A Zig Canister

Ben Lynn has a blog post series about "Organic Apps", he creates canisters with clang, and lld only.

Quint and Enzo, over beers, thought it would be fun to create a canister in zig, so we looked at Ben's Hello, Internet Computer blog post and decided to port it to Zig the following day.

Anyways, here is the C code from Ben:

#define IMPORT(m,n) __attribute__((import_module(m))) __attribute__((import_name(n)));
#define EXPORT(n) asm(n) __attribute__((visibility("default")))

void reply_append(void*, unsigned) IMPORT("ic0", "msg_reply_data_append");
void reply       (void)            IMPORT("ic0", "msg_reply");

void go() EXPORT("canister_query hi");

void go() {
  char msg[] = "Hello, World!\n";
  reply_append(msg, sizeof(msg) - 1);
  reply();
}

And here is our zig code:

extern "ic0" fn msg_reply_data_append(ptr: [*]const u8, len: usize) void;
extern "ic0" fn msg_reply() void;

export fn @"canister_query hi"() callconv(.C) void {
    const msg = "Hello, World!\n";
    msg_reply_data_append(msg, msg.len);
    msg_reply();
}

Let's compile the C code:

# we compile the object file
clang --target=wasm32 -c -O3 src/main.c -o main_c.o
# we link the object file
wasm-ld --no-entry --export-dynamic --allow-undefined main_c.o -o main_c.wasm
# translate to wat
wasm2wat main_c.wasm > main_c.wat
# we strip the wasm binary
wasm-strip main_c.wasm

Let's compile the Zig code:

# we compile zig
zig build
# translate to wat
wasm2wat zig-out/bin/main.wasm > zig-out/bin/main.wat

Now let's compare the two WASMs:

enzo@merlaux:~/code/zig-cdk$ ll *.wasm
-rwxrwxr-x 1 enzo enzo 170 May 22 18:03 main.wasm*
-rwxrwxr-x 1 enzo enzo 308 May 22 18:04 main_c.wasm*

We have created a 170 bytes canister in Zig. Let us see if it works. First we need to create a minimal dfx.json:

{
  "canisters": {
    "hello_zig": {
      "type": "custom",
      "build": "zig build",
      "candid": "not.did",
      "wasm": "zig-out/bin/main.wasm"
    }
  }
}

Then let's create a minimal candid file not.did:

service: {}

We check if it actually works, start-up dfx:

dfx start
dfx deploy

Now, let's call the canister:

enzo@merlaux:~/code/zig-cdk$ dfx canister call hello_zig hi --output raw  | xxd -r -p
WARN: Cannot fetch Candid interface for hi, sending arguments with inferred types.
Hello, World!

IT WORKS!

Dev

To replicate the code, install nix and direnv:

• Install nix with Determinate Systems Nix Installer

curl --proto '=https' --tlsv1.2 -sSf -L https://install.determinate.systems/nix | sh -s -- install

• Install direnv - installation page

• hook direnv into your shell

Run direnv allow. You should be all set-up!