qml: sharing large psbt raises android TransactionTooLargeException

[f321x]

Description

When clicking on the share button of a large (>1mb) psbt in QML, Android will raise a android.os.TransactionTooLargeException as the size limit for data shared through an Activity seems to be ~1mb.
We could for example allow exporting the psbt by saving it as file instead of sharing it.

Traceback (most recent call last):
  File "app/electrum/gui/qml/qeapp.py", line 272, in doShare
  File "jnius/jnius_export_class.pxi", line 1187, in jnius.JavaMultipleMethod.__call__
  File "jnius/jnius_export_class.pxi", line 897, in jnius.JavaMethod.__call__
  File "jnius/jnius_export_class.pxi", line 991, in jnius.JavaMethod.call_method
  File "jnius/jnius_utils.pxi", line 79, in jnius.check_exception
jnius.JavaException: JVM exception occurred: java.lang.RuntimeException: Failure from system
java.lang.RuntimeException: Failure from system
	android.app.Instrumentation.execStartActivity(Instrumentation.java:2002)
	android.app.Activity.startActivityForResult(Activity.java:6133)
	android.app.Activity.startActivityForResult(Activity.java:6090)
	android.app.Activity.startActivity(Activity.java:6597)
	android.app.Activity.startActivity(Activity.java:6564)
	org.qtproject.qt.android.QtNative.startQtApplication(Native Method)
	org.qtproject.qt.android.QtNative$$ExternalSyntheticLambda5.run(D8$$SyntheticClass:0)
	org.qtproject.qt.android.QtThread$1.run(QtThread.java:25)
	java.lang.Thread.run(Thread.java:1572)
	Caused by:
	android.os.TransactionTooLargeException: data parcel size 1422480 bytes
	android.os.BinderProxy.transactNative(Native Method)
	android.os.BinderProxy.transact(BinderProxy.java:595)
	android.app.IActivityTaskManager$Stub$Proxy.startActivity(IActivityTaskManager.java:2329)
	android.app.Instrumentation.execStartActivity(Instrumentation.java:1995)
	android.app.Activity.startActivityForResult(Activity.java:6133)
	android.app.Activity.startActivityForResult(Activity.java:6090)
	android.app.Activity.startActivity(Activity.java:6597)
	android.app.Activity.startActivity(Activity.java:6564)
	org.qtproject.qt.android.QtNative.startQtApplication(Native Method)
	org.qtproject.qt.android.QtNative$$ExternalSyntheticLambda5.run(D8$$SyntheticClass:0)
	org.qtproject.qt.android.QtThread$1.run(QtThread.java:25)
	java.lang.Thread.run(Thread.java:1572)

Related #4686 (comment)

[SomberNight]

large (>1mb) psbt

well... the standardness limit for a tx is 400k weight units, which is 400 kilobytes network serialized, 800 kilobytes hex-serialized. Txs we copy out as base64 psbts I guess, so 400*8/6 = 533 kilobytes base64 serialized. Although note that psbts contain supplementary info such as previous UTXOs serialized as full txs, which themselves in the extreme case could be really large. Still, my point is that it seems psbts so large are likely too large to be relayed anyway.

What about the clipboard? We also allow copying stuff to the clipboard. What's the max for that?

From that trace it could also be that someone just entered e.g. the Sign/Verify message dialog, and copied/entered something really long into the message or signature fields, and then tried to share it.

[f321x]

From that trace it could also be that someone just entered e.g. the Sign/Verify message dialog

I was able to reproduce it by loading a watch only wallet from 1K6KoYC69NnafWJ7YgtrpwJxBLiijWqwa6 and trying to create a psbt that spends all the wallets utxos to an address. So it is reachable from the UI through "regular usage".
But yeah it seems unlikely to happen considering that only one crash with this traceback was reported in #4686 (comment), so it might not be important to get fixed now.

What about the clipboard?

Copying seems to break in another way, there is no exception (or log) but it also doesn't copy the psbt to clipboard (nothing happens).

What's the max for that?

I cannot find a source stating a specific size limit right now but Signal seemed to have a similar crash when copying logs to clipboard: signalapp/Signal-Android#8082 (comment). I assume it has a limit similar to the sharing function.

[SomberNight]

I was able to reproduce it by loading a watch only wallet from 1K6KoYC69NnafWJ7YgtrpwJxBLiijWqwa6 and trying to create a psbt that spends all the wallets utxos to an address. So it is reachable from the UI through "regular usage".

Ok, I tried that too and it created a tx with 15.7k inputs and Size: 2328530 vbytes. That would be larger than a block :D