accounts/abi: add support for fixed bytes with size > 32

[zhiqiangxu]

This PR fixes this testcase :

type fixedBytes struct {
	Chunk [4 * 1024]byte
	A     *big.Int
}

func TestMinimal(t *testing.T) {
	IntTy, _ := abi.NewType("uint256", "", nil)
	Bytes4096Ty, _ := abi.NewType("bytes4096", "", nil)
	Abi := abi.Arguments{
		{Type: Bytes4096Ty, Name: "Chunk"},
		{Type: IntTy, Name: "A"},
	}
	a := big.NewInt(10)
	chunk := [4 * 1024]byte{0x03, 0x4}
	packed, err := Abi.Pack(chunk, a)
	if err != nil {
		t.Fatal(err)
	}

	values, err := Abi.Unpack(packed)
	if err != nil {
		t.Fatal(err)
	}

	var decoded fixedBytes
	err = Abi.Copy(&decoded, values)
	if err != nil {
		t.Fatal(err)
	}
	if decoded.Chunk != chunk {
		t.Fatal("Chunk mismatch")
	}
	if decoded.A.Cmp(a) != 0 {
		t.Fatal("A mismatch")
	}
}

[karalabe]

Thanks for the PR, however these types of changes will not be accepted without extensive tests. You are introducing new functionality, we need to ensure it works as intended.

[zhiqiangxu]

Thanks for the PR, however these types of changes will not be accepted without extensive tests. You are introducing new functionality, we need to ensure it works as intended.

I see, that's understandable.

[rjl493456442]

According to ABI spec the maximum length supported for fixed size is 32, https://docs.soliditylang.org/en/v0.8.17/abi-spec.html.

bytes<M>: binary type of M bytes, 0 < M <= 32.

Can you share the link if the type is newly introduced?

[zhiqiangxu]

According to ABI spec the maximum length supported for fixed size is 32, https://docs.soliditylang.org/en/v0.8.17/abi-spec.html.

bytes<M>: binary type of M bytes, 0 < M <= 32.

Can you share the link if the type is newly introduced?

Oops, didn't know the spec. If fixed bytes size is specified to be <= 32, maybe abi.NewType("bytes4096", "", nil) should return a non nil error?

[rjl493456442]

@zhiqiangxu yeah, technically we can build bytes4096, but in practice there is no such type. But maybe we can add a check for rejecting non-spec'd type.

Feel free to open PR for the additional check. But I will close this PR if you are fine for it.