Nearby user discovery through MultipeerConnectivity in Swift

Codable+JSONObjects.swift

import Foundation

/**
 Extensions that allow `JSONEncoder` and `JSONDecoder` to produce/consume dictionaries, instead of simply raw data.
 */

extension JSONEncoder {
    func encodeAsJSONObject<T>(_ value: T) throws -> Any where T: Encodable {
        return try JSONSerialization.jsonObject(with: try encode(value), options: [])
    }
}

extension JSONDecoder {
    func decode<T>(_ type: T.Type, fromJSONObject object: Any) throws -> T where T: Decodable {
        return try decode(T.self, from: try JSONSerialization.data(withJSONObject: object, options: []))
    }
}

PeerConnector.swift

import Foundation
import MultipeerConnectivity

typealias DiscoveryInfo = [String: String]

protocol PeerConnectorDelegate: class {
    func peerConnectorFoundPeer(id: MCPeerID, withDiscoveryInfo info: DiscoveryInfo?)
    
    func peerConnectorLostPeer(id: MCPeerID)
}

final class PeerConnector: NSObject {
    private let peerID: MCPeerID
    private let serviceAdvertiser: MCNearbyServiceAdvertiser?
    private let serviceBrowser: MCNearbyServiceBrowser
    
    // MARK: - Inputs
    
    weak var delegate: PeerConnectorDelegate?
    
    // MARK: - Initialization
    
    init(displayName: String, discoveryInfo: DiscoveryInfo?) {
        self.peerID = MCPeerID(displayName: displayName)
        
        // Must be a unique, at most 15 characters long, and contain only ASCII lowercase letters, numbers and hyphens
        let serviceType = "my-service"

        if let discoveryInfo = discoveryInfo {
            serviceAdvertiser = MCNearbyServiceAdvertiser(peer: peerID, discoveryInfo: discoveryInfo, serviceType: serviceType)
        }
        else {
            serviceAdvertiser = nil
        }
        
        serviceBrowser = MCNearbyServiceBrowser(peer: peerID, serviceType: serviceType)
        
        super.init()
        
        serviceBrowser.delegate = self
    }
    
    func start() {
        serviceAdvertiser?.startAdvertisingPeer()
        serviceBrowser.startBrowsingForPeers()
    }
    
    func stop() {
        serviceAdvertiser?.stopAdvertisingPeer()
        serviceBrowser.stopBrowsingForPeers()
    }
}

// MARK: - MCNearbyServiceBrowserDelegate

extension PeerConnector: MCNearbyServiceBrowserDelegate {
    func browser(_ browser: MCNearbyServiceBrowser, foundPeer peerID: MCPeerID, withDiscoveryInfo info: [String: String]?) {
        log.info("Found peer: \(peerID)")
        
        delegate?.peerConnectorFoundPeer(id: peerID, withDiscoveryInfo: info)
    }
    
    func browser(_ browser: MCNearbyServiceBrowser, didNotStartBrowsingForPeers error: Error) {
        log.warn("Did not start browsing for peers: \(error)")
    }
    
    func browser(_ browser: MCNearbyServiceBrowser, lostPeer peerID: MCPeerID) {
        log.info("Lost peer: \(peerID)")
        
        delegate?.peerConnectorLostPeer(id: peerID)
    }
}

PeerDiscoveryInfo.swift

import Foundation

struct PeerDiscoveryInfo: Codable {
    let id: String
    let firstName: String
    let lastName: String?
    let mediumAvatar: String?
    let jobTitle: String?
}

extension User {
        init?(discoveryInfo: DiscoveryInfo?) {
        guard
            let discoveryInfo = discoveryInfo,
            let peerDiscoveryInfo = try? JSONDecoder().decode(PeerDiscoveryInfo.self, fromJSONObject: discoveryInfo),
            let id = Int(peerDiscoveryInfo.id)
        else {
            return nil
        }
        
        self.init(
            id: id,
            firstName: peerDiscoveryInfo.firstName,
            lastName: peerDiscoveryInfo.lastName,
            avatar: peerDiscoveryInfo.mediumAvatar
                .map(URL.init)
                .map({ RemoteImage(medium: $0 )}),
            jobTitle: peerDiscoveryInfo.jobTitle
                .map({ JobTitle(name: $0, id: nil) })
        )
    }
    
    func toDiscoveryInfo() -> DiscoveryInfo? {
        let peerDiscoveryInfo = PeerDiscoveryInfo(
            id: String(id),
            firstName: firstName,
            lastName: lastName,
            mediumAvatar: avatar?.medium?.absoluteString,
            jobTitle: jobTitle?.name
        )

        return (try? JSONEncoder().encodeAsJSONObject(peerDiscoveryInfo))
            .flatMap({ $0 as? DiscoveryInfo })
    }
}