service_attributes

Service-Attributes

This example illustrates the definition and usage of custom service attributes. Service attributes are key-value pairs that can be defined via the service builder like so:

node.service_builder(&service_name)
    //...
    .create_with_attributes(
        AttributeSpecifier()
            .define("my_custom_key", "some_funky_value")
            .define("my_custom_key", "another_value_for_the_same_key")
            .define("another_key", "another_value")
        );

When the service is created, the attributes are set. When the service is opened, these attributes are interpreted as requirements. If a required attribute is not set, or if its value differs, the service will not be opened. For example, the following service can be opened because it matches an attribute defined in the previous example:

node.service_builder(&service_name)
    //...
    .open_with_attributes(
        AttributeVerifier()
            .require("my_custom_key", "some_funky_value")
            // don't care for the value but the key must be present
            .require_key("another_key")
    );

In contrast, the following example cannot open the service because it requires an attribute that is not set and another attribute where the value does not match:

node.service_builder(&service_name)
    //...
    .open_with_attributes(
        AttributeVerifier()
            .require("another_key", "zero")
            .require_key("unknown_key")
    );

To list all attributes of a service, you can use the following code:

let service = node.service_builder(&service_name)
    //...
    .open().expect("");

for (auto i = 0; i < service.attributes().len(); i++) {
    std::cout << service.attributes().at(i) << std::endl;
}

To observe the service attributes in action, open three separate terminals and execute the following commands.

How to Build

Before proceeding, all dependencies need to be installed. You can find instructions in the C++ Examples Readme.

First you have to build the C++ examples:

cmake -S . -B target/ff/cc/build -DBUILD_EXAMPLES=ON
cmake --build target/ff/cc/build

How to Run

Terminal 1

./target/ff/cc/build/examples/cxx/service_attributes/example_cxx_service_attributes_creator

Terminal 2

./target/ff/cc/build/examples/cxx/service_attributes/example_cxx_service_attributes_opener

Terminal 3

./target/ff/cc/build/examples/cxx/service_attributes/example_cxx_service_attributes_incompatible

The application in Terminal 3 will fail since it requires incompatible service attributes.