Refit is a library heavily inspired by Square's Retrofit library, and it turns your REST API into a live interface:
public interface IGitHubApi
{
[Get("/users/{user}")]
Task<User> GetUser(string user);
}
The RestService
class generates an implementation of IGitHubApi
that uses
HttpClient
to make its calls:
var gitHubApi = RestService.For<IGitHubApi>("https://api.github.com");
var octocat = await gitHubApi.GetUser("octocat");
Refit currently supports the following platforms and any .NET Standard 1.4 target:
- UWP
- Xamarin.Android
- Xamarin.Mac
- Xamarin.iOS
- Desktop .NET 4.5
- .NET Core
For .NET Core build-time support, you must use the .NET Core 2 SDK. You can target any supported platform in your library, long as the 2.0+ SDK is used at build-time.
Every method must have an HTTP attribute that provides the request method and relative URL. There are five built-in annotations: Get, Post, Put, Delete, and Head. The relative URL of the resource is specified in the annotation.
[Get("/users/list")]
You can also specify query parameters in the URL:
[Get("/users/list?sort=desc")]
A request URL can be updated dynamically using replacement blocks and parameters on the method. A replacement block is an alphanumeric string surrounded by { and }.
If the name of your parameter doesn't match the name in the URL path, use the
AliasAs
attribute.
[Get("/group/{id}/users")]
Task<List<User>> GroupList([AliasAs("id")] int groupId);
Parameters that are not specified as a URL substitution will automatically be used as query parameters. This is different than Retrofit, where all parameters must be explicitly specified.
The comparison between parameter name and URL parameter is not
case-sensitive, so it will work correctly if you name your parameter groupId
in the path /group/{groupid}/show
for example.
[Get("/group/{id}/users")]
Task<List<User>> GroupList([AliasAs("id")] int groupId, [AliasAs("sort")] string sortOrder);
GroupList(4, "desc");
>>> "/group/4/users?sort=desc"
If you specify an object
as a query parameter, all public properties which are not null are used as query parameters.
Use the Query
attribute the change the behavior to 'flatten' your query parameter object. If using this Attribute you can specify values for the Delimiter and the Prefix which are used to 'flatten' the object.
public class MyQueryParams
{
[AliasAs("order")]
public string SortOrder { get; set; }
public int Limit { get; set; }
}
[Get("/group/{id}/users")]
Task<List<User>> GroupList([AliasAs("id")] int groupId, MyQueryParams params);
[Get("/group/{id}/users")]
Task<List<User>> GroupListWithAttribute([AliasAs("id")] int groupId, [Query(".","search")] MyQueryParams params);
params.SortOrder = "desc";
params.Limit = 10;
GroupList(4, params)
>>> "/group/4/users?order=desc&Limit=10"
GroupListWithAttribute(4, params)
>>> "/group/4/users?search.order=desc&search.Limit=10"
A similar behavior exists if using a Dictionary, but without the advantages of the AliasAs
attributes and of course no intellisense and/or type safety.
Use the Query
attribute to specify format in which collections should be formatted in query string
[Get("/users/list")]
Task Search([Query(CollectionFormat.Multi)]int[] ages);
Search(new [] {10, 20, 30})
>>> "/users/list?ages=10&ages=20&ages=30"
[Get("/users/list")]
Task Search([Query(CollectionFormat.Csv)]int[] ages);
Search(new [] {10, 20, 30})
>>> "/users/list?ages=10%2C20%2C30"
One of the parameters in your method can be used as the body, by using the Body attribute:
[Post("/users/new")]
Task CreateUser([Body] User user);
There are four possibilities for supplying the body data, depending on the type of the parameter:
- If the type is
Stream
, the content will be streamed viaStreamContent
- If the type is
string
, the string will be used directly as the content - If the parameter has the attribute
[Body(BodySerializationMethod.UrlEncoded)]
, the content will be URL-encoded (see form posts below) - For all other types, the object will be serialized as JSON.
By default, Refit streams the body content without buffering it. This means you can
stream a file from disk, for example, without incurring the overhead of loading
the whole file into memory. The downside of this is that no Content-Length
header
is set on the request. If your API needs you to send a Content-Length
header with
the request, you can disable this streaming behavior by setting the buffered
argument
of the [Body]
attribute to true
:
Task CreateUser([Body(buffered: true)] User user);
JSON requests and responses are serialized/deserialized using Json.NET. By default, Refit will use the serializer settings that can be configured by setting Newtonsoft.Json.JsonConvert.DefaultSettings:
JsonConvert.DefaultSettings =
() => new JsonSerializerSettings() {
ContractResolver = new CamelCasePropertyNamesContractResolver(),
Converters = {new StringEnumConverter()}
};
// Serialized as: {"day":"Saturday"}
await PostSomeStuff(new { Day = DayOfWeek.Saturday });
As these are global settings they will affect your entire application. It
might be beneficial to isolate the settings for calls to a particular API.
When creating a Refit generated live interface, you may optionally pass a
RefitSettings
that will allow you to specify what serializer settings you
would like. This allows you to have different serializer settings for separate
APIs:
var gitHubApi = RestService.For<IGitHubApi>("https://api.github.com",
new RefitSettings {
JsonSerializerSettings = new JsonSerializerSettings {
ContractResolver = new SnakeCasePropertyNamesContractResolver()
}
});
var otherApi = RestService.For<IOtherApi>("https://api.example.com",
new RefitSettings {
JsonSerializerSettings = new JsonSerializerSettings {
ContractResolver = new CamelCasePropertyNamesContractResolver()
}
});
Property serialization/deserialization can be customised using Json.NET's JsonProperty attribute:
public class Foo
{
// Works like [AliasAs("b")] would in form posts (see below)
[JsonProperty(PropertyName="b")]
public string Bar { get; set; }
}
For APIs that take form posts (i.e. serialized as application/x-www-form-urlencoded
),
initialize the Body attribute with BodySerializationMethod.UrlEncoded
.
The parameter can be an IDictionary
:
public interface IMeasurementProtocolApi
{
[Post("/collect")]
Task Collect([Body(BodySerializationMethod.UrlEncoded)] Dictionary<string, object> data);
}
var data = new Dictionary<string, object> {
{"v", 1},
{"tid", "UA-1234-5"},
{"cid", new Guid("d1e9ea6b-2e8b-4699-93e0-0bcbd26c206c")},
{"t", "event"},
};
// Serialized as: v=1&tid=UA-1234-5&cid=d1e9ea6b-2e8b-4699-93e0-0bcbd26c206c&t=event
await api.Collect(data);
Or you can just pass any object and all public, readable properties will
be serialized as form fields in the request. This approach allows you to alias
property names using [AliasAs("whatever")]
which can help if the API has
cryptic field names:
public interface IMeasurementProtocolApi
{
[Post("/collect")]
Task Collect([Body(BodySerializationMethod.UrlEncoded)] Measurement measurement);
}
public class Measurement
{
// Properties can be read-only and [AliasAs] isn't required
public int v { get { return 1; }
[AliasAs("tid")]
public string WebPropertyId { get; set; }
[AliasAs("cid")]
public Guid ClientId { get;set; }
[AliasAs("t")]
public string Type { get; set; }
public object IgnoreMe { private get; set; }
}
var measurement = new Measurement {
WebPropertyId = "UA-1234-5",
ClientId = new Guid("d1e9ea6b-2e8b-4699-93e0-0bcbd26c206c"),
Type = "event"
};
// Serialized as: v=1&tid=UA-1234-5&cid=d1e9ea6b-2e8b-4699-93e0-0bcbd26c206c&t=event
await api.Collect(measurement);
If you have a type that has [JsonProperty(PropertyName)]
attributes setting property aliases, Refit will use those too ([AliasAs]
will take precedence where you have both).
This means that the following type will serialize as one=value1&two=value2
:
public class SomeObject
{
[JsonProperty(PropertyName = "one")]
public string FirstProperty { get; set; }
[JsonProperty(PropertyName = "notTwo")]
[AliasAs("two")]
public string SecondProperty { get; set; }
}
NOTE: This use of AliasAs
applies to querystring parameters and form body posts, but not to response objects; for aliasing fields on response objects, you'll still need to use [JsonProperty("full-property-name")]
.
You can set one or more static request headers for a request applying a Headers
attribute to the method:
[Headers("User-Agent: Awesome Octocat App")]
[Get("/users/{user}")]
Task<User> GetUser(string user);
Static headers can also be added to every request in the API by applying the
Headers
attribute to the interface:
[Headers("User-Agent: Awesome Octocat App")]
public interface IGitHubApi
{
[Get("/users/{user}")]
Task<User> GetUser(string user);
[Post("/users/new")]
Task CreateUser([Body] User user);
}
If the content of the header needs to be set at runtime, you can add a header
with a dynamic value to a request by applying a Header
attribute to a parameter:
[Get("/users/{user}")]
Task<User> GetUser(string user, [Header("Authorization")] string authorization);
// Will add the header "Authorization: token OAUTH-TOKEN" to the request
var user = await GetUser("octocat", "token OAUTH-TOKEN");
The most common reason to use headers is for authorization. Today most API's use some flavor of oAuth with access tokens that expire and refresh tokens that are longer lived.
One way to encapsulate these kinds of token usage, a custom HttpClientHandler
can be inserted instead.
For example:
class AuthenticatedHttpClientHandler : HttpClientHandler
{
private readonly Func<Task<string>> getToken;
public AuthenticatedHttpClientHandler(Func<Task<string>> getToken)
{
if (getToken == null) throw new ArgumentNullException("getToken");
this.getToken = getToken;
}
protected override async Task<HttpResponseMessage> SendAsync(HttpRequestMessage request, CancellationToken cancellationToken)
{
// See if the request has an authorize header
var auth = request.Headers.Authorization;
if (auth != null)
{
var token = await getToken().ConfigureAwait(false);
request.Headers.Authorization = new AuthenticationHeaderValue(auth.Scheme, token);
}
return await base.SendAsync(request, cancellationToken).ConfigureAwait(false);
}
}
While HttpClient contains a nearly identical method signature, it is used differently. HttpClient.SendAsync is not called by Refit. The HttpClientHandler must be modified instead.
This class is used like so (example uses the ADAL library to manage auto-token refresh but the principal holds for Xamarin.Auth or any other library:
class LoginViewModel
{
AuthenticationContext context = new AuthenticationContext(...);
private async Task<string> GetToken()
{
// The AcquireTokenAsync call will prompt with a UI if necessary
// Or otherwise silently use a refresh token to return
// a valid access token
var token = await context.AcquireTokenAsync("http://my.service.uri/app", "clientId", new Uri("callback://complete"));
return token;
}
public async void LoginAndCallApi()
{
var api = RestService.For<IMyRestService>(new HttpClient(new AuthenticatedHttpClientHandler(GetToken)) { BaseAddress = new Uri("https://the.end.point/") });
var location = await api.GetLocationOfRebelBase();
}
}
interface IMyRestService
{
[Get("/getPublicInfo")]
Task<Foobar> SomePublicMethod();
[Get("/secretStuff")]
[Headers("Authorization: Bearer")]
Task<Location> GetLocationOfRebelBase();
}
In the above example, any time a method that requires authentication is called, the AuthenticatedHttpClientHandler
will try to get a fresh access token. It's up to the app to provide one, checking the expiration time of an existing access token and obtaining a new one if needed.
Unlike Retrofit, where headers do not overwrite each other and are all added to the request regardless of how many times the same header is defined, Refit takes a similar approach to the approach ASP.NET MVC takes with action filters — redefining a header will replace it, in the following order of precedence:
Headers
attribute on the interface (lowest priority)Headers
attribute on the methodHeader
attribute on a method parameter (highest priority)
[Headers("X-Emoji: :rocket:")]
public interface IGitHubApi
{
[Get("/users/list")]
Task<List> GetUsers();
[Get("/users/{user}")]
[Headers("X-Emoji: :smile_cat:")]
Task<User> GetUser(string user);
[Post("/users/new")]
[Headers("X-Emoji: :metal:")]
Task CreateUser([Body] User user, [Header("X-Emoji")] string emoji);
}
// X-Emoji: :rocket:
var users = await GetUsers();
// X-Emoji: :smile_cat:
var user = await GetUser("octocat");
// X-Emoji: :trollface:
await CreateUser(user, ":trollface:");
Headers defined on an interface or method can be removed by redefining
a static header without a value (i.e. without : <value>
) or passing null
for
a dynamic header. Empty strings will be included as empty headers.
[Headers("X-Emoji: :rocket:")]
public interface IGitHubApi
{
[Get("/users/list")]
[Headers("X-Emoji")] // Remove the X-Emoji header
Task<List> GetUsers();
[Get("/users/{user}")]
[Headers("X-Emoji:")] // Redefine the X-Emoji header as empty
Task<User> GetUser(string user);
[Post("/users/new")]
Task CreateUser([Body] User user, [Header("X-Emoji")] string emoji);
}
// No X-Emoji header
var users = await GetUsers();
// X-Emoji:
var user = await GetUser("octocat");
// No X-Emoji header
await CreateUser(user, null);
// X-Emoji:
await CreateUser(user, "");
Methods decorated with Multipart
attribute will be submitted with multipart content type.
At this time, multipart methods support the following parameter types:
- string (parameter name will be used as name and string value as value)
- byte array
- Stream
- FileInfo
The parameter name will be used as the name of the field in the multipart data. This can be overridden with the AliasAs
attribute.
To specify the file name and content type for byte array (byte[]
), Stream
and FileInfo
parameters, use of a wrapper class is required.
The wrapper classes for these types are ByteArrayPart
, StreamPart
and FileInfoPart
.
public interface ISomeApi
{
[Multipart]
[Post("/users/{id}/photo")]
Task UploadPhoto(int id, [AliasAs("myPhoto")] StreamPart stream);
}
To pass a Stream to this method, construct a StreamPart object like so:
someApiInstance.UploadPhoto(id, new StreamPart(myPhotoStream, "photo.jpg", "image/jpeg"));
Note: The AttachmentName attribute that was previously described in this section has been deprecated and its use is not recommended.
Note that in Refit unlike in Retrofit, there is no option for a synchronous
network request - all requests must be async, either via Task
or via
IObservable
. There is also no option to create an async method via a Callback
parameter unlike Retrofit, because we live in the async/await future.
Similarly to how body content changes via the parameter type, the return type will determine the content returned.
Returning Task without a type parameter will discard the content and solely tell you whether or not the call succeeded:
[Post("/users/new")]
Task CreateUser([Body] User user);
// This will throw if the network call fails
await CreateUser(someUser);
If the type parameter is 'HttpResponseMessage' or 'string', the raw response message or the content as a string will be returned respectively.
// Returns the content as a string (i.e. the JSON data)
[Get("/users/{user}")]
Task<string> GetUser(string user);
// Returns the raw response, as an IObservable that can be used with the
// Reactive Extensions
[Get("/users/{user}")]
IObservable<HttpResponseMessage> GetUser(string user);
When using something like ASP.NET Web API, it's a fairly common pattern to have a whole stack of CRUD REST services. Refit now supports these, allowing you to define a single API interface with a generic type:
public interface IReallyExcitingCrudApi<T, in TKey> where T : class
{
[Post("")]
Task<T> Create([Body] T payload);
[Get("")]
Task<List<T>> ReadAll();
[Get("/{key}")]
Task<T> ReadOne(TKey key);
[Put("/{key}")]
Task Update(TKey key, [Body]T payload);
[Delete("/{key}")]
Task Delete(TKey key);
}
Which can be used like this:
// The "/users" part here is kind of important if you want it to work for more
// than one type (unless you have a different domain for each type)
var api = RestService.For<IReallyExcitingCrudApi<User, string>>("http://api.example.com/users");