Pegasus’s request/response framework, often called R2, includes abstractions for REST and RPC requests and responses, filter chains for customized processing, and transport abstraction.
R2 can be used in conjunction with the Dynamic Discovery system (also known as D2). The combined stack can be referred to as “R2D2”. R2 can be used independently as well.
The R2 framework in Rest.li contains a filter chain layer. This allows developers to process and modify the content, the associated wire attributes, and the local attributes for each request/response.
To implement a filter, simply implement the relevant Filter interface (for REST, this is
RestFilter; for RPC, use
To use a filter, instantiate a Rest.li server/client with a
FilterChain that contains the filters you want to use in the order that you would like to use them in. Note that the order of processing is as follows:
Consider the example given in the Rest.li client tutorial:
final HttpClientFactory http = new HttpClientFactory(); final Client r2Client = new TransportClientAdapter( http.getClient(Collections.<String, String>emptyMap()));
Suppose your filter was implemented in some class
MyClientFilter. To add this filter, you might do something like this:
FilterChain fc = FilterChains.empty().addFilter(new MyClientFilter()); final HttpClientFactory http = new HttpClientFactory(fc); final Client r2Client = new TransportClientAdapter( http.getClient(Collections.<String, String>emptyMap()));
So how would one go about writing a filter? As an example, suppose we wanted to use filters to compress the responses we receive from the server.
A client filter could do this:
A corresponding server might do this:
See an implementation example here: https://github.com/linkedin/rest.li/tree/master/r2/src/main/java/com/linkedin/r2/filter/compression
For a full list of filters, see: List-of-R2-filters