Square API API in Swift

Square API API in Swift

This guide shows you how to integrate the Square API into your Swift application. Payments, Catalog, Orders, Customers, and Inventory APIs for omnichannel commerce.

Prerequisites

Installation

// Use URLSession (built-in) or Swift Package Manager:
// .package(url: "https://github.com/Alamofire/Alamofire", from: "5.0.0")

Basic Usage

import Foundation

let apiKey = ProcessInfo.processInfo.environment["API_KEY"] ?? "YOUR_API_KEY"
let baseURL = "https://api.squareup.com"
let url = URL(string: "\(baseURL)/v1/resources")!

var request = URLRequest(url: url)
request.httpMethod = "GET"
request.setValue("Bearer \(apiKey)", forHTTPHeaderField: "Authorization")
request.setValue("application/json", forHTTPHeaderField: "Content-Type")

let task = URLSession.shared.dataTask(with: request) { data, response, error in
    if let error = error {
        print("Error: \(error)")
        return
    }
    if let httpResponse = response as? HTTPURLResponse {
        print("Status: \(httpResponse.statusCode)")
    }
    if let data = data, let body = String(data: data, encoding: .utf8) {
        print(body)
    }
}

task.resume()
RunLoop.main.run(until: Date(timeIntervalSinceNow: 10))

Error Handling

import Foundation

func callAPIWithRetry(url: URL, headers: [String: String]) {
    func attemptRequest() {
        var request = URLRequest(url: url)
        request.httpMethod = "GET"
        for (k, v) in headers { request.setValue(v, forHTTPHeaderField: k) }
        URLSession.shared.dataTask(with: request) { data, response, error in
            if let error = error { print("Error: \(error)"); return }
            if let httpResponse = response as? HTTPURLResponse {
                if httpResponse.statusCode == 429 {
                    print("Rate limited. Waiting 60s...")
                    DispatchQueue.global().asyncAfter(deadline: .now() + .seconds(60)) { attemptRequest() }
                    return
                }
                print("Status: \(httpResponse.statusCode)")
            }
            if let data = data, let body = String(data: data, encoding: .utf8) { print(body) }
        }.resume()
    }
    attemptRequest()
    RunLoop.main.run(until: Date(timeIntervalSinceNow: 60))
}

let apiKey = ProcessInfo.processInfo.environment["API_KEY"] ?? "YOUR_API_KEY"
let url = URL(string: "https://api.squareup.com/v1/resources")!
callAPIWithRetry(url: url, headers: ["Authorization": "Bearer \(apiKey)", "Content-Type": "application/json"])

Advanced Usage

import Foundation

class SquareClient {
    let apiKey: String
    let baseURL: String
    let session: URLSession

    init(apiKey: String, baseURL: String = "https://api.squareup.com") {
        self.apiKey = apiKey
        self.baseURL = baseURL.hasSuffix("/") ? String(baseURL.dropLast()) : baseURL
        self.session = URLSession.shared
    }

    func request(method: String, path: String, completion: @escaping (Result<Data, Error>) -> Void) {
        let urlString = "\(baseURL)/v1\(path)"
        guard let url = URL(string: urlString) else {
            completion(.failure(NSError(domain: "InvalidURL", code: 0)))
            return
        }
        var request = URLRequest(url: url)
        request.httpMethod = method
        request.setValue("Bearer \(apiKey)", forHTTPHeaderField: "Authorization")
        request.setValue("application/json", forHTTPHeaderField: "Content-Type")
        session.dataTask(with: request) { data, response, error in
            if let error = error { completion(.failure(error)); return }
            if let httpResponse = response as? HTTPURLResponse, httpResponse.statusCode >= 400 {
                completion(.failure(NSError(domain: "APIError", code: httpResponse.statusCode))); return
            }
            completion(.success(data ?? Data()))
        }.resume()
    }

    func listResources(completion: @escaping (Result<Data, Error>) -> Void) {
        request(method: "GET", path: "/resources", completion: completion)
    }
}

let client = SquareClient(apiKey: ProcessInfo.processInfo.environment["API_KEY"] ?? "YOUR_API_KEY")
client.listResources { result in
    switch result {
    case .success(let data): print("Got \(data.count) bytes")
    case .failure(let error): print("Error: \(error)")
    }
}
RunLoop.main.run(until: Date(timeIntervalSinceNow: 10))

Best Practices

  • Store your API key in an environment variable, never in source code
  • Implement retry logic with exponential backoff for 429 and 5xx errors
  • Set reasonable timeouts (10-30 seconds) for all API calls
  • Log request IDs from response headers for debugging
  • Cache responses where appropriate to reduce API calls

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