logging support

Motivation:

AsyncHTTPClient is not a simple piece of software and nowadays also
quite stateful. To debug issues, the user may want logging.

Modification:

Support passing a logger to the request methods.

Result:

Debugging simplified.

Author: weissi

Diff for: Package.swift

@@ -25,15 +25,18 @@ let package = Package(
         .package(url: "https://github.com/apple/swift-nio-ssl.git", from: "2.7.0"),
         .package(url: "https://github.com/apple/swift-nio-extras.git", from: "1.3.0"),
         .package(url: "https://github.com/apple/swift-nio-transport-services.git", from: "1.5.1"),
+        .package(url: "https://github.com/apple/swift-log.git", from: "1.0.0"),
     ],
     targets: [
         .target(
             name: "AsyncHTTPClient",
-            dependencies: ["NIO", "NIOHTTP1", "NIOSSL", "NIOConcurrencyHelpers", "NIOHTTPCompression", "NIOFoundationCompat", "NIOTransportServices"]
+            dependencies: ["NIO", "NIOHTTP1", "NIOSSL", "NIOConcurrencyHelpers", "NIOHTTPCompression",
+                           "NIOFoundationCompat", "NIOTransportServices", "Logging"]
         ),
         .testTarget(
             name: "AsyncHTTPClientTests",
-            dependencies: ["NIO", "NIOConcurrencyHelpers", "NIOSSL", "AsyncHTTPClient", "NIOFoundationCompat", "NIOTestUtils"]
+            dependencies: ["NIO", "NIOConcurrencyHelpers", "NIOSSL", "AsyncHTTPClient", "NIOFoundationCompat",
+                           "NIOTestUtils", "Logging"]
         ),
     ]
 )

Diff for: Sources/AsyncHTTPClient/ConnectionPool.swift

@@ -13,6 +13,7 @@
 //===----------------------------------------------------------------------===//
 
 import Foundation
+import Logging
 import NIO
 import NIOConcurrencyHelpers
 import NIOFoundationCompat
@@ -494,17 +495,19 @@ extension HTTPClient {
         var connection: Connection?
         var cancelled: Bool
         let lock: Lock
+        let logger: Logger // We are okay to store the logger here because a Task is for only ond request.
 
-        init(eventLoop: EventLoop) {
+        init(eventLoop: EventLoop, logger: Logger) {
             self.eventLoop = eventLoop
             self.promise = eventLoop.makePromise()
             self.completion = self.promise.futureResult.map { _ in }
             self.cancelled = false
             self.lock = Lock()
+            self.logger = logger
         }
 
-        static func failedTask(eventLoop: EventLoop, error: Error) -> Task<Response> {
-            let task = self.init(eventLoop: eventLoop)
+        static func failedTask(eventLoop: EventLoop, error: Error, logger: Logger) -> Task<Response> {
+            let task = self.init(eventLoop: eventLoop, logger: logger)
             task.promise.fail(error)
             return task
         }
@@ -546,13 +549,18 @@ extension HTTPClient {
             }
         }
 
-        func succeed<Delegate: HTTPClientResponseDelegate>(promise: EventLoopPromise<Response>?, with value: Response, delegateType: Delegate.Type, closing: Bool) {
-            self.releaseAssociatedConnection(delegateType: delegateType, closing: closing).whenSuccess {
+        func succeed<Delegate: HTTPClientResponseDelegate>(promise: EventLoopPromise<Response>?,
+                                                           with value: Response,
+                                                           delegateType: Delegate.Type,
+                                                           closing: Bool) {
+            self.releaseAssociatedConnection(delegateType: delegateType,
+                                             closing: closing).whenSuccess {
                 promise?.succeed(value)
             }
         }
 
-        func fail<Delegate: HTTPClientResponseDelegate>(with error: Error, delegateType: Delegate.Type) {
+        func fail<Delegate: HTTPClientResponseDelegate>(with error: Error,
+                                                        delegateType: Delegate.Type) {
             if let connection = self.connection {
                 self.releaseAssociatedConnection(delegateType: delegateType, closing: true)
                     .whenSuccess {
@@ -562,13 +570,14 @@ extension HTTPClient {
             }
         }
 
-        func releaseAssociatedConnection<Delegate: HTTPClientResponseDelegate>(delegateType: Delegate.Type, closing: Bool) -> EventLoopFuture<Void> {
+        func releaseAssociatedConnection<Delegate: HTTPClientResponseDelegate>(delegateType: Delegate.Type,
+                                                                               closing: Bool) -> EventLoopFuture<Void> {
             if let connection = self.connection {
                 // remove read timeout handler
                 return connection.removeHandler(IdleStateHandler.self).flatMap {
                     connection.removeHandler(TaskHandler<Delegate>.self)
                 }.map {
-                    connection.release(closing: closing)
+                    connection.release(closing: closing, logger: self.logger)
                 }.flatMapError { error in
                     fatalError("Couldn't remove taskHandler: \(error)")
                 }
@@ -600,6 +609,7 @@ internal class TaskHandler<Delegate: HTTPClientResponseDelegate>: RemovableChann
     let delegate: Delegate
     let redirectHandler: RedirectHandler<Delegate.Response>?
     let ignoreUncleanSSLShutdown: Bool
+    let logger: Logger // We are okay to store the logger here because a TaskHandler is just for one request.
 
     var state: State = .idle
     var pendingRead = false
@@ -617,12 +627,14 @@ internal class TaskHandler<Delegate: HTTPClientResponseDelegate>: RemovableChann
          kind: HTTPClient.Request.Kind,
          delegate: Delegate,
          redirectHandler: RedirectHandler<Delegate.Response>?,
-         ignoreUncleanSSLShutdown: Bool) {
+         ignoreUncleanSSLShutdown: Bool,
+         logger: Logger) {
         self.task = task
         self.delegate = delegate
         self.redirectHandler = redirectHandler
         self.ignoreUncleanSSLShutdown = ignoreUncleanSSLShutdown
         self.kind = kind
+        self.logger = logger
     }
 }
 
@@ -678,7 +690,10 @@ extension TaskHandler {
             do {
                 let result = try body(self.task)
 
-                self.task.succeed(promise: promise, with: result, delegateType: Delegate.self, closing: self.closing)
+                self.task.succeed(promise: promise,
+                                  with: result,
+                                  delegateType: Delegate.self,
+                                  closing: self.closing)
             } catch {
                 self.task.fail(with: error, delegateType: Delegate.self)
             }

Diff for: Sources/AsyncHTTPClient/HTTPClient.swift

@@ -0,0 +1,40 @@
+//===----------------------------------------------------------------------===//
+//
+// This source file is part of the AsyncHTTPClient open source project
+//
+// Copyright (c) 2020 Apple Inc. and the AsyncHTTPClient project authors
+// Licensed under Apache License v2.0
+//
+// See LICENSE.txt for license information
+// See CONTRIBUTORS.txt for the list of AsyncHTTPClient project authors
+//
+// SPDX-License-Identifier: Apache-2.0
+//
+//===----------------------------------------------------------------------===//
+
+import Logging
+
+internal struct NoOpLogHandler: LogHandler {
+    func log(level: Logger.Level, message: Logger.Message, metadata: Logger.Metadata?, file: String, function: String, line: UInt) {}
+
+    subscript(metadataKey _: String) -> Logger.Metadata.Value? {
+        get {
+            return nil
+        }
+        set {}
+    }
+
+    var metadata: Logger.Metadata {
+        get {
+            return [:]
+        }
+        set {}
+    }
+
+    var logLevel: Logger.Level {
+        get {
+            return .critical
+        }
+        set {}
+    }
+}

Diff for: Sources/AsyncHTTPClient/HTTPHandler.swift

@@ -0,0 +1,31 @@
+//===----------------------------------------------------------------------===//
+//
+// This source file is part of the AsyncHTTPClient open source project
+//
+// Copyright (c) 2020 Apple Inc. and the AsyncHTTPClient project authors
+// Licensed under Apache License v2.0
+//
+// See LICENSE.txt for license information
+// See CONTRIBUTORS.txt for the list of AsyncHTTPClient project authors
+//
+// SPDX-License-Identifier: Apache-2.0
+//
+//===----------------------------------------------------------------------===//
+
+extension Connection: CustomStringConvertible {
+    var description: String {
+        return "\(self.channel)"
+    }
+}
+
+extension HTTP1ConnectionProvider.Waiter: CustomStringConvertible {
+    var description: String {
+        return "HTTP1ConnectionProvider.Waiter(\(self.preference))"
+    }
+}
+
+extension HTTPClient.EventLoopPreference: CustomStringConvertible {
+    public var description: String {
+        return "\(self.preference)"
+    }
+}