Rork × Notification Service Extension 本番実装ガイド — 画像付き通知・暗号化ペイロード・通知の動的書き換えで開封率を底上げする

import UserNotifications
 
class NotificationService: UNNotificationServiceExtension {
    var contentHandler: ((UNNotificationContent) -> Void)?
    var bestAttemptContent: UNMutableNotificationContent?
 
    override func didReceive(
        _ request: UNNotificationRequest,
        withContentHandler contentHandler: @escaping (UNNotificationContent) -> Void
    ) {
        self.contentHandler = contentHandler
        bestAttemptContent = (request.content.mutableCopy() as? UNMutableNotificationContent)
 
        if let bestAttemptContent = bestAttemptContent {
            // ここで通知を加工する
            bestAttemptContent.title = "\(bestAttemptContent.title) [modified]"
            contentHandler(bestAttemptContent)
        }
    }
 
    override func serviceExtensionTimeWillExpire() {
        // 30秒制限が近い場合の救済処理
        if let contentHandler = contentHandler, let bestAttemptContent = bestAttemptContent {
            contentHandler(bestAttemptContent)
        }
    }
}

{
  "aps": {
    "alert": {
      "title": "新しい記事が公開されました",
      "body": "Rork × Notification Service Extension の本番実装ガイド"
    },
    "mutable-content": 1,
    "sound": "default"
  },
  "image_url": "https://cdn.example.com/notifications/article-cover-12345.jpg"
}

override func didReceive(
    _ request: UNNotificationRequest,
    withContentHandler contentHandler: @escaping (UNNotificationContent) -> Void
) {
    self.contentHandler = contentHandler
    bestAttemptContent = (request.content.mutableCopy() as? UNMutableNotificationContent)
 
    guard let bestAttemptContent = bestAttemptContent,
          let imageURLString = request.content.userInfo["image_url"] as? String,
          let imageURL = URL(string: imageURLString) else {
        contentHandler(self.bestAttemptContent ?? request.content)
        return
    }
 
    // 画像をダウンロード（30秒制限の中で完了する必要がある）
    let task = URLSession.shared.downloadTask(with: imageURL) { [weak self] localURL, response, error in
        guard let self = self,
              let localURL = localURL,
              error == nil else {
            // 画像取得失敗時は本文だけで通知を出す（無音失敗より優先）
            contentHandler(bestAttemptContent)
            return
        }
 
        // 一時ディレクトリにユニークな名前で保存（拡張子は重要）
        let tmpDir = FileManager.default.temporaryDirectory
        let ext = imageURL.pathExtension.isEmpty ? "jpg" : imageURL.pathExtension
        let savedURL = tmpDir.appendingPathComponent(UUID().uuidString + "." + ext)
 
        do {
            try FileManager.default.moveItem(at: localURL, to: savedURL)
            let attachment = try UNNotificationAttachment(
                identifier: "image",
                url: savedURL,
                options: nil
            )
            bestAttemptContent.attachments = [attachment]
            contentHandler(bestAttemptContent)
        } catch {
            // 添付失敗時もテキスト通知は出す
            contentHandler(bestAttemptContent)
        }
    }
    task.resume()
}

import CryptoKit
import Security
 
private func loadSymmetricKey() -> SymmetricKey? {
    let query: [String: Any] = [
        kSecClass as String: kSecClassGenericPassword,
        kSecAttrService as String: "com.example.myapp.notification.key",
        kSecAttrAccessGroup as String: "group.com.example.myapp",
        kSecReturnData as String: true,
        kSecMatchLimit as String: kSecMatchLimitOne
    ]
    var item: CFTypeRef?
    let status = SecItemCopyMatching(query as CFDictionary, &item)
    guard status == errSecSuccess, let data = item as? Data else { return nil }
    return SymmetricKey(data: data)
}
 
private func decryptPayload(
    cipherBase64: String,
    nonceBase64: String,
    tagBase64: String,
    key: SymmetricKey
) -> String? {
    guard let cipher = Data(base64Encoded: cipherBase64),
          let nonceData = Data(base64Encoded: nonceBase64),
          let tag = Data(base64Encoded: tagBase64),
          let nonce = try? AES.GCM.Nonce(data: nonceData) else {
        return nil
    }
    let sealedBox = try? AES.GCM.SealedBox(nonce: nonce, ciphertext: cipher, tag: tag)
    guard let box = sealedBox,
          let plaintext = try? AES.GCM.open(box, using: key) else {
        return nil
    }
    return String(data: plaintext, encoding: .utf8)
}

private func renderLocalized(
    key: String,
    args: [String: String],
    locale: Locale
) -> String {
    // App Group 内に保存された言語ファイル（JSON）を読み込む
    let containerURL = FileManager.default
        .containerURL(forSecurityApplicationGroupIdentifier: "group.com.example.myapp")
    let langCode = locale.identifier.prefix(2) // "ja", "en" など
    let url = containerURL?
        .appendingPathComponent("notifications-\(langCode).json")
 
    guard let url = url,
          let data = try? Data(contentsOf: url),
          let dict = try? JSONSerialization.jsonObject(with: data) as? [String: String],
          let template = dict[key] else {
        return key // フォールバックとしてキーをそのまま返す
    }
 
    var result = template
    for (placeholder, value) in args {
        result = result.replacingOccurrences(of: "{\(placeholder)}", with: value)
    }
    return result
}

override func serviceExtensionTimeWillExpire() {
    // ダウンロード中だった画像は諦め、テキストだけで通知を出す
    if let contentHandler = contentHandler, let bestAttemptContent = bestAttemptContent {
        contentHandler(bestAttemptContent)
    }
}

import ImageIO
 
private func downsample(imageAt url: URL, to maxPixelSize: CGFloat) -> URL? {
    let options: [CFString: Any] = [
        kCGImageSourceShouldCache: false
    ]
    guard let src = CGImageSourceCreateWithURL(url as CFURL, options as CFDictionary) else {
        return nil
    }
    let thumbnailOptions: [CFString: Any] = [
        kCGImageSourceCreateThumbnailFromImageAlways: true,
        kCGImageSourceCreateThumbnailWithTransform: true,
        kCGImageSourceShouldCacheImmediately: true,
        kCGImageSourceThumbnailMaxPixelSize: maxPixelSize
    ]
    guard let cgImage = CGImageSourceCreateThumbnailAtIndex(src, 0, thumbnailOptions as CFDictionary) else {
        return nil
    }
    let outputURL = FileManager.default.temporaryDirectory
        .appendingPathComponent(UUID().uuidString + ".jpg")
    guard let dst = CGImageDestinationCreateWithURL(outputURL as CFURL, "public.jpeg" as CFString, 1, nil) else {
        return nil
    }
    CGImageDestinationAddImage(dst, cgImage, nil)
    guard CGImageDestinationFinalize(dst) else { return nil }
    return outputURL
}