Extract RESTClient with automatic retry attempts on rate-limits

Author: Jeehut

Sources/HandySwift/Types/RESTClient.swift

@@ -0,0 +1,262 @@
+import Foundation
+#if canImport(FoundationNetworking)
+import FoundationNetworking
+#endif
+
+/// A client to consume a REST API. Uses JSON to encode/decode body data.
+@available(iOS 16, macOS 13, tvOS 16, watchOS 9, *)
+public final class RESTClient: Sendable {
+   public enum RequestError: Error, LocalizedError, Sendable {
+      public typealias Context = String
+
+      case failedToEncodeBody(Error, Context?)
+      case failedToLoadData(Error, Context?)
+      case failedToDecodeSuccessBody(Error, Context?)
+      case failedToDecodeClientErrorBody(Error, Context?)
+      case clientError(String, Context?)
+      case unexpectedResponseType(URLResponse, Context?)
+      case unexpectedStatusCode(Int, Context?)
+
+      public var errorDescription: String? {
+         switch self {
+         case .failedToEncodeBody(let error, _):
+            "\(self.errorContext) Failed to encode body: \(error.localizedDescription)"
+         case .failedToLoadData(let error, _):
+            "\(self.errorContext) Failed to load data: \(error.localizedDescription)"
+         case .failedToDecodeSuccessBody(let error, _):
+            "\(self.errorContext) Failed to decode success body: \(error.localizedDescription)"
+         case .failedToDecodeClientErrorBody(let error, _):
+            "\(self.errorContext) Failed to decode client error body: \(error.localizedDescription)"
+         case .clientError(let string, _):
+            "\(self.errorContext) \(string)"
+         case .unexpectedResponseType(let urlResponse, _):
+            "\(self.errorContext) Unexpected response type (non-HTTP): \(String(describing: type(of: urlResponse)))"
+         case .unexpectedStatusCode(let int, _):
+            "\(self.errorContext) Unexpected status code: \(int)"
+         }
+      }
+
+      private var errorContext: String {
+         switch self {
+         case .failedToEncodeBody(_, let context), .failedToLoadData(_, let context), .failedToDecodeSuccessBody(_, let context),
+               .failedToDecodeClientErrorBody(_, let context), .clientError(_, let context):
+            if let context {
+               return "[\(context): Client Error]"
+            } else {
+               return "[Client Error]"
+            }
+
+         case .unexpectedResponseType(_, let context), .unexpectedStatusCode(_, let context):
+            if let context {
+               return "[\(context): Server Error]"
+            } else {
+               return "[Server Error]"
+            }
+         }
+      }
+   }
+
+   public enum HTTPMethod: String, Sendable {
+      case get = "GET"
+      case post = "POST"
+      case put = "PUT"
+      case patch = "PATCH"
+      case delete = "DELETE"
+   }
+
+   public enum Body: Sendable {
+      case binary(Data)
+      case json(Encodable & Sendable)
+      case string(String)
+      case form([URLQueryItem])
+
+      var contentType: String {
+         switch self {
+         case .binary: return "application/octet-stream"
+         case .json: return "application/json"
+         case .string: return "text/plain"
+         case .form: return "application/x-www-form-urlencoded"
+         }
+      }
+
+      func httpData() throws -> Data {
+         switch self {
+         case .binary(let data):
+            return data
+
+         case .json(let json):
+            return try JSONEncoder().encode(json)
+
+         case .string(let string):
+            return Data(string.utf8)
+
+         case .form(let queryItems):
+            var urlComponents = URLComponents(string: "https://example.com")!
+            urlComponents.queryItems = queryItems
+            return Data(urlComponents.percentEncodedQuery!.utf8)
+         }
+      }
+   }
+
+   let baseURL: URL
+   let baseHeaders: [String: String]
+   let baseQueryItems: [URLQueryItem]
+   let jsonEncoder: JSONEncoder
+   let jsonDecoder: JSONDecoder
+   let baseErrorContext: String?
+   let errorBodyToMessage: @Sendable (Data) throws -> String
+
+   // no need to pass 'application/json' to `baseHeaders`, it'll automatically be added of a body is sent
+   public init(
+      baseURL: URL,
+      baseHeaders: [String: String] = [:],
+      baseQueryItems: [URLQueryItem] = [],
+      jsonEncoder: JSONEncoder = .init(),
+      jsonDecoder: JSONDecoder = .init(),
+      baseErrorContext: String? = nil,
+      errorBodyToMessage: @Sendable @escaping (Data) throws -> String
+   ) {
+      self.baseURL = baseURL
+      self.baseHeaders = baseHeaders
+      self.baseQueryItems = baseQueryItems
+      self.jsonEncoder = jsonEncoder
+      self.jsonDecoder = jsonDecoder
+      self.baseErrorContext = baseErrorContext
+      self.errorBodyToMessage = errorBodyToMessage
+   }
+
+   public func requestObject<ResponseBodyType: Decodable>(
+      method: HTTPMethod,
+      path: String,
+      body: Body? = nil,
+      extraHeaders: [String: String] = [:],
+      extraQueryItems: [URLQueryItem] = [],
+      errorContext: String? = nil
+   ) async throws(RequestError) -> ResponseBodyType {
+      let responseData = try await self.requestData(method: method, path: path, body: body, extraHeaders: extraHeaders, extraQueryItems: extraQueryItems)
+
+      do {
+         return try self.jsonDecoder.decode(ResponseBodyType.self, from: responseData)
+      } catch {
+         throw .failedToDecodeSuccessBody(error, self.errorContext(requestContext: errorContext))
+      }
+   }
+
+   @discardableResult
+   public func requestData(
+      method: HTTPMethod,
+      path: String,
+      body: Body? = nil,
+      extraHeaders: [String: String] = [:],
+      extraQueryItems: [URLQueryItem] = [],
+      errorContext: String? = nil
+   ) async throws(RequestError) -> Data {
+      let url = self.baseURL
+         .appending(path: path)
+         .appending(queryItems: self.baseQueryItems + extraQueryItems)
+
+      var request = URLRequest(url: url)
+      request.httpMethod = method.rawValue
+
+      for (field, value) in self.baseHeaders.merging(extraHeaders, uniquingKeysWith: { $1 }) {
+         request.setValue(value, forHTTPHeaderField: field)
+      }
+
+      if let body {
+         do {
+            request.httpBody = try body.httpData()
+         } catch {
+            throw RequestError.failedToEncodeBody(error, self.errorContext(requestContext: errorContext))
+         }
+
+         request.setValue(body.contentType, forHTTPHeaderField: "Content-Type")
+      }
+
+      request.setValue("application/json", forHTTPHeaderField: "Accept")
+
+      let (data, response) = try await self.performRequest(request, errorContext: errorContext)
+      return try await self.handle(data: data, response: response, for: request, errorContext: errorContext)
+   }
+
+   private func errorContext(requestContext: String?) -> String? {
+      let context = [self.baseErrorContext, requestContext].compactMap { $0 }.joined(separator: "->")
+      guard !context.isEmpty else { return nil }
+      return context
+   }
+
+   private func performRequest(_ request: URLRequest, errorContext: String?) async throws(RequestError) -> (Data, URLResponse) {
+      self.logRequestIfDebug(request)
+
+      let data: Data
+      let response: URLResponse
+      do {
+         (data, response) = try await URLSession.shared.data(for: request)
+      } catch {
+         throw RequestError.failedToLoadData(error, self.errorContext(requestContext: errorContext))
+      }
+
+      self.logResponseIfDebug(response, data: data)
+      return (data, response)
+   }
+
+   private func handle(data: Data, response: URLResponse, for request: URLRequest, errorContext: String?, attempt: Int = 1) async throws(RequestError) -> Data {
+      guard let httpResponse = response as? HTTPURLResponse else {
+         throw .unexpectedResponseType(response, self.errorContext(requestContext: errorContext))
+      }
+
+      switch httpResponse.statusCode {
+      case 200..<300:
+         return data
+
+      case 429:
+         guard attempt < 5 else  { fallthrough }
+
+         #if DEBUG
+         print("Received Status Code 429 'Too Many Requests'. Retrying in \(attempt) second(s)...")
+         #endif
+
+         try? await Task.sleep(for: .seconds(attempt))
+
+         let (newData, newResponse) = try await self.performRequest(request, errorContext: errorContext)
+         return try await self.handle(data: newData, response: newResponse, for: request, errorContext: errorContext, attempt: attempt + 1)
+
+      case 400..<500:
+         guard !data.isEmpty else {
+            throw .clientError("Unexpected status code \(httpResponse.statusCode) without a response body.", self.errorContext(requestContext: errorContext))
+         }
+
+         let clientErrorMessage: String
+         do {
+            clientErrorMessage = try self.errorBodyToMessage(data)
+         } catch {
+            throw .failedToDecodeClientErrorBody(error, self.errorContext(requestContext: errorContext))
+         }
+         throw .clientError(clientErrorMessage, self.errorContext(requestContext: errorContext))
+
+      default:
+         throw .unexpectedStatusCode(httpResponse.statusCode, self.errorContext(requestContext: errorContext))
+      }
+   }
+
+   private func logRequestIfDebug(_ request: URLRequest) {
+      #if DEBUG
+      var requestBodyString: String?
+      if let bodyData = request.httpBody {
+         requestBodyString = String(data: bodyData, encoding: .utf8)
+      }
+
+      print("[\(self)] Sending \(request.httpMethod!) request to '\(request.url!)': \(request)\n\nHeaders:\n\(request.allHTTPHeaderFields ?? [:])\n\nBody:\n\(requestBodyString ?? "No body")")
+      #endif
+   }
+
+   private func logResponseIfDebug(_ response: URLResponse, data: Data?) {
+      #if DEBUG
+      var responseBodyString: String?
+      if let data = data {
+         responseBodyString = String(data: data, encoding: .utf8)
+      }
+
+      print("[\(self)] Received response & body from '\(response.url!)': \(response)\n\nResponse headers:\n\((response as? HTTPURLResponse)?.allHeaderFields ?? [:])\n\nResponse body:\n\(responseBodyString ?? "No body")")
+      #endif
+   }
+}