service_attributes

Service-Attributes

Running the Example

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::new()
            .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 a attribute defined in the previous example:

node.service_builder(&service_name)
    //...
    .open_with_attributes(
        AttributeVerifier::new()
            .require("my_custom_key", "some_funky_value")
            // dont 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::new()
            .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()?;

for attribute in service.attributes().iter() {
    println!("{} = {}", attribute.key(), attribute.value());
}

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

Terminal 1

cargo run --example service_attributes_creator

Terminal 2

cargo run --example service_attributes_opener

Terminal 3

cargo run --example service_attributes_incompatible

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