## Usage

### Making a Request

```swift
import Alamofire

Alamofire.request("https://httpbin.org/get")
```

### Response Handling

Handling the `Response` of a `Request` made in Alamofire involves chaining a response handler onto the `Request`.

```swift
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
    }
}
```

In the above example, the `responseJSON` handler is appended to the `Request` to be executed once the `Request` is complete. Rather than blocking execution to wait for a response from the server, a [callback](https://en.wikipedia.org/wiki/Callback_%28computer_programming%29) in the form of a closure is specified to handle the response once it's received. The result of a request is only available inside the scope of a response closure. Any execution contingent on the response or data received from the server must be done within a response closure.

> Networking in Alamofire is done _asynchronously_. Asynchronous programming may be a source of frustration to programmers unfamiliar with the concept, but there are [very good reasons](https://developer.apple.com/library/ios/qa/qa1693/_index.html) for doing it this way.

Alamofire contains five different response handlers by default including:

```swift
// Response Handler - Unserialized Response
func response(
    queue: DispatchQueue?,
    completionHandler: @escaping (DefaultDataResponse) -> Void)
    -> Self

// Response Data Handler - Serialized into Data
func responseData(
    queue: DispatchQueue?,
    completionHandler: @escaping (DataResponse<Data>) -> Void)
    -> Self

// Response String Handler - Serialized into String
func responseString(
    queue: DispatchQueue?,
    encoding: String.Encoding?,
    completionHandler: @escaping (DataResponse<String>) -> Void)
    -> Self

// Response JSON Handler - Serialized into Any
func responseJSON(
    queue: DispatchQueue?,
    completionHandler: @escaping (DataResponse<Any>) -> Void)
    -> Self

// Response PropertyList (plist) Handler - Serialized into Any
func responsePropertyList(
    queue: DispatchQueue?,
    completionHandler: @escaping (DataResponse<Any>) -> Void))
    -> Self
```

None of the response handlers perform any validation of the `HTTPURLResponse` it gets back from the server.

> For example, response status codes in the `400..<500` and `500..<600` ranges do NOT automatically trigger an `Error`. Alamofire uses [Response Validation](#response-validation) method chaining to achieve this.

#### Response Handler

The `response` handler does NOT evaluate any of the response data. It merely forwards on all information directly from the URL session delegate. It is the Alamofire equivalent of using `cURL` to execute a `Request`.

```swift
Alamofire.request("https://httpbin.org/get").response { response in
    print("Request: \(response.request)")
    print("Response: \(response.response)")
    print("Error: \(response.error)")

    if let data = response.data, let utf8Text = String(data: data, encoding: .utf8) {
    	print("Data: \(utf8Text)")
    }
}
```

> We strongly encourage you to leverage the other response serializers taking advantage of `Response` and `Result` types.

#### Response Data Handler

The `responseData` handler uses the `responseDataSerializer` (the object that serializes the server data into some other type) to extract the `Data` returned by the server. If no errors occur and `Data` is returned, the response `Result` will be a `.success` and the `value` will be of type `Data`.

```swift
Alamofire.request("https://httpbin.org/get").responseData { response in
    debugPrint("All Response Info: \(response)")

    if let data = response.result.value, let utf8Text = String(data: data, encoding: .utf8) {
    	print("Data: \(utf8Text)")
    }
}
```

#### Response String Handler

The `responseString` handler uses the `responseStringSerializer` to convert the `Data` returned by the server into a `String` with the specified encoding. If no errors occur and the server data is successfully serialized into a `String`, the response `Result` will be a `.success` and the `value` will be of type `String`.

```swift
Alamofire.request("https://httpbin.org/get").responseString { response in
    print("Success: \(response.result.isSuccess)")
    print("Response String: \(response.result.value)")
}
```

> If no encoding is specified, Alamofire will use the text encoding specified in the `HTTPURLResponse` from the server. If the text encoding cannot be determined by the server response, it defaults to `.isoLatin1`.

#### Response JSON Handler

The `responseJSON` handler uses the `responseJSONSerializer` to convert the `Data` returned by the server into an `Any` type using the specified `JSONSerialization.ReadingOptions`. If no errors occur and the server data is successfully serialized into a JSON object, the response `Result` will be a `.success` and the `value` will be of type `Any`.

```swift
Alamofire.request("https://httpbin.org/get").responseJSON { response in
    debugPrint(response)

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

> All JSON serialization is handled by the `JSONSerialization` API in the `Foundation` framework.

#### Chained Response Handlers

Response handlers can even be chained:

```swift
Alamofire.request("https://httpbin.org/get")
    .responseString { response in
        print("Response String: \(response.result.value)")
    }
    .responseJSON { response in
        print("Response JSON: \(response.result.value)")
    }
```

> It is important to note that using multiple response handlers on the same `Request` requires the server data to be serialized multiple times. Once for each response handler.

#### Response Handler Queue

Response handlers by default are executed on the main dispatch queue. However, a custom dispatch queue can be provided instead.

```swift
let utilityQueue = DispatchQueue.global(qos: .utility)

Alamofire.request("https://httpbin.org/get").responseJSON(queue: utilityQueue) { response in
    print("Executing response handler on utility queue")
}
```

### Response Validation

By default, Alamofire treats any completed request to be successful, regardless of the content of the response. Calling `validate` before a response handler causes an error to be generated if the response had an unacceptable status code or MIME type.

#### Manual Validation

```swift
Alamofire.request("https://httpbin.org/get")
    .validate(statusCode: 200..<300)
    .validate(contentType: ["application/json"])
    .responseData { response in
        switch response.result {
        case .success:
            print("Validation Successful")
        case .failure(let error):
            print(error)
        }
    }
```

#### Automatic Validation

Automatically validates status code within `200..<300` range, and that the `Content-Type` header of the response matches the `Accept` header of the request, if one is provided.

```swift
Alamofire.request("https://httpbin.org/get").validate().responseJSON { response in
    switch response.result {
    case .success:
        print("Validation Successful")
    case .failure(let error):
        print(error)
    }
}
```

### Response Caching

Response Caching is handled on the system framework level by [`URLCache`](https://developer.apple.com/reference/foundation/urlcache). It provides a composite in-memory and on-disk cache and lets you manipulate the sizes of both the in-memory and on-disk portions.

> By default, Alamofire leverages the shared `URLCache`. In order to customize it, see the [Session Manager Configurations](AdvancedUsage.md#session-manager) section.

### HTTP Methods

The `HTTPMethod` enumeration lists the HTTP methods defined in [RFC 7231 §4.3](https://tools.ietf.org/html/rfc7231#section-4.3):

```swift
public enum HTTPMethod: String {
    case options = "OPTIONS"
    case get     = "GET"
    case head    = "HEAD"
    case post    = "POST"
    case put     = "PUT"
    case patch   = "PATCH"
    case delete  = "DELETE"
    case trace   = "TRACE"
    case connect = "CONNECT"
}
```

These values can be passed as the `method` argument to the `Alamofire.request` API:

```swift
Alamofire.request("https://httpbin.org/get") // method defaults to `.get`

Alamofire.request("https://httpbin.org/post", method: .post)
Alamofire.request("https://httpbin.org/put", method: .put)
Alamofire.request("https://httpbin.org/delete", method: .delete)
```

> The `Alamofire.request` method parameter defaults to `.get`.

### Parameter Encoding

Alamofire supports three types of parameter encoding including: `URL`, `JSON` and `PropertyList`. It can also support any custom encoding that conforms to the `ParameterEncoding` protocol.

#### URL Encoding

The `URLEncoding` type creates a url-encoded query string to be set as or appended to any existing URL query string or set as the HTTP body of the URL request. Whether the query string is set or appended to any existing URL query string or set as the HTTP body depends on the `Destination` of the encoding. The `Destination` enumeration has three cases:

- `.methodDependent` - Applies encoded query string result to existing query string for `GET`, `HEAD` and `DELETE` requests and sets as the HTTP body for requests with any other HTTP method.
- `.queryString` - Sets or appends encoded query string result to existing query string.
- `.httpBody` - Sets encoded query string result as the HTTP body of the URL request.

The `Content-Type` HTTP header field of an encoded request with HTTP body is set to `application/x-www-form-urlencoded; charset=utf-8`. Since there is no published specification for how to encode collection types, the convention of appending `[]` to the key for array values (`foo[]=1&foo[]=2`), and appending the key surrounded by square brackets for nested dictionary values (`foo[bar]=baz`).

##### GET Request With URL-Encoded Parameters

```swift
let parameters: Parameters = ["foo": "bar"]

// All three of these calls are equivalent
Alamofire.request("https://httpbin.org/get", parameters: parameters) // encoding defaults to `URLEncoding.default`
Alamofire.request("https://httpbin.org/get", parameters: parameters, encoding: URLEncoding.default)
Alamofire.request("https://httpbin.org/get", parameters: parameters, encoding: URLEncoding(destination: .methodDependent))

// https://httpbin.org/get?foo=bar
```

##### POST Request With URL-Encoded Parameters

```swift
let parameters: Parameters = [
    "foo": "bar",
    "baz": ["a", 1],
    "qux": [
        "x": 1,
        "y": 2,
        "z": 3
    ]
]

// All three of these calls are equivalent
Alamofire.request("https://httpbin.org/post", method: .post, parameters: parameters)
Alamofire.request("https://httpbin.org/post", method: .post, parameters: parameters, encoding: URLEncoding.default)
Alamofire.request("https://httpbin.org/post", method: .post, parameters: parameters, encoding: URLEncoding.httpBody)

// HTTP body: foo=bar&baz[]=a&baz[]=1&qux[x]=1&qux[y]=2&qux[z]=3
```

##### Configuring the Encoding of `Bool` Parameters

The `URLEncoding.BoolEncoding` enumeration provides the following methods for encoding `Bool` parameters:

- `.numeric` - Encode `true` as `1` and `false` as `0`.
- `.literal` - Encode `true` and `false` as string literals.

By default, Alamofire uses the `.numeric` encoding.

You can create your own `URLEncoding` and specify the desired `Bool` encoding in the initializer:

```swift
let encoding = URLEncoding(boolEncoding: .literal)
```

##### Configuring the Encoding of `Array` Parameters

The `URLEncoding.ArrayEncoding` enumeration provides the following methods for encoding `Array` parameters:

- `.brackets` - An empty set of square brackets is appended to the key for every value.
- `.noBrackets` - No brackets are appended. The key is encoded as is.

By default, Alamofire uses the `.brackets` encoding, where `foo=[1,2]` is encoded as `foo[]=1&foo[]=2`.

Using the `.noBrackets` encoding will encode `foo=[1,2]` as `foo=1&foo=2`.

You can create your own `URLEncoding` and specify the desired `Array` encoding in the initializer:

```swift
let encoding = URLEncoding(arrayEncoding: .noBrackets)
```

#### JSON Encoding

The `JSONEncoding` type creates a JSON representation of the parameters object, which is set as the HTTP body of the request. The `Content-Type` HTTP header field of an encoded request is set to `application/json`.

##### POST Request with JSON-Encoded Parameters

```swift
let parameters: Parameters = [
    "foo": [1,2,3],
    "bar": [
        "baz": "qux"
    ]
]

// Both calls are equivalent
Alamofire.request("https://httpbin.org/post", method: .post, parameters: parameters, encoding: JSONEncoding.default)
Alamofire.request("https://httpbin.org/post", method: .post, parameters: parameters, encoding: JSONEncoding(options: []))

// HTTP body: {"foo": [1, 2, 3], "bar": {"baz": "qux"}}
```

#### Property List Encoding

The `PropertyListEncoding` uses `PropertyListSerialization` to create a plist representation of the parameters object, according to the associated format and write options values, which is set as the body of the request. The `Content-Type` HTTP header field of an encoded request is set to `application/x-plist`.

#### Custom Encoding

In the event that the provided `ParameterEncoding` types do not meet your needs, you can create your own custom encoding. Here's a quick example of how you could build a custom `JSONStringArrayEncoding` type to encode a JSON string array onto a `Request`.

```swift
struct JSONStringArrayEncoding: ParameterEncoding {
    private let array: [String]

    init(array: [String]) {
        self.array = array
    }

    func encode(_ urlRequest: URLRequestConvertible, with parameters: Parameters?) throws -> URLRequest {
        var urlRequest = try urlRequest.asURLRequest()

        let data = try JSONSerialization.data(withJSONObject: array, options: [])

        if urlRequest.value(forHTTPHeaderField: "Content-Type") == nil {
            urlRequest.setValue("application/json", forHTTPHeaderField: "Content-Type")
        }

        urlRequest.httpBody = data

        return urlRequest
    }
}
```

#### Manual Parameter Encoding of a URLRequest

The `ParameterEncoding` APIs can be used outside of making network requests.

```swift
let url = URL(string: "https://httpbin.org/get")!
var urlRequest = URLRequest(url: url)

let parameters: Parameters = ["foo": "bar"]
let encodedURLRequest = try URLEncoding.queryString.encode(urlRequest, with: parameters)
```

### HTTP Headers

Adding a custom HTTP header to a `Request` is supported directly in the global `request` method. This makes it easy to attach HTTP headers to a `Request` that can be constantly changing.

```swift
let headers: HTTPHeaders = [
    "Authorization": "Basic QWxhZGRpbjpvcGVuIHNlc2FtZQ==",
    "Accept": "application/json"
]

Alamofire.request("https://httpbin.org/headers", headers: headers).responseJSON { response in
    debugPrint(response)
}
```

> For HTTP headers that do not change, it is recommended to set them on the `URLSessionConfiguration` so they are automatically applied to any `URLSessionTask` created by the underlying `URLSession`. For more information, see the [Session Manager Configurations](AdvancedUsage.md#session-manager) section.

The default Alamofire `SessionManager` provides a default set of headers for every `Request`. These include:

- `Accept-Encoding`, which defaults to `gzip;q=1.0, compress;q=0.5`, per [RFC 7230 §4.2.3](https://tools.ietf.org/html/rfc7230#section-4.2.3).
- `Accept-Language`, which defaults to up to the top 6 preferred languages on the system, formatted like `en;q=1.0`, per [RFC 7231 §5.3.5](https://tools.ietf.org/html/rfc7231#section-5.3.5).
- `User-Agent`, which contains versioning information about the current app. For example: `iOS Example/1.0 (com.alamofire.iOS-Example; build:1; iOS 10.0.0) Alamofire/4.0.0`, per [RFC 7231 §5.5.3](https://tools.ietf.org/html/rfc7231#section-5.5.3).

If you need to customize these headers, a custom `URLSessionConfiguration` should be created, the `defaultHTTPHeaders` property updated and the configuration applied to a new `SessionManager` instance.

### Authentication

Authentication is handled on the system framework level by [`URLCredential`](https://developer.apple.com/reference/foundation/nsurlcredential) and [`URLAuthenticationChallenge`](https://developer.apple.com/reference/foundation/urlauthenticationchallenge).

**Supported Authentication Schemes**

- [HTTP Basic](https://en.wikipedia.org/wiki/Basic_access_authentication)
- [HTTP Digest](https://en.wikipedia.org/wiki/Digest_access_authentication)
- [Kerberos](https://en.wikipedia.org/wiki/Kerberos_%28protocol%29)
- [NTLM](https://en.wikipedia.org/wiki/NT_LAN_Manager)

#### HTTP Basic Authentication

The `authenticate` method on a `Request` will automatically provide a `URLCredential` to a `URLAuthenticationChallenge` when appropriate:

```swift
let user = "user"
let password = "password"

Alamofire.request("https://httpbin.org/basic-auth/\(user)/\(password)")
    .authenticate(user: user, password: password)
    .responseJSON { response in
        debugPrint(response)
    }
```

Depending upon your server implementation, an `Authorization` header may also be appropriate:

```swift
let user = "user"
let password = "password"

var headers: HTTPHeaders = [:]

if let authorizationHeader = Request.authorizationHeader(user: user, password: password) {
    headers[authorizationHeader.key] = authorizationHeader.value
}

Alamofire.request("https://httpbin.org/basic-auth/user/password", headers: headers)
    .responseJSON { response in
        debugPrint(response)
    }
```

#### Authentication with URLCredential

```swift
let user = "user"
let password = "password"

let credential = URLCredential(user: user, password: password, persistence: .forSession)

Alamofire.request("https://httpbin.org/basic-auth/\(user)/\(password)")
    .authenticate(usingCredential: credential)
    .responseJSON { response in
        debugPrint(response)
    }
```

> It is important to note that when using a `URLCredential` for authentication, the underlying `URLSession` will actually end up making two requests if a challenge is issued by the server. The first request will not include the credential which "may" trigger a challenge from the server. The challenge is then received by Alamofire, the credential is appended and the request is retried by the underlying `URLSession`.

### Downloading Data to a File

Requests made in Alamofire that fetch data from a server can download the data in-memory or on-disk. The `Alamofire.request` APIs used in all the examples so far always downloads the server data in-memory. This is great for smaller payloads because it's more efficient, but really bad for larger payloads because the download could run your entire application out-of-memory. Because of this, you can also use the `Alamofire.download` APIs to download the server data to a temporary file on-disk.

> This will only work on `macOS` as is. Other platforms don't allow access to the filesystem outside of your app's sandbox. To download files on other platforms, see the [Download File Destination](#download-file-destination) section.

```swift
Alamofire.download("https://httpbin.org/image/png").responseData { response in
    if let data = response.result.value {
        let image = UIImage(data: data)
    }
}
```

> The `Alamofire.download` APIs should also be used if you need to download data while your app is in the background. For more information, please see the [Session Manager Configurations](AdvancedUsage.md#session-manager) section.

#### Download File Destination

You can also provide a `DownloadFileDestination` closure to move the file from the temporary directory to a final destination. Before the temporary file is actually moved to the `destinationURL`, the `DownloadOptions` specified in the closure will be executed. The two currently supported `DownloadOptions` are:

- `.createIntermediateDirectories` - Creates intermediate directories for the destination URL if specified.
- `.removePreviousFile` - Removes a previous file from the destination URL if specified.

```swift
let destination: DownloadRequest.DownloadFileDestination = { _, _ in
    let documentsURL = FileManager.default.urls(for: .documentDirectory, in: .userDomainMask)[0]
    let fileURL = documentsURL.appendingPathComponent("pig.png")

    return (fileURL, [.removePreviousFile, .createIntermediateDirectories])
}

Alamofire.download(urlString, to: destination).response { response in
    print(response)

    if response.error == nil, let imagePath = response.destinationURL?.path {
        let image = UIImage(contentsOfFile: imagePath)
    }
}
```

You can also use the suggested download destination API.

```swift
let destination = DownloadRequest.suggestedDownloadDestination(for: .documentDirectory)
Alamofire.download("https://httpbin.org/image/png", to: destination)
```

#### Download Progress

Many times it can be helpful to report download progress to the user. Any `DownloadRequest` can report download progress using the `downloadProgress` API.

```swift
Alamofire.download("https://httpbin.org/image/png")
    .downloadProgress { progress in
        print("Download Progress: \(progress.fractionCompleted)")
    }
    .responseData { response in
        if let data = response.result.value {
            let image = UIImage(data: data)
        }
    }
```

The `downloadProgress` API also takes a `queue` parameter which defines which `DispatchQueue` the download progress closure should be called on.

```swift
let utilityQueue = DispatchQueue.global(qos: .utility)

Alamofire.download("https://httpbin.org/image/png")
    .downloadProgress(queue: utilityQueue) { progress in
        print("Download Progress: \(progress.fractionCompleted)")
    }
    .responseData { response in
        if let data = response.result.value {
            let image = UIImage(data: data)
        }
    }
```

#### Resuming a Download

If a `DownloadRequest` is cancelled or interrupted, the underlying URL session may generate resume data for the active `DownloadRequest`. If this happens, the resume data can be re-used to restart the `DownloadRequest` where it left off. The resume data can be accessed through the download response, then reused when trying to restart the request.

> **IMPORTANT:** On some versions of all Apple platforms (iOS 10 - 10.2, macOS 10.12 - 10.12.2, tvOS 10 - 10.1, watchOS 3 - 3.1.1), `resumeData` is broken on background URL session configurations. There's an underlying bug in the `resumeData` generation logic where the data is written incorrectly and will always fail to resume the download. For more information about the bug and possible workarounds, please see this [Stack Overflow post](https://stackoverflow.com/a/39347461/1342462).

```swift
class ImageRequestor {
    private var resumeData: Data?
    private var image: UIImage?

    func fetchImage(completion: (UIImage?) -> Void) {
        guard image == nil else { completion(image) ; return }

        let destination: DownloadRequest.DownloadFileDestination = { _, _ in
            let documentsURL = FileManager.default.urls(for: .documentDirectory, in: .userDomainMask)[0]
            let fileURL = documentsURL.appendingPathComponent("pig.png")

            return (fileURL, [.removePreviousFile, .createIntermediateDirectories])
        }

        let request: DownloadRequest

        if let resumeData = resumeData {
            request = Alamofire.download(resumingWith: resumeData)
        } else {
            request = Alamofire.download("https://httpbin.org/image/png")
        }

        request.responseData { response in
            switch response.result {
            case .success(let data):
                self.image = UIImage(data: data)
            case .failure:
                self.resumeData = response.resumeData
            }
        }
    }
}
```

### Uploading Data to a Server

When sending relatively small amounts of data to a server using JSON or URL encoded parameters, the `Alamofire.request` APIs are usually sufficient. If you need to send much larger amounts of data from a file URL or an `InputStream`, then the `Alamofire.upload` APIs are what you want to use.

> The `Alamofire.upload` APIs should also be used if you need to upload data while your app is in the background. For more information, please see the [Session Manager Configurations](AdvancedUsage.md#session-manager) section.

#### Uploading Data

```swift
let imageData = UIImagePNGRepresentation(image)!

Alamofire.upload(imageData, to: "https://httpbin.org/post").responseJSON { response in
    debugPrint(response)
}
```

#### Uploading a File

```swift
let fileURL = Bundle.main.url(forResource: "video", withExtension: "mov")

Alamofire.upload(fileURL, to: "https://httpbin.org/post").responseJSON { response in
    debugPrint(response)
}
```

#### Uploading Multipart Form Data

```swift
Alamofire.upload(
    multipartFormData: { multipartFormData in
        multipartFormData.append(unicornImageURL, withName: "unicorn")
        multipartFormData.append(rainbowImageURL, withName: "rainbow")
    },
    to: "https://httpbin.org/post",
    encodingCompletion: { encodingResult in
    	switch encodingResult {
    	case .success(let upload, _, _):
            upload.responseJSON { response in
                debugPrint(response)
            }
    	case .failure(let encodingError):
    	    print(encodingError)
    	}
    }
)
```

#### Upload Progress

While your user is waiting for their upload to complete, sometimes it can be handy to show the progress of the upload to the user. Any `UploadRequest` can report both upload progress and download progress of the response data using the `uploadProgress` and `downloadProgress` APIs.

```swift
let fileURL = Bundle.main.url(forResource: "video", withExtension: "mov")

Alamofire.upload(fileURL, to: "https://httpbin.org/post")
    .uploadProgress { progress in // main queue by default
        print("Upload Progress: \(progress.fractionCompleted)")
    }
    .downloadProgress { progress in // main queue by default
        print("Download Progress: \(progress.fractionCompleted)")
    }
    .responseJSON { response in
        debugPrint(response)
    }
```

### Statistical Metrics

#### Timeline

Alamofire collects timings throughout the lifecycle of a `Request` and creates a `Timeline` object exposed as a property on all response types.

```swift
Alamofire.request("https://httpbin.org/get").responseJSON { response in
    print(response.timeline)
}
```

The above reports the following `Timeline` info:

- `Latency`: 0.428 seconds
- `Request Duration`: 0.428 seconds
- `Serialization Duration`: 0.001 seconds
- `Total Duration`: 0.429 seconds

#### URL Session Task Metrics

In iOS and tvOS 10 and macOS 10.12, Apple introduced the new [URLSessionTaskMetrics](https://developer.apple.com/reference/foundation/urlsessiontaskmetrics) APIs. The task metrics encapsulate some fantastic statistical information about the request and response execution. The API is very similar to the `Timeline`, but provides many more statistics that Alamofire doesn't have access to compute. The metrics can be accessed through any response type.

```swift
Alamofire.request("https://httpbin.org/get").responseJSON { response in
    print(response.metrics)
}
```

It's important to note that these APIs are only available on iOS and tvOS 10 and macOS 10.12. Therefore, depending on your deployment target, you may need to use these inside availability checks:

```swift
Alamofire.request("https://httpbin.org/get").responseJSON { response in
    if #available(iOS 10.0, *) {
        print(response.metrics)
    }
}
```

### cURL Command Output

Debugging platform issues can be frustrating. Thankfully, Alamofire `Request` objects conform to both the `CustomStringConvertible` and `CustomDebugStringConvertible` protocols to provide some VERY helpful debugging tools.

#### CustomStringConvertible

```swift
let request = Alamofire.request("https://httpbin.org/ip")

print(request)
// GET https://httpbin.org/ip (200)
```

#### CustomDebugStringConvertible

```swift
let request = Alamofire.request("https://httpbin.org/get", parameters: ["foo": "bar"])
debugPrint(request)
```

Outputs:

```bash
$ curl -i \
    -H "User-Agent: Alamofire/4.0.0" \
    -H "Accept-Encoding: gzip;q=1.0, compress;q=0.5" \
    -H "Accept-Language: en;q=1.0,fr;q=0.9,de;q=0.8,zh-Hans;q=0.7,zh-Hant;q=0.6,ja;q=0.5" \
    "https://httpbin.org/get?foo=bar"
```

---