wasi (wasm v0.1.0)

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Run a WASI command module and get its exit status and output back.

Use this when your guest is a program with a main rather than a library of exported functions. A _start module reports its exit status by trapping and writes its output to whatever sink your capability map names; collecting both is mechanical and easy to get subtly wrong, so it lives here rather than in every caller.

{ok, Mod} = wasm:load_file("hello.wasm"),
{ok, 0, Stdout, _Stderr} =
    wasi:run(Mod, #{args => [~"hello"],
                    dirs => [{~"/data", "/srv/app/data", read}]}).

wasi_preview1 documents the capabilities. The short version: leave a key out and the module does not have that capability, and no dirs means no filesystem at all rather than one rooted at your working directory.

Summary

Functions

imports(Config)

Build the WASI import map for a capability configuration.

run(Module)
run(Module, Config0)

Instantiate a module, run _start, and collect its exit status and output.

Functions

imports(Config)

-spec imports(map()) -> map().

Build the WASI import map for a capability configuration.

run(Module)

-spec run(wasm:module_()) -> {ok, integer(), binary(), binary()} | {error, term()}.

run(Module, Config0)

-spec run(wasm:module_(), map()) -> {ok, integer(), binary(), binary()} | {error, term()}.

Instantiate a module, run _start, and collect its exit status and output.

You get the exit status back from the trap proc_exit raises, because trapping is the only way to unwind a WebAssembly stack. A module that returns from _start without calling proc_exit exits 0, which is what the WASI command model specifies.

Output is captured by pointing stdout and stderr at this process and draining the mailbox, so any stdout or stderr you put in Config is overridden.