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<ol class="chapter"><li class="chapter-item expanded "><a href="index.html"><strong aria-hidden="true">1.</strong> Top</a></li><li class="chapter-item expanded "><a href="tutorial.html"><strong aria-hidden="true">2.</strong> Tutorial</a></li><li><ol class="section"><li class="chapter-item expanded "><a href="setup.html"><strong aria-hidden="true">2.1.</strong> Setting-up</a></li><li class="chapter-item expanded "><a href="pubsub.html"><strong aria-hidden="true">2.2.</strong> Publish and Subscribe</a></li><li class="chapter-item expanded "><a href="timer.html"><strong aria-hidden="true">2.3.</strong> Timer</a></li><li class="chapter-item expanded "><a href="multi_pubsub.html"><strong aria-hidden="true">2.4.</strong> Multi-threaded Publish and Subscribe</a></li><li class="chapter-item expanded "><a href="message.html"><strong aria-hidden="true">2.5.</strong> User Defined Data Structure</a></li><li class="chapter-item expanded "><a href="service.html" class="active"><strong aria-hidden="true">2.6.</strong> Service</a></li><li class="chapter-item expanded "><a href="parameter.html"><strong aria-hidden="true">2.7.</strong> Parameter</a></li><li class="chapter-item expanded "><a href="zerocopy.html"><strong aria-hidden="true">2.8.</strong> Zero Copy Publish and Subscribe</a></li><li class="chapter-item expanded "><a href="allocator.html"><strong aria-hidden="true">2.9.</strong> Custom Memory Allocator</a></li><li class="chapter-item expanded "><a href="pusbsub_and_service.html"><strong aria-hidden="true">2.10.</strong> Request to Server in Callback</a></li></ol></li><li class="chapter-item expanded "><a href="contribution.html"><strong aria-hidden="true">3.</strong> Contribution Guide</a></li><li><ol class="section"><li class="chapter-item expanded "><a href="setup_contribution.html"><strong aria-hidden="true">3.1.</strong> Setting-up for Contribution</a></li><li class="chapter-item expanded "><a href="build_and_test.html"><strong aria-hidden="true">3.2.</strong> Build and Test</a></li><li class="chapter-item expanded "><a href="editor_setup.html"><strong aria-hidden="true">3.3.</strong> Editor Setting-up</a></li><li class="chapter-item expanded "><a href="internal_msgs.html"><strong aria-hidden="true">3.4.</strong> Generating Messages Included by safe_drive</a></li><li class="chapter-item expanded "><a href="c_apis.html"><strong aria-hidden="true">3.5.</strong> C APIs</a></li><li class="chapter-item expanded "><a href="document.html"><strong aria-hidden="true">3.6.</strong> Documentation</a></li></ol></li></ol>
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<h1 class="menu-title">safe_drive: Formally Specified Rust Bindings for ROS2</h1>
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<h1 id="service"><a class="header" href="#service">Service</a></h1>
<p><a href="https://github.com/tier4/safe_drive_tutorial/tree/main/srvtest">Source code</a>.</p>
<p>A service is a communication consisting requests and responses.
There are a server and clients for a service as follows.</p>
<pre class="mermaid">graph TD;
Server--response-->Client1;
Server--response-->Client2;
Server--response-->Client3;
Client1--request-->Server;
Client2--request-->Server;
Client3--request-->Server;
</pre>
<p>A client sends a request and the server replies the request.
In this tutorial, we will describe how to implement a client and a server in Rust by using <code>safe_drive</code>.</p>
<h2 id="create-base-files"><a class="header" href="#create-base-files">Create Base Files</a></h2>
<p>In this tutorial, we prepare 3 Rust's projects and 1 C's project.
The following table shows the directories we use.</p>
<div class="table-wrapper"><table><thead><tr><th>Directories</th><th>Description</th></tr></thead><tbody>
<tr><td>srvtest/src/server</td><td>server in Rust</td></tr>
<tr><td>srvtest/src/client</td><td>client in Rust</td></tr>
<tr><td>srvtest/src/srvmsg</td><td>message type</td></tr>
</tbody></table>
</div>
<p><code>srvmsg</code> is a ROS2's project to define a user defined type for a service we implement.</p>
<pre><code class="language-text">$ mkdir -p srvtest/src
$ cd srvtest/src
$ cargo new server
$ cargo new client
$ ros2 pkg create --build-type ament_cmake srvmsg
</code></pre>
<p>In addition to that, create the workspace's <code>Cargo.toml</code> as follows.</p>
<p><code>srvtest/src/Cargo.toml</code></p>
<pre><code class="language-toml">[workspace]
members = [ "client", "server"]
</code></pre>
<h2 id="define-protocol"><a class="header" href="#define-protocol">Define Protocol</a></h2>
<p>First of all, let's define a protocol for a service.
ROS2 provides a special format to define a protocol,
and it should be described in a <code>.srv</code> file.</p>
<p>Usually, <code>.srv</code> files are placed in a <code>srv</code> directory.
So, we create <code>srv</code> directory as follows.</p>
<pre><code class="language-text">$ cd srvtest/src/srvmsg
$ mkdir srv
</code></pre>
<h3 id="create-srvmsgsrvaddtwointssrv"><a class="header" href="#create-srvmsgsrvaddtwointssrv">Create <code>srvmsg/srv/AddTwoInts.srv</code></a></h3>
<p>Then, create <code>AddTwoInts.srv</code> file in which a protocol is specified as follows.</p>
<pre><code class="language-text">uint32 x
uint32 y
---
uint32 result
</code></pre>
<p><code>uint32 x</code> and <code>uint32 y</code> above <code>--</code> are types which must be
included in a request, and <code>uint32 result</code> is a type which must be
included in a response.
We will implement a server which takes 2 integer values
and returns the summation of the values.</p>
<h3 id="edit-srvmsgcmakeliststxt"><a class="header" href="#edit-srvmsgcmakeliststxt">Edit <code>srvmsg/CMakeLists.txt</code></a></h3>
<p>To generate shared libraries from <code>AddTwoInts.srv</code>,
<code>CMakeLists.txt</code> must be updated as follows.</p>
<pre><code class="language-cmake"># srvtest/src/srvmsg/CMakeLists.txt
find_package(rosidl_default_generators REQUIRED)
rosidl_generate_interfaces(${PROJECT_NAME}
"srv/AddTwoInts.srv"
)
</code></pre>
<h3 id="edit-srvmsgpackagexml"><a class="header" href="#edit-srvmsgpackagexml">Edit <code>srvmsg/package.xml</code></a></h3>
<p>In addition to that, the following lines must be added to <code>package.xml</code>.</p>
<p><code>srvtest/src/srvmsg/package.xml</code></p>
<pre><code class="language-xml"><build_depend>rosidl_default_generators</build_depend>
<exec_depend>rosidl_default_runtime</exec_depend>
<member_of_group>rosidl_interface_packages</member_of_group>
</code></pre>
<h2 id="server"><a class="header" href="#server">Server</a></h2>
<p>A server can be implemented in a straightforward way.</p>
<h3 id="edit-servercargotoml"><a class="header" href="#edit-servercargotoml">Edit <code>server/Cargo.toml</code></a></h3>
<p>To generate Rust types from <code>.srv</code> files,
we have to edit <code>Cargo.toml</code> as follows.</p>
<pre><code class="language-toml">[dependencies]
safe_drive = "0.4"
srvmsg = { path = "/tmp/safe_drive_tutorial/srvtest/srvmsg" }
tokio = { version = "1", features = ["full"] }
[package.metadata.ros]
msg = ["srvmsg"]
msg_dir = "/tmp/safe_drive_tutorial/srvtest"
safe_drive_version = "0.3"
</code></pre>
<h3 id="create-serverpackagexml"><a class="header" href="#create-serverpackagexml">Create <code>server/package.xml</code></a></h3>
<p><code>package.xml</code> is also required as follows.</p>
<p><code>srvtest/src/server/package.xml</code></p>
<pre><code class="language-xml"><?xml version="1.0"?>
<?xml-model href="http://download.ros.org/schema/package_format3.xsd" schematypens="http://www.w3.org/2001/XMLSchema"?>
<package format="3">
<name>server</name>
<version>0.0.0</version>
<description>Server in Rust</description>
<maintainer email="yuuki.takano@tier4.jp">Yuuki Takano</maintainer>
<license>Apache License 2.0</license>
<test_depend>ament_lint_auto</test_depend>
<test_depend>ament_lint_common</test_depend>
<depend>srvmsg</depend>
<export>
<build_type>ament_cargo</build_type>
</export>
</package>
</code></pre>
<p>Don't forget <code><depend>srvmsg</depend></code>.</p>
<h2 id="generate-types"><a class="header" href="#generate-types">Generate Types</a></h2>
<p><code>AddTwoInts.srv</code> will be translated to <code>struct AddTwoInts</code> as follows.</p>
<pre><pre class="playground"><code class="language-rust"><span class="boring">#![allow(unused)]
</span><span class="boring">fn main() {
</span>#[derive(Debug)]
pub struct AddTwoInts;
impl ServiceMsg for AddTwoInts {
type Request = AddTwoInts_Request;
type Response = AddTwoInts_Response;
fn type_support() -> *const rcl::rosidl_service_type_support_t {
unsafe {
rosidl_typesupport_c__get_service_type_support_handle__srvmsg__srv__AddTwoInts()
}
}
}
<span class="boring">}</span></code></pre></pre>
<p><code>struct AddTwoInts</code> implements <code>ServiceMsg trait</code>.
<code>ServiceMsg::Request</code> and <code>ServiceMsg::Response</code> are types of request and response, respectively.
<code>AddTwoInts_Request</code> and <code>AddTowInts_Response</code> are as follows.</p>
<pre><pre class="playground"><code class="language-rust"><span class="boring">#![allow(unused)]
</span><span class="boring">fn main() {
</span>#[repr(C)]
#[derive(Debug)]
pub struct AddTwoInts_Request {
pub x: u32,
pub y: u32,
}
#[repr(C)]
#[derive(Debug)]
pub struct AddTwoInts_Response {
pub result: u32,
}
<span class="boring">}</span></code></pre></pre>
<h3 id="edit-serversrcmainrs"><a class="header" href="#edit-serversrcmainrs">Edit <code>server/src/main.rs</code></a></h3>
<p>You have to create a server by <code>create_server()</code> method and register a callback function to a selector as follows.</p>
<pre><pre class="playground"><code class="language-rust">use safe_drive::{context::Context, error::DynError, logger::Logger, pr_error, qos::Profile};
use srvmsg::srv::{AddTwoInts, AddTwoInts_Response};
fn main() -> Result<(), DynError> {
// Create a context.
let ctx = Context::new()?;
// Create a node.
let node = ctx.create_node("server_node", None, Default::default())?;
// Create a server.
let server = node.create_server::<AddTwoInts>("my_service", Some(Profile::default()))?;
// Create a selector.
let mut selector = ctx.create_selector()?;
// Create a logger.
let logger = Logger::new("server");
selector.add_server(
server,
Box::new(move |msg, _header| {
let mut response = AddTwoInts_Response::new().unwrap();
pr_error!(logger, "recv: {:?}", msg);
response.result = msg.x + msg.y;
response
}),
);
loop {
selector.wait()?; // Spin.
}
}</code></pre></pre>
<p>Let's dig into detail.</p>
<pre><pre class="playground"><code class="language-rust"><span class="boring">#![allow(unused)]
</span><span class="boring">fn main() {
</span>// Create a server.
let server = node.create_server::<AddTwoInts>("my_service", Some(Profile::default()))?;
<span class="boring">}</span></code></pre></pre>
<p><code>AddTwoInts</code> of <code>create_server::<AddTwoInts></code> indicates the protocol of the server.
The arguments of <code>"my_service"</code> and <code>Some(Profile::default())</code> are the service name and QoS.
If you pass <code>None</code> instead of <code>Some(Profile::default())</code>, <code>Profile::default()</code> is used.</p>
<p>The callback was passed as follows.</p>
<pre><pre class="playground"><code class="language-rust"><span class="boring">#![allow(unused)]
</span><span class="boring">fn main() {
</span>selector.add_server(
server,
Box::new(move |msg, _header| {
let mut response = AddTwoInts_Response::new().unwrap();
pr_error!(logger, "recv: {:?}", msg);
response.result = msg.x + msg.y;
response
}),
);
<span class="boring">}</span></code></pre></pre>
<p>The callback function must take a message sent by a client and a header including sequence number, time, etc.
<code>msg</code>'s types is <code>AddTwoInts_Request</code> and a value of <code>AddTwoInts_Response</code>, which is a response, must be returned.</p>
<h2 id="client"><a class="header" href="#client">Client</a></h2>
<h3 id="edit-clientcargotoml"><a class="header" href="#edit-clientcargotoml">Edit <code>client/Cargo.toml</code></a></h3>
<p><code>safe_drive</code>, and <code>tokio</code> must be added to <code>Cargo.toml</code> as follows.</p>
<p><code>srvtest/src/client/Cargo.toml</code></p>
<pre><code class="language-toml">[dependencies]
safe_drive = "0.4"
srvmsg = { path = "/tmp/safe_drive_tutorial/srvtest/srvmsg" }
tokio = { version = "1", features = ["full"] }
[package.metadata.ros]
msg = ["srvmsg"]
msg_dir = "/tmp/safe_drive_tutorial/srvtest"
safe_drive_version = "0.3"
</code></pre>
<h3 id="create-clientpackagexml"><a class="header" href="#create-clientpackagexml">Create <code>client/package.xml</code></a></h3>
<p><code>package.xml</code> is also required as follows.</p>
<p><code>srvtest/src/client/package.xml</code></p>
<pre><code class="language-xml"><?xml version="1.0"?>
<?xml-model href="http://download.ros.org/schema/package_format3.xsd" schematypens="http://www.w3.org/2001/XMLSchema"?>
<package format="3">
<name>client</name>
<version>0.0.0</version>
<description>Client in Rust</description>
<maintainer email="yuuki.takano@tier4.jp">Yuuki Takano</maintainer>
<license>Apache License 2.0</license>
<test_depend>ament_lint_auto</test_depend>
<test_depend>ament_lint_common</test_depend>
<depend>srvmsg</depend>
<export>
<build_type>ament_cargo</build_type>
</export>
</package>
</code></pre>
<p>Don't forget <code><depend>srvmsg</depend></code>.</p>
<h3 id="edit-clientsrcmainrs"><a class="header" href="#edit-clientsrcmainrs">Edit <code>client/src/main.rs</code></a></h3>
<p>We recommend to use async/await to implement a client,
because a client wait a response, but when the response is replied is unpredictable.
In this tutorial, we use <a href="https://tokio.rs/">Tokio</a>, which is the most popular asynchronous library of Rust.</p>
<pre><pre class="playground"><code class="language-rust">use safe_drive::{
context::Context, error::DynError, logger::Logger, pr_error, pr_info, pr_warn, qos::Profile,
};
use srvmsg::srv::{AddTwoInts, AddTwoInts_Request};
use std::time::Duration;
use tokio::time::timeout;
#[tokio::main]
async fn main() -> Result<(), DynError> {
// Create a context and a node.
let ctx = Context::new()?;
let node = ctx.create_node("client", None, Default::default())?;
let logger = Logger::new("client");
// Create a client.
let mut client = node.create_client::<AddTwoInts>("my_service", Some(Profile::default()))?;
let mut n = 0;
loop {
let mut request = AddTwoInts_Request::new().unwrap();
request.x = n;
request.y = n + 1;
n += 1;
// Send a request.
let client_rcv = client.send(&request)?;
// Receive a request.
let mut receiver = client_rcv.recv();
match timeout(Duration::from_secs(1), &mut receiver).await {
Ok(Ok((c, response, _header))) => {
pr_info!(logger, "received {:?}", response);
client = c;
}
Ok(Err(e)) => {
pr_error!(logger, "error: {e}");
return Err(e);
}
Err(elapsed) => {
pr_warn!(logger, "timeout: {elapsed}");
client = receiver.give_up();
}
}
tokio::time::sleep(Duration::from_secs(1)).await;
}
}</code></pre></pre>
<p>Because a response will be never returned,
we use <code>tokio::time::timeout</code> to receive a response.
<code>timeout(Duration::from_secs(1), &mut receiver).await</code>
takes a duration and a awaitable future.
The awaitable future can be taken by <code>client_rcv.recv()</code>.</p>
<p>Note that it uses <code>tokio::time::sleep</code> instead of
<code>std::thread::sleep</code> because to avoid calling blocking functions.</p>
<p><code>client.send()</code> consumes <code>client</code> and it returns <code>client_recv</code>
to receive a response.
<code>client_rcv.recv()</code> consumes <code>client_recv</code> and <code>client_rcv.recv().await</code>
returns new client, a response, and a header.
The new client must be used to send next request.</p>
<p>This means that you cannot ignore receiving a response.
If you forget to receive a response,
you cannot send any request again,
because you need to get a new client by receiving a response..
Otherwise, you encountered compilation errors.</p>
<h2 id="execution"><a class="header" href="#execution">Execution</a></h2>
<p>First of all, you have to compile it and execute a server as follows.</p>
<pre><code class="language-text">$ cd srvtest
$ colcon build --cargo-args --release
$ . ./install/setup.bash
$ ros2 run server server
</code></pre>
<p>Then, in another terminal, execute a client as follows.</p>
<pre><code class="language-text">$ cd srvtest
$ . ./install/setup.bash
$ ros2 run client client
[WARN] [1659604527.720730018] [client]: timeout: deadline has elapsed
[INFO] [1659604528.722220697] [client]: received AddTwoInts_Response { result: 3 }
[INFO] [1659604529.723525686] [client]: received AddTwoInts_Response { result: 5 }
[INFO] [1659604530.724820326] [client]: received AddTwoInts_Response { result: 7 }
</code></pre>
<p>Nicely done!
We used async/await for the client,
and it can be used for the server as follows.</p>
<pre><pre class="playground"><code class="language-rust"><span class="boring">#![allow(unused)]
</span><span class="boring">fn main() {
</span>async { server.recv().await };
<span class="boring">}</span></code></pre></pre>
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