nspcc-dev/neo-go

Item cast to struct does not ensure/convert field type

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#3,610 opened on Oct 11, 2024

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Description

Tried to cast item from contract's storage and use it.

Current Behavior

	newNodes := storage.Find(ctx, newNodesPrefix, storage.None)
	for iterator.Next(newNodes) {
		newNode := iterator.Value(newNodes).(struct {
			key []byte
			val []byte
		})

		newNode.key[0] = 1
	}

leads to SETITEM: invalid item type ByteString

newNode.key[:][0] = 1 solves the issue... why?

Expected Behavior

I said (asserted/converted) that it is a []byte, i want to use it as []byte.

Possible Solution

Ensure, cast or throw an exception at .() operator, not when it is tried to be used later.

Steps to Reproduce

Code from Current Behavior.

Context

https://github.com/nspcc-dev/neofs-contract/pull/438#discussion_r1786975526

Regression

Not sure.

Your Environment

github.com/nspcc-dev/neo-go v0.106.3

Contributor guide

Research direction
Investigate how the NeoGo VM handles type assertions for struct fields. Determine why the field type is not converted/ensured at assertion time and propose a fix to throw an error or convert types properly at the assertion operator.
Tech stack
go
Domain
backend
Issue type
Bug
DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.
3
Estimated timeA rough time range for an experienced contributor to investigate, implement, test, and prepare a pull request.
1-3 hours
Activity statusHow available the issue appears right now: fresh, active, stale, blocked, or waiting on maintainer input.
Fresh
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
Clear
Prerequisites
Go
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
40