iOS：下载AWS S3映像并将其缓存以备将来使用

Question

I have been pulling my hair out from Morning on trying to download the images (webp image) from Amazon S3 bucket and cache it. Whatever the approach I took, I have hit some or the other road block. Different ways I tried to achieve this,

1. Subclassing NSURLProtocol & Using the SDWebImage to retrieve the image as shown in the blog post here . The problem with this approach is that, the canInitWithRequest method of the subclassed protocol will never get called even tough I have registered my subclassed NSURLProtocol class.
2. Planned to use the SDWebImage and other libraries directly, but we can't do that since there is no provision to set the Authorization headers in SDWebImage, even tough if we try setting it, SDWebImage will ignore it while creating an NSMutableURLRequest for downloading.

So right now I am left with an option either to use the Amazon SDK to download the image and then cache it using the SDWebImage's SDImageCache independently, or I need to add the SDWebImage source code to my project and then I need to modify it's source to take the authorization header.

Please let me know if there's any better way to achieve this, it'd be great if I could some pointers on what'd be the best way to achieve what I am trying to do.

Thanks in advance.

Answer 1

To be honest, I looked into this myself for a long time and was unsatisfied with the built in caching system offered by AWS. Instead, I chose to use Kingfisher https://github.com/onevcat/Kingfisher since it is built in swift and well used. I highly recommend it because it is highly customizable but also works perfectly "out of the box"

Answer 2

You can choose what key Kingfisher uses for the cache. So, create a presigned s3 url, then when loading the image use your s3 key as the cache rather then the full presigned url.

            let getPreSignedURLRequest = AWSS3GetPreSignedURLRequest()
            getPreSignedURLRequest.bucket = media.bucket
            getPreSignedURLRequest.key = media.key
            getPreSignedURLRequest.httpMethod = .GET
            getPreSignedURLRequest.expires = Date(timeIntervalSinceNow: 3600)  // Change the value of the expires time interval as required
            AWSS3PreSignedURLBuilder.default().getPreSignedURL(getPreSignedURLRequest).continueWith { (task:AWSTask<NSURL>) -> Any? in
                if let error = task.error as NSError? {
                    print("Error: \(error)")
                    return nil
                }
                if let presignedURL = task.result {
                    DispatchQueue.main.async {
                        self.imageView.kf.indicatorType = .activity
                        let resource = ImageResource(downloadURL: URL(string: presignedURL.absoluteString!)!, cacheKey: media.key)
                        self.imageView.kf.setImage(with: resource)
                    }
                }
                return nil
            }