swift: update demos to use direct API (#349)

**This is a working end-to-end iOS implementation using Envoy Mobile as a library!**

Depends on #312 and #353.

Updates our Swift example app to use the Envoy Mobile direct interfaces rather than using `URLSession` and Envoy as a listener.

Note: For now, we are no longer showing the text response of the response body due to the fact that the underlying implementation is not yet complete for bodied requests (headers-only).

Signed-off-by: Michael Rebello <me@michaelrebello.com>

![Simulator Screen Shot - TestDevice - 2019-08-20 at 13 57 44](https://user-images.githubusercontent.com/2643476/63383898-8f466280-c352-11e9-8c2e-944efda59ea2.png)

examples/swift/hello_world/AppDelegate.swift

@@ -1,10 +1,7 @@
-import Envoy
 import UIKit
 
 @UIApplicationMain
 final class AppDelegate: UIResponder, UIApplicationDelegate {
-  private let envoy = try! EnvoyBuilder().build()
-
   var window: UIWindow?
 
   func application(
@@ -15,8 +12,8 @@ final class AppDelegate: UIResponder, UIApplicationDelegate {
     window.rootViewController = ViewController()
     window.makeKeyAndVisible()
     self.window = window
-    NSLog("Finished launching!")
 
+    NSLog("Finished launching!")
     return true
   }
 }

examples/swift/hello_world/ViewController.swift

@@ -1,22 +1,28 @@
+import Envoy
 import UIKit
 
 private let kCellID = "cell-id"
-// swiftlint:disable:next force_unwrapping
-private let kURL = URL(string: "http://localhost:9001/api.lyft.com/static/demo/hello_world.txt")!
+private let kRequestAuthority = "s3.amazonaws.com"
+private let kRequestPath = "/api.lyft.com/static/demo/hello_world.txt"
+private let kRequestScheme = "http"
 
 final class ViewController: UITableViewController {
-  private let session: URLSession = {
-    let configuration = URLSessionConfiguration.default
-    configuration.urlCache = nil
-    configuration.timeoutIntervalForRequest = 10
-    return URLSession(configuration: configuration)
-  }()
   private var requestCount = 0
   private var results = [Result<Response, RequestError>]()
   private var timer: Timer?
+  private var envoy: Envoy?
 
   override func viewDidLoad() {
     super.viewDidLoad()
+    do {
+      NSLog("Starting Envoy...")
+      self.envoy = try EnvoyBuilder()
+        .build()
+    } catch let error {
+      NSLog("Starting Envoy failed: \(error)")
+    }
+
+    NSLog("Started Envoy, beginning requests...")
     self.startRequests()
   }
 
@@ -34,47 +40,34 @@ final class ViewController: UITableViewController {
   }
 
   private func performRequest() {
-    self.requestCount += 1
-    let requestID = self.requestCount
-    var request = URLRequest(url: kURL)
-    request.addValue("s3.amazonaws.com", forHTTPHeaderField: "host")
-
-    // Note that the request is sent to the envoy thread listening locally on port 9001.
-    NSLog("Starting request to '\(kURL.path)'")
-    self.session.dataTask(with: request) { [weak self] data, response, error in
-      DispatchQueue.main.async {
-        self?.handle(response: response, with: data, error: error, id: requestID)
-      }
-    }.resume()
-  }
-
-  private func handle(response: URLResponse?, with data: Data?, error: Error?, id: Int) {
-    if let error = error {
-      return self.add(result: .failure(RequestError(id: id, message: "\(error)")))
-    }
-
-    guard let response = response as? HTTPURLResponse, let data = data else {
-      return self.add(result: .failure(RequestError(id: id, message: "missing response data")))
+    guard let envoy = self.envoy else {
+      NSLog("Failed to start request - Envoy is not running")
+      return
     }
 
-    guard response.statusCode == 200 else {
-      let error = RequestError(id: id, message: "failed with status \(response.statusCode)")
-      return self.add(result: .failure(error))
-    }
-
-    guard let body = String(data: data, encoding: .utf8) else {
-      return self.add(result: .failure(RequestError(id: id, message: "failed to deserialize body")))
-    }
+    self.requestCount += 1
+    NSLog("Starting request to '\(kRequestPath)'")
 
-    let untypedHeaders = response.allHeaderFields
-    let headers = Dictionary(uniqueKeysWithValues: untypedHeaders.map
-    { header -> (String, String) in
-      return (header.key as? String ?? String(describing: header.key), "\(header.value)")
-    })
+    let requestID = self.requestCount
+    let request = RequestBuilder(method: .get, scheme: kRequestScheme,
+                                 authority: kRequestAuthority,
+                                 path: kRequestPath).build()
+    let handler = ResponseHandler()
+      .onHeaders { [weak self] headers, statusCode, _ in
+        NSLog("Response status (\(requestID)): \(statusCode)\n\(headers)")
+        self?.add(result: .success(Response(id: requestID, body: "Status: \(statusCode)",
+                                            serverHeader: headers["server"]?.first ?? "")))
+      }
+      .onData { data, _ in
+        NSLog("Response data (\(requestID)): \(data.count) bytes")
+      }
+      .onError { [weak self] in
+        NSLog("Error (\(requestID)): Request failed")
+        self?.add(result: .failure(RequestError(id: requestID,
+                                                message: "failed within Envoy library")))
+      }
 
-    // Deserialize the response, which will include a `Server` header set by Envoy.
-    NSLog("Response:\n\(data.count) bytes\n\(body)\n\(headers)")
-    self.add(result: .success(Response(id: id, body: body, serverHeader: headers["Server"] ?? "")))
+    envoy.sendUnary(request, handler: handler)
   }
 
   private func add(result: Result<Response, RequestError>) {
@@ -102,7 +95,7 @@ final class ViewController: UITableViewController {
     switch result {
     case .success(let response):
       cell.textLabel?.text = "[\(response.id)] \(response.body)"
-      cell.detailTextLabel?.text = "'Server' header: \(response.serverHeader)"
+      cell.detailTextLabel?.text = "'server' header: \(response.serverHeader)"
 
       cell.textLabel?.textColor = .black
       cell.detailTextLabel?.textColor = .black