Such an approach can be used to abstract away server-side inconsistencies and provide type-safe routing, as well as manage authentication credentials and other state. Most web services these days are behind some sort of authentication system. One of the more common ones today is OAuth. This generally involves generating an access token authorizing your application or user to call the various supported web services. While creating these initial access tokens can be laborsome, it can be even more complicated when your access token expires and you need to fetch a new one.
There are many thread-safety issues that need to be considered. The RequestAdapter and RequestRetrier protocols were created to make it much easier to create a thread-safe authentication system for a specific set of web services. The RequestAdapter protocol allows each Request made on a SessionManager to be inspected and adapted before being created.
One very specific way to use an adapter is to append an Authorization header to requests behind a certain type of authentication. The RequestRetrier protocol allows a Request that encountered an Error while being executed to be retried. When using both the RequestAdapter and RequestRetrier protocols together, you can create credential refresh systems for OAuth1, OAuth2, Basic Auth and even exponential backoff retry policies.
The possibilities are endless. It is merely an example demonstrating how one could use the RequestAdapter in conjunction with the RequestRetrier to create a thread-safe refresh system.
To reiterate, do NOT copy this sample code and drop it into a production application. This is merely an example. Each authentication system must be tailored to a particular platform and authentication type. Once the OAuth2Handler is applied as both the adapter and retrier for the SessionManager , it will handle an invalid access token error by automatically refreshing the access token and retrying all failed requests in the same order they failed.
If you needed them to execute in the same order they were created, you could sort them by their task identifiers. The example above only checks for a response code which is not nearly robust enough, but does demonstrate how one could check for an invalid access token error. In a production application, one would want to check the realm and most likely the www-authenticate header response although it depends on the OAuth2 implementation. Another important note is that this authentication system could be shared between multiple session managers.
For example, you may need to use both a default and ephemeral session configuration for the same set of web services. The example above allows the same oauthHandler instance to be shared across multiple session managers to manage the single refresh flow. There are two basic options: passing existing errors along unmodified, to be dealt with at response time; or, wrapping all errors in an Error type specific to your app.
Alamofire provides built-in response serialization for strings, JSON, and property lists, but others can be added in extensions on Alamofire. The same approach can also be used to handle endpoints that return a representation of a collection of objects:. Using a secure HTTPS connection when communicating with servers and web services is an important step in securing sensitive data. While this guarantees the certificate chain is valid, it does not prevent man-in-the-middle MITM attacks or other potential vulnerabilities.
In order to mitigate MITM attacks, applications dealing with sensitive customer data or financial information should use certificate or public key pinning provided by the ServerTrustPolicy. There are many different cases of server trust evaluation giving you complete control over the validation process:. The ServerTrustPolicyManager is responsible for storing an internal mapping of server trust policies to a particular host.
This allows Alamofire to evaluate each host against a different server trust policy. Make sure to keep a reference to the new SessionManager instance, otherwise your requests will all get cancelled when your sessionManager is deallocated. If you find yourself needing more flexible server trust policy matching behavior i. Setting the value to true will cause the server trust evaluation to verify that hostname in the certificate matches the hostname of the challenge.
If they do not match, evaluation will fail. A validateHost value of false will still evaluate the full certificate chain, but will not validate the hostname of the leaf certificate. It is recommended that validateHost always be set to true in production environments. Pinning certificates and public keys both have the option of validating the certificate chain using the validateCertificateChain parameter.
By setting this value to true , the full certificate chain will be evaluated in addition to performing a byte equality check against the pinned certificates or public keys.
A value of false will skip the certificate chain validation, but will still perform the byte equality check. There are several cases where it may make sense to disable certificate chain validation.
The most common use cases for disabling validation are self-signed and expired certificates. The evaluation would always fail in both of these cases, but the byte equality check will still ensure you are receiving the certificate you expect from the server. It is recommended that validateCertificateChain always be set to true in production environments. If you run into this problem high probability with self-signed certificates , you can work around this issue by adding the following to your Info.
In certain cases, it will need to be set to NO. Once the challenge callbacks are being called, the ServerTrustPolicyManager will take over the server trust evaluation. Make sure to remember to retain the manager in the above example, or no status changes will be reported. There are some important things to remember when using network reachability to determine what to do next.
Alamofire is named after the Alamo Fire flower , a hybrid variant of the Bluebonnet, the official state flower of Texas. Simple, static data such as paths, parameters and common headers belong in the Router. Dynamic data such as an Authorization header whose value can changed based on an authentication system belongs in a RequestAdapter. When a Request is retried, the original request is not rebuilt meaning the Router will not be called again.
The RequestAdapter is called again allowing the dynamic data to be updated on the original request before retrying the Request. To get the table view to show the content, you must make some further changes. Here, you set up the cell with the film name and episode ID, using the properties provided via Displayable.
This property does not contain all of the starship data, but rather an array of endpoints to the starship data. This is a common pattern programmers use to provide access to data without providing more data than necessary. Instead, the server sends you a list of endpoints for each starship so that if you want the starship data, you can fetch it. Before fetching any starships, you first need a new data model to handle the starship data. Your next step is to create one. In the Networking group, add a new Swift file.
Name it Starship. As with the other data models, you simply list all the response data you want to use, along with any relevant coding keys.
You also want to be able to display information about individual ships, so Starship must conform to Displayable. Add the following at the end of the file:. Just like you did with Film before, this extension allows DetailViewController to get the correct labels and values from the model itself. Open DetailViewController. Now that you have your helper built, you need to actually fetch the list of starships from a film.
Add the following inside your extension:. Build and run, then tap any film. Neat, right? The app is starting to look pretty solid. For the search to work, you need a list of the starships that match the search criteria.
To accomplish this, you need to send the search criteria to the endpoint for getting starships. The swapi. To do this, you use a key of search with the search criteria as the value.
But before you dive into that, you need to set up a new model called Starships so that you can decode the response just like you do with the other responses.
Create a new Swift file in the Networking group. Name it Starships. Next, open MainTableViewController. This code gets the text typed into the search bar and calls the new searchStarships for: method you just implemented. When the user cancels a search, you want to redisplay the list of films. Add the following property at the top of the class to cache the list of films:. Next, add the following code after the guard statement in fetchFilms :. Here, you remove any search text entered, hide the keyboard using resignFirstResponder and reload the table view, which causes it to show films again.
Search for wing. If you tap one of the ships, the list of films that ship appears in is empty. This is easy to fix thanks to all the work you did before. Right now, it only knows how to fetch the list associated with a film. You need to fetch the list for a starship. Add the following just before the default: label in the switch statement:.
Alamofire support different ways on how to handle a response. A response is expected to provide the client with the resource it requested, or inform the client that the action it requested has been carried out; or else to inform the client that an error occurred in processing its request.
This basic response does not evaluate any of the response data it just forwards information directly from URLSessionDelegate. Think of it as the Alamofire equivalent of cURL to execute a request. The responseData handler uses a DataResponseSerializer to extract and validate the Data returned by the server. The responseString handler uses a StringResponseSerializer to convert the Data returned by the server into a String with the specified encoding.
The responseDecodable handler uses a DecodableResponseSerializer to convert the Data returned by the server into the passed Decodable type using the specified DataDecoder. Alamofire supports multiple ways of handling data, some data is fine by just fetching by memory, but for larger sets of data Session.
Basic fetching of an image by memory, it is not saved and will require loading again if being fetched again. Uploading data is somewhat easy, you just need to specify what kind of Data you are sending and let alamofire do the rest, it works the same as a POST.
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