rust-app.py

# Based on https://github.com/wasmerio/wasmer-python/blob/master/examples/wasi.py

import sys # access cli arguments

from wasmer import engine, wasi, Store, Module, ImportObject, Instance
from wasmer_compiler_cranelift import Compiler
import os

# Let's get the `wasi.wasm` bytes!
__dir__ = os.path.dirname(os.path.realpath(__file__))
wasm_bytes = open(__dir__ + '/rust-app.wasm', 'rb').read()

# Create a store.
store = Store(engine.JIT(Compiler))

# Let's compile the Wasm module, as usual.
module = Module(store, wasm_bytes)

# Here we go.
#
# First, let's extract the WASI version from the module. Why? Because
# WASI already exists in multiple versions, and it doesn't work the
# same way. So, to ensure compatibility, we need to know the version.
wasi_version = wasi.get_version(module, strict=True)

# Second, create a `wasi.Environment`. It contains everything related
# to WASI. To build such an environment, we must use the
# `wasi.StateBuilder`.
#
# In this case, we specify the program name is `wasi_test_program`. We
# also specify the program is invoked with the `--test` argument, in
# addition to two environment variable: `COLOR` and
# `APP_SHOULD_LOG`. Finally, we map the `the_host_current_dir` to the
# current directory. There it is:
arguments_to_pass = sys.argv.copy()
arguments_to_pass.pop(0)
wasi_env = \
    wasi.StateBuilder('wasi_test_program'). \
        arguments(arguments_to_pass). \
        map_directory('.', '.'). \
        finalize()

# From the WASI environment, we generate a custom import object. Why?
# Because WASI is, from the user perspective, a bunch of
# imports. Consequently `generate_import_object`… generates a
# pre-configured import object.
#
# Do you remember when we said WASI has multiple versions? Well, we
# need the WASI version here!
import_object = wasi_env.generate_import_object(store, wasi_version)

# Now we can instantiate the module.
instance = Instance(module, import_object)

# One last thing. This WASI module expects a memory! But it has no
# memory “instance”. So let's bind the WASI memory and the instance
# exported memory together.
# ⚠ Fails 👇
# wasi_env.memory = instance.exports.memory

# The entry point for a WASI WebAssembly module is a function named
# `_start`. Let's call it and see what happens!
instance.exports._start()