What it is
Alamofire is Swift's most widely used HTTP networking library, layering request building, validation, retry and authentication over URLSession.
A Session issues requests built fluently. Responses can be validated and decoded automatically, and an interceptor can adapt or retry requests centrally.
Installation
.package(url: "https://github.com/Alamofire/Alamofire.git", from: "5.10.0")Getting started
The smallest useful thing you can do with it, and what each part means.
struct Book: Decodable { let id: Int; let title: String }
let books: [Book] = try await AF
.request("https://api.example.com/books", parameters: ["year": 1990])
.validate() // turn non-2xx into an error
.serializingDecodable([Book].self)
.value
let created: Book = try await AF
.request("https://api.example.com/books",
method: .post,
parameters: newBook,
encoder: JSONParameterEncoder.default)
.validate()
.serializingDecodable(Book.self)
.valueAdvanced usage
Where the library earns its place over a simpler alternative.
final class AuthInterceptor: RequestInterceptor {
func adapt(_ request: URLRequest, for session: Session,
completion: @escaping (Result<URLRequest, Error>) -> Void) {
var request = request
request.setValue("Bearer \(tokenStore.current)", forHTTPHeaderField: "Authorization")
completion(.success(request))
}
func retry(_ request: Request, for session: Session, dueTo error: Error,
completion: @escaping (RetryResult) -> Void) {
guard request.response?.statusCode == 401, request.retryCount < 1 else {
return completion(.doNotRetry)
}
Task {
try await tokenStore.refresh()
completion(.retry)
}
}
}
let session = Session(interceptor: AuthInterceptor())Errors and fixes
The failures you are most likely to hit, and what actually resolves them.
- responseSerializationFailed
- The response body does not match the Decodable type. Print the raw data — it is often an HTML error page.
- Requests hang after backgrounding
- A standard Session is suspended in the background. Use a background URLSessionConfiguration for transfers that must continue.
Best practices
- Always call validate(); Alamofire does not treat HTTP error statuses as failures otherwise.
- Create one Session and reuse it — a Session per request loses connection reuse.
- Put authentication in a RequestInterceptor rather than setting headers at each call site.
- Consider plain URLSession for simple needs; modern async URLSession covers a lot.
Background
Why it exists, and what it was reacting to.
Alamofire grew out of AFNetworking, the Objective-C standard. URLSession has improved considerably since, so Alamofire's value is now in what it adds around it: interceptors, automatic retry and request adaptation.