How to use StreamSaver.js in Android webview like Chrome

[Sonumohammad]

Chrome (Android app) is handling downloads from StreamSaver.js How can I achieve this with Android's webview? https://stackoverflow.com/questions/67708173/how-to-download-stream-streamsaver-js-files-in-android-webview

[jimmywarting]

I'm not sure...

maybe this can help. https://stackoverflow.com/questions/10069050/download-file-inside-webview

@warting do you have any suggestion?

[Sonumohammad]

These solutions are for normal file downloads with URLs. In these solutions, download info from Webview will be passed to DownloadManager only once. But in the StreamSaver.js case, the download simply starts and fails because DownloadManager doesn't communicate with Webview in real-time.

do you have any solution?

[jimmywarting]

ok, i might have found something when i explained to my brother how streamsaver works

the url that is generated from streamsaver is a uniq "one-time" download link and totally client side generated by a service worker... You can't simply take the url that is generated and pass it to another browser (or another download mananger) to download it cuz it's generated by a service worker (in the browser). opening this url again will result in 404

I guess what you actually have to do is to download/intercept the content that flows in as a readable stream. so this will probably not work...

        public void onDownloadStart(String url, String userAgent, String contentDisposition, String mimetype, long contentLength) {
            // Downloading with DownloadManager is not working.
            // A notification says, download failed.
        }

i found something that might be of interest doe and it's probably something that i would have used... it's called shouldOverrideUrlLoading and conn.getInputStream

https://stackoverflow.com/a/38732113/1008999

from my understanding this should give you the content as a InputStream which you can use to write to any destination.

[gwdp]

I'm working to solve an issue where it seems that streamsaver does not work on the following Chrome mobile environments:

• Android Chrome (download does fail)
• iOS Chrome (download does fail)
• Android Web View (download does not come as a blob and fail silent) - (Using Capacitor webview implementation on the default saving-multiple-files.html example)
• Belive https://github.com/jimmywarting/StreamSaver.js/issues/195 is also the same issue and should be fixed if we are able to make this work on Chrome mobile envs.

Few details on the investigation:

• WebView public WebResourceResponse shouldInterceptRequest (WebView view, WebResourceRequest request) method will not be called by/for blobs as a design decision documented here
• setDownloadListener + public void onDownloadStart solution does not work out of the box with streamsaver, that's why:
  • useBlobFallback as pointed out by @jimmywarting on https://github.com/jimmywarting/StreamSaver.js/issues/195 is coming false and the additional try/catch test Jimmy posted, does not make any effect on it.
  • Forcing useBlobFallback does make onDownloadStart to be called with a blob: URL, which must be solved by the webcontext other than a background download AFAIK.
  • Aside from that, I mitigate the same issue on the Capacitor iOS implementation using WKWebview and Webkit team does expose a way for us to intercept a request as ask the browser context to download a per iOS 14.5 but using overrides. (Sample here)

All being said, I might need to improve the useBlobFallback detection for those environments (unsure if we can handle without blobs) and find a way to download blobs using onDownloadStart; However, making it work on Chrome App is also important and I have no clues on doing so ( for now 🤓 )

[Sonumohammad]

I am JavascriptInterface instead of StreamSaver Send Bytes from Javascript to Java, Write bytes to file stream in Java

1. Set JavascriptInterface with Webview 1.1 Create a class MyJSInterface 1.1 Create method(s) in MyJSInterface with @JavascriptInterface annotation so you can call the methods from Javascript, you cannot send byte arrays from Javascript to android For that we convert byte array to string before sending 1.2 create method, newBytes(String convertedString) in MyJSInterface 1.2 Add MyJSInterface to Webview webview.addJavascriptInterface(new MyJSInterface(this), "Android")

2. Javascript 2.1 Convert bytes to string 2.2 Send to Java environment with MyJSInterface Android.newBytes(convertedString)

3. Java 3.1 Handle newBytes(convertedString) Convert string to bytes 3.2 Write the bytes to FileStream

Use webworker(JS) to asynchronously pass byte stream to Java

Reference: https://stackoverflow.com/a/45506857/14421932

[gwdp]

Hi @Sonumohammad, thanks for the reply..

My goal is more specifically on making streamsaver work with those cases instead of replacing its usage.

Further testing it, I was able to make it work with Android WebView using JavascriptInterface + ajax injection + java callback on the blob: schema, however, attempting to make it work without the blobfallback is giving me nightmares. Will stick on the attempt for a while, if no success will probably need to patch streamsaver to fallback to blob on those cases (which is not doing right not 2.0.6.

If I understood the depth of this issue correctly, streamsaver is currently not working on any Android mobile engine, so needs attention for sure. Any thoughts are much appreciated :)