LLCPP FIDL library

Prerequisites

This tutorial builds on the Compiling FIDL tutorial. For more information on other FIDL tutorials, see the Overview.

Overview

This tutorial details how to use the LLCPP FIDL bindings by creating a unit test that you can use as a “playground” for exploring the LLCPP bindings.

This document covers how to complete the following tasks:

• Write a C++ device test.
• Add the LLCPP bindings of a FIDL library as a build dependency.
• Import the LLCPP bindings crate into your code.
• Inspect and use the generated bindings code.

The example code is located in your Fuchsia checkout in //examples/fidl/llcpp/unittests/. If you want to write all the code as you follow this tutorial, you can remove the example code:

rm -r examples/fidl/llcpp/unittests/*

Write a C++ device test

1. Add a gtest stub to examples/fidl/llcpp/unittests/main.cc:

   #include <gtest/gtest.h>
   
   namespace {
   
   } // namespace
   

2. Define a test target, and a package containg the test in examples/fidl/llcpp/unittests/BUILD.gn:

   {%includecode gerrit_repo="fuchsia/fuchsia" gerrit_path="examples/fidl/llcpp/unittests/BUILD.gn" region_tag="imports" %}
   
   test("test") {
     testonly = true
     output_name = "fidl_example_llcpp_test"
     sources = [ "main.cc" ]
     deps = [ "//third_party/googletest:gtest_main" ]
   }
   
   {%includecode gerrit_repo="fuchsia/fuchsia" gerrit_path="examples/fidl/llcpp/unittests/BUILD.gn" region_tag="package" %}
   

   Note: The executable_path in the package needs to match the output_name of the test binary. By default, the binary is placed in the test/ directory. Packages are explained further in the next tutorial

3. Build and run the empty test suite on a running instance of Fuchsia:

   fx set core.x64 --with //examples/fidl/llcpp/unittests:fidl-example-llcpp-test
   fx build
   

   In a separate terminal, run

   fx qemu -kN
   

   In a separate terminal, run

   fx serve
   

   Back in the original terminal (with fx build), run

   fx test -vo fidl-example-llcpp-test
   

   You should see test output indicating that zero tests have run, since no tests have been added yet.

Add the LLCPP FIDL bindings as a dependency

For each FIDL library declaration, including the one in Compiling FIDL, C++ library containing LLCPP bindings code for that library is generated under the original target name appended with _llcpp.

Add a dependency on the LLCPP bindings by referencing this target. The new test target should look like:

{%includecode gerrit_repo="fuchsia/fuchsia" gerrit_path="examples/fidl/llcpp/unittests/BUILD.gn" region_tag="test" %}

(Optional) To view the newly generated bindings:

1. Rebuild using fx build.
2. Change to the generated files directory: out/default/fidling/gen/examples/fidl/fuchsia.examples/fuchsia/examples, where the generated files are located. You may need to change out/default if you have set a different build output directory. You can check your build output directory with cat .fx-build-dir.

For more information on how to find generated bindings code, see Viewing generated bindings code.

Include the LLCPP bindings in your C++ code

To include the bindings, add the following include statement to the top of examples/fidl/llcpp/unittests/main.cc

{%includecode gerrit_repo="fuchsia/fuchsia" gerrit_path="examples/fidl/llcpp/unittests/main.cc" region_tag="include" %}

Inspect and use the generated bindings code

You can now write some tests by referring to the generated code. For more information on the bindings, see LLCPP Bindings Reference.

To get started, you can also use some example code. You can add this inside the anonymous namespace in main.cc:

{%includecode gerrit_repo="fuchsia/fuchsia" gerrit_path="examples/fidl/llcpp/unittests/main.cc" region_tag="bits" %}

{%includecode gerrit_repo="fuchsia/fuchsia" gerrit_path="examples/fidl/llcpp/unittests/main.cc" region_tag="enums" %}

{%includecode gerrit_repo="fuchsia/fuchsia" gerrit_path="examples/fidl/llcpp/unittests/main.cc" region_tag="structs" %}

{%includecode gerrit_repo="fuchsia/fuchsia" gerrit_path="examples/fidl/llcpp/unittests/main.cc" region_tag="unions" %}

{%includecode gerrit_repo="fuchsia/fuchsia" gerrit_path="examples/fidl/llcpp/unittests/main.cc" region_tag="tables" %}

To rebuild and rerun the tests, run:

fx test -vo fidl_crates_test