linstrom/plugins/pluginLoader.go

package plugins

import (
	"bufio"
	"crypto/sha256"
	"encoding/hex"
	"encoding/json"
	"errors"
	"fmt"
	"io"
	"os"
	"path"
	"sync"

	"git.mstar.dev/mstar/goutils/other"
	lua "github.com/yuin/gopher-lua"
	"github.com/yuin/gopher-lua/parse"
)

/*
Plugin structure expectation:
- meta.json for plugin metadata:
  - version
  - name
  - source location (where the plugin can be sourced from)
  - license
  - file hashes (every file in the plugin dir, sha256, hex encoded)
  - entry file name
  - Hook to table key name list (which function in the returned table is for what hook)
- Entry script returns a table
*/

const PluginMetadataFileName = "meta.json"

var (
	ErrNoHashForFile           = errors.New("no hash for file in the metadata")
	ErrInvalidHash             = errors.New("hashes don't match")
	ErrMissingFile             = errors.New("a required file is missing")
	ErrInvalidEntryReturnValue = errors.New(
		"entry script returned an invalid value. Must be a table",
	)
)

var compCache = map[string]*lua.FunctionProto{}
var compCacheLock = sync.RWMutex{}

// Load the plugin located in a provided folder into the given state.
// Validates the data, compiles it for future reuse and links up the hooks
func LoadPlugin(location string, lState *lua.LState) (*pluginHolder, error) {
	metaFileData, err := os.ReadFile(location + "/" + PluginMetadataFileName)
	if err != nil {
		return nil, err
	}
	metadata := PluginMetadata{}
	err = json.Unmarshal(metaFileData, &metadata)
	if err != nil {
		return nil, err
	}
	compCacheLock.RLock()
	precompiled, ok := compCache[metadata.Name+metadata.Version]
	compCacheLock.RUnlock()
	if !ok {
		// This version of a plugin not in the cache yet, validate the plugin dir, compile it and add it to the cache
		precompiled, err = compilePluginDir(&metadata, location)
		if err != nil {
			return nil, err
		}
		compCacheLock.Lock()
		compCache[metadata.Name+metadata.Version] = precompiled
		compCacheLock.Unlock()
	}
	lFunc := lState.NewFunctionFromProto(precompiled)
	lState.Push(lFunc)
	if err = lState.PCall(0, lua.MultRet, nil); err != nil {
		return nil, err
	}
	return generatePluginHolder(lState, &metadata)
}

// Compiles a given lua file for future use
func compileFile(filePath string) (*lua.FunctionProto, error) {
	file, err := os.Open(filePath)
	defer func() { _ = file.Close() }()
	if err != nil {
		return nil, err
	}
	reader := bufio.NewReader(file)
	chunk, err := parse.Parse(reader, filePath)
	if err != nil {
		return nil, err
	}
	proto, err := lua.Compile(chunk, filePath)
	if err != nil {
		return nil, err
	}
	return proto, nil
}

// Validates the given plugin dir and compiles it for future use
func compilePluginDir(metadata *PluginMetadata, location string) (*lua.FunctionProto, error) {
	if err := checkDir(location, "", metadata.Hashes); err != nil {
		return nil, err
	}
	entryFileName := path.Join(location, metadata.EntryFile)
	if _, err := os.Stat(entryFileName); err != nil {
		return nil, other.Error("plugins", fmt.Sprintf("missing entry file %s", entryFileName), err)
	}
	compiled, err := compileFile(entryFileName)
	if err != nil {
		return nil, err
	}
	return compiled, nil
}

// Ensures that all files in the given root directory (plus suffix) match the expected hashes provided in the metadata
func checkDir(rootPath string, suffix string, expectedHashes map[string]string) error {
	rootEntries, err := os.ReadDir(path.Join(rootPath, suffix))
	if err != nil {
		return err
	}
	for _, entry := range rootEntries {
		if suffix == "" && entry.Name() == PluginMetadataFileName {
			continue
		}
		if entry.IsDir() {
			if err = checkDir(rootPath, path.Join(suffix, entry.Name()), expectedHashes); err != nil {
				return err
			}
		}
		fileName := path.Join(rootPath, suffix, entry.Name())
		expectedHash, ok := expectedHashes[fileName]
		if !ok {
			return other.Error(
				"plugins",
				fmt.Sprintf("No hash found in metadata for file %s", fileName),
				ErrNoHashForFile,
			)
		}
		f, err := os.Open(fileName)
		if err != nil {
			return err
		}
		defer func() { _ = f.Close() }()
		if err = checkHash(f, expectedHash); err != nil {
			return err
		}
	}
	return nil
}

// Checks if a hash matches the given file
func checkHash(file *os.File, expected string) error {
	hasher := sha256.New()
	_, err := io.Copy(hasher, file)
	if err != nil {
		return err
	}
	sum := hasher.Sum([]byte{})
	if expected != hex.EncodeToString(sum) {
		return ErrInvalidHash
	}
	return nil
}

// Properly inserts the plugin into the state's global context.
// Also gets links to all functions found that are named as hook in the metadata.
// Assumptions: Called after the entry file has been run, but before any other operations
func generatePluginHolder(l *lua.LState, meta *PluginMetadata) (*pluginHolder, error) {
	pluginTable, ok := l.Get(1).(*lua.LTable)
	if !ok || pluginTable.MaxN() != 0 {
		return nil, ErrInvalidEntryReturnValue
	}
	l.SetGlobal(meta.Name, pluginTable)
	pMap := lTableToMap(pluginTable)
	holder := pluginHolder{
		meta:  meta,
		table: pluginTable,
	}
	if postLocalMessageHookName, ok := meta.HookNames[HookPostLocalMessage]; ok {
		if lV, ok := pMap[lua.LString(postLocalMessageHookName)].(*lua.LFunction); ok {
			holder.postLocalMessage = lV
		}
	}
	if postExternalMessageHookName, ok := meta.HookNames[HookPostExternalMessage]; ok {
		if lV, ok := pMap[lua.LString(postExternalMessageHookName)].(*lua.LFunction); ok {
			holder.postExternalMessage = lV
		}
	}
	if postNewLocalAccountName, ok := meta.HookNames[HookPostNewLocalAccount]; ok {
		if lV, ok := pMap[lua.LString(postNewLocalAccountName)].(*lua.LFunction); ok {
			holder.postNewLocalAccount = lV
		}
	}
	if postRemoteAccountDiscoveredName, ok := meta.HookNames[HookPostRemoteAccountDiscovered]; ok {
		if lV, ok := pMap[lua.LString(postRemoteAccountDiscoveredName)].(*lua.LFunction); ok {
			holder.postRemoteAccountDiscovered = lV
		}
	}
	return &holder, nil
}