docs/development/inspect/codelab/cpp.md

# Inspect C++ codelab

This document contains the codelab for Inspect using C++.

The code is available at
[//src/diagnostics/examples/inspect/cpp][inspect-cpp-codelab].

This codelab is organized into several parts, each with their own
subdirectory. The starting point for the codelab is [part 1][part1],
and the code for each part contains the solution for the previous parts.

When working on this codelab, you may continue adding your solutions to
"part\_1", or you may skip around by building on the existing solutions.

## Prerequisites

Set up your development environment.

This codelab assumes you have completed [Getting Started](/docs/getting_started.md) and have:

1. A checked out and built Fuchsia tree.
2. A device or emulator (`fx emu`) that runs Fuchsia.
3. A workstation to serve components (`fx serve`) to your Fuchsia device or emulator.

To build and run the examples in this codelab, add the following arguments
to your `fx set` invocation:

Note: Replace core.x64 with your product and board configuration.

```
fx set core.x64 \
--with //src/diagnostics/examples/inspect/cpp \
--with //src/diagnostics/examples/inspect/cpp:tests
```

## Part 1: A buggy component

There is a component that serves a protocol called [Reverser][fidl-reverser]:

```
// Implementation of a string reverser.
[Discoverable]
protocol Reverser {
    // Returns the input string reversed character-by-character.
    Reverse(string:1024 input) -> (string:1024 response);
};
```

This protocol has a single method, called "Reverse," that simply reverses
any string passed to it. An implementation of the protocol is provided,
but it has a critical bug. The bug makes clients who attempt to call
the Reverse method see that their call hangs indefinitely. It is up to
you to fix this bug.

### Run the component

There is a client application called `inspect_cpp_codelab_client` that
will launch the Reverser component and send the rest of its command line
arguments as strings to Reverse:

1. See usage

  ```
  fx shell run inspect_cpp_codelab_client
  ```

2. Run part 1 code, and reverse the string "Hello"

  ```
  fx shell run inspect_cpp_codelab_client 1 Hello
  ```

  This command hangs.

3. Press Ctrl+C to stop the client and try running with
  more arguments:

  ```
  fx shell run inspect_cpp_codelab_client 1 Hello World
  ```

  This command also hangs.

You are now ready to look through the code to troubleshoot the issue.

### Look through the code

Now that you can reproduce the problem, take a look at what the
[client][client-main] is doing:

```
// Repeatedly send strings to be reversed to the other component.
for (int i = 2; i < argc; i++) {
  printf("Input: %s\n", argv[i]);

  std::string output;
  if (ZX_OK != reverser->Reverse(argv[i], &output)) {
    printf("Error: Failed to reverse string.\nPerhaps %s was not found?\n",
           reverser_component_url.c_str());
    exit(1);
  }

  printf("Output: %s\n", output.c_str());
}
```

In this code snippet, the client calls the `Reverse` method but never
seems to get a response. There doesn't seem to be an error message
or output.

Take a look at the [server code][part1-main] for this part of the
codelab. There is a lot of standard component setup:

- Logging initialization

  ```
InitLogger({"inspect_cpp_codelab", "part1"});
  ```

- Creating an asynchronous executor

  ```
async::Loop loop(&kAsyncLoopConfigAttachToCurrentThread);
auto context = sys::ComponentContext::Create();
  ```

- Serving a public service

  ```
context->outgoing()->AddPublicService(Reverser::CreateDefaultHandler());
  ```

See what the [reverser definition][part1-reverser-h] is:

```
class Reverser final : public fuchsia::examples::inspect::Reverser {
 public:
  // Implementation of Reverser.Reverse().
  void Reverse(std::string input, ReverseCallback callback) override;

  // Return a request handler for the Reverser protocol that binds
  // incoming requests to new Reversers.
  static fidl::InterfaceRequestHandler<fuchsia::examples::inspect::Reverser>
   CreateDefaultHandler();
};
```

This class implements the `Reverser` protocol. A helper method called
`CreateDefaultHandler` constructs an `InterfaceRequestHandler` that
creates new `Reverser`s for incoming requests.

### Add Inspect

Now that you know the code structure, you can start to instrument the
code with Inspect to find the problem.


Note: [Inspect](/docs/development/inspect/README.md) is a powerful instrumentation feature for
Fuchsia Components. You can expose structured information about the component's state to diagnose
the problem.

You may have previously debugged programs by printing or logging. While
this is often effective, asynchronous Components that run persistently
often output numerous logs about their internal state over time. This
codelab shows how Inspect provides snapshots of your component's current
state without needing to dig through logs.

1. Include Inspect dependencies in [BUILD.gn][part1-build]:

  ```
source_set("lib") {
  ...

  public_deps = [
    "//sdk/lib/sys/inspect/cpp",
    ...
  ]
}
  ```

2. Initialize Inspect in [main.cc][part1-main]:

  ```
  async::Loop loop(&kAsyncLoopConfigAttachToCurrentThread);
  auto context = sys::ComponentContext::Create();

  // Create an inspector for this component.
  sys::ComponentInspector inspector(context.get());
  ```

  You are now using Inspect.

3. Add a simple "version" property to show which version is running:

  ```
inspector.root().CreateString("version", "part1", &inspector);
  ```

This snippet does the following:

1. Obtain the "root" node of the Inspect hierarchy.

  The Inspect hierarchy for your component consists of a tree of Nodes,
  each of which contains any number of properties.

2. Create a new property using `CreateString`.

  This adds a new `StringProperty` on the root. This `StringProperty`
  is called "version", and its value is "part1".

3. Emplace the new property in the inspector.

  The lifetime of a property is tied to an object returned by `Create`,
  and destroying the object causes the property to disappear. The
  optional third parameter emplaces the new property in `inspector`
  rather than return it.  As a result, the new property lives as long
  as the inspector itself (the entire execution of the component).

### Reading Inspect Data

Now that you have added Inspect to your component, you can read what it says:

1. Rebuild and push the component:

  ```
  fx build-push inspect_cpp_codelab
  ```

  Note: In some cases you may find it useful to rebuild and update all components:

  ```
  fx build && fx update
  ```

2. Run the client (should still hang):

  ```
  fx shell run inspect_cpp_codelab_client 1 Hello
  ```

3. Use `iquery` (Inspect query) to view your output:

  ```
  fx iquery
  ```

  This dumps all of the Inspect data for the entire system, which may be a lot of data.

4. Since `iquery` supports regex matching, run:

  ```
  $ fx iquery inspect_cpp_codelab_part_1
  /hub/r/codelab/1234/c/inspect_cpp_codelab_part_1.cmx/1234/out/diagnostics/root.inspect:
    version = part1
  ```

5. You can also view the output as JSON:

  ```
  $ fx iquery -f json inspect_cpp_codelab_part_1
  [
      {
          "contents": {
              "root": {
                  "version": "part1"
              }
          },
          "path": "/hub/r/codelab/1234/c/inspect_cpp_codelab_part_1.cmx/1234/out/diagnostics/root.inspect"
      }
  ]
  ```

### Instrumenting the code to find the bug

Now that you have initialized Inspect and know how to read data, you
are ready to instrument your code and uncover the bug.

The previous output shows you how the component is actually running
and that the component is not hanging completely. Otherwise the Inspect
read would hang.

Add new information per-connection to observe if the connection
is even being handled by your component.

1. Add a new child to your root node to contain statistics about the `reverser` service:

  ```
  context->outgoing()->AddPublicService(
      Reverser::CreateDefaultHandler(inspector.root().CreateChild("reverser_service")));
  ```

2. Update the definition of `CreateDefaultHandler` to accept this node in
[reverser.h][part1-reverser-h] and [reverser.cc][part1-reverser-cc]:

  ```
  fidl::InterfaceRequestHandler<fuchsia::examples::inspect::Reverser> Reverser::CreateDefaultHandler(
      inspect::Node node) { ...
  ```

3. Add a property to keep track of the number of connections:

  Note: Nesting related data under a child is a powerful feature of Inspect.

  ```
  return [connection_count = node.CreateUint("connection_count", 0),
          node = std::move(node),
          binding_set =
              std::make_unique<fidl::BindingSet<ReverserProto,
                                                std::unique_ptr<Reverser>>>()](
             fidl::InterfaceRequest<ReverserProto> request) mutable {
    connection_count.Add(1);
    ...
  ```

  This snippet demonstrates creating a new `UintProperty` (containing a
  uint64\_t) called `connection_count` and setting it to 0. In the handler
  (which runs for each connection), the property is incremented by 1.

  Note: `node` is moved into the handler so that it is not dropped and
  deleted from the output.

4. Run iquery:

  ```
  $ fx iquery inspect_cpp_codelab_part_1
  ...
  "contents": {
      "root": {
          "reverser_service": {
              "connection_count": 1,
          },
          "version": "part1"
      }
  }
  ```

The output above demonstrates that the client successfully connected
to the service, so the hanging problem must be caused by the Reverser
implementation itself. In particular, it will be helpful to know:

1. If the connection is still open while the client is hanging.

2. If the `Reverse` method was called.





**Exercise**: Create a child node for each connection, and record
"request\_count" inside the Reverser.

- *Hint*: There is a utility function for generating unique names:

  ```
  auto child = node.CreateChild(node.UniqueName("connection-"));
  ```

  This will create unique names starting with "connection-".

- *Hint*: You will find it helpful to create a constructor for Reverser
that takes `inspect::Node`. [Part 3](#part-3) of this codelab explains why this is
a useful pattern.

- *Hint*: You will need to create a member on Reverser to hold the
`request_count` property. Its type will be `inspect::UintProperty`.

- *Follow up*: Does request count give you all of the information you
need? Add `response_count` as well.

- *Advanced*: Can you add a count of *all* requests on *all*
connections? The Reverser objects must share some state. You may find
it helpful to refactor arguments to Reverser into a separate struct
(See solution in [part 2](#part-2) for this approach).

After completing this exercise, you should see something like this:

```
$ fx iquery inspect_cpp_codelab_part_1
...
"contents": {
    "root": {
        "reverser_service": {
            "connection-0x0": {
                "request_count": 1,
            },
            "connection_count": 1,
        },
        "version": "part1"
    }
}
```

The output above shows that the connection is still open and it received one request.

If you added "response\_count" as well, you may have noticed the bug.
The `Reverse` method receives a `callback`, but it is never called with the value of `output`.


1. Add a call to `callback` to fix the bug:

  ```
  // At the end of Reverser::Reverse
  callback(std::move(output));
  ```

2. Run the client again:

  ```
  fx shell run inspect_cpp_codelab_client 1 hello
  Input: hello
  Output: olleh
  Done. Press Ctrl+C to exit
  ```

  The component continues running until Ctrl+C is pressed to give you
  a chance to run iquery and observe your output.

This concludes part 1. You may commit your changes so far:

```
git commit -am "solution to part 1"
```

## Part 2: Diagnosing inter-component problems {#part-2}

Note: All links and examples in this section refer to "part\_2" code. If
you are following along, you may continue using "part\_1."

You received a bug report, the "FizzBuzz" team is saying they
are not receiving data from your component.

In addition to serving the Reverser protocol, the component also reaches
out to the "FizzBuzz" service and prints the response:

```
// Send a request to the FizzBuzz service and print the response when it arrives.
fuchsia::examples::inspect::FizzBuzzPtr fizz_buzz;
context->svc()->Connect(fizz_buzz.NewRequest());
fizz_buzz->Execute(30, [](std::string result) { FX_LOGS(INFO) << "Got FizzBuzz: " << result; });
```

If you use `fx log --tag inspect_cpp_codelab`, you will see that this
log is never printed. You will need to diagnose and solve this problem.

### Diagnose the issue with Inspect

1. Run the component to see what is happening:

  Note: Replace 2 with 1 if you are continuing from part 1.

  ```
  $ fx shell run inspect_cpp_codelab_client 2 hello
  ```

  Fortunately the FizzBuzz team instrumented their component using Inspect.

2. Read the FizzBuzz Inspect data:

  ```
  $ fx iquery -f json inspect_cpp_codelab_fizzbuzz
  "contents": {
      "root": {
          "fizzbuzz_service": {
              "closed_connection_count": 0,
              "incoming_connection_count": 0,
              "request_count": 0,
              ...
  ```

  This output confirms that FizzBuzz is not receiving any connections.

3. Add Inspect to identify the problem:

  ```
  // Send a request to the FizzBuzz service and print the response when it arrives.
  fuchsia::examples::inspect::FizzBuzzPtr fizz_buzz;
  context->svc()->Connect(fizz_buzz.NewRequest());

  // Create an error handler for the FizzBuzz service.
  fizz_buzz.set_error_handler([&](zx_status_t status) {
    // CODELAB: Add Inspect here to see if there is an error
  });

  fizz_buzz->Execute(30, [&](std::string result) {
    // CODELAB: Add Inspect here to see if there is a response.
    FX_LOGS(INFO) << "Got FizzBuzz: " << result;
  });
  ```

**Exercise**: Add Inspect to the FizzBuzz connection to identify the problem

- *Hint*: Use the snippet above as a starting point, it provides an
error handler for the connection attempt.

- *Follow up*: Can you store the status somewhere? You can convert it
to a string using `zx_status_get_string(status)`.

- *Advanced*: `inspector` has a method called `Health()` that announces
overall health status in a special location. Since our service is not
healthy unless it can connect to FizzBuzz, can you incorporate this:

  ```
  /*
  "fuchsia.inspect.Health": {
      "status": "STARTING_UP"
  }
  */
  inspector.Health().StartingUp();

  /*
  "fuchsia.inspect.Health": {
      "status": "OK"
  }
  */
  inspector.Health().Ok();

  /*
  "fuchsia.inspect.Health": {
      "status": "UNHEALTHY",
      "message": "Something went wrong!"
  }
  */
  inspector.Health().Unhealthy("Something went wrong!");
  ```

Once you complete this exercise, you should see that the connection
error handler is being called with a "not found" error. Inspect
output showed that FizzBuzz is running, so maybe something is
misconfigured. Unfortunately not everything uses Inspect (yet!) so
look at the logs:

```
$ fx log --only FizzBuzz
...
... Component fuchsia-pkg://fuchsia.com/inspect_cpp_codelab_part_2.cmx
is not allowed to connect to fuchsia.examples.inspect.FizzBuzz...
```

Sandboxing errors are a common pitfall that are sometimes difficult to uncover.

Note: While you could have looked at the logs from the beginning to find
the problem, the log output for the system can be extremely verbose. The
particular log that you are looking for was a kernel log from the framework,
which is additionally difficult to test for.

Looking at the [sandbox][part2-meta], you can see it is missing the service:

```
"sandbox": {
    "services": [
        "fuchsia.logger.LogSink"
    ]
}
```

Add "fuchsia.examples.inspect.FizzBuzz" to the services array, rebuild,
and run again. You should now see FizzBuzz in the logs and an OK status:

```
$ fx log --tag inspect_cpp_codelab
[inspect_cpp_codelab, part3] INFO: main.cc(57): Got FizzBuzz: 1 2 Fizz
4 Buzz Fizz 7 8 Fizz Buzz 11 Fizz 13 14 FizzBuzz 16 17 Fizz 19 Buzz Fizz
22 23 Fizz Buzz 26 Fizz 28 29 FizzBuzz
```

This concludes Part 2.

You can now commit your solution:

```
git commit -am "solution for part 2"
```

## Part 3: Unit Testing for Inspect {#part-3}

Note: All links and examples in this section refer to "part\_3" code. If
you are following along, you may continue using the part you started with.

All code on Fuchsia should be tested, and this applies to Inspect data as well.

While Inspect data is not *required* to be tested in general, you
need to test Inspect data that is depended upon by other tools such as
Triage or Feedback.

Reverser has a basic unit test called [reverser\_unittests.cc][part3-unittest].

Run the unit test:

```
fx run-test inspect_cpp_codelab_unittests
```

Note: This runs unit tests for all parts of this codelab.

The unit test ensures that Reverser works properly (and doesn't hang!), but it does
not check that the Inspect output is as expected.

Note: If you are following along from part\_1, you will need to uncomment
some lines in the [unit test][part1-unittest] and pass default values
for the Inspect properties to your Reverser.

Passing Nodes into constructors is a form of [Dependency
Injection](https://en.wikipedia.org/wiki/Dependency_injection), which
allows you to pass in test versions of dependencies to check their state.

The code to open a Reverser looks like the following:

```
binding_set_.AddBinding(std::make_unique<Reverser>(ReverserStats::CreateDefault()),
                        ptr.NewRequest());

// Alternatively
binding_set_.AddBinding(std::make_unique<Reverser>(inspect::Node()),
                        ptr.NewRequest());
```

A default version of the Inspect Node is passed into the Reverser. This
allows the reverser code to run properly in tests, but it does not
support asserting on Inspect output.

**Exercise**: Change `OpenReverser` to take the dependency for Reverser
as an argument and use it when constructing Reverser.

- *Hint*: Create an `inspect::Inspector` in the test function. You can
get the root using `inspector.GetRoot()`.

- *Hint*: You will need to create a child on the root to pass in to `OpenReverser`.

- *Follow up*: Create multiple reverser connections and test them independently.

Following this exercise, your unit test will set real values in an
Inspect hierarchy.

Add code to test the output in Inspect:

```
#include <lib/inspect/cpp/reader.h>
...

fit::result<inspect::Hierarchy> hierarchy = inspect::ReadFromVmo(inspector.DuplicateVmo());
ASSERT_TRUE(hierarchy.is_ok();
```

Note: If you use the LazyNode or LazyValues features, you will need to
use inspect::ReadFromInspector and run the returned fit::promise to
completion. See the solution to this part for an example.

The snippet above reads the underlying virtual memory object (VMO)
containing Inspect data and parses it into a readable hierarchy.

You can now read individual properties and children as follows:

```
// Get the property on root called "request_count"
auto* global_count =
        hierarchy.value().node().get_property<inspect::UintPropertyValue>("request_count");
// Ensure it is valid.
ASSERT_TRUE(global_count);
// Check its value.
EXPECT_EQ(3u, global_count->value());

// Get connection 0 by path.
auto* connection_0 = hierarchy.value().GetByPath({"connection_0x0"});
// Check it is valid and obtain the request_count.
ASSERT_TRUE(connection_0);
auto* requests_0 =
    connection_0->node().get_property<inspect::UintPropertyValue>("request_count");
// Check that is valid, and check its value.
ASSERT_TRUE(requests_0);
EXPECT_EQ(2u, requests_0->value());
```

**Exercise**: Add assertions for the rest of your Inspect data.

This concludes Part 3.

You may commit your changes:

```
git commit -am "solution to part 3"
```


## Part 4: Integration Testing for Inspect

Note: All links and examples in this section refer to "part\_4" code. If
you are following along, you may continue using the part you started with.

[Integration testing](https://en.wikipedia.org/wiki/Integration_testing)
is an important part of the software development workflow for
Fuchsia. Integration tests allow you to observe the behavior of your
actual component when it runs on the system.

### Running integration tests

You can run the integration tests for the codelab as follows:

```
$ fx run-test inspect_cpp_codelab_integration_tests
```

Note: This runs integration tests for all parts of this codelab.

### View the code

Look at how the integration test is setup:

1. View the [component manifest (cmx)][part4-integration-meta]:

  ```
  {
      "facets": {
          "fuchsia.test": {
              "injected-services": {
                  "fuchsia.diagnostics.Archive": "fuchsia-pkg://fuchsia.com/archivist#meta/observer.cmx"
              }
          }
      },
      "program": {
          "binary": "test/integration_part_4"
      },
      "sandbox": {
          "services": [
              "fuchsia.logger.LogSink",
              "fuchsia.sys.Loader",
              "fuchsia.sys.Environment"
          ]
      }
  }
  ```

  The important parts of this file are:

  - Injected services

    The `fuchsia.test` facet includes configuration for tests.

    In this file, the `fuchsia.diagnostics.Archive` service is injected
    and points to a component called `observer.cmx`. The observer collects
    information from all components in your test environment and provides
    a reading interface. You can use this information to look at your
    Inspect output.

  - Sandbox services

    Integration tests need to start other components in the test
    environment and wire them up. For this you need `fuchsia.sys.Loader`
    and `fuchsia.sys.Environment`.

2. Look at the [integration test][part4-integration] itself. The individual test cases are fairly straightforward:

  ```
  TEST_F(CodelabTest, StartWithFizzBuzz) {
    auto ptr = StartComponentAndConnect({.include_fizzbuzz_service = true});

    bool error = false;
    ptr.set_error_handler([&](zx_status_t unused) { error = true; });

    bool done = false;
    std::string result;
    ptr->Reverse("hello", [&](std::string value) {
      result = std::move(value);
      done = true;
    });

    // Run until either the error handler reports an error or the result is set.
    RunLoopUntil([&] { return done || error; });

    ASSERT_FALSE(error);
    EXPECT_EQ("olleh", result);
  }
  ```

  `StartComponentAndConnect` is responsible for creating a new test
  environment and starting the codelab component inside of it. The
  `include_fizzbuzz_service` option instructs the method to optionally
  include FizzBuzz. This feature tests that your Inspect output is as
  expected in case it fails to connect to FizzBuzz as in Part 2.

5. Add the following method to your test fixture to read from the Archive service:

  ```
  #include <rapidjson/document.h>
  #include <rapidjson/pointer.h>

  std::string GetInspectJson() {
      // Connect to the Archive.
      fuchsia::diagnostics::ArchivePtr archive;
      real_services()->Connect(archive.NewRequest());

      // Open a Reader for each type of data the Archive contains.
      fuchsia::diagnostics::ReaderPtr reader;
      archive->ReadInspect(reader.NewRequest(), {} /* selectors */,
                           [](auto res) { ASSERT_FALSE(res.is_err()) << "Failed to get reader"; });

      // Since components are asynchronous, you do not know if the observer has seen the test
      // components yet. You will need to repeatedly read the data.
      while (true) {
        std::vector<fuchsia::diagnostics::FormattedContent> current_entries;

        // Get a new snapshot in JSON format.
        fuchsia::diagnostics::BatchIteratorPtr iterator;
        reader->GetSnapshot(fuchsia::diagnostics::Format::JSON, iterator.NewRequest(),
                            [](auto res) { ASSERT_FALSE(res.is_err()) << "Failed to get snapshot"; });

        // Get individual batches from the iterator.
        bool done;
        iterator->GetNext([&](auto result) {
          auto res = fit::result<ContentVector, fuchsia::diagnostics::ReaderError>(std::move(result));
          if (res.is_ok()) {
            current_entries = res.take_value();
          }

          done = true;
        });

        RunLoopUntil([&] { return done; });

        // Find the returned value that contains the name of your component, this is the
        // JSON you want.
        for (const auto& content : current_entries) {
          std::string json;
          fsl::StringFromVmo(content.formatted_json_hierarchy(), &json);
          if (json.find("sys/inspect_cpp_codelab_part_5.cmx") != std::string::npos) {
            return json;
          }
        }

        // Retry with delay until the data appears.
        usleep(150000);
      }

      return "";
    }
  ```

6. Use rapidjson to parse the returned data in your tests:

  ```
  rapidjson::Document document;
  document.Parse(GetInspectJson());
  ```

**Exercise**: Add assertions on the returned JSON data.

- *Hint*: It may help to print the JSON output to view the schema.

- *Hint*: You can read values by path as follows:

  ```
  rapidjson::GetValueByPointerWithDefault(
    document, "/contents/root/fuchsia.inspect.Health/status", ""));
  ```

- *Hint*: You can `EXPECT_EQ` by passing in the expected value as a rapidjson::Value: `rapidjson::Value("OK")`.

Your integration test will now ensure your inspect output is correct.

This concludes Part 4.

You may commit your solution:

```
git commit -am "solution to part 4"
```

## Part 5: Feedback Selectors

This section is under construction.

- TODO: Writing a feedback selector and adding tests to your integration test.

- TODO: Selectors for Feedback and other pipelines

[inspect-cpp-codelab]: /src/diagnostics/examples/inspect/cpp
[part1]: /src/diagnostics/examples/inspect/cpp/part_1
[part1-unittest]: /src/diagnostics/examples/inspect/cpp/part_1/reverser_unittests.cc
[part1-main]: /src/diagnostics/examples/inspect/cpp/part_1/main.cc
[part1-reverser-h]: /src/diagnostics/examples/inspect/cpp/part_1/reverser.h
[part1-reverser-cc]: /src/diagnostics/examples/inspect/cpp/part_1/reverser.cc
[part1-build]: /src/diagnostics/examples/inspect/cpp/part_1/BUILD.gn
[fidl-reverser]: /src/diagnostics/examples/inspect/fidl/reverser.test.fidl
[fidl-fizzbuzz]: /src/diagnostics/examples/inspect/fidl/fizzbuzz.test.fidl
[client-main]: /src/diagnostics/examples/inspect/cpp/client/main.cc#118
[part2-meta]: /src/diagnostics/examples/inspect/cpp/part_2/meta/inspect_cpp_codelab_part_2.cmx
[part3-unittest]: /src/diagnostics/examples/inspect/cpp/part_3/reverser_unittests.cc
[part3-build]: /src/diagnostics/examples/inspect/cpp/part_3/BUILD.gn
[part4-integration]: /src/diagnostics/examples/inspect/cpp/part_4/tests/integration_test.cc
[part4-integration-meta]: /src/diagnostics/examples/inspect/cpp/meta/integration_part_4.cmx