Alamofire中Request和Response是关于网络请求请求响应，Request有四种类型data，download，upload和stream类型，stream只有在iOS9 之后才可以使用.

<pre><code>enum RequestTask { case data(TaskConvertible?, URLSessionTask?) case download(TaskConvertible?, URLSessionTask?) case upload(TaskConvertible?, URLSessionTask?) case stream(TaskConvertible?, URLSessionTask?) }</code></pre>

Request

Request初始化，保存了原始的Task任务和结束的绝对时间.
<pre><code>` init(session: URLSession, requestTask: RequestTask, error: Error? = nil) {
self.session = session

    switch requestTask {
    case .data(let originalTask, let task):
        taskDelegate = DataTaskDelegate(task: task)
        self.originalTask = originalTask
    case .download(let originalTask, let task):
        taskDelegate = DownloadTaskDelegate(task: task)
        self.originalTask = originalTask
    case .upload(let originalTask, let task):
        taskDelegate = UploadTaskDelegate(task: task)
        self.originalTask = originalTask
    case .stream(let originalTask, let task):
        taskDelegate = TaskDelegate(task: task)
        self.originalTask = originalTask
    }

    delegate.error = error
    delegate.queue.addOperation { self.endTime = CFAbsoluteTimeGetCurrent() }
}`</code></pre>

TaskConvertible协议提供了一个接口返回URLSessionTask:
<pre><code>protocol TaskConvertible { func task(session: URLSession, adapter: RequestAdapter?, queue: DispatchQueue) throws -> URLSessionTask }</code></pre>

<pre><code>`open class DataRequest: Request {

// MARK: Helper Types

struct Requestable: TaskConvertible {
    let urlRequest: URLRequest

    func task(session: URLSession, adapter: RequestAdapter?, queue: DispatchQueue) throws -> URLSessionTask {
        do {
            let urlRequest = try self.urlRequest.adapt(using: adapter)
            return queue.sync { session.dataTask(with: urlRequest) }
        } catch {
            throw AdaptError(error: error)
        }
    }
}`</code></pre>

Response

Response中提供四个重要的结构体DefaultDataResponse ，DataResponse，DefaultDownloadResponse与DownloadResponse.

DataResponse扩展实现了CustomDebugStringConvertible协议，返回值的整体输出debugDescription.
<pre><code>`extension DataResponse: CustomStringConvertible, CustomDebugStringConvertible {
/// The textual representation used when written to an output stream, which includes whether the result was a
/// success or failure.
public var description: String {
return result.debugDescription
}

/// The debug textual representation used when written to an output stream, which includes the URL request, the URL
/// response, the server data, the response serialization result and the timeline.
public var debugDescription: String {
    var output: [String] = []

    output.append(request != nil ? "[Request]: \(request!.httpMethod ?? "GET") \(request!)" : "[Request]: nil")
    output.append(response != nil ? "[Response]: \(response!)" : "[Response]: nil")
    output.append("[Data]: \(data?.count ?? 0) bytes")
    output.append("[Result]: \(result.debugDescription)")
    output.append("[Timeline]: \(timeline.debugDescription)")

    return output.joined(separator: "\n")
}

}`</code></pre>

Alamofire的开发中最常见的代码如下:
<pre><code>`Alamofire.request("https://httpbin.org/get").responseJSON { response in
print("Request: (String(describing: response.request))") // original url request
print("Response: (String(describing: response.response))") // http url response
print("Result: (response.result)") // response serialization result

if let json = response.result.value {
    print("JSON: \(json)") // serialized json response
}

if let data = response.data, let utf8Text = String(data: data, encoding: .utf8) {
    print("Data: \(utf8Text)") // original server data as UTF8 string
}

}`</code></pre>

responseJSON在Request和Response文件中都没有，将请求和响应的完美衔接的代码在ResponseSerialization.swift文件中.

<pre><code>extension DataRequest { /// Creates a response serializer that returns a JSON object result type constructed from the response data using ///JSONSerializationwith the specified reading options. /// /// - parameter options: The JSON serialization reading options. Defaults to.allowFragments`.
///
/// - returns: A JSON object response serializer.
public static func jsonResponseSerializer(
options: JSONSerialization.ReadingOptions = .allowFragments)
-> DataResponseSerializer<Any>
{
return DataResponseSerializer { _, response, data, error in
return Request.serializeResponseJSON(options: options, response: response, data: data, error: error)
}
}

/// Adds a handler to be called once the request has finished.
///
/// - parameter options:           The JSON serialization reading options. Defaults to `.allowFragments`.
/// - parameter completionHandler: A closure to be executed once the request has finished.
///
/// - returns: The request.
@discardableResult
public func responseJSON(
    queue: DispatchQueue? = nil,
    options: JSONSerialization.ReadingOptions = .allowFragments,
    completionHandler: @escaping (DataResponse<Any>) -> Void)
    -> Self
{
    return response(
        queue: queue,
        responseSerializer: DataRequest.jsonResponseSerializer(options: options),
        completionHandler: completionHandler
    )
}

}`</code></pre>

response函数实现代码:
<pre><code>`extension DataRequest {
/// Adds a handler to be called once the request has finished.
///
/// - parameter queue: The queue on which the completion handler is dispatched.
/// - parameter completionHandler: The code to be executed once the request has finished.
///
/// - returns: The request.
@discardableResult
public func response(queue: DispatchQueue? = nil, completionHandler: @escaping (DefaultDataResponse) -> Void) -> Self {
delegate.queue.addOperation {
(queue ?? DispatchQueue.main).async {
var dataResponse = DefaultDataResponse(
request: self.request,
response: self.response,
data: self.delegate.data,
error: self.delegate.error,
timeline: self.timeline
)

            dataResponse.add(self.delegate.metrics)

            completionHandler(dataResponse)
        }
    }

    return self
}

/// Adds a handler to be called once the request has finished.
///
/// - parameter queue:              The queue on which the completion handler is dispatched.
/// - parameter responseSerializer: The response serializer responsible for serializing the request, response,
///                                 and data.
/// - parameter completionHandler:  The code to be executed once the request has finished.
///
/// - returns: The request.
@discardableResult
public func response<T: DataResponseSerializerProtocol>(
    queue: DispatchQueue? = nil,
    responseSerializer: T,
    completionHandler: @escaping (DataResponse<T.SerializedObject>) -> Void)
    -> Self
{
    delegate.queue.addOperation {
        let result = responseSerializer.serializeResponse(
            self.request,
            self.response,
            self.delegate.data,
            self.delegate.error
        )

        var dataResponse = DataResponse<T.SerializedObject>(
            request: self.request,
            response: self.response,
            data: self.delegate.data,
            result: result,
            timeline: self.timeline
        )

        dataResponse.add(self.delegate.metrics)

        (queue ?? DispatchQueue.main).async { completionHandler(dataResponse) }
    }

    return self
}

}`</code></pre>

Result

网络请求不管成功与否，最终都会有响应结果，Alamofire中的网络请求结果通过Result泛型枚举来表示.
<pre><code>`public enum Result<Value> {
case success(Value)
case failure(Error)

/// Returns `true` if the result is a success, `false` otherwise.
public var isSuccess: Bool {
    switch self {
    case .success:
        return true
    case .failure:
        return false
    }
}

/// Returns `true` if the result is a failure, `false` otherwise.
public var isFailure: Bool {
    return !isSuccess
}

/// Returns the associated value if the result is a success, `nil` otherwise.
public var value: Value? {
    switch self {
    case .success(let value):
        return value
    case .failure:
        return nil
    }
}

/// Returns the associated error value if the result is a failure, `nil` otherwise.
public var error: Error? {
    switch self {
    case .success:
        return nil
    case .failure(let error):
        return error
    }
}

}`</code></pre>

Result结果解包:
<pre><code>public func unwrap() throws -> Value { switch self { case .success(let value): return value case .failure(let error): throw error } }</code></pre>

Result扩展的map，flatMap函数:
<pre><code>` public func map<T>(_ transform: (Value) -> T) -> Result<T> {
switch self {
case .success(let value):
return .success(transform(value))
case .failure(let error):
return .failure(error)
}
}

/// Evaluates the specified closure when the `Result` is a success, passing the unwrapped value as a parameter.
///
/// Use the `flatMap` method with a closure that may throw an error. For example:
///
///     let possibleData: Result<Data> = .success(Data(...))
///     let possibleObject = possibleData.flatMap {
///         try JSONSerialization.jsonObject(with: $0)
///     }
///
/// - parameter transform: A closure that takes the success value of the instance.
///
/// - returns: A `Result` containing the result of the given closure. If this instance is a failure, returns the
///            same failure.
public func flatMap<T>(_ transform: (Value) throws -> T) -> Result<T> {
    switch self {
    case .success(let value):
        do {
            return try .success(transform(value))
        } catch {
            return .failure(error)
        }
    case .failure(let error):
        return .failure(error)
    }
}`</code></pre>

Swift水平有限，如有不当，欢迎多多指正~