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Asynchronous I/O that doesn’t get in your way, written in D


Automatic high-level RESTful client/server interface generation facilities.

This modules aims to provide a typesafe way to deal with RESTful APIs. D's interfaces are used to define the behavior of the API, so that they can be used transparently within the application. This module assumes that HTTP is used as the underlying transport for the REST API.

While convenient means are provided for generating both, the server and the client side, of the API from a single interface definition, it is also possible to use as a pure client side implementation to target existing web APIs.

The following paragraphs will explain in detail how the interface definition is mapped to the RESTful API, without going into specifics about the client or server side. Take a look at registerRestInterface and RestInterfaceClient for more information in those areas.

These are the main adantages of using this module to define RESTful APIs over defining them manually by registering request handlers in a URLRouter:

  • Automatic client generation: once the interface is defined, it can be used both by the client side and the server side, which means that there is no way to have a protocol mismatch between the two.
  • Automatic route generation for the server: one job of the REST module is to generate the HTTP routes/endpoints for the API.
  • Automatic serialization/deserialization: Instead of doing manual serialization and deserialization, just normal statically typed member functions are defined and the code generator takes care of converting to/from wire format. Custom serialization can be achieved by defining JSON or string parameters/return values together with the appropriate @bodyParam annotations.
  • Higher level representation integrated into D: Some concepts of the interfaces, such as optional parameters or in/out/ref parameters, as well as Nullable!T, are translated naturally to the RESTful protocol.

The most basic interface that can be defined is as follows:

interface APIRoot {
    string get();

This defines an API that has a single endpoint, 'GET /api/'. So if the server is found at, performing a GET request to will call the get() method and send its return value verbatim as the response body.

Endpoint generation

An endpoint is a combination of an HTTP method and a local URI. For each public method of the interface, one endpoint is registered in the URLRouter.

By default, the method and URI parts will be inferred from the method name by looking for a known prefix. For example, a method called getFoo will automatically be mapped to a 'GET /foo' request. The recognized prefixes are as follows:

Prefix HTTP verb
get GET
query GET
set PUT
put PUT
update PATCH
patch PATCH
add POST
create POST
post POST

Member functions that have no valid prefix default to 'POST'. Note that any of the methods defined in HTTPMethod are supported through manual endpoint specifications, as described in the next section.

After determining the HTTP method, the rest of the method's name is then treated as the local URI of the endpoint. It is expected to be in standard D camel case style and will be transformed into the style that is specified in the call to registerRestInterface, which defaults to MethodStyle.lowerUnderscored.

Manual endpoint specification

Endpoints can be controlled manually through the use of @path and @method annotations:

interface APIRoot {
    // Here we use a POST method
	// Our method will located at '/api/foo'
	void doSomething();

Manual path annotations also allows defining custom path placeholders that will be mapped to function parameters. Placeholders are path segments that start with a colon:

interface UsersAPI {
    Json getUserByName(string _name);

This will cause a request "GET /users/peter" to be mapped to the getUserByName method, with the _name parameter receiving the string "peter". Note that the matching parameter must have an underscore prefixed so that it can be distinguished from normal form/query parameters.

It is possible to partially rely on the default behavior and to only customize either the method or the path of the endpoint:

void getFoo();

In the above case, as 'POST' is set explicitly, the route would be 'POST /foo'. On the other hand, if the declaration had been:

void getFoo();

The route generated would be 'GET /bar'.


@property functions have a special mapping: property getters (no parameters and a non-void return value) are mapped as GET functions, and property setters (a single parameter) are mapped as PUT. No prefix recognition or trimming will be done for properties.

Method style

Method names will be translated to the given 'MethodStyle'. The default style is MethodStyle.lowerUnderscored, so that a function named getFooBar will match the route 'GET /foo_bar'. See MethodStyle for more information about the available styles.


By default the return values of the interface methods are serialized as a JSON text and sent back to the REST client. To override this, you can use the @resultSerializer attribute

struct TestStruct {int i;}

interface IService {
		// output_stream implements OutputRange
		function (output_stream, test_struct) {
			output_stream ~= serializeToJsonString(test_struct);
		// input_stream implements InputStream
		function (input_stream) {
			return deserializeJson!TestStruct(input_stream.readAllUTF8());
		// output_stream implements OutputRange
		function (output_stream, test_struct) {
			output_stream ~=!string();
		// input_stream implements InputStream
		function (input_stream) {
			TestStruct test_struct;
			test_struct.i = input_stream.readAllUTF8().to!int();
			return test_struct;
	TestStruct getTest();

class Service : IService {
	TestStruct getTest() {
		TestStruct test_struct = {42};
		return test_struct;

Serialization policies

You can customize the serialization of any type used by an interface by using serialization policies. The following example is using the Base64ArrayPolicy, which means if X contains any ubyte arrays, they will be serialized to their base64 encoding instead of their normal string representation (e.g. "[1, 2, 255]").

interface ITestBase64
	@safe X getTest();


Function parameters may be populated from the route, query string, request body, or headers. They may optionally affect the route URL itself.

By default, parameters are passed differently depending on the type of request (i.e., HTTP method). For GET and PUT, parameters are passed via the query string (<route>?paramA=valueA[?paramB=...]), while for POST and PATCH, they are passed via the request body as a JSON object.

The default behavior can be overridden using one of the following annotations, put as UDA on the relevant parameter:

  • @viaHeader("field"): Will source the parameter on which it is applied from the request headers named "field". If the parameter is ref, it will also be set as a response header. Parameters declared as out will only be set as a response header.
  • @viaQuery("field"): Will source the parameter on which it is applied from a field named "field" of the query string.
  • @viaBody("field"): Will source the parameter on which it is applied from a field named "field" of the request body in JSON format, or, if no field is passed, will represent the whole body. Note that in the later case, there can be no other viaBody parameters.

interface APIRoot {
	// GET /api/header with 'Authorization' set
	string getHeader(@viaBody("Authorization") string param);

	// GET /api/foo?param=...
	string getFoo(@viaQuery("param") int param);

	// GET /api/body with body set to { "myFoo": {...} }
	string getBody(@viaBody("parameter") FooType myFoo);

	// GET /api/full_body with body set to {...}
	string getFullBody(@viaBody() FooType myFoo);

Further, how function parameters are named may affect the route:

  • Parameters with leading underscores (e.g. _slug) are also interpreted as a route component, but only in the presence of a @path UDA annotation. See Manual endpoint specification above.

  • Other function parameters do not affect or come from the path portion of the URL, and are are passed according to the default rules above: query string for GET and PUT; request body JSON for POST and PATCH.

  • Deprecated: If the first parameter is named id, this is interpreted as a leading route component. For example, getName(int id) becomes /:id/name.

    Note that this style of parameter-based URL routing is different than in many other web frameworks, where instead this example would be routed as /name/:id.

    See Collection for the preferred way to represent object collections in REST interfaces

Default values

Parameters with default values behave as optional parameters. If one is set in the interface declaration of a method, the client can omit a value for the corresponding field in the request and the default value is used instead.

Note that if default parameters are not evaluable by CTFE, compilation may fail due to DMD bug #14369 (Vibe.d tracking issue: #1043).


When passing aggregates as parameters, those are serialized differently depending on the way they are passed, which may be especially important when interfacing with an existing RESTful API:

  • If the parameter is passed via the headers or the query, either implicitly or explicitly, the aggregate is serialized to JSON. If the JSON representation is a single string, the string value will be used verbatim. Otherwise the JSON representation will be used
  • If the parameter is passed via the body, the datastructure is serialized to JSON and set as a field of the main JSON object that is expected in the request body. Its field name equals the parameter name, unless an explicit @bodyParam annotation is used.

See Also

To see how to implement the server side in detail, jump to registerRestInterface.

To see how to implement the client side in detail, jump to the RestInterfaceClient documentation.


generateRestJSClient(output, settings) Generates JavaScript code to access a REST interface from the browser.
registerRestInterface(router, instance, settings) Registers a server matching a certain REST interface.
serveRestJSClient(settings) Returns a HTTP handler delegate that serves a JavaScript REST client.


RestInterfaceClient Implements the given interface by forwarding all public methods to a REST server.
RestInterfaceSettings Encapsulates settings used to customize the generated REST interface.


Collection Models REST collection interfaces using natural D syntax.
RestErrorInformation Contains detailed informations about the error


after vibe.internal.meta.funcattr.after Allows processing the return value of a handler method and the request/response objects.
before vibe.internal.meta.funcattr.before Allows processing the server request/response before the handler method is called.
RestErrorHandler @safe void delegate(HTTPServerRequest, HTTPServerResponse, RestErrorInformation) Type of the optional handler used to render custom replies in case of errors.

Sönke Ludwig, Михаил Страшун, Mathias 'Geod24' Lang


© 2012-2018 Sönke Ludwig


Subject to the terms of the MIT license, as written in the included LICENSE.txt file.