Implement Encode/Decode for Box<T>

[kostko]

No description provided.

[peternose]

Looks good.

Be aware that in one of the previous commits we fixed encoding of omitempty structs with empty omitempty fields. This could cause problems with backwards compatibility as some old signatures might become invalid. For example, cbor 0.5.2 encodes OuterStruct to the same bytes as EmptyStruct if OuterStruct.A.B == 0. Before, it encoded the same way as OuterStruct2.

I doubt that we ever signed such structs, as is totally unsafe as two structs with different meaning could have the same encoding and a signature for one would be valid for both structs. For example, OuterStruct encodes to the same value as MyStruct and EmptyStruct if OuterStruct.A.B == 0 and MyStruct.C == 0. Therefore, if one signs OuterStruct he also signs the other two. Which could be dangerous if one struct is used for transfering funds.

Using Go instead of Rust for clarity :)

type OuterStruct struct {
	A InnerStruct `json:"a,omitempty"`
}

type InnerStruct struct {
	B uint `json:"b,omitempty"`
}

type EmptyStruct struct {
}

type MyStruct struct {
	C uint `json:"c,omitempty"`
}

type OuterStruct2 struct {
	A InnerStruct `json:"a"`
}

Once we are sure that this is not a problem, the following PR can be merged:

• runtime: Upgrade cbor to 0.5.2 oasis-core#5391