Panic inside io.PutVarUint

[cthulhu-rider]

Current Behavior

panic: runtime error: index out of range [8] with length 5 [recovered]
	panic: runtime error: index out of range [8] with length 5

goroutine 19 [running]:
testing.tRunner.func1.2({0x5dd0c0, 0xc0000f6180})
	/usr/local/go/src/testing/testing.go:1631 +0x24a
testing.tRunner.func1()
	/usr/local/go/src/testing/testing.go:1634 +0x377
panic({0x5dd0c0?, 0xc0000f6180?})
	/usr/local/go/src/runtime/panic.go:770 +0x132
github.com/nspcc-dev/neo-go/pkg/io.PutVarUint(...)
	/home/ll/projects/neo/go/pkg/io/binaryWriter.go:109
github.com/nspcc-dev/neo-go/pkg/io_test.TestPutVarUint(0xc0000d8b60?)

Expected Behavior

no panic when buffer has enough len, only otherwise (similar to https://pkg.go.dev/encoding/binary#PutUvarint)

Possible Solution

do not do

neo-go/pkg/io/binaryWriter.go

Line 109 in 9189b3e

_ = data[8]

Steps to Reproduce

func TestPutVarUint(t *testing.T) {
	const n = uint64(123456787890)
	io.PutVarUint(make([]byte, io.GetVarSize(n)), n)
}

Regression

no

Your Environment

• Version of the product used: v0.107.2

[roman-khimov]

This one was added specifically as canary (17a3f17). At the same time users of this API can expect some symmetry between GetVarSize() and PutVarUint(). And it'll fail later if buffer is too short.

[cthulhu-rider]

io.GetVarSize(uint64(math.MaxInt + 1)) returns 1 which is also unexpected to me. Caused by cast

neo-go/pkg/io/size.go

Line 58 in 9189b3e

return getVarIntSize(int(v.Uint()))

[cthulhu-rider]

At the same time users of this API can expect some symmetry between GetVarSize() and PutVarUint().

exactly. But this is unexpected even within oneself:

func TestPutVarUint(t *testing.T) {
	const n = uint64(123)
	b := make([]byte, 32)
	ln := io.PutVarUint(b, n)
	io.PutVarUint(b[:ln], n)
}

panic: runtime error: index out of range [8] with length 1 [recovered]
	panic: runtime error: index out of range [8] with length 1