Neo: New API for NeoContract: System.Runtime.GetNotifications
System.Runtime.GetNotifications receives a scripthash as an argument, and returns all notifications from that contract in current InvocationTransaction.
Consider that we have an InvocationTransaction with the following Script:
APPCALL <A>
APPCALL <B>
SYSCALL System.Runtime.GetNotifications <A>
erikzhang
All 17 comments
Will be the notification that was sent with System.Runtime.Notify right?
shargon
on 13 Jul 2018
Will be the notification that was sent with
System.Runtime.Notifyright?
Yes.
erikzhang
on 13 Jul 2018
Oh, I love new things :) but what is a possible application for this? hahahah
igormcoelho
on 8 Aug 2018
Oh, I love new things :) but what is a possible application for this? hahahah
Consider a contract to run a decentralized exchange. When a user needs to deposit, he will first transfer some NEP-5 tokens to this contract and then call its deposit method. In the deposit method, the contract can confirm that the user actually transferred the tokens by calling System.Runtime.GetNotifications.
erikzhang
on 9 Aug 2018
@erikzhang Couldn't they just check that the tokens were deposited by querying the smart contract? System.Runtime.GetNotifications seems unreliable, at least in the dynamic call case - what happens if the contract incorrectly implements the notifications? I.e. at a high level, notifications are not the source of truth.
dicarlo2
on 9 Aug 2018
@erikzhang will any Verification contracts be able to produce (and store) such notifications (verified later in Application)? That would be amazingly useful!
Will this GetNotifications be able to filter them somehow by some prefix? Or the whole list will be returned?
igormcoelho
on 10 Aug 2018
@igormcoelho System.Runtime.GetNotifications can get the notifications that sent from the same InvocationTransaction.
erikzhang
on 13 Aug 2018
Is there a way to check if the invocation faulted?
RavenXce
on 13 Aug 2018
Why is this in the 3.0 Milestone? Wouldn't this be applicable in e.g. 2.7?
deanpress
on 14 Aug 2018
Is there a way to check if the invocation faulted?
If the invocation faulted, it will not continue to execute. There is currently no way to recover from an exception.
I have planned to add a mechanism for smart contract exception handling in NEO 3.0. https://github.com/neo-project/neo/issues/310
Why is this in the 3.0 Milestone? Wouldn't this be applicable in e.g. 2.7?
It can be applicable in 2.x if necessary.
erikzhang
on 14 Aug 2018
If the invocation faulted, it will not continue to execute. There is currently no way to recover from an exception.
So this mean System.Runtime.GetNotifications will never have notifications after faulting, even if a notify opcode was done before that? In the current version, execution results are not cleared, so this notification remains.
RavenXce
on 14 Aug 2018
In the current version, execution results are not cleared, so this notification remains.
If the invocation faulted, everything will be rolled back.
erikzhang
on 14 Aug 2018
Yes that is true, state changes are not committed, but the notifications are still added to execution results as a copy:
Just confirming the behavior should not be the same for this API.
Edit: Actually GetNotifications would simply read from the actual state, so that goes without saying. Thanks!
RavenXce
on 14 Aug 2018
Scripthash will be included too, right? For that other proposal of Native contracts (https://github.com/neo-project/neo/issues/303), it would be nice to each contract having an unique name (as explained there), and that would be useful here too... so if we are catching a notification from contract named "Neo.Native.NEO" regarding a "transfer"... transfer is done, utxo is gone ;)
igormcoelho
on 22 Aug 2018
@shargon @erikzhang @vncoelho time to implement this. I was sure it had passed already haha took time to find this here, still open.
I think we can have parameter one, saying which scripthash to look for, and if empty scripthash, we receive all notifications. Result can be an array stack item, filled with Notification interopinterfaces.
We will need two more interop calls: System.Notification.GetScriptHash, and
System.Notification.GetMessage. probably a third one, System.Notification.GetAttributes, where one of these attributes is if notification is currently hidden (we could flag other interesting things too, lets think)
igormcoelho
on 7 Jul 2019
@igormcoelho @shargon to clarify, this only applies to notifications from the current transaction right? (Sorry if this is an obvious question, I haven't been following NEO 3.0 changes too closely - yet anyways)
dicarlo2
on 16 Jul 2019
Yes @dicarlo2 exactly as you said
shargon
on 16 Jul 2019
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Most helpful comment
@shargon @erikzhang @vncoelho time to implement this. I was sure it had passed already haha took time to find this here, still open.
I think we can have parameter one, saying which scripthash to look for, and if empty scripthash, we receive all notifications. Result can be an array stack item, filled with Notification interopinterfaces.
We will need two more interop calls: System.Notification.GetScriptHash, and
System.Notification.GetMessage. probably a third one, System.Notification.GetAttributes, where one of these attributes is if notification is currently hidden (we could flag other interesting things too, lets think)