HTTP (REST and RPC)
The embeddable HTTP server for Reactive REST backed by XOOM Actors and XOOM Wire.
Last updated
The embeddable HTTP server for Reactive REST backed by XOOM Actors and XOOM Wire.
Last updated
The XOOM HTTP component supports reactive, scalable, and resilient HTTP servers and REST services running as a small, fast, embedded server. Thus, this component does not run standalone, but is meant to provide very lightweight and high-performing HTTP support within a application- or microservice-based runtime, such as a Bounded Context. The server supports REST and RPC dispatching to implementations of fluent APIs.
It is common for developers to think of REST over HTTP in terms of CRUD because the primary methods provided by the protocol are: POST, GET, PUT, and DELETE. If taken at face value, these verbs are CRUD through and through. Yet, almost no one uses the methods to map directly from browser to a database. Most contemporary applications instead map the HTTP methods to procedures (i.e. a method on a Java or C# class) within the application. Those procedures are responsible for adapting path parameters, headers, and the request body to a form that can be consumed by the inner application components.
The procedure to which the HTTP request is mapped need not represent a CRUD operation at all. When you consider that POST, GET, PUT, DELETE, and others such as PATCH, are message categories that map to procedures, not only ways to perform CRUD operations on data, it makes for a lot more flexibility in how HTTP can be used.
For example, a POST method would always be used with the intention to create some entity resource, such as a product; that is, POST is in the procedure category of creation. Yet, there is no reason for the procedure to which that HTTP request is mapped to be named postProduct()
or even the "obvious" createProduct()
. Instead, the procedure could be named something more in line with the language spoken by the business, such a catalogProduct()
. Here catalog is used as a verb; that is, our company is not in the business of creating new products. The products come to the company already created by a manufacturer. Our company sells products through catalogs. For us, products need to be cataloged (verb) for them to be accessible for purchase through a catalog (noun). With that in mind, establishing a new kind of catalog for a kind of product might be thought of as defining a catalog. Thus, the procedure would be named defineCatalog()
.
Given this line of reasoning, the ways that HTTP methods are mapped are virtually unlimited, and all the while still honoring the REST way of doing things. The older SOAP protocol used to implement RPC-based APIs, was known to those who could cut through the jargon as "XML over HTTP." Thus, if XML over HTTP can be used to implement RPC, certainly it stands to reason that JSON over HTTP could be used in the same way.
The following sections demonstrate the flexibility of using HTTP as a means to support far more than CRUD. Avoid pedantic opinions that limit creativity. Such opinions are generally held by those who think only in terms of technology and expect the business to speak their language, which is composed mostly of CRUD and collection-oriented (add, insert, remove) terminology.
Consider the overall architecture of our HTTP server. It is highly Reactive by employing actors at every major operational junction.
REST over HTTP is quite commonly employed to support user interfaces, service integrations, and even distribution of event streams. Of course, we don't suggest that your services should be primarily REST-based, we provide our HTTP server for when REST it is useful. Even RPC can be supported. See the above information box. Since REST over HTTP is the most common contemporary use case, the documentation mostly refers to REST rather than RPC, but everything herein is equally applicable to RPC using the style discussed in the above information box.
With any use of the XOOM HTTP server, which might be with a REST flavor as more so as RPC, the use of a few Domain-Driven Design patterns are common. Among the Context Mapping patterns, the Open-Host Service and Published Language patterns naturally support these API styles. The Open-Host Service is the well defined API that is open for public use, with the possible requirement of client credentials. The Published Language is the REST resources or RPC response values that are provided.
Our HTTP component can help you create REST-based services rapidly and with great simplicity. One glance at the REST request mappings to Java objects is all it takes to understand this. The following demonstrates both file-based and code-based fluent request handler mappings.
The above declarations are made in the vlingo-http.properties
file. The following is the resource handler implementation to match it.
By means of the ResourceHandler
base class, there are several Request parts available: URI, headers, body, and any query parameters. You may also access the default ContentType
, which may be overridden. See the following queryUsers()
handler method.
The above is from file-based request/response resource mappings defined in the properties filevlingo-http.properties
. Yet, our versatile API also supports fluent mappings in source code.
In the above example only the routes()
is shown, and would replace the file-based route mappings previously shown. Also note in this example, when using the fluent routes API your resource class should not extend ResourceHandler
. Although you may do so, at time of execution its state will be hollow because the runtime does not support ResourceHandler
. Instead, to get similar base class state and behavior with dynamic resources created with the fluent API, use the optional DynamicResourceHandler
.
By extending DynamicResourceHandler
your resource may use the Stage
managing this resource, the Logger
and Scheduler
of that Stage
, and the Context
with the current Request
. The Request
provides various request parts such as the URI, headers, body, and any query parameters. You may also access the default ContentType
, which may be overridden. See the register(UserData)
handler method for an example accessing the query parameters and ContentType
.
Query parameters may be mapped more naturally using the fluent API as seen below.
The concrete resource handler must provide a Stage
to the DynamicResourceHandler
constructor. It is assumed that the concrete resource handler's constructor will take at least the Stage
as a parameter. The DynamicResourceHandler
declares the routes()
method abstract, so it must be overridden in the concrete extender. As you can see above, routes()
returns resource()
with an optional parameter of the DynamicResourceHandler
as thethis
object, which is to be given the current request Context
before each handler invocation.
In the following sections you will learn how to quickly set up and start your server with resources handlers.
If you will use the file-based configuration you must create vlingo-http.properties
. Otherwise you will write source code to define the server configuration. First the file-based configuration is explained, and then the source code and fluent API approach.
Create the file vlingo-http.properties
and place it into the project directory hierarchy used for resources. For Maven that would be src/main/resources
for production and if you are defining the properties for test, it would be src/test/resources
. In this file create the following properties. Your values may differ.
This is the basic minimum configuration necessary to start the server. There are other properties that you will learn about later. The following summarizes these properties.
server.http.port
: the socket port to be used by the server, which here is 8080.
server.dispatcher.pool
: the server uses a pool of actors to dispatch incoming requests asynchronous. Here the dispatcher pool size is 10.
server.buffer.pool.size
: used by the server to create a pool of reusable ByteBuffer instances to use for incoming requests and outgoing resources. There will be at least 100 buffers in this pool. Yet, the elastic pool design enables it to grow dynamically under heavy load and contract back down to 100 buffers as load diminishes.
server.message.buffer.size
: used by the server when creating the buffer pool to allocate each buffer with this many bytes. Here the buffers will each be 65,535 bytes. (a) This does not limit the overall size of a given incoming message because these may be read in chunks and span multiple buffers. (b) This also does not limit the size of outgoing responses because a non-pooled buffer will be temporarily allocated to send payloads larger than this maximum. Serving larger responses should be the exception rather than common, otherwise performance will suffer. If a common occurrence consider setting this buffer limit to the largest common payload size.
server.probe.interval
: determines the number of milliseconds between each socket channel probe to receive new connections and requests, and to send new responses. Be careful with this value as various O/S and JDKs deal differently with intervals, possibly being too fast to too slow.
server.probe.timeout
: the amount of time in milliseconds that the socket channel probe will wait for new connections and requests, and to check for writable status used for sending responses. Be careful with this value as when there are no new requests, it causes the actor's thread to block inside the socket channel probe until this timeout is reached.
server.processor.pool.size
: used by the server to size the pool of socket channel processors. Here the processor pool size is 10. There will be 10 total actors created and used in round-robin order as new connections are accepted, which will each read from and write to every newly accepted client socket channel connection.
server.request.missing.content.timeout
: as previously indicated, very large incoming request messages of byte length greater than server.message.buffer.size
will require spanning two or more total buffers. This value indicates how long the incomplete message will be retained in the server before it is considered a bad request (missing bytes). This example indicates that such an incomplete request may be retained for a maximum of 100 milliseconds in anticipation of remaining bytes being received.
resource.dispatcher.generated.sources.???
: These four properties define where generated source code is to be saved as Java source files and where class files are save after dynamic compilation. This example uses the Maven target layout and defines both main and test areas.
In addition to this, it only makes sense to include the description of at least one resource handler (a.k.a. endpoint or controller).
This is a more complete resource routing definition. The properties are summarized next.
resource.name.{name}
: The first property of any resource handler is the name, which above is resource.name.user
. This says, here is a resource named user
. The property's value is an array of method names that are used as individual route request handlers. Each of these names must have a corresponding set of action.{name}...
properties, which are documented in a following numbered descriptions. If you do not list a name in this array for every route request handler, the corresponding handler action definition will not be found for the missing name.
All properties associated with the named resource are in the form resource.name.property
, such as resource.user.handler
.
resource.{name}.handler
: the fully-qualified class name of the concrete ResourceHandler
extender. The server will dispatch to actions matching the URI patterns to the methods in this ResourceHandler
. The above example references the UserResource
, but along with it's package name.
resource.{name}.pool
: used to create a pool of actors for ResourceHandler
instances of the type defined by the resource.{name}.handler
property. Individual requests are handled in a round-robin fashion. In this example the resource.user.pool
defines a pool size of 10. Note that this pool is created for each server.dispatcher.pool
, meaning that there will be a total of server.dispatcher.pool
* resource.name.pool
actors to handle requests to this named resource.
resource.{name}.disallowPathParametersWithSlash
: deprecated and must always be true
. Above is for the resource named user
, as in resource.user.disallow...
action.{name}.{endpoint}.method
: used to define the HTTP method to be used to make a matching request to the given URI. Here {name}
and {endpoint}
are placeholders for the actual names. In the first example above {name}
is user
and the {endpoint}
method is register
. Note that this property's value may be one of: POST
, GET
, PUT
, PATCH
, DELETE
, HEAD
, TRACE
, OPTIONS
, or CONNECT
.
action.{name}.{endpoint}.uri
: used to define the URI that will map to the given endpoint. Here {name}
and {endpoint}
are placeholders for the actual names. In the first example above {name}
is user
and the {endpoint}
method is register
. Path parameters, if any, are surrounded by curly braces, such as in /users/{userId}/contact
, where the parameter name is userId
. In the actual URI, userId must be replaced with some sort of identity, such as may be mapped to a String
value.
action.{name}.{endpoint}.to
: used to define the method name and signature to which this route mapping will dispatch to on the given resource.{name}.handler
class instance. Here {name}
and {endpoint}
are placeholders for the actual names. In the first example above {name}
is user
and the {endpoint}
method is register
. When the HTTP method is POST
and the URI is /users
then the match will route to the given Java method, such as register(UserData userData)
. In the above example the body:
keyword indicates that the UserData
will be found in the request body. Depending on the content type, which is by default JSON, the body will be automatically deserialized into an instance of the given type, such as UserData
. Note that when the URI contains one or more path parameters, the {paramName}
will be mapped to the matching Java method parameter with the same name, and automatically deserialized into the given Java parameter type. In the above example the /users/{userId}/contact
maps to the Java method parameter String userId
.
When using the file-based configuration there is no limit to the number of path parameters. However, the greater the number of parameters the more complex the Java method will be to create and maintain.
It is quite simple to start a server from file-based configuration.
Using the above examples, this Server
is started on port 8080 and has a single resource handler, UserResource
. The remaining properties are applied to the server as previously explained.
The ResourceHandler
and DynamicResourceHandler
base classes provide access to several request parts, such as headers, query parameters, and other environmental objects.
ResourceHandler
and DynamicResourceHandler
:Type Accessor | Description |
| The |
| The details about the content type of the request. (only on |
| The means to log debug, error, and informational messages. |
| Use to manage the scheduling of future tasks. |
| The |
The following provides a very simple example of source code configuration along with the XOOM HTTP fluent route mapping API. This provides the minimum code to create an endpoint that responds with "Hello, World!"
. Both Java and Kotlin examples are available. The tutorial descriptions refer to the Java code.
Create a new project with your favorite editor/IDE and create a Bootstrap
class with the following content.
Compile and run the server by means of the Java main()
method. Check the results by running the following command-line.
The curl
command should print the following text into the terminal window: Hello, World!
The Server
logs informational output by means of the World
standard Logger
configuration.
The Resources
(23) is the set of HTTP endpoints, which in this case is only one. The Server
instance (25) is where the Resources
are held and used to match and dispatch on requests. To start a Server
you simply provide a Stage
and the Resources
. When created, the Server
starts listening on port 8080 for HTTP requests.
Sizing
(30) is the configuration parameter with the processor pool size, dispatcher pool size, max buffer pool size, and max message size. Timing
(31) is the configuration with the probe interval and timeout parameters. For now, we use the default configuration.
The next sections use the previous code as starting point.
There are some additional features available through configuration: static file resources, server-sent events, and feed resources.
Static file resources are ordinary content in disk files, such as HTML, images, and video. To serve static file resources use the vlingo-http.properties
file-based configuration.
This configuration auto-creates io.vlingo.xoom.http.resource.StaticFilesResource
that serves files from the resource root /siteroot/content
directory structure. Any request URI that begins with the static.files.resource.subpaths
list will be served.
Virtual URI | Physical URI |
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You may create a pre-packaged SSE resource using the following configuration.
This enables clients to register for a long-lasting stream of events from the server. The URI used by clients is the value of sse.stream.name.{name}
. In the above example the name is all
and the URL is /eventstreams/all
.
The sse.stream.all.feed.class
is provided by the custom service/application, and in this case is io.vlingo.xoom.http.sample.user.AllSseFeedActor
. The fully-qualified class name must be given. There may be up to 50 events in a single feed (one send to a client) with an interval of 1,000 milliseconds between feeds. If the client does not provide an id for the starting event, the default.id
is used. In this case it is -1. There will be 10 total feed instances created in the pool.
A client makes a request to subscribe, such as the following.
In the above example the asynchronous io.vlingo.xoom.http.resource.Client
will continue to receive responses as feeds occur because it is configured for keep-alive mode and tells the Completes<Response>
to repeat()
after every feed is received.
The following is a skeleton of class AllSseFeedActor
.
In the above example the custom feed actor is class AllSseFeedActor
, which must extend Actor
and implement io.vlingo.xoom.http.resource.sse.SseFeed
. See the io.vlingo.xoom.http.resource.sse.SseStreamResource
that manages the feed generation process, using the custom SseFeed
actor when needed.
The feed must follow the SSE standard definition. The following is one example, but not the only possibility.
There is a complete example in the xoom-http-frontservice
and xoom-http-backservice
in the Github repository vlingo/xoom-examples.
There is another kind of feed resource, one that is not a SSE stream, but has similar characteristics. It is a stream of any kind and defines its own response body payload. You might think of such as Atom feeds, or similar.
The feed has a name, in this case feed.resource.name.events
, which is the URI /feeds/events
. Clients may request a feed region by providing an id. The ...elements
property indicates the maximum number of 20 elements may be in a given feed. There will be 10 total feed instances created in the pool.
In the above example the custom feed actor is class EventsFeedProducerActor
, which must extend Actor
and implement io.vlingo.xoom.http.resource.feed.FeedProducer
. The format of the feed itself is not standardized, but may be JSON, XML, or otherwise follow the Atom standard. The EventsFeedProducerActor
itself may be backed by the XOOM Lattice exchange feed type, which may stream from a XOOM Symbio Journal
, or any kind of EntryReader
for the storage types ObjectStore
and StateStore
.
The above DefaultFeed
is a factory for actor-based Feeder
types. Invoking the Feed::feeder()
will return a new actor-based Feeder
of feederType
with the given entryReaderType
.
There is a default Feeder
, the TextEntryReaderFeeder
, that can consume text entries from any XOOM Symbio EntryReader
implementation and produce simple feeds.
It should be clear how you can stitch together a number of feeds to provide HTTP feeds of event streams: Response <- http-Feed <- lattice-Feed <- symbio-EntryReader
You can register filters with the Server
for both requests and responses. The following is an example of how to start the Server with any number and type of filters:
The following is an example of a RequestFilter
that is used to ensure that every request has a Date
header:
The return type of Tuple2<Request, Boolean>
provides both the Request
results of the filter and a Boolean
to indicate whether the filter chain should continue (true
) or short circuit (false
).
The following ResponseFilter
does the same as the previous, but for responses:
The return type is the same as for the RequestFilter
and has the same meaning.
There is a special ResponseFilter
that supports CORS request-response from cross-origin clients:
Register the kinds of access control headers that are supported by the receiving application. There must always be an Access-Control-Allow-Origin
header, which is used to match that sent by the client agent. The matching string may be "*"
for any origin or some well-know URI of a acceptable application. Other headers are as follows, and each has a corresponding constant in class ResponseHeader
:
Header | Constant in Class |
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As noted earlier, XOOM HTTP provides a special Client
used for making HTTP requests and reacting to responses as they happen. Being reactive, this Client
is a non-blocking tool. The above example showed how to use a reactive pipeline to both request and reactive to the eventual response. Here is a similar example that could be used for GET
requests and responses:
Assume that the catalog
object is backed by an actor. In this example the close()
occurs just after the offer()
message is sent to the catalog
. The Client
could have remained open if it was configured for keep-alive mode, and if it had used repeat()
as the final pipeline expression (demonstrated previously).
The Client
provides a factory with the means to configure the resulting Client
object along with one of three client types by means of the ClientConsumerType
.
The Configuration
has a number of factories that arrange for defaults to be set, and one that accepts all possible configuration parameters:
Factory | Description |
---|---|
| The |
| The same as above, but with the |
| The same as above, but provides the size (length) of write and read |
| The same as above, but requests that the the connection channel be kept alive (keep-alive is |
| Creates the The |
The ClientConsumerType
is an enum
that enables the following dispatcher types:
Type | Description |
---|---|
| Used to create a When used, it is often advantageous that the When the response is received and parsed, it is provided through the platform standard |
| Used to create a
When the response is received and parsed, it is provided through the platform standard |
| Used to create a |
Determine which kind of Client
to create for various request-response situations.
XOOM HTTP provides a fluent API to define HTTP endpoints and corresponding Java handler methods. These kinds of resources are different than those loaded from the file vlingo-http.properties
. You had a brief introduction to the handler methods at the outset of this chapter. Here you will see them in more detail.
The following is the ResourceBuilder
used to fluently create route mappings.
You give the Resource
a name and a varargs list of RequestHandler
definitions. This method returns a Resource
. The Server
needs a set of Resource
instances to match and route HTTP requests to handlers that respond. Each of the RequestHandler instances are mapped by means of declaring HTTP methods, as next discussed.
The fluent API supports the following HTTP methods.
ResourceBuilder.post(final String uri)
ResourceBuilder.get(final String uri)
ResourceBuilder.put(final String uri)
ResourceBuilder.patch(final String uri)
ResourceBuilder.delete(final String uri)
ResourceBuilder.head(final String uri)
ResourceBuilder.options(final String uri)
ResourceBuilder.trace(final String uri)
ResourceBuilder.connect(final String uri)
All of the above methods answer a new resource handler instance, whether or not it extends the base class DynamicRequestHandler
. We recommend using static imports for the most fluent use of the API.
The above shows other common static imports besides those needed for fluent resource wiring.
The request handler enforces type safety on the handler function method definition through the declaration of expected parameters. There are several mapping options, so consider each.
Map path parameters by identifying them in the URI as a {variable}
and then indicate the type in the path()
method to be used by your handler.
Here the userId
will be mapped to a String
because the method path(String.class)
specifies that type. You can specify parameter mappings to any of the following types.
String
Long
Integer
Float
Double
Boolean
Short
Character
The path()
method must be used before any other route mapping method, otherwise an exception will be thrown when the Server
starts.
When using path()
be sure you have the same path variable in the URI between brackets {<variable>}
as the path()
methods reference.
The body()
method maps the HTTP body into the type you specify.
You may use query parameters in the expected way. For example, page=5 is a query parameter in this curl command.
You may map this specific query parameter fluently in three different ways.
By default, the type of all query parameters is String
. When the query parameter isn't present, the value is null
. It's good practice to always specify a default value for query parameters to avoid unexpected behavior.
You may access request headers as expected.
The following is an example showing all of the above parameter options.