Latest 4.1.1
License Custom
Platforms ios 10.0
Dependencies PeakOperation

Peak Network

PeakNetwork is a Swift networking microframework, built on top of Session and leveraging the power of Codable.


Implement this protocol to signify that the object can be converted into a URLRequest. This allows you to package URL request information as a custom type, and perform a request using it.

A common pattern is to implement this as an extension to an enum which describes your API endpoints:

enum ApiEndpoint {
    case search(query: String)

extension ApiEndpoins: Requestable {
    var request: URLRequest {
        switch self {
        case .search(let query):
            var urlRequest = URLRequest()
            return urlRequest

 let requestable: Requestable =
    query: "Hello World"

 let request: URLRequest = requestable.request

The library also provides 2 implementations:


Creates a Requestable using a given URL.

let requestable = URLRequestable(url: url)


Creates a Requestable using a given block.

let requestable = BlockRequestable {
    return urlRequest

Network Operations

The core of PeakNetwork is made up of Operation subclasses which wrap a URLSessionTask. These are built on top of RetryingOperation from PeakOperation.

Each of these operations accepts a Requestable, converts it to a URLRequest, and then performs it on the shared or provided URLSession. These operations all conform to ProducesResult from PeakOperation, so they produce a Result and can therefore be chained, potentially with database import operations or similar.

DecodableOperation (Decodable)

This operation will attept to parse the URLResponse‘s as the provided Decodable type. For example, given the struct:

struct Item: Decodable {
    let name: String

and a JSON body of the form:

    "name": "PeakNetwork"

you can request a item from your server like so:

let networkOperation = DecodableOperation<Item>(requestable)
networkOperation.addResultBlock { result in
    // The result of the operation will be 
    // .success(Item) or .failure(error)
    let item = try? result.resolve()


A list of Items can be requested with the operation DecodableOperation<[Item]> – the generic behaviour matches that of Decoder and Encoder, as they are used internally.

DecodableResponseOperation (Decodable, HTTPURLResponse)

Identical to DecodableOperation, but adds the raw URLResponse to the operation’s Result, in case you need to inspect the status code or other property:

let networkOperation = DecodableResponseOperation<[Item]>(requestable)
networkOperation.addResultBlock { result in
    let (items, response) = try? result.resolve()

URLResponseOperation (HTTPURLResponse)

This operation performs the request and sets its result to the raw URLResponse. No other parsing is performed.

You may want to use this when you only care about the returned status code.

DataResponseOperation (Data, HTTPURLResponse)

This operation performs the request and sets its result to the raw URLResponse as well as the returned Data. No other parsing is performed.

ImageResponseOperation (UIImage, HTTPURLResponse)

This operation performs the request and sets its result to the raw URLResponse and converts the returned Data to a UIImage.


ImageController manages starting, cancelling, and mapping of ImageResponseOperations. This allows remote images to be easily set on UI elements.

let controller = ImageController()
controller.getImage(requestable), object: context) { image, context, source in
    // use image

You can use any NSObject as the context parameter – it will be used as a unique key for the request.

It is recommended to use the UI element (such as a UIImageView) as the context – that way, you are passed the element in the block, and any repeated requests for the same UI element are cancelled (for example, when reusing a UITableViewCell).

It has several optimisations to reduce memory usage. If you share an instance of the controller, then repeated requests for the same image will be combined into one, even if the first request has not completed yet.

let imageView1 = ...
let imageView2 = ...

    object: imageView1
) { image, view, source in
    // this imageview requests it first

    object: imageView2
) { image, view, source in
    // but both get the same UIImage delivered at the same time

Extensions are provided for UIImageView and UIButton to simplify usage further. These use ImageController.sharedInstance, which can be configured.

ImageController.sharedInstance = ImageController() // optional

Certificate Pinning

Certificate/SSL pinning can be used to ensure that an app communicates only with a designated server, avoiding MITM attacks using mis-issued or otherwise fraudulent certificates.

PeakNetwork provides CertificatePinningSessionDelegate which you can use with any URLSession.

All that you need to do is add the valid certificates to your bundle with a file name corresponding to the domain you want to pin; for example, for connections to After that, just create the delegate and set it on your URLSession:

let delegate = CertificatePinningSessionDelegate()

let urlSession = URLSession(
    configuration: URLSessionConfiguration.default, 
    delegate: certificatePinningSessionDelegate, 
    delegateQueue: nil

If a certificate is missing, the terminal command to fetch it will be printed to the console:

openssl s_client -showcerts -connect DOMAIN:PORT < /dev/null | openssl x509 -outform DER > DOMAIN.cernn


You may notice that PeakNetwork does not use URLSession in its method signatures. Instead, the framework adds a protocol Session which is implemented by both Apple’s URLSession and our MockSession. It is therefore recommended to always pass a Session to your web service calls, so you can swap in a mock implementation.

By implementing this shared interface, we can easily swap out a real session, that hits the web, with a mocked one which returns responses from strings or loaded from files.

This is very useful in unit tests, for testing behaviour without hitting a real web server. You could also use it in the app target to test your UI before you have a real server, or for demo purposes.

Creating a MockSession is simple:

let session = MockSession { session in
    session.queue(response: MockResponse(statusCode: .ok))

let networkOperation = URLResponseOperation(requestable, session: session)

Here, we mock a response with a 200 status, and nothing else. This is the minimum MockResponse we can make. The next time a request is made using this session, the mock response will be returned. Once all the responses have been used, a fatal error will occur.

In this next example, we queue up 2 responses: a dictionary, which will be delivered to the next request as JSON data, and an error. They will be returned in the order they are queued:

session.queue(response: MockResponse(json: ["name" : "Peak"], statusCode: .ok))
session.queue(response: MockResponse(statusCode: .internalServerError, sticky: true))

In the previous examples we return the response regardless of the request made. If you provide a block, you can inspect the request and decide if you should respond. This example is only returned if the URL is for a resource at

session.queue(response: MockResponse(statusCode: .badGateway) { request in 
    return request.url?.host == "" 

We can also load JSON from files in the bundle:

session.queue(response: MockResponse(fileName: "searchResults", statusCode: .ok, sticky: true) { request in 
    return request.url?.absoluteString.contains("search") 

Here we also set sticky: true. This means that the response is nt consumed, and multiple requests will receive this same response.

There are many other options and combinations of arguments for MockResponse.


Please see the included sample project (Examples/PeakNetworkExamples.xcworkspace) for examples and a suggested structure for your networking code.

Please see the tests for further examples.

Getting Started


  • Using Cocoapods, add pod 'PeakNetwork' to your Podfile.
  • import PeakNetwork where necessary.


Please read for details on our code of conduct, and the process for submitting pull requests to us.


We use SemVer for versioning.


This project is licensed under the MIT License – see the file for details


Peak Framework

The Peak Framework is a collection of open-source microframeworks created by the team at 3Squared, named for the Peak District. It is made up of:

Name Description
PeakResult A simple Result type.
PeakOperation Provides enhancement and conveniences to Operation, making use of the Result type.

Latest podspec

    "name": "PeakNetwork",
    "version": "4.1.1",
    "summary": "A collection of classes to aid performing network operations.",
    "homepage": "",
    "license": {
        "type": "Custom",
        "file": ""
    "authors": {
        "Sam Oakley": "[email protected]"
    "platforms": {
        "ios": "10.0"
    "source": {
        "git": "",
        "tag": "4.1.1"
    "source_files": [
    "dependencies": {
        "PeakOperation": []
    "swift_version": "4.2"

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