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Once the initial connection is made, the "client" vs "server" distinction is lost as
both sides become symmetrical and each side can initiate one of the above interactions.
This is why in the protocol calls the participating sides "requester" and "responder"
while the above interactions are called "request streams" or simply "requests".
Reactive Streams semantics across network boundary for streaming requests such as Request-Stream and Channel, back pressure signals
travel between requester and responder, allowing a requester to slow down a responder at
the source, hence reducing reliance on network layer congestion control, and the need
for buffering at the network level or at any level.
Session resumption this is designed for loss of connectivity and requires some state
to be maintained. The state management is transparent for applications, and works well
in combination with back pressure which can stop a producer when possible and reduce
the amount of state required.
One of the benefits of RSocket is that it has well defined behavior on the wire and an
easy to read specification along with some protocol
extensions. Therefore it is
a good idea to read the spec, independent of language implementations and higher level
framework APIs. This section provides a succinct overview to establish some context.
Initially a client connects to a server via some low level streaming transport such
as TCP or WebSocket and sends a SETUP frame to the server to set parameters for the
connection.
The server may reject the SETUP frame, but generally after it is sent (for the client)
and received (for the server), both sides can begin to make requests, unless SETUP
indicates use of leasing semantics to limit the number of requests, in which case
both sides must wait for a LEASE frame from the other end to permit making requests.
Once a connection is established, both sides may initiate a request through one of the
frames REQUEST_RESPONSE, REQUEST_STREAM, REQUEST_CHANNEL, or REQUEST_FNF. Each of
those frames carries one message from the requester to the responder.
The responder may then return PAYLOAD frames with response messages, and in the case
of REQUEST_CHANNEL the requester may also send PAYLOAD frames with more request
messages.
When a request involves a stream of messages such as Request-Stream and Channel,
the responder must respect demand signals from the requester. Demand is expressed as a
number of messages. Initial demand is specified in REQUEST_STREAM and
REQUEST_CHANNEL frames. Subsequent demand is signaled via REQUEST_N frames.
Each side may also send metadata notifications, via the METADATA_PUSH frame, that do not
pertain to any individual request but rather to the connection as a whole.
RSocket messages contain data and metadata. Metadata can be used to send a route, a
security token, etc. Data and metadata can be formatted differently. Mime types for each
are declared in the SETUP frame and apply to all requests on a given connection.
While all messages can have metadata, typically metadata such as a route are per-request
and therefore only included in the first message on a request, i.e. with one of the frames
REQUEST_RESPONSE, REQUEST_STREAM, REQUEST_CHANNEL, or REQUEST_FNF.
The Java implementation for RSocket is built on
Project Reactor. The transports for TCP and WebSocket are
built on Reactor Netty. As a Reactive Streams
library, Reactor simplifies the job of implementing the protocol. For applications it is
a natural fit to use Flux and Mono with declarative operators and transparent back
pressure support.
The API in RSocket Java is intentionally minimal and basic. It focuses on protocol
features and leaves the application programming model (e.g. RPC codegen vs other) as a
higher level, independent concern.
The main contract
io.rsocket.RSocket
models the four request interaction types with Mono representing a promise for a
single message, Flux a stream of messages, and io.rsocket.Payload the actual
message with access to data and metadata as byte buffers. The RSocket contract is used
symmetrically. For requesting, the application is given an RSocket to perform
requests with. For responding, the application implements RSocket to handle requests.
This is not meant to be a thorough introduction. For the most part, Spring applications
will not have to use its API directly. However it may be important to see or experiment
with RSocket independent of Spring. The RSocket Java repository contains a number of
sample apps that
demonstrate its API and protocol features.
RSocketRequester fluent API to make requests through an io.rsocket.RSocket
with data and metadata encoding/decoding.
Annotated Responders @MessageMapping annotated handler methods for
responding.
The spring-web module contains Encoder and Decoder implementations such as Jackson
CBOR/JSON, and Protobuf that RSocket applications will likely need. It also contains the
PathPatternParser that can be plugged in for efficient route matching.
Spring Boot 2.2 supports standing up an RSocket server over TCP or WebSocket, including
the option to expose RSocket over WebSocket in a WebFlux server. There is also client
support and auto-configuration for an RSocketRequester.Builder and RSocketStrategies.
See the
RSocket section
in the Spring Boot reference for more details.
Spring Integration 5.2 provides inbound and outbound gateways to interact with RSocket
clients and servers. See the Spring Integration Reference Manual for more details.
RSocketRequester provides a fluent API to perform RSocket requests, accepting and
returning objects for data and metadata instead of low level data buffers. It can be used
symmetrically, to make requests from clients and to make requests from servers.
To obtain an RSocketRequester on the client side is to connect to a server which involves
sending an RSocket SETUP frame with connection settings. RSocketRequester provides a
builder that helps to prepare an io.rsocket.core.RSocketConnector including connection
settings for the SETUP frame.
URI url = URI.create("https://example.org:8080/rsocket");
RSocketRequester requester = RSocketRequester.builder().webSocket(url);
URI url = URI.create("https://example.org:8080/rsocket");
val requester = RSocketRequester.builder().webSocket(url)
The above does not connect immediately. When requests are made, a shared connection is
established transparently and used.
RSocketRequester.Builder provides the following to customize the initial SETUP frame:
For data, the default mime type is derived from the first configured Decoder. For
metadata, the default mime type is
composite metadata which allows multiple
metadata value and mime type pairs per request. Typically both don t need to be changed.
Data and metadata in the SETUP frame is optional. On the server side,
@ConnectMapping methods can be used to handle the start of a
connection and the content of the SETUP frame. Metadata may be used for connection
level security.
RSocketRequester.Builder accepts RSocketStrategies to configure the requester.
You ll need to use this to provide encoders and decoders for (de)-serialization of data and
metadata values. By default only the basic codecs from spring-core for String,
byte[], and ByteBuffer are registered. Adding spring-web provides access to more that
can be registered as follows:
RSocketStrategies strategies = RSocketStrategies.builder()
.encoders(encoders - encoders.add(new Jackson2CborEncoder()))
.decoders(decoders - decoders.add(new Jackson2CborDecoder()))
.build();
RSocketRequester requester = RSocketRequester.builder()
.rsocketStrategies(strategies)
.tcp("localhost", 7000);
val strategies = RSocketStrategies.builder()
.encoders { it.add(Jackson2CborEncoder()) }
.decoders { it.add(Jackson2CborDecoder()) }
.build()
val requester = RSocketRequester.builder()
.rsocketStrategies(strategies)
.tcp("localhost", 7000)
RSocketStrategies is designed for re-use. In some scenarios, e.g. client and server in
the same application, it may be preferable to declare it in Spring configuration.
RSocketRequester.Builder can be used to configure responders to requests from the
server.
You can use annotated handlers for client-side responding based on the same
infrastructure that s used on a server, but registered programmatically as follows:
RSocketStrategies strategies = RSocketStrategies.builder()
.routeMatcher(new PathPatternRouteMatcher()) (1)
.build();
SocketAcceptor responder =
RSocketMessageHandler.responder(strategies, new ClientHandler()); (2)
RSocketRequester requester = RSocketRequester.builder()
.rsocketConnector(connector - connector.acceptor(responder)) (3)
.tcp("localhost", 7000);
val strategies = RSocketStrategies.builder()
.routeMatcher(PathPatternRouteMatcher()) (1)
.build()
val responder =
RSocketMessageHandler.responder(strategies, new ClientHandler()); (2)
val requester = RSocketRequester.builder()
.rsocketConnector { it.acceptor(responder) } (3)
.tcp("localhost", 7000)
Note the above is only a shortcut designed for programmatic registration of client
responders. For alternative scenarios, where client responders are in Spring configuration,
you can still declare RSocketMessageHandler as a Spring bean and then apply as follows:
ApplicationContext context = ... ;
RSocketMessageHandler handler = context.getBean(RSocketMessageHandler.class);
RSocketRequester requester = RSocketRequester.builder()
.rsocketConnector(connector - connector.acceptor(handler.responder()))
.tcp("localhost", 7000);
val context: ApplicationContext = ...
val handler = context.getBean RSocketMessageHandler ()
val requester = RSocketRequester.builder()
.rsocketConnector { it.acceptor(handler.responder()) }
.tcp("localhost", 7000)
For the above you may also need to use setHandlerPredicate in RSocketMessageHandler to
switch to a different strategy for detecting client responders, e.g. based on a custom
annotation such as @RSocketClientResponder vs the default @Controller. This
is necessary in scenarios with client and server, or multiple clients in the same
application.
RSocketRequesterBuilder provides a callback to expose the underlying
io.rsocket.core.RSocketConnector for further configuration options for keepalive
intervals, session resumption, interceptors, and more. You can configure options
at that level as follows:
RSocketRequester requester = RSocketRequester.builder()
.rsocketConnector(connector - {
// ...
.tcp("localhost", 7000);
To make requests from a server to connected clients is a matter of obtaining the
requester for the connected client from the server.
In Annotated Responders, @ConnectMapping and @MessageMapping methods support an
RSocketRequester argument. Use it to access the requester for the connection. Keep in
mind that @ConnectMapping methods are essentially handlers of the SETUP frame which
must be handled before requests can begin. Therefore, requests at the very start must be
decoupled from handling. For example:
GlobalScope.launch {
requester.route("status").data("5").retrieveFlow StatusReport ().collect { (1)
// ...
/// ... (2)
Once you have a client or
server requester, you can make requests as follows:
Flux AirportLocation locations = requester.route("locate.radars.within") (1)
.data(viewBox) (2)
.retrieveFlux(AirportLocation.class); (3)
The interaction type is determined implicitly from the cardinality of the input and
output. The above example is a Request-Stream because one value is sent and a stream
of values is received. For the most part you don t need to think about this as long as the
choice of input and output matches an RSocket interaction type and the types of input and
output expected by the responder. The only example of an invalid combination is many-to-one.
The data(Object) method also accepts any Reactive Streams Publisher, including
Flux and Mono, as well as any other producer of value(s) that is registered in the
ReactiveAdapterRegistry. For a multi-value Publisher such as Flux which produces the
same types of values, consider using one of the overloaded data methods to avoid having
type checks and Encoder lookup on every element:
data(Object producer, Class ? elementClass);
data(Object producer, ParameterizedTypeReference ? elementTypeRef);
Mono AirportLocation location = requester.route("find.radar.EWR"))
.retrieveMono(AirportLocation.class);
Extra metadata values can be added if using
composite metadata (the default) and if the
values are supported by a registered Encoder. For example:
ViewBox viewBox = ... ;
MimeType mimeType = MimeType.valueOf("message/x.rsocket.authentication.bearer.v0");
Flux AirportLocation locations = requester.route("locate.radars.within")
.metadata(securityToken, mimeType)
.data(viewBox)
.retrieveFlux(AirportLocation.class);
val viewBox: ViewBox = ...
val mimeType = MimeType.valueOf("message/x.rsocket.authentication.bearer.v0")
val locations = requester.route("locate.radars.within")
.metadata(securityToken, mimeType)
.data(viewBox)
.retrieveFlow AirportLocation ()
For Fire-and-Forget use the send() method that returns Mono Void . Note that the Mono
indicates only that the message was successfully sent, and not that it was handled.
RSocket responders can be implemented as @MessageMapping and @ConnectMapping methods.
@MessageMapping methods handle individual requests while @ConnectMapping methods handle
connection-level events (setup and metadata push). Annotated responders are supported
symmetrically, for responding from the server side and for responding from the client side.
To use annotated responders on the server side, add RSocketMessageHandler to your Spring
configuration to detect @Controller beans with @MessageMapping and @ConnectMapping
methods:
public RSocketMessageHandler rsocketMessageHandler() {
RSocketMessageHandler handler = new RSocketMessageHandler();
handler.routeMatcher(new PathPatternRouteMatcher());
return handler;
fun rsocketMessageHandler() = RSocketMessageHandler().apply {
routeMatcher = PathPatternRouteMatcher()
Then start an RSocket server through the Java RSocket API and plug the
RSocketMessageHandler for the responder as follows:
ApplicationContext context = ... ;
RSocketMessageHandler handler = context.getBean(RSocketMessageHandler.class);
CloseableChannel server =
RSocketServer.create(handler.responder())
.bind(TcpServerTransport.create("localhost", 7000))
.block();
val context: ApplicationContext = ...
val handler = context.getBean RSocketMessageHandler ()
val server = RSocketServer.create(handler.responder())
.bind(TcpServerTransport.create("localhost", 7000))
.awaitSingle()
You ll need to set the Encoder and Decoder instances required for metadata and data
formats to support. You ll likely need the spring-web module for codec implementations.
By default SimpleRouteMatcher is used for matching routes via AntPathMatcher.
We recommend plugging in the PathPatternRouteMatcher from spring-web for
efficient route matching. RSocket routes can be hierarchical but are not URL paths.
Both route matchers are configured to use "." as separator by default and there is no URL
decoding as with HTTP URLs.
RSocketMessageHandler can be configured via RSocketStrategies which may be useful if
you need to share configuration between a client and a server in the same process:
public RSocketMessageHandler rsocketMessageHandler() {
RSocketMessageHandler handler = new RSocketMessageHandler();
handler.setRSocketStrategies(rsocketStrategies());
return handler;
@Bean
public RSocketStrategies rsocketStrategies() {
return RSocketStrategies.builder()
.encoders(encoders - encoders.add(new Jackson2CborEncoder()))
.decoders(decoders - decoders.add(new Jackson2CborDecoder()))
.routeMatcher(new PathPatternRouteMatcher())
.build();
fun rsocketMessageHandler() = RSocketMessageHandler().apply {
rSocketStrategies = rsocketStrategies()
@Bean
fun rsocketStrategies() = RSocketStrategies.builder()
.encoders { it.add(Jackson2CborEncoder()) }
.decoders { it.add(Jackson2CborDecoder()) }
.routeMatcher(PathPatternRouteMatcher())
.build()
Annotated responders on the client side need to be configured in the
RSocketRequester.Builder. For details, see
Client Responders.
Once server or
client responder configuration is in place,
@MessageMapping methods can be used as follows:
@MessageMapping("locate.radars.within")
public Flux AirportLocation radars(MapRequest request) {
// ...
@MessageMapping("locate.radars.within")
fun radars(request: MapRequest): Flow AirportLocation {
// ...
The above @MessageMapping method responds to a Request-Stream interaction having the
route "locate.radars.within". It supports a flexible method signature with the option to
use the following method arguments:
@Payload
The payload of the request. This can be a concrete value of asynchronous types like
Mono or Flux.
Note: Use of the annotation is optional. A method argument that is not a simple type
and is not any of the other supported arguments, is assumed to be the expected payload.
@DestinationVariable
Value extracted from the route based on variables in the mapping pattern, e.g.
@MessageMapping("find.radar.{id}").
@Header
Metadata value registered for extraction as described in MetadataExtractor.
@Headers Map String, Object
All metadata values registered for extraction as described in MetadataExtractor.
The return value is expected to be one or more Objects to be serialized as response
payloads. That can be asynchronous types like Mono or Flux, a concrete value, or
either void or a no-value asynchronous type such as Mono Void .
The RSocket interaction type that an @MessageMapping method supports is determined from
the cardinality of the input (i.e. @Payload argument) and of the output, where
cardinality means the following:
1
Either an explicit value, or a single-value asynchronous type such as Mono T .
For input this means the method does not have an @Payload argument.
For output this is void or a no-value asynchronous type such as Mono Void .
The table below shows all input and output cardinality combinations and the corresponding
interaction type(s):
@ConnectMapping handles the SETUP frame at the start of an RSocket connection, and
any subsequent metadata push notifications through the METADATA_PUSH frame, i.e.
metadataPush(Payload) in io.rsocket.RSocket.
@ConnectMapping methods support the same arguments as
@MessageMapping but based on metadata and data from the SETUP and
METADATA_PUSH frames. @ConnectMapping can have a pattern to narrow handling to
specific connections that have a route in the metadata, or if no patterns are declared
then all connections match.
@ConnectMapping methods cannot return data and must be declared with void or
Mono Void as the return value. If handling returns an error for a new
connection then the connection is rejected. Handling must not be held up to make
requests to the RSocketRequester for the connection. See
Server Requester for details.
Responders must interpret metadata.
Composite metadata allows independently
formatted metadata values (e.g. for routing, security, tracing) each with its own mime
type. Applications need a way to configure metadata mime types to support, and a way
to access extracted values.
MetadataExtractor is a contract to take serialized metadata and return decoded
name-value pairs that can then be accessed like headers by name, for example via @Header
in annotated handler methods.
DefaultMetadataExtractor can be given Decoder instances to decode metadata. Out of
the box it has built-in support for
"message/x.rsocket.routing.v0" which it decodes to
String and saves under the "route" key. For any other mime type you ll need to provide
a Decoder and register the mime type as follows:
DefaultMetadataExtractor extractor = new DefaultMetadataExtractor(metadataDecoders);
extractor.metadataToExtract(fooMimeType, Foo.class, "foo");
val extractor = DefaultMetadataExtractor(metadataDecoders)
extractor.metadataToExtract Foo (fooMimeType, "foo")
Composite metadata works well to combine independent metadata values. However the
requester might not support composite metadata, or may choose not to use it. For this,
DefaultMetadataExtractor may needs custom logic to map the decoded value to the output
map. Here is an example where JSON is used for metadata:
DefaultMetadataExtractor extractor = new DefaultMetadataExtractor(metadataDecoders);
extractor.metadataToExtract(
MimeType.valueOf("application/vnd.myapp.metadata+json"),
new ParameterizedTypeReference Map String,String () {},
(jsonMap, outputMap) - {
outputMap.putAll(jsonMap);
val extractor = DefaultMetadataExtractor(metadataDecoders)
extractor.metadataToExtract Map String, String (MimeType.valueOf("application/vnd.myapp.metadata+json")) { jsonMap, outputMap -
outputMap.putAll(jsonMap)
When configuring MetadataExtractor through RSocketStrategies, you can let
RSocketStrategies.Builder create the extractor with the configured decoders, and
simply use a callback to customize registrations as follows:
RSocketStrategies strategies = RSocketStrategies.builder()
.metadataExtractorRegistry(registry - {
registry.metadataToExtract(fooMimeType, Foo.class, "foo");
// ...
.build();
val strategies = RSocketStrategies.builder()
.metadataExtractorRegistry { registry: MetadataExtractorRegistry -
registry.metadataToExtract Foo (fooMimeType, "foo")
// ...
.build()
The Spring Framework lets you define an RSocket service as a Java interface with annotated
methods for RSocket exchanges. You can then generate a proxy that implements this interface
and performs the exchanges. This helps to simplify RSocket remote access by wrapping the
use of the underlying RSocketRequester.
@RSocketExchange("radars")
Flux AirportLocation getRadars(@Payload MapRequest request);
// more RSocket exchange methods...
RSocketRequester requester = ... ;
RSocketServiceProxyFactory factory = RSocketServiceProxyFactory.builder(requester).build();
RepositoryService service = factory.createClient(RadarService.class);
Annotated, RSocket exchange methods support flexible method signatures with the following
method parameters:
@DestinationVariable
Add a route variable to pass to RSocketRequester along with the route from the
@RSocketExchange annotation in order to expand template placeholders in the route.
This variable can be a String or any Object, which is then formatted via toString().
@Payload
Set the input payload(s) for the request. This can be a concrete value, or any producer
of values that can be adapted to a Reactive Streams Publisher via
ReactiveAdapterRegistry
Object, if followed by MimeType
The value for a metadata entry in the input payload. This can be any Object as long
as the next argument is the metadata entry MimeType. The value can be a concrete
value or any producer of a single value that can be adapted to a Reactive Streams
Publisher via ReactiveAdapterRegistry.
MimeType
The MimeType for a metadata entry. The preceding method argument is expected to be
the metadata value.
Annotated, RSocket exchange methods support return values that are concrete value(s), or
any producer of value(s) that can be adapted to a Reactive Streams Publisher via
ReactiveAdapterRegistry.
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