Add basic memory module

[jozanza]

I was running through the documentation for invoking functions and ran into trouble reading env vars and stdin from Rust.

After some exploration of the AssemblyScript bindings, I realized that std::io was not the expected way to gather these inputs. It's actually done via two externs: memory_read and env_var_read in the blockless_memory wasm import module.

Locally, I added the externs and some basic wrapper functions to read the data. There aren't any utility methods for reading to strings and json in the module, and I wasn't sure what the error code enumeration was 😅. But I'm using this code locally right now, so I thought I'd share.

Example

If this code were merged, you could read stdin and env vars like so:

use blockless_sdk::*;

fn main() -> std::io::Result<()> {
    let mut buf = [0; 1024];
    let len = memory::read_stdin(&mut buf)?;
    let str = std::str::from_utf8(&buf[..len as usize]);
    println!("STDIN: {:?}", str);

    let mut buf = [0; 1024];
    let len = memory::read_env_vars(&mut buf)?;
    let str = std::str::from_utf8(&buf[..len as usize]);
    println!("ENV: {:?}", str);

    Ok(())
}

Invoking the function with stdin would yield the following:

bls function invoke --stdin ARG1=VAL1 --env FOO=BAR

STDIN: Ok("ARG1=VAL1\n")
ENV: Ok("{\"FOO\": \"BAR\"}")

[Joinhack]

thank you.

[jozanza]

np!