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Lightweight REST for Swift
.package(url: "https://github.com/HTTP-RPC/Kilo.git", from: "3.0.1")



Kilo is a Swift package for consuming RESTful and REST-like web services. The project's name comes from the nautical K or Kilo flag, which means "I wish to communicate with you":

For example, the following Swift code uses Kilo's WebServiceProxy class to access a simple web service that returns the first n values in the Fibonacci sequence:

let webServiceProxy = WebServiceProxy(session: URLSession.shared, baseURL: baseURL)

// GET test/fibonacci?count=8
webServiceProxy.invoke(.get, path: "test/fibonacci", arguments: [
    "count": 8
]) { (result: Result<[Int], Error>) in
    switch (result) {
    case .success(let value):
        print(value) // [0, 1, 1, 2, 3, 5, 8, 13]

    case .failure(let error):


The WebServiceProxy class is used to issue API requests to the server. This class provides a single initializer that accepts the following arguments:

  • session - a URLSession instance
  • baseURL - the base URL of the service

Service operations are initiated via one of the following methods:

public func invoke(_ method: Method, path: String,
    arguments: [String: Any] = [:], content: Data? = nil, contentType: String? = nil,
    resultHandler: @escaping ResultHandler<Void>) -> URLSessionDataTask? { ... }

public func invoke<B: Encodable>(_ method: Method, path: String,
    arguments: [String: Any] = [:], body: B,
    resultHandler: @escaping ResultHandler<Void>) throws -> URLSessionDataTask? { ... }

public func invoke<T: Decodable>(_ method: Method, path: String,
    arguments: [String: Any] = [:], content: Data? = nil, contentType: String? = nil,
    resultHandler: @escaping ResultHandler<T>) -> URLSessionDataTask? { ... }

public func invoke<B: Encodable, T: Decodable>(_ method: Method, path: String,
    arguments: [String: Any] = [:], body: B,
    resultHandler: @escaping ResultHandler<T>) throws -> URLSessionDataTask? { ... }

public func invoke<T>(_ method: Method, path: String,
    arguments: [String: Any] = [:], content: Data? = nil, contentType: String? = nil,
    responseHandler: @escaping ResponseHandler<T>,
    resultHandler: @escaping ResultHandler<T>) -> URLSessionDataTask? { ... }

All variants accept the following arguments:

  • method - the HTTP method to execute
  • path - the path to the requested resource, relative to the base URL
  • arguments - a dictionary containing the method arguments as key/value pairs
  • resultHandler - a callback that will be invoked upon completion of the request

The first two versions execute a service method that does not return a value. The following two versions deserialize the service response using JSONDecoder. The final version accepts a responseHandler callback to facilitate decoding of custom response content.

Three of the methods accept the following arguments for specifying custom request body content:

  • content - an optional Data instance representing the body of the request
  • contentType - an optional string value containing the MIME type of the content

The other two methods accept an encodable body argument that is serialized using JSONEncoder.

JSON data is encoded and decoded using a date strategy of millisecondsSince1970.

Response and result handler callbacks are defined as follows:

public typealias ResponseHandler<T> = (_ content: Data, _ contentType: String?) throws -> T

public typealias ResultHandler<T> = (_ result: Result<T, Error>) -> Void

All methods return an instance of URLSessionDataTask representing the invocation request. This allows an application to monitor the status of outstanding requests or cancel a request, if needed.


Like HTML forms, arguments are submitted either via the query string or in the request body. Arguments for GET, PUT, and DELETE requests are always sent in the query string. POST arguments are typically sent in the request body, and may be submitted as either "application/x-www-form-urlencoded" or "multipart/form-data" (determined via the service proxy's encoding property). However, if a custom body is specified via either the content or body parameter, POST arguments will be sent in the query string.

Any value may be used as an argument. However, Date instances are automatically converted to a 64-bit integer value representing epoch time (the number of milliseconds that have elapsed since midnight on January 1, 1970). Array instances represent multi-value parameters and behave similarly to <select multiple> tags in HTML. When using the multi-part encoding, instances of URL represent file uploads and behave similarly to <input type="file"> tags in HTML forms.

The undefined property of the WebServiceProxy class can be used to represent unspecified or unknown values.

Return Values

The result handler is called upon completion of the operation. If successful, the result will contain a deserialized representation of the content returned by the server. Otherwise, it will contain an error describing the problem that occurred. If the content type of the error response is "text/*", the deserialized response body will be provided in the error's localized description.

Threading Considerations

While service requests are typically processed on a background thread, result handlers are always executed on the main thread. This allows the callback to update an application's user interface directly, rather than posting a separate update operation to the main queue.

Response handlers are always executed in the background, before the result handler is invoked.

Additional Information

For more information, see the test cases.


Stars: 4
Last commit: 3 weeks ago

Release Notes

Kilo 3.0.1
3 weeks ago
  • Simplify WebServiceProxy class

Swiftpack is being maintained by Petr Pavlik | @ptrpavlik | @swiftpackco