Feature/transport prepare request delegate

Apollo.xcodeproj/project.pbxproj

@@ -8,6 +8,9 @@
 
 /* Begin PBXBuildFile section */
 		54DDB0921EA045870009DD99 /* InMemoryNormalizedCache.swift in Sources */ = {isa = PBXBuildFile; fileRef = 54DDB0911EA045870009DD99 /* InMemoryNormalizedCache.swift */; };
+		5B53E4E3207FC1A900878639 /* HTTPNetworkTransportDelegateTests.swift in Sources */ = {isa = PBXBuildFile; fileRef = 5B53E4E2207FC1A900878639 /* HTTPNetworkTransportDelegateTests.swift */; };
+		5B53E4E6207FCC9C00878639 /* MockURLProtocol.swift in Sources */ = {isa = PBXBuildFile; fileRef = 5B53E4E4207FCC9300878639 /* MockURLProtocol.swift */; };
+		5B565283207FA0010022C67C /* URLRequestOperation.swift in Sources */ = {isa = PBXBuildFile; fileRef = 5B565282207FA0010022C67C /* URLRequestOperation.swift */; };
 		9F0CA4451EE7F9E90032DD39 /* ApolloTestSupport.framework in Frameworks */ = {isa = PBXBuildFile; fileRef = 9F8A95781EC0FC1200304A2D /* ApolloTestSupport.framework */; };
 		9F0CA4461EE7F9E90032DD39 /* ApolloTestSupport.framework in Embed Frameworks */ = {isa = PBXBuildFile; fileRef = 9F8A95781EC0FC1200304A2D /* ApolloTestSupport.framework */; settings = {ATTRIBUTES = (CodeSignOnCopy, RemoveHeadersOnCopy, ); }; };
 		9F10A51E1EC1BA0F0045E62B /* MockNetworkTransport.swift in Sources */ = {isa = PBXBuildFile; fileRef = 9F10A51D1EC1BA0F0045E62B /* MockNetworkTransport.swift */; };
@@ -228,6 +231,9 @@
 
 /* Begin PBXFileReference section */
 		54DDB0911EA045870009DD99 /* InMemoryNormalizedCache.swift */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.swift; path = InMemoryNormalizedCache.swift; sourceTree = "<group>"; };
+		5B565282207FA0010022C67C /* URLRequestOperation.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = URLRequestOperation.swift; sourceTree = "<group>"; };
+		5B53E4E2207FC1A900878639 /* HTTPNetworkTransportDelegateTests.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = HTTPNetworkTransportDelegateTests.swift; sourceTree = "<group>"; };
+		5B53E4E4207FCC9300878639 /* MockURLProtocol.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = MockURLProtocol.swift; sourceTree = "<group>"; };
 		9F10A51D1EC1BA0F0045E62B /* MockNetworkTransport.swift */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.swift; path = MockNetworkTransport.swift; sourceTree = "<group>"; };
 		9F19D8431EED568200C57247 /* ResultOrPromise.swift */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.swift; path = ResultOrPromise.swift; sourceTree = "<group>"; };
 		9F19D8451EED8D3B00C57247 /* ResultOrPromiseTests.swift */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.swift; path = ResultOrPromiseTests.swift; sourceTree = "<group>"; };
@@ -428,6 +434,7 @@
 				9F8A95811EC0FD3300304A2D /* XCTAssertHelpers.swift */,
 				9F8A95831EC0FD6100304A2D /* XCTestCase+Promise.swift */,
 				9F10A51D1EC1BA0F0045E62B /* MockNetworkTransport.swift */,
+				5B53E4E4207FCC9300878639 /* MockURLProtocol.swift */,
 				9F8A95851EC0FD9800304A2D /* TestCacheProvider.swift */,
 				9F8A957A1EC0FC1200304A2D /* ApolloTestSupport.h */,
 				9F8A957B1EC0FC1200304A2D /* Info.plist */,
@@ -556,6 +563,7 @@
 				9FE1C6E61E634C8D00C02284 /* PromiseTests.swift */,
 				9F19D8451EED8D3B00C57247 /* ResultOrPromiseTests.swift */,
 				9FADC8531E6B86D900C677E6 /* DataLoaderTests.swift */,
+				5B53E4E2207FC1A900878639 /* HTTPNetworkTransportDelegateTests.swift */,
 				9FC750551D2A532D00458D91 /* Info.plist */,
 			);
 			path = ApolloTests;
@@ -580,6 +588,7 @@
 				9F69FFA81D42855900E000B1 /* NetworkTransport.swift */,
 				9F4DAF2D1E48B84B00EBFF0B /* HTTPNetworkTransport.swift */,
 				9FF90A5B1DDDEB100034C3B6 /* GraphQLResponse.swift */,
+				5B565282207FA0010022C67C /* URLRequestOperation.swift */,
 			);
 			name = Network;
 			sourceTree = "<group>";
@@ -1033,6 +1042,7 @@
 			files = (
 				9F8A95841EC0FD6100304A2D /* XCTestCase+Promise.swift in Sources */,
 				9F8A95821EC0FD3300304A2D /* XCTAssertHelpers.swift in Sources */,
+				5B53E4E6207FCC9C00878639 /* MockURLProtocol.swift in Sources */,
 				9F10A51E1EC1BA0F0045E62B /* MockNetworkTransport.swift in Sources */,
 				9F8A95861EC0FD9800304A2D /* TestCacheProvider.swift in Sources */,
 			);
@@ -1099,6 +1109,7 @@
 				9F27D4641D40379500715680 /* JSONStandardTypeConversions.swift in Sources */,
 				9FA6F3681E65DF4700BF8D73 /* GraphQLResultAccumulator.swift in Sources */,
 				9FF90A651DDDEB100034C3B6 /* GraphQLExecutor.swift in Sources */,
+				5B565283207FA0010022C67C /* URLRequestOperation.swift in Sources */,
 				9FC750611D2A59C300458D91 /* GraphQLOperation.swift in Sources */,
 				9FE941D01E62C771007CDD89 /* Promise.swift in Sources */,
 				9FC750631D2A59F600458D91 /* ApolloClient.swift in Sources */,
@@ -1118,6 +1129,7 @@
 				9FF90A6F1DDDEB420034C3B6 /* InputValueEncodingTests.swift in Sources */,
 				9FE1C6E71E634C8D00C02284 /* PromiseTests.swift in Sources */,
 				9FADC8541E6B86D900C677E6 /* DataLoaderTests.swift in Sources */,
+				5B53E4E3207FC1A900878639 /* HTTPNetworkTransportDelegateTests.swift in Sources */,
 				9F8622FA1EC2117C00C38162 /* FragmentConstructionAndConversionTests.swift in Sources */,
 				9FF90A711DDDEB420034C3B6 /* ReadFieldValueTests.swift in Sources */,
 				9F295E311E27534800A24949 /* NormalizeQueryResults.swift in Sources */,

Sources/Apollo/HTTPNetworkTransport.swift

@@ -41,22 +41,32 @@ public struct GraphQLHTTPResponseError: Error, LocalizedError {
   }
 }
 
+/// Delegate to respond to hooks in the network request lifecycle.
+public protocol HTTPNetworkTransportDelegate: class {
+  /// Opportunity for the delegate to modify the URLRequest before it is sent. `completionHandler` must be called with the
+  /// desired URLRequest to send. 
+  func networkTransport(_ networkTransport: HTTPNetworkTransport, prepareRequest request: URLRequest, completionHandler: @escaping (URLRequest) -> Void)
+}
+
 /// A network transport that uses HTTP POST requests to send GraphQL operations to a server, and that uses `URLSession` as the networking implementation.
 public class HTTPNetworkTransport: NetworkTransport {
   let url: URL
   let session: URLSession
   let serializationFormat = JSONSerializationFormat.self
-
+  public weak var delegate: HTTPNetworkTransportDelegate?
+
   /// Creates a network transport with the specified server URL and session configuration.
   ///
   /// - Parameters:
   ///   - url: The URL of a GraphQL server to connect to.
   ///   - configuration: A session configuration used to configure the session. Defaults to `URLSessionConfiguration.default`.
   ///   - sendOperationIdentifiers: Whether to send operation identifiers rather than full operation text, for use with servers that support query persistence. Defaults to false.
-  public init(url: URL, configuration: URLSessionConfiguration = URLSessionConfiguration.default, sendOperationIdentifiers: Bool = false) {
+  ///   - delegate: Delegate to respond to hooks in the network request lifecycle. Defaults to nil.
+  public init(url: URL, configuration: URLSessionConfiguration = URLSessionConfiguration.default, sendOperationIdentifiers: Bool = false, delegate: HTTPNetworkTransportDelegate? = nil) {
     self.url = url
     self.session = URLSession(configuration: configuration)
     self.sendOperationIdentifiers = sendOperationIdentifiers
+    self.delegate = delegate
   }
 
   /// Send a GraphQL operation to a server and return a response.
@@ -76,7 +86,7 @@ public class HTTPNetworkTransport: NetworkTransport {
     let body = requestBody(for: operation)
     request.httpBody = try! serializationFormat.serialize(value: body)
 
-    let task = session.dataTask(with: request) { (data: Data?, response: URLResponse?, error: Error?) in
+    let requestOperation = URLRequestOperation(session: session, request: request) { (data: Data?, response: URLResponse?, error: Error?) in
       if error != nil {
         completionHandler(nil, error)
         return
@@ -107,9 +117,16 @@ public class HTTPNetworkTransport: NetworkTransport {
       }
     }
 
-    task.resume()
-
-    return task
+    if let delegate = delegate {
+      delegate.networkTransport(self, prepareRequest: request) { (modifiedRequest: URLRequest) in
+        requestOperation.request = modifiedRequest
+        requestOperation.start()
+      }
+    } else {
+      requestOperation.start()
+    }
+
+    return requestOperation
   }
 
   private let sendOperationIdentifiers: Bool

Sources/Apollo/URLRequestOperation.swift

@@ -0,0 +1,44 @@
+import Foundation
+
+/// Wrapper operation around a URLSessionTask.
+final class URLRequestOperation: AsynchronousOperation, Cancellable {
+
+  let session: URLSession
+  var request: URLRequest
+  let resultHandler: ((Data?, URLResponse?, Error?) -> Void)?
+
+  private var sessionTask: URLSessionTask?
+
+  init(session: URLSession, request: URLRequest, resultHandler: ((Data?, URLResponse?, Error?) -> Void)?) {
+    self.session = session
+    self.request = request
+    self.resultHandler = resultHandler
+  }
+
+  override func start() {
+    guard !isCancelled else {
+      state = .finished
+      return
+    }
+
+    state = .executing
+
+    let task = session.dataTask(with: request) { (data: Data?, response: URLResponse?, error: Error?) in
+      self.notifyResultHandler(data: data, response: response, error: error)
+      self.state = .finished
+    }
+
+    task.resume()
+    self.sessionTask = task
+  }
+
+  override func cancel() {
+    super.cancel()
+    sessionTask?.cancel()
+  }
+
+  private func notifyResultHandler(data: Data?, response: URLResponse?, error: Error?) {
+    guard let resultHandler = resultHandler else { return }
+    resultHandler(data, response, error)
+  }
+}

Tests/ApolloTestSupport/MockURLProtocol.swift

@@ -0,0 +1,52 @@
+import Foundation
+
+public class MockURLProtocol: URLProtocol {
+
+  public static var lastRequest: URLRequest?
+  public static var nextResponse: Response?
+
+  public enum Response {
+    case success(URLResponse, Data)
+    case error(Error)
+  }
+
+  override public class func canInit(with request: URLRequest) -> Bool {
+    lastRequest = request
+    return true
+  }
+
+  override public class func canonicalRequest(for request: URLRequest) -> URLRequest {
+    return request
+  }
+
+  override public func startLoading() {
+    DispatchQueue.main.async {
+      guard let response = MockURLProtocol.nextResponse else {
+        self.client?.urlProtocolDidFinishLoading(self)
+        return
+      }
+
+      switch response {
+      case .success(let urlResponse, let data):
+        self.client?.urlProtocol(self, didReceive: urlResponse, cacheStoragePolicy: .notAllowed)
+        self.client?.urlProtocol(self, didLoad: data)
+        self.client?.urlProtocolDidFinishLoading(self)
+      case .error(let error):
+        self.client?.urlProtocol(self, didFailWithError: error)
+      }
+    }
+  }
+
+  override public func stopLoading() {
+    // Nothing to do
+  }
+}
+
+public extension MockURLProtocol.Response {
+
+  public static func make(url: URL, response bodyString: String, statusCode: Int) -> MockURLProtocol.Response {
+    let data = bodyString.data(using: .utf8)!
+    let urlResponse = HTTPURLResponse(url: url, statusCode: 200, httpVersion: nil, headerFields: nil)!
+    return MockURLProtocol.Response.success(urlResponse, data)
+  }
+}

Tests/ApolloTests/HTTPNetworkTransportDelegateTests.swift

@@ -0,0 +1,69 @@
+import XCTest
+@testable import Apollo
+import ApolloTestSupport
+
+class HTTPNetworkTransportDelegateTests: XCTestCase {
+
+  func testPrepareRequest() {
+    let delegate = TransportDelegate()
+    delegate.requestPreparation = { request in
+      var mutableRequest = request
+      mutableRequest.addValue("value", forHTTPHeaderField: "custom")
+      return mutableRequest
+    }
+
+    let url = URL(string: "http://localhost/endpoint")!
+    MockURLProtocol.nextResponse = MockURLProtocol.Response.make(url: url, response: "{}", statusCode: 200)
+    let transport = HTTPNetworkTransport(url: url, configuration: .mock(), sendOperationIdentifiers: false, delegate: delegate)
+
+    let expectation = self.expectation(description: "Trigger request with custom preparation hook")
+    _ = transport.send(operation: MockGraphQLQuery()) { (_, _) in
+      XCTAssertEqual(MockURLProtocol.lastRequest?.value(forHTTPHeaderField: "custom"), "value")
+      expectation.fulfill()
+    }
+    self.waitForExpectations(timeout: 1)
+  }
+}
+
+private class TransportDelegate: HTTPNetworkTransportDelegate {
+
+  var requestPreparation: ((URLRequest) -> URLRequest)?
+
+  func networkTransport(_ networkTransport: HTTPNetworkTransport, prepareRequest request: URLRequest, completionHandler: @escaping (URLRequest) -> Void) {
+    DispatchQueue.main.async {
+      if let requestPreparation = self.requestPreparation {
+        completionHandler(requestPreparation(request))
+      } else {
+        completionHandler(request)
+      }
+    }
+  }
+}
+
+private extension URLSessionConfiguration {
+  static func mock() -> URLSessionConfiguration {
+    let config = URLSessionConfiguration.default
+    config.protocolClasses = [MockURLProtocol.self]
+    return config
+  }
+}
+
+private class MockGraphQLQuery: GraphQLQuery {
+
+  var operationDefinition: String {
+    return "query SampleQuery { object { property } }"
+  }
+
+  struct Data: GraphQLSelectionSet {
+
+    static var selections: [GraphQLSelection] {
+      return []
+    }
+
+    var resultMap: ResultMap
+
+    init(unsafeResultMap: ResultMap) {
+      self.resultMap = unsafeResultMap
+    }
+  }
+}