README.md

waPC Guest Library for Swift

This is the Swift implementation of the waPC standard for WebAssembly guest modules. It allows any waPC-compliant WebAssembly host to invoke to procedures inside a Swift compiled guest and similarly for the guest to invoke procedures exposed by the host.

The Swift compiler provided by the Swiftwasm project is required.

Example

The following is a simple example of synchronous, bi-directional procedure calls between a WebAssembly host runtime and the guest module.

import wapc

@_cdecl("__guest_call")
func __guest_call(operation_size: UInt, payload_size: UInt) -> Bool {
  return wapc.handleCall(operation_size: operation_size, payload_size: payload_size)
}

func hello(payload: String) -> String {
  // call the host from the Wasm module
  let hostMsg = wapc.hostCall(
    binding: "binding_name",
    namespace: "namespace_name",
    operation: "operation_name",
    payload: "that's the payload"
  )

  if hostMsg == nil {
    return "the validate function called the host but something went wrong"
  }
  return "the validate function called the host and received back: '\(hostMsg!)'"
}

// register the function
wapc.registerFunction(name: "hello", fn: hello)

The Wasm module must declare a __guest_call function and export it. The linker must be instructed to export this function (see the official documentation).

When using SwiftPM to manage a package, the linker can be instruted by adding few lines to the Packages.swift file:

.target(
    name: "demo",
    dependencies: ["wapc"],
    linkerSettings: [
        .unsafeFlags(
            [
                "-Xlinker",
                "--export=__guest_call",
            ]
        )
    ]
),

Working example

This GitHub repository contains a full working example.

Call for help

I'm new to Swift, I would appreciate help on the following topics from some more seasoned Swift develper:

• Generic code review, ensure I'm not doing something stupid
• Question about the API to expose, this is tracked on this issue