Bifrost

Bifrost is a lightweight, scalable framework for interacting with JSON, REST APIs.

Instalation

Bifrost is available via Swift Package Manager.

dependencies: [
  .package(url: "https://github.com/mtzaquia/bifrost.git", from: "3.0.4"),
],

Usage

API

Simply declare an entity conforming to API to start, then fulfill the required protocol conformances:

struct MyAPI: API {
  let baseURL: URL = URL(string: "https://api.myapi.com/v2/")!
  // ...
}

You can define default query parameters that will apply to all requests. You can also configure the decoder for your specific use-case.

struct MyAPI: API {
  // ...
  func queryParameters() -> [URLQueryItem]
    [
      URLQueryItem(name: "api-key", value: "<my secret key>")
    ]
  }

  var jsonDecoder: JSONDecoder = {
    let jd = JSONDecoder()
    jd.dateDecodingStrategy = .iso8601
    return jd
  }()
}

Requests

For each request, create a type with its supported parameters. Make sure this type conforms to Requestable. You can also provide header fields for a specific request if needed, and you can choose the HTTP method for that request.

struct MyRequest {
  private(set) var name: String
  private(set) var anotherParam: String?
}

extension MyRequest: Requestable {
  var path: String { "api/my-request" }
  
  struct Response: Decodable {
    let results: [MyResultObject]
  }
}

Note

If you expect an empty response, the built-in EmptyResponse type is avaiable for convenience.

Making the call

Finally, you are ready to submit a request! Concurrency allows you to inline your call easily:

// ...
let response = try await MyAPI().response(for: MyRequest(name: "My fancy name"))
print(response.results) // Our response is already a Swift type! More specifically, an instance of `MyRequest.Response`.

Intercepting requests and responses

You can define request and response interceptors on your API for request mutation, mocking, and response post-processing.

• requestInterceptors run after Bifrost builds the final URLRequest and before transport
• request-local headers belong in Requestable.headerFields; API-wide headers belong in request interceptors
• responseInterceptors run on raw response data before Bifrost decodes the final success body
• both phases use InterceptionResult<T> with .continue, .return(...), and .restart
• mocked and real responses share the same InterceptedResponse wrapper, which exposes body, httpResponse, statusCode, and normalized headerFields
• interceptors can return .restart to rerun the full request and response interceptor pipeline
• unsuccessful HTTP statuses are surfaced after the response phase, so response interceptors can recover from responses like 401

struct AddAuthorization: RequestInterceptor {
  let token: String

  func intercept<Request>(
    _ context: inout InterceptionContext<Request>
  ) async throws -> InterceptionResult<InterceptedResponse> where Request: Requestable {
    if context.request is MyRequest {
      context.urlRequest.setValue("Bearer \(token)", forHTTPHeaderField: "Authorization")
    }

    return .continue
  }
}

struct RewriteResponse: ResponseInterceptor {
  func intercept(
    _ response: inout InterceptedResponse
  ) async throws -> InterceptionResult<InterceptedResponse> {
    return .continue
  }
}

struct MyAPI: API {
  let baseURL = URL(string: "https://api.myapi.com/v2/")!

  var requestInterceptors: [any RequestInterceptor] {
    [AddAuthorization(token: "<token>")]
  }

  var responseInterceptors: [any ResponseInterceptor] {
    [RewriteResponse()]
  }
}

Request interceptors receive an InterceptionContext with the original typed request as read-only context and the final built URLRequest as the mutable request that will be sent.

struct MockUser: RequestInterceptor {
  func intercept<Request>(
    _ context: inout InterceptionContext<Request>
  ) async throws -> InterceptionResult<InterceptedResponse> where Request: Requestable {
    guard context.request is GetUserRequest else {
      return .continue
    }

    let httpResponse = HTTPURLResponse(
      url: URL(string: "https://api.myapi.com/v2/user")!,
      statusCode: 200,
      httpVersion: nil,
      headerFields: ["X-Mocked": "true"]
    )!

    return .return(
      InterceptedResponse(
        body: Data(#"{"name":"Mocked User"}"#.utf8),
        httpResponse: httpResponse
      )
    )
  }
}

Response interceptors always receive the full intercepted response, including metadata, so they can make decisions based on the HTTP code, headers, and raw body bytes before decoding happens. They can also return .restart after doing recovery work like refreshing a token.

struct NormalizeUser: ResponseInterceptor {
  func intercept(
    _ response: inout InterceptedResponse
  ) async throws -> InterceptionResult<InterceptedResponse> {
    if response.statusCode == 202 {
      response.httpResponse = HTTPURLResponse(
        url: response.httpResponse.url!,
        statusCode: 200,
        httpVersion: nil,
        headerFields: response.headerFields
      )!
    }

    return .continue
  }
}

License

Copyright (c) 2025 @mtzaquia

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.