|---|
IntMetric | A metric containing a signed 64-bit integer. | All Languages |
UIntMetric | A metric containing an unsigned 64-bit integer. | Not supported in Dart |
DoubleMetric | A metric containing a double floating-point number. | All Languages |
{Int,Double,UInt}Array | An array of metric types, includes typed wrappers for various histograms. | Same language support as base metric type |
StringProperty | A property with a UTF-8 string value. | All Languages |
ByteVectorProperty | A property with an arbitrary byte value. | All Languages |
Node | A node under which metrics, properties, and more nodes may be nested. | All Languages |
LazyMetric | A metric which dynamically sets its value as the result of a callback. | DEPRECATED: C++ Only |
LazyProperty | A property which dynamically sets its value as the result of a callback. | DEPRECATED: C++ Only |
ChildrenCallback | A callback that dynamically injects children into a Node on demand. | DEPRECATED: C++ Only |
Link | Instantiates a complete tree of Nodes dynamically. | IN PROGRESS(CF-761): This will replace Lazy metrics, properties, and children |