<<../../_common/components/_declaring_intro.md>>
<<../../_common/components/_declaring_manifests.md>>
<<../../_common/components/_declaring_shards.md>>
The Fuchsia build system provides templates as GN imports in //build/components.gni
to build and package software into Fuchsia components. Below is an example of a BUILD.gn
file for a simple C++ component:
{% verbatim %} import("//build/components.gni") executable("bin") { sources = [ "main.cc" ] } resource("my_file") { sources = [ "my_file.txt" ] outputs = [ "data/{{source_file_part}}" ] } fuchsia_component("hello-world-component") { component_name = "hello-world" deps = [ ":bin", ":my_file", ] manifest = "meta/hello-world.cml" } fuchsia_package("hello-world") { package-name = "hello-world" deps = [ ":hello-world-component", ] } {% endverbatim %}
This file contains the following main elements:
executable()
: Compiles the source code into a binary. This target varies depending on the programming language. For example, an executable
target can be used for C++, rustc_binary
for Rust, go_binary
for Golang.resource()
: Optional named collection of data files to copy as resources into another GN target. These files are accessible to the binary inside the component's namespace.fuchsia_component()
: Collects the binary, component manifest, and additional resources together into a single target. This target compiles the manifest source into a component declaration using cmc
.fuchsia_package()
: Unit of distribution for components. Allows one or more components to be hosted in a package repository and included in the target device's package sets. This target generates the package metadata and builds the Fuchsia Archive (.far
) file.Packages can contain multiple components, listed as deps
in the fuchsia_package()
template. You can simplify the build file for packages containing only one component using the fuchsia_package_with_single_component()
template.
The following simplified BUILD.gn
example is equivalent to to the previous example:
{% verbatim %} import("//build/components.gni") executable("bin") { sources = [ "main.cc" ] } resource("my_file") { sources = [ "my_file.txt" ] outputs = [ "data/{{source_file_part}}" ] } fuchsia_package_with_single_component("hello-world") { manifest = "meta/hello-world.cml" deps = [ ":bin", ":my_file", ] } {% endverbatim %}
Note: For more details on the GN syntax of the component build rules, see the components build reference.
In this exercise, you'll build and run a basic component that reads the program arguments and echoes a greeting out the system log.
To begin, create a project scaffold for a new component called echo-args
under the //vendor/fuchsia-codelab
directory:
{Rust}
fx create component --path vendor/fuchsia-codelab/echo-args --lang rust
{C++}
fx create component --path vendor/fuchsia-codelab/echo-args --lang cpp
This creates a project directory structure with a basic component template:
{Rust}
echo-args |- BUILD.gn |- meta | |- echo_args.cml | |- src |- main.rs
BUILD.gn
: GN build targets for the executable binaries, component, and package.meta/echo_args.cml
: Manifest declaring the component's executable and required capabilities.src/main.rs
: Source code for the Rust executable binary and unit tests.{C++}
echo-args |- BUILD.gn |- meta | |- echo_args.cml | |- echo_args.cc |- echo_args.h |- echo_args_unittest.cc |- main.cc
BUILD.gn
: GN build targets for the executable binaries, component, and package.meta/echo_args.cml
: Manifest declaring the component's executable and required capabilities.echo_args.cc
: Source code for the C++ component functionality.echo_args_unittest.cc
: Source code for the C++ unit tests.main.cc
: Source code for the C++ executable binary main entry point.Open the component manifest file in your editor and locate the program
block. This defines the attributes of the component's executable. Add an args
array to supply the list of names to greet:
{Rust}
echo-args/meta/echo_args.cml
:
{% includecode gerrit_repo="fuchsia/fuchsia" gerrit_path="examples/components/echo/rust/meta/echo.cml" region_tag="manifest" adjust_indentation="auto" highlight="15,16,17,18,19,21,22" %}
{C++}
echo-args/meta/echo_args.cml
:
{% includecode gerrit_repo="fuchsia/fuchsia" gerrit_path="examples/components/echo/cpp/meta/echo.cml" region_tag="manifest" adjust_indentation="auto" highlight="15,16,17,18,19,21,22" %}
Update the manifest includes to provide logging support on stdout:
{Rust}
echo-args/meta/echo_args.cml
:
{ include: [ "inspect/client.shard.cml", // Enable logging on stdout "syslog/elf_stdio.shard.cml", ], // ... }
{C++}
echo-args/meta/echo_args.cml
:
{ include: [ "inspect/client.shard.cml", // Enable logging on stdout "syslog/elf_stdio.shard.cml", ], // ... }
Open the source file for the main executable and replace the import statements with the following code:
{Rust}
echo-args/src/main.rs
:
{% includecode gerrit_repo="fuchsia/fuchsia" gerrit_path="examples/components/echo/rust/src/main.rs" region_tag="imports" adjust_indentation="auto" %}
{C++}
echo-args/main.cc
:
{% includecode gerrit_repo="fuchsia/fuchsia" gerrit_path="examples/components/echo/cpp/main.cc" region_tag="imports" adjust_indentation="auto" %} #include "vendor/fuchsia-codelab/echo-args/echo_args.h"
Replace the main()
function with the following code:
{Rust}
echo-args/src/main.rs
:
{% includecode gerrit_repo="fuchsia/fuchsia" gerrit_path="examples/components/echo/rust/src/main.rs" region_tag="main" adjust_indentation="auto" %}
{C++}
echo-args/main.cc
:
{% includecode gerrit_repo="fuchsia/fuchsia" gerrit_path="examples/components/echo/cpp/main.cc" region_tag="main" adjust_indentation="auto" %}
This code reads the program arguments and passes them to a function called greeting()
to generate a response for the syslog entry.
Add the following code to implement the greeting()
function:
{Rust}
echo-args/src/main.rs
:
{% includecode gerrit_repo="fuchsia/fuchsia" gerrit_path="examples/components/echo/rust/src/main.rs" region_tag="greeting" adjust_indentation="auto" %}
{C++}
echo-args/echo_args.h
:
#include "vendor/fuchsia-codelab/echo-args/echo_args.h" {% includecode gerrit_repo="fuchsia/fuchsia" gerrit_path="examples/components/echo/cpp/echo_component.h" region_tag="greeting" adjust_indentation="auto" %}
echo-args/echo_args.cc
:
{% includecode gerrit_repo="fuchsia/fuchsia" gerrit_path="examples/components/echo/cpp/echo_component.cc" region_tag="greeting" adjust_indentation="auto" %}
This function creates a simple string from the list of provided arguments based on the length of the list.
Add your new component to the build configuration:
fx set workstation.qemu-x64 --with //vendor/fuchsia-codelab/echo-args
Run fx build
and verify that the build completes successfully:
fx build
In the next section, you'll integrate this component into the build and test the output in the system log.