rpcchannel

A simple system for doing remote procedure calls (RPCs) in JS/TS.

Note: This is experimental software ATM and is under active development. Use with caution. Consider all APIs unstable.

This assumes that there are only two peers per RpcChannel. An RpcChannel is created with a send function that sends to whichever transport is being used. This could literally just be a wrapper for a MessagePort's postMessage function. Messages are processed by calling the recieve function on the RpcChannel object.

Each RPC function has a particular address, which is just an array of multiple strings. They are determined using the Java package naming convention, like so:

["net", "kb1rd", "mycoolprotocol"]

Here's the most basic example: (in Typescript. Just remove the type annotations for normal JS)

const {
  RpcChannel,
  RpcAddress,
  EnforceMethodArgSchema
} = require('@kb1rd/rpcchannel')
 
// Just pretend these are in different browsing contexts :P
const a: RpcChannel = new RpcChannel((msg) =>
  b.receive(JSON.parse(JSON.stringify(msg)))
)
const b = new RpcChannel((msg) => a.receive(JSON.parse(JSON.stringify(msg))))
 
b.register(['net', 'kb1rd', 'sayhi'], (): string => {
  console.log('Hi!')
  return 'hi'
})
 
// Send is unidirectional and does not wait for a response
a.send(['net', 'kb1rd', 'sayhi']) // Prints "Hi!"
 
async function test() {
  // Prints "Hi!" and waits for the remote function to terminate
  const value = await a.call(['net', 'kb1rd', 'sayhi'])
  console.log(value) // Prints "hi"
}
test()

A part of the address can also be undefined, which acts as a wildcard, like so:

const {
  RpcChannel,
  RpcAddress,
  EnforceMethodArgSchema
} = require('@kb1rd/rpcchannel')
 
// Just pretend these are in different browsing contexts :P
const a: RpcChannel = new RpcChannel((msg) =>
  b.receive(JSON.parse(JSON.stringify(msg)))
)
const b = new RpcChannel((msg) => a.receive(JSON.parse(JSON.stringify(msg))))
 
b.register(['net', 'kb1rd', 'say', undefined], (channel, wc) => {
  console.log(wc[0])
})
 
a.send(['net', 'kb1rd', 'say', 'Hello!']) // Prints "Hello!"

Note the arguments of the function. channel is the RPC channel that recieved the call, and wc is an array of values for wildcards. Wildcards can be filtered by permissions, whereas arguments cannot be.

Here's an example of setting permissions to a particular endpoint: Permissions are being reworked, this will be updated.

Functions can also be given arguments

const {
  RpcChannel,
  RpcAddress,
  EnforceArgumentSchema
} = require('@kb1rd/rpcchannel')
 
// Just pretend these are in different browsing contexts :P
const a: RpcChannel = new RpcChannel((msg) =>
  b.receive(JSON.parse(JSON.stringify(msg)))
)
const b = new RpcChannel((msg) => a.receive(JSON.parse(JSON.stringify(msg))))
 
b.register(
  ['net', 'kb1rd', 'add'],
  // This enforces a JSON schema on the function's arguments
  EnforceArgumentSchema(
    {
      type: 'array',
      items: [
        { type: 'object' },
        { type: 'array', items: { type: 'string' } },
        { type: 'number' },
        { type: 'number' }
      ]
    },
    // Arguments come after then channel and wildcards
    (channel, wc, a: number, b: number) => (a + b)
  )
)
 
async function test() {
  // The last array is the arguments to pass to the function
  const value = await a.call(['net', 'kb1rd', 'add'], [1, 2])
  console.log(value) // Prints "3"
}
test()

Finally, here's a big example demonstrating registerAll:

const {
  RpcChannel,
  RpcAddress,
  EnforceMethodArgSchema
} = require('@kb1rd/rpcchannel')
 
const a: RpcChannel = new RpcChannel((msg) =>
  b.receive(JSON.parse(JSON.stringify(msg)))
)
const b = new RpcChannel((msg) => a.receive(JSON.parse(JSON.stringify(msg))))
 
class TestClass {
  test = 1234
  // RpcAddress decorator always comes first since `EnforceMethodArgSchema`
  // will overwrite it
  @RpcAddress(['net', 'kb1rd', 'addto'])
  @EnforceMethodArgSchema({
    type: 'array',
    items: [
      { type: 'object' },
      { type: 'array', items: { type: 'string' } },
      { type: 'number' }
    ]
  })
  addto(chan: RpcChannel, wc: string[], n: number): number {
    return (this.test += n)
  }
  @RpcAddress(['net', 'kb1rd', 'greet', undefined])
  @EnforceMethodArgSchema({
    type: 'array',
    items: [{ type: 'object' }, { type: 'array', items: { type: 'string' } }]
  })
  greet(chan: RpcChannel, wc: string[]): string {
    return `Hello, ${wc[0]}`
  }
}
 
// This registers all members of an object with `@RpcAddress` applied to them
// You can also set the RpcFunctionAddress (imported from `rpcchannel`) on a
// member function to the address you'd like and it will be seen by
// `registerAll` (@RpcAddress literally just does
// `func[RpcFunctionAddress] = address`)
b.registerAll(new TestClass())
 
async function test() {
  a.send(['net', 'kb1rd', 'sayhi']) // "Hi!"
 
  let data = await a.call(['net', 'kb1rd', 'addto'], [1])
  console.log(data) // "1235"
 
  // Access `call_obj` to get an object that will return a function for every
  // string you can access. This is just a prettier way of doing `call`.
  data = await a.call_obj.net.kb1rd.addto(20)
  console.log(data) // "1255"
 
  try {
    const data = await a.call(['net', 'kb1rd', 'addto'], ['hi'])
    console.log(data)
  } catch (e) {
    console.error('ERROR:', e) // "ERROR: ... validation failed"
  }
 
  data = await a.call_obj.net.kb1rd.greet['World!']()
  console.log(data) // "Hello, World!"
}
test()