Handling multiple clients
Prerequisites
This tutorial builds on the [HLCPP getting started tutorials][overview].
Overview
This tutorial updates the [Echo client][client-tut] from the getting started tutorials to make multiple connections to the server, and update the [Echo server][server-tut] to handle multiple client connections. For running multiple instances of a server (or multiple FIDL protocols), see the tutorial on [services][services-tut].
The full example code for this tutorial is located at
[//examples/fidl/hlcpp/multiple_clients][src].
Implement the server
In the [previous implementation][server-tut-impl], the main() function initialized
a single fidl::Binding, and bound any incoming requests to it:
{% includecode gerrit_repo="fuchsia/fuchsia" gerrit_path="examples/fidl/hlcpp/server/main.cc" region_tag="main" highlight="5,7,8,9,10,12" %}
This means that if a second client tries to connect to the server at the same
time, the second call to binding.Bind will overwrite the channel from the
first client. To support multiple clients, keep track of multiple
fidl::Bindings (one for each client) using a fidl::BindingSet:
{% includecode gerrit_repo="fuchsia/fuchsia" gerrit_path="examples/fidl/hlcpp/multiple_clients/server/main.cc" region_tag="main" highlight="5,7" %}
A binding set also simplifies the code since it no longer
needs to create a custom handler. The binding set has a GetHandler method,
which returns a handler that creates a new Binding and stores it in a vector.
To use fidl::BindingSet, include lib/fidl/cpp/binding_set.h.
Implement the client
In order to manage multiple clients connected to a protocol, the FIDL HLCPP
runtime library provides an anolog to fidl::BindingSet: the
fidl::InterfacePtrSet. Use the class to write code that makes multiple
connections to the same protocol:
{% includecode gerrit_repo="fuchsia/fuchsia" gerrit_path="examples/fidl/hlcpp/multiple_clients/client/main.cc" region_tag="main" %}
The code for setting up a proxy and making requests is the same as in the
[client tutorial][client-tut-main] except it uses
an interface pointer set to simplify the process of broadcasting a message
to a set of clients. An added benefit of using fidl::InterfacePtrSet and
fidl::BindingSet is that any binding or interface pointer that experiences an
error on its channel is automatically removed from the set.
To use fidl::InterfacePtrSet, include lib/fidl/cpp/interface_ptr_set.h.
Run the example
In order for the client and server to communicate using the Echo protocol,
component framework must route the fuchsia.examples.Echo capability from the
server to the client. For this tutorial, a [realm][glossary.realm] component is
provided to declare the appropriate capabilities and routes.
Note: You can explore the full source for the realm component at
//examples/fidl/echo-realm
-
Configure your build to include the provided package that includes the echo realm, server, and client:
-
Build the Fuchsia image:
-
Run the
echo_realmcomponent. This creates the client and server component instances and routes the capabilities: -
Start the
echo_clientinstance:
The server component starts when the client attempts to connect to the Echo
protocol. You should see output similar to the following in the device logs
(ffx log):
```none {:.devsite-disable-click-to-copy} [echo_server][][I] Running echo server [echo_client][][I] Got response Hello echoer 0
Terminate the realm component to stop execution and clean up the component
instances:
```posix-terminal
ffx component destroy /core/ffx-laboratory:echo_realm
glossary.realm /development/languages/fidl/tutorials/hlcpp/basics/client.md client-main /development/languages/fidl/tutorials/hlcpp/basics/server.md server-tut-impl /development/languages/fidl/tutorials/hlcpp/topics/services.md srcoverview