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Your first Go mod

This builds examples/hello-pier-go: a command, a listener on player joins, and a task that runs one second after the mod is enabled.

The module

A mod is an ordinary Go module whose main package is built as a DLL:

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go.mod
main.go
manifest.json

go.mod requires the binding. Inside the Pier repository the example points at it with a replace; a mod of your own requires it by version instead.

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module hello-pier-go

go 1.21

require github.com/Maskviva/pier/bindings/go v0.0.0

replace github.com/Maskviva/pier/bindings/go => ../../bindings/go

main.go

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package main

import (
    "time"

    "github.com/Maskviva/pier/bindings/go/levilamina"
)

type hello struct {
    joins *levilamina.Listener
}

func (h *hello) Enable(ctx *levilamina.Context) error {
    log := ctx.Logger()
    joins, err := levilamina.Subscribe("ll::event::PlayerJoinEvent", levilamina.PriorityNormal, func(ev *levilamina.Event) {
        log.Info("a player joined: " + ev.SNBT)
    })
    if err != nil {
        return err
    }
    h.joins = joins

    err = levilamina.RegisterCommand("hellogo", "Says hello from a Go mod.", levilamina.PermissionAny, func(inv *levilamina.Invocation) {
        inv.Success("hello from a Go mod, " + inv.Origin)
    })
    if err != nil {
        log.Warn(err.Error())
    }

    _, err = levilamina.ScheduleAfter(time.Second, func() { log.Info("one second later") })
    return err
}

func (h *hello) Disable(ctx *levilamina.Context) error {
    return h.joins.Unsubscribe()
}

func init() {
    levilamina.Register("hello-pier-go", &hello{})
}

func main() {}

Register runs from init, because the host calls pier_main after the Go runtime has run every init and before anything else. main is required by the build mode and never runs.

A failed command registration logs a warning and enabling goes on: the rest of the mod does not need the command, and the warning says which command is missing and why.

Build

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set CGO_ENABLED=1
go build -buildmode=c-shared -trimpath -o hello_pier_go.dll .

build.bat in the example does the same and says what is missing when Go or gcc is not on PATH.

Install

manifest.json names the DLL and declares the mod as type pier:

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{
    "name": "hello-pier-go",
    "entry": "hello_pier_go.dll",
    "type": "pier",
    "version": "0.1.0",
    "dependencies": [{ "name": "pier" }]
}

Put both files in plugins/hello-pier-go/ and start the server. The log shows the mod loading and enabling, and one second later the line from the task. /hellogo answers in game and from the console.

If the mod does not load, Troubleshooting lists the log lines and what each means.