Context Feature

The context feature adds the following to Helidon WebServer:

1. Request Context
2. Context Propagation

Both can be configured through configuration or a builder.

This feature is a separate module, as it adds a performance overhead to processing, and is not required be every application.

Request Context

The Context Feature adds a filter to WebServer, that runs each (subsequent processing of) request within an io.helidon.common.context.Context.

This enables the method io.helidon.common.context.Contexts.context(). This method will return the same instance you can obtain from ServerRequest even when an instance of the request is not available.

Context Propagation

NOTE The headers are added as is to the context from EVERY incoming request. Be extremely careful when using these values, as they may be fabricated by the user!

The Context Feature allows reading explicitly configured headers and adding them to the request context.

This is implemented in the same filter as the addition of the request context as mentioned above.

The headers must be named, to avoid full materialization of headers from the request.

This feature is only available for String and String array values.

Example configuration:

server:
  features:
    context:
      records:
          - header: "X-Custom"
            default-value: "default-value"
          - header: "traceparent"
            classifier: "opentelemetry.tracing.parent"
          - header: "X-Helidon-TID"
            array: true
            default-values: ["first", "second"]

For such a configuration, each request will be scanned for the configured headers. If there is a traceparent header present, it will be added to the context as a String with opentelemetry.tracing.parent classifier, if it is not present, a value default-value will be added with that classifier. If there is an X-Custom header present, it will be added to the context as a String with X-Custom classifier. If there is an X-Helidon-TID header present, its values will be added to context as a String[] with X-Helidon-TID classifier; if not present, the value will be array of first and second.