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package plugin
import (
"context"
"fmt"
"os"
"path/filepath"
"sync"
"sync/atomic"
"time"
lua "github.com/yuin/gopher-lua"
"github.com/shiv/internal/logger"
"github.com/shiv/internal/store"
)
const callTimeout = 500 * time.Millisecond
// Plugin is a single loaded Lua script with its own isolated VM.
// mu serialises all VM access — gopher-lua LState is not goroutine-safe.
type Plugin struct {
name string
path string
L *lua.LState
mu sync.Mutex
// enabled controls whether this plugin's hooks are called.
// Uses atomic.Bool so the engine can check it without acquiring mu.
enabled atomic.Bool
// logBuf accumulates log() calls made during a Lua hook execution.
// Written only while mu is held (log() can only be called from within
// a Lua hook, which always runs under mu). Drained by the engine after
// each hook call via drainLogs, which also acquires mu.
logBuf []string
}
// load reads the Lua file, registers the full API, executes the script,
// then calls on_load() if defined.
func load(path string, st *store.Store) (*Plugin, error) {
name := filepath.Base(path)
L := lua.NewState(lua.Options{
SkipOpenLibs: false,
})
p := &Plugin{name: name, path: path, L: L}
p.enabled.Store(true)
// Register API before executing the script so on_load can use it.
// The logFn closure appends to p.logBuf. It is safe without acquiring
// mu because log() is only ever invoked from within a Lua hook, which
// always runs under mu via callNoReturn or callWithBuilder.
registerAPI(L, st, func(msg string) {
p.logBuf = append(p.logBuf, msg)
})
if err := L.DoFile(path); err != nil {
L.Close()
return nil, fmt.Errorf("plugin %s: load: %w", name, err)
}
// Call on_load() if defined — errors are logged but not fatal.
if L.GetGlobal("on_load") != lua.LNil {
if err := p.callNoReturn("on_load", lua.LNil); err != nil {
logger.Error("plugin %s: on_load: %v", name, err)
}
}
return p, nil
}
// callNoReturn invokes a Lua function that returns nothing.
// Holds mu for the duration. Enforces callTimeout. Recovers panics.
func (p *Plugin) callNoReturn(fn string, arg lua.LValue) (retErr error) {
p.mu.Lock()
defer p.mu.Unlock()
defer func() {
if r := recover(); r != nil {
retErr = fmt.Errorf("panic: %v", r)
}
}()
f := p.L.GetGlobal(fn)
if f == lua.LNil {
return nil
}
ctx, cancel := context.WithTimeout(context.Background(), callTimeout)
defer cancel()
p.L.SetContext(ctx)
defer p.L.SetContext(context.Background())
params := lua.P{Fn: f, NRet: 0, Protect: true}
if arg != lua.LNil {
return p.L.CallByParam(params, arg)
}
return p.L.CallByParam(params)
}
// callWithBuilder builds a Lua table and calls fn with it in a single locked
// section, returning the result table. builder receives the VM and must
// construct and return the argument table — it runs under mu. The Lua call
// also runs under mu, so no VM access escapes the lock at any point.
// Returns the returned table, or nil if the function returned nothing.
func (p *Plugin) callWithBuilder(fn string, builder func(L *lua.LState) *lua.LTable) (ret *lua.LTable, retErr error) {
p.mu.Lock()
defer p.mu.Unlock()
defer func() {
if r := recover(); r != nil {
retErr = fmt.Errorf("panic: %v", r)
}
}()
f := p.L.GetGlobal(fn)
if f == lua.LNil {
return nil, nil
}
arg := builder(p.L)
ctx, cancel := context.WithTimeout(context.Background(), callTimeout)
defer cancel()
p.L.SetContext(ctx)
defer p.L.SetContext(context.Background())
if err := p.L.CallByParam(lua.P{Fn: f, NRet: 1, Protect: true}, arg); err != nil {
return nil, err
}
top := p.L.Get(-1)
p.L.Pop(1)
if tbl, ok := top.(*lua.LTable); ok {
return tbl, nil
}
return nil, nil
}
// drainLogs returns all buffered log lines and clears the buffer.
// Called by the engine after each hook invocation so log lines can be
// emitted onto the bus. Acquires mu independently of the hook call.
func (p *Plugin) drainLogs() []string {
p.mu.Lock()
defer p.mu.Unlock()
if len(p.logBuf) == 0 {
return nil
}
lines := p.logBuf
p.logBuf = nil
return lines
}
// close shuts down the Lua VM.
func (p *Plugin) close() {
p.mu.Lock()
defer p.mu.Unlock()
p.L.Close()
}
// has returns true if the plugin defines the named global function.
func (p *Plugin) has(fn string) bool {
p.mu.Lock()
defer p.mu.Unlock()
return p.L.GetGlobal(fn) != lua.LNil
}
// loadDir scans dir for *.lua files and loads each as a Plugin.
// Files that fail to load are logged and skipped.
func loadDir(dir string, st *store.Store) ([]*Plugin, error) {
entries, err := os.ReadDir(dir)
if err != nil {
if os.IsNotExist(err) {
return nil, nil
}
return nil, fmt.Errorf("plugin: read dir %s: %w", dir, err)
}
var plugins []*Plugin
for _, e := range entries {
if e.IsDir() || filepath.Ext(e.Name()) != ".lua" {
continue
}
path := filepath.Join(dir, e.Name())
p, err := load(path, st)
if err != nil {
logger.Error("plugin: skip %s: %v", e.Name(), err)
continue
}
logger.Info("plugin: loaded %s", e.Name())
plugins = append(plugins, p)
}
return plugins, nil
}
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