OTP-encryption | An example of one-time pad encryption in C language | File Sharing library

For share file image you can use this flutter_share_file

You will probably find it easier for the client to upload the file to your http server with a room name and then have your http server send a message to all the other clients in the room via socket.io with a URL where the client can download the file using http. socket.io is just not a streaming protocol, it's a packet or message-based protocol so to send large things, it has to be broken up into messages and then reassembled on the client. This can be done, but it's just extra non-standard work that http uploads and downloads already know how to do.

Here would be the steps:

1. Client uploads file to server via http post with the room name as a field in the form.
2. Server receives uploaded file, assigns it a unique ID and stores it in a temporary location on the server on disk.
3. When file upload completes server notifies all other clients in the room via socket.io that the file is uploaded and ready for download and sends them the URL for download that has the uniqueID in it.
4. Each client sends request to download the file via http using the unique URL they received.
5. Server serves the file to each client as requested over http.
6. Server either keeps track of whether all clients have now finished downloading or just removes the file after some period of time based on timestamp of the file (to just clean up disk space) with some regular cleanup function on a recurring timer.

You can create a single route that handles all the downloads:

You can use WalletConnect mobile linking to communicate between Android apps and Ethereum wallets for signing the documents.

You can use Web3j to communicate with Ethereum JSON-RPC.

Although it is generally advisable to serve docs through your own backend,but you could simplify that effort by using some standard angular packages. Below are some of the options:

1. ngx-doc-viewer - Probably the best library and support a lot of file types. This demo can help you know it better.
2. ng2-pdf-viewer - When your concerns are limited to pdf, this is a much simpler package to use, but do not have a wide range of customizations.Stackblitz demo
3. ngx-extended-pdf-viewer - This has a wide range of customizations and can be really cool if your concerns are regarding doc display with a toolbar.Demo
4. NodeJs + DB - Last but not least, the most customizable and standard approach for complex applications would be building your own backend. The backend server can actually be allocated a folder for docs, and the documents can be uploaded/saved by users/admin in that specific folder.

Finally found a work around and got it working using this answer. What I ended up doing was opening the file in the app delegate, saving the file to the apps documents directory, then passing that url to the Flutter application. I opened the iOS module in xcode and changed the AppDelegate.swift to the following:

Just replace url with urls

In this case, how about using Drive API? I think that you can set them using Drive API. In this answer, the method of "Files: update" of Drive API v3 is used.

Before you use this script, please enable Drive API at Advanced Google services.

So after the conversations in comments and as @MarquisofLorne told to delete the line that i have written in my server side code. i.e either delete this line from server side code:

Change this and it will work- I have taken hint from here and tried different configuration and this works, I don't know why.