forge-exec-ipc-client

Execute a program as a separate process and connect to it via IPC.

Used by forge-exec to establish a open 2-way communication channel with forge

Because forge expect ffi output to be given to stdout after program exit, forge-exec-ipc-client is executed for every message pair and exit on each reply from the program.

how does it work?

forge-exec is used in your forge project and will do the following

• will ffi execute forge-exec-ipc-client init <program> [...<args>]
• forge-exec-ipc-client (this package) will then execute the program along with the provided argument and create a new process for it
• When doing so it will also apend a randonly generated socket/named-pipe path/name, that we call the socketID (prefixed with ipc:)
• the program will thus be called via <program> [...<args>] ipc:<socketID>
• That program need to create an ipc server to listen on the given socketID as soon as it can.
• forge-exec-ipc-client will then attempt to connect to that socket/named-pipe for 3 seconds and upon success will print to stdout the socketID as an abi encoded string and exit.
• forge will pick that up and forge-exec will now perform a new ffi call : forge-exec-ipc-client exec <socketID> 0x
• forge-exec-ipc-client will detect an exec as first argument and connect to the ipc server created by the program
• Once connected it will send the data argument to it (first call is always 0x)
• This means that the program can (and need to) stay alive and listen for these call
• Upon receiveing the first call 0x the program should start executing its user code.
• When it need to make a request back to forge it will simply have to reply on the ipc socket established with abi encoded data (see format below)
• forge-exec-ipc-client will write that to stdin on reception and exit immediatly (the program continue to run though, unless it execute its last reply (termination))
• forge-exec will pick up the data and interpret it as a request. One of this request is to terminate and can include an data the program may wish to return.
• if the data was not a termination request, forge-exec will execute the request (currently only send_transaction and getBalance is supported) and send that data back
• It send the data back via forge-exec-ipc-client exec <socketID> <data>
• this get repeated until the program send the termination request
• On some error case forge-exec can also call the terminate request to ask the program to stop, this will cause a revert on forge side.
• Currently abi decoding can fails on forge-exec side and the program will not be abel to be notified. As such the program should handle a timeout case to stop its ipc server to not hang on os resources.

ipc-server implementations

While you could write the ipc handling yourself in the program executed by forge-exec-ipc-client it is likely you want that abstracted.

There is currentlty one implemented in typescript which abstract away the flow and let you write the following:

import { execute } from "forge-exec-ipc-server";
execute(async (forge) => {
  const address = await forge.create({
    from: "0xFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFF",
    data: "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",
  });
  return {
    types: [{ type: "address" }],
    values: [address],
  };
});

forge-exec-ipc-server also handle timeout.

Note that while nodejs has a startup overhead, once the program is executed it stays alive and so long complicate script are possible.

format

The format of communication between the ipc client and server is as follow:

From the program

The program (which act as the ipc server) can only send one type of message to the ipc client.

All of them must end with the \n character which act as the ipc message delimiter

These are abi encoded message represented as hex string and are forwarded as is (minus the \n character) to forge-exec solidity code.

The format to encode is a tuple (uint32, bytes) where the uint32 represent the type of request and bytes is the abi encoded data specific to the request type.

The request type 0 is the termination signal and indicate that the program has finished executing, the bytes data represent whatever the program want and is what is returned by forge-exec execute function call.

Else there is currently 2 more request with more going to be added soon

See list of requests

From forge

there is only 2 type of data send to the ipc server: response and terminate.

All of them must end with the \n character

Responses

Responses are prefixed with response:

the first message the program actually receive is a special one : response:0x\n and just indicate that the program can start executing and make request back to forge.

Apart form this special request, there are currently on 2 types of request that a program can send back to forge and so there are only 2 types of response as of now

See list of requests

examples

• "response:<data send back from forge as string>\n"

Termination

Termination request are prefixed with terminate:

After the prefix is the error message

examples

• "terminate:Something Wrong Happened\n"

List of Requests

termination

from the program

example:

encode(["uint32", "bytes"],[0, "0x01"])

This will terminate execution and return 0x1 as bytes

Nothing is expected from forge back

send transaction

from the program

example:

encode(["uint32", "bytes"],[1, encode(["","","",""], [])])

from forge-exec-ipc-client

example:

"response:0xFFEEFFEEFFEEFFEEFFEEFFEEFFEEFFEEFFEEFFEE\n"

this return the deployed contract address