[x/programs] All host functions (that get linked) should follow the same two argument calling convention

[richardpringle]

Similarly to #638, we want to serialize all the arguments into a single Vec<u8>. Further, we need to make sure that the bytes aren't dropped before they're read by the host.

I'm going to propose that all host functions (on the Rust side) have a safe wrapper and that their actual definition is written with a macro instead of being called directly.

Right now, the code looks something like this:

#[link(wasm_import_module = "state")]
extern "C" {
    #[link_name = "put"]
    fn _put(caller: i64, key: i64, value: i64) -> i64;
}

pub unsafe fn put_bytes<V>(caller: &Program, key: &Key, value: &V) -> Result<(), Error>
where
    V: BorshSerialize,
{
    let value_bytes = borsh::to_vec(value).map_err(|_| Error::Serialization)?;
    let caller = to_host_ptr(caller.id())?;
    let value = to_host_ptr(&value_bytes)?;
    let key = to_host_ptr(key)?;

    match unsafe { _put(caller, key, value) } {
        0 => Ok(()),
        _ => Err(Error::Write),
    }
}

But this functionality should look something like this:

pub fn put_bytes<V>(caller: &Program, key: &Key, value: &V) -> Result<(), Error>
where
    V: BorshSerialize,
{
    call_host_fn! {
        wasm_import_module = "state";
        link_name = "put";
        args = (caller, key, value);
    }
}

Here the macro would actually define the external function. Alternatively, if there is no module, there should be another pattern to patch the following:

pub fn put_bytes<V>(caller: &Program, key: &Key, value: &V) -> Result<(), Error>
where
    V: BorshSerialize,
{
    call_host_fn!("put", (caller, key, value))
}

Inside the macro, the actual name of the function inside the extern block doesn't matter; it's only the link name that does something.

Could also fix #849 while fixing this.

[richardpringle]

Actually assigned to @iFrostizz

[iFrostizz]

TODO: after merging #872, we should serialize the parameters being (ptr_offset, data_len)* with Borsh and just pass one of these CPointer which will simplify the API a lot.

[richardpringle]

TODO: after merging #872, we should serialize the parameters being (ptr_offset, data_len)* with Borsh and just pass one of these CPointer which will simplify the API a lot.

done

[richardpringle]

Going to close this as #900 essentially achieves everything we want. I think we want to make one more minor change in that we want to generically call functions with context + n args (including the trivial case)... but I don't think we need an issue tracking that.