Fastly Zig Wasm

hostcalls.zig

const std = @import("std");
const fmt = std.fmt;

extern fn hostcall_kvstore_upsert(
    key_ptr: [*]const u8,
    key_len: usize,
    value_ptr: [*]const u8,
    value_len: usize,
) bool;

extern fn hostcall_kvstore_get(
    value_ptr_p: *[*]u8,
    value_len_p: *usize,
    key_ptr: [*]const u8,
    key_len: usize,
) bool;

extern fn hostcall_kvstore_insert(
    key_ptr: [*]const u8,
    key_len: usize,
    value_ptr: [*]const u8,
    value_len: usize,
) bool;

extern fn hostcall_resp_set_body(
    resp: i32,
    body_ptr: [*]const u8,
    body_len: usize,
) i32;

export fn run() void {
    const key = "count";

    const init = "0";
    _ = hostcall_kvstore_upsert(&key, key.len, &init, init.len);

    var value_ptr: [*]u8 = undefined;
    var value_len: usize = 0;

    _ = hostcall_kvstore_get(&value_ptr, &value_len, &key, key.len);

    const count = fmt.parseInt(u32, value_ptr[0..value_len], 10) catch unreachable;

    var buffer: [64]u8 = undefined;
    const newcount = fmt.bufPrint(buffer[0..], "{}", count + 1) catch unreachable;
    _ = hostcall_kvstore_insert(&key, key.len, newcount.ptr, newcount.len);

    const body = fmt.bufPrint(buffer[0..], "Hello Webassembly from zig: {}", count + 1) catch unreachable;
    _ = hostcall_resp_set_body(0, body.ptr, body.len);
}

Compile with zig build-exe -target wasm32-freestanding hostcalls.zig --release-fast --name module.wasm.

• Go to: https://wasm.fastlylabs.com
• Create empty WAT project
• Delete line 5-7 from build.ts and save
• Right click on the sidebar and upload module.wasm
• Click Build and deploy

Note: ziglang/zig#2248 is required for memcpy