Add scripting (tengo) support for every incoming message (#731)

TengoModifyMessage allows you to specify the location of a tengo (https://github.com/d5/tengo/) script.
This script will receive every incoming message and can be used to modify the Username and the Text of that message.
The script will have the following global variables:
to modify: msgUsername and msgText
to read: msgChannel and msgAccount

The script is reloaded on every message, so you can modify the script on the fly.

Example script can be found in https://github.com/42wim/matterbridge/tree/master/gateway/bench.tengo
and https://github.com/42wim/matterbridge/tree/master/contrib/example.tengo

The example below will check if the text contains blah and if so, it'll replace the text and the username of that message.
text := import("text")
if text.re_match("blah",msgText) {
    msgText="replaced by this"
    msgUsername="fakeuser"
}

More information about tengo on: https://github.com/d5/tengo/blob/master/docs/tutorial.md and
https://github.com/d5/tengo/blob/master/docs/stdlib.md

vendor/github.com/d5/tengo/script/compiled.go

@@ -0,0 +1,113 @@
+package script
+
+import (
+	"context"
+	"fmt"
+
+	"github.com/d5/tengo/compiler"
+	"github.com/d5/tengo/objects"
+	"github.com/d5/tengo/runtime"
+)
+
+// Compiled is a compiled instance of the user script.
+// Use Script.Compile() to create Compiled object.
+type Compiled struct {
+	symbolTable *compiler.SymbolTable
+	machine     *runtime.VM
+}
+
+// Run executes the compiled script in the virtual machine.
+func (c *Compiled) Run() error {
+	return c.machine.Run()
+}
+
+// RunContext is like Run but includes a context.
+func (c *Compiled) RunContext(ctx context.Context) (err error) {
+	ch := make(chan error, 1)
+
+	go func() {
+		ch <- c.machine.Run()
+	}()
+
+	select {
+	case <-ctx.Done():
+		c.machine.Abort()
+		<-ch
+		err = ctx.Err()
+	case err = <-ch:
+	}
+
+	return
+}
+
+// IsDefined returns true if the variable name is defined (has value) before or after the execution.
+func (c *Compiled) IsDefined(name string) bool {
+	symbol, _, ok := c.symbolTable.Resolve(name)
+	if !ok {
+		return false
+	}
+
+	v := c.machine.Globals()[symbol.Index]
+	if v == nil {
+		return false
+	}
+
+	return *v != objects.UndefinedValue
+}
+
+// Get returns a variable identified by the name.
+func (c *Compiled) Get(name string) *Variable {
+	value := &objects.UndefinedValue
+
+	symbol, _, ok := c.symbolTable.Resolve(name)
+	if ok && symbol.Scope == compiler.ScopeGlobal {
+		value = c.machine.Globals()[symbol.Index]
+		if value == nil {
+			value = &objects.UndefinedValue
+		}
+	}
+
+	return &Variable{
+		name:  name,
+		value: value,
+	}
+}
+
+// GetAll returns all the variables that are defined by the compiled script.
+func (c *Compiled) GetAll() []*Variable {
+	var vars []*Variable
+	for _, name := range c.symbolTable.Names() {
+		symbol, _, ok := c.symbolTable.Resolve(name)
+		if ok && symbol.Scope == compiler.ScopeGlobal {
+			value := c.machine.Globals()[symbol.Index]
+			if value == nil {
+				value = &objects.UndefinedValue
+			}
+
+			vars = append(vars, &Variable{
+				name:  name,
+				value: value,
+			})
+		}
+	}
+
+	return vars
+}
+
+// Set replaces the value of a global variable identified by the name.
+// An error will be returned if the name was not defined during compilation.
+func (c *Compiled) Set(name string, value interface{}) error {
+	obj, err := objects.FromInterface(value)
+	if err != nil {
+		return err
+	}
+
+	symbol, _, ok := c.symbolTable.Resolve(name)
+	if !ok || symbol.Scope != compiler.ScopeGlobal {
+		return fmt.Errorf("'%s' is not defined", name)
+	}
+
+	c.machine.Globals()[symbol.Index] = &obj
+
+	return nil
+}

vendor/github.com/d5/tengo/script/conversion.go

@@ -0,0 +1,33 @@
+package script
+
+import (
+	"github.com/d5/tengo/objects"
+)
+
+func objectToInterface(o objects.Object) interface{} {
+	switch val := o.(type) {
+	case *objects.Array:
+		return val.Value
+	case *objects.Map:
+		return val.Value
+	case *objects.Int:
+		return val.Value
+	case *objects.Float:
+		return val.Value
+	case *objects.Bool:
+		if val == objects.TrueValue {
+			return true
+		}
+		return false
+	case *objects.Char:
+		return val.Value
+	case *objects.String:
+		return val.Value
+	case *objects.Bytes:
+		return val.Value
+	case *objects.Undefined:
+		return nil
+	}
+
+	return o
+}

vendor/github.com/d5/tengo/script/script.go

@@ -0,0 +1,180 @@
+package script
+
+import (
+	"context"
+	"fmt"
+
+	"github.com/d5/tengo/compiler"
+	"github.com/d5/tengo/compiler/parser"
+	"github.com/d5/tengo/compiler/source"
+	"github.com/d5/tengo/objects"
+	"github.com/d5/tengo/runtime"
+	"github.com/d5/tengo/stdlib"
+)
+
+// Script can simplify compilation and execution of embedded scripts.
+type Script struct {
+	variables         map[string]*Variable
+	removedBuiltins   map[string]bool
+	removedStdModules map[string]bool
+	userModuleLoader  compiler.ModuleLoader
+	input             []byte
+}
+
+// New creates a Script instance with an input script.
+func New(input []byte) *Script {
+	return &Script{
+		variables: make(map[string]*Variable),
+		input:     input,
+	}
+}
+
+// Add adds a new variable or updates an existing variable to the script.
+func (s *Script) Add(name string, value interface{}) error {
+	obj, err := objects.FromInterface(value)
+	if err != nil {
+		return err
+	}
+
+	s.variables[name] = &Variable{
+		name:  name,
+		value: &obj,
+	}
+
+	return nil
+}
+
+// Remove removes (undefines) an existing variable for the script.
+// It returns false if the variable name is not defined.
+func (s *Script) Remove(name string) bool {
+	if _, ok := s.variables[name]; !ok {
+		return false
+	}
+
+	delete(s.variables, name)
+
+	return true
+}
+
+// DisableBuiltinFunction disables a builtin function.
+func (s *Script) DisableBuiltinFunction(name string) {
+	if s.removedBuiltins == nil {
+		s.removedBuiltins = make(map[string]bool)
+	}
+
+	s.removedBuiltins[name] = true
+}
+
+// DisableStdModule disables a standard library module.
+func (s *Script) DisableStdModule(name string) {
+	if s.removedStdModules == nil {
+		s.removedStdModules = make(map[string]bool)
+	}
+
+	s.removedStdModules[name] = true
+}
+
+// SetUserModuleLoader sets the user module loader for the compiler.
+func (s *Script) SetUserModuleLoader(loader compiler.ModuleLoader) {
+	s.userModuleLoader = loader
+}
+
+// Compile compiles the script with all the defined variables, and, returns Compiled object.
+func (s *Script) Compile() (*Compiled, error) {
+	symbolTable, stdModules, globals, err := s.prepCompile()
+	if err != nil {
+		return nil, err
+	}
+
+	fileSet := source.NewFileSet()
+	srcFile := fileSet.AddFile("(main)", -1, len(s.input))
+
+	p := parser.NewParser(srcFile, s.input, nil)
+	file, err := p.ParseFile()
+	if err != nil {
+		return nil, fmt.Errorf("parse error: %s", err.Error())
+	}
+
+	c := compiler.NewCompiler(srcFile, symbolTable, nil, stdModules, nil)
+
+	if s.userModuleLoader != nil {
+		c.SetModuleLoader(s.userModuleLoader)
+	}
+
+	if err := c.Compile(file); err != nil {
+		return nil, err
+	}
+
+	return &Compiled{
+		symbolTable: symbolTable,
+		machine:     runtime.NewVM(c.Bytecode(), globals, nil),
+	}, nil
+}
+
+// Run compiles and runs the scripts.
+// Use returned compiled object to access global variables.
+func (s *Script) Run() (compiled *Compiled, err error) {
+	compiled, err = s.Compile()
+	if err != nil {
+		return
+	}
+
+	err = compiled.Run()
+
+	return
+}
+
+// RunContext is like Run but includes a context.
+func (s *Script) RunContext(ctx context.Context) (compiled *Compiled, err error) {
+	compiled, err = s.Compile()
+	if err != nil {
+		return
+	}
+
+	err = compiled.RunContext(ctx)
+
+	return
+}
+
+func (s *Script) prepCompile() (symbolTable *compiler.SymbolTable, stdModules map[string]bool, globals []*objects.Object, err error) {
+	var names []string
+	for name := range s.variables {
+		names = append(names, name)
+	}
+
+	symbolTable = compiler.NewSymbolTable()
+	for idx, fn := range objects.Builtins {
+		if !s.removedBuiltins[fn.Name] {
+			symbolTable.DefineBuiltin(idx, fn.Name)
+		}
+	}
+
+	stdModules = make(map[string]bool)
+	for name := range stdlib.Modules {
+		if !s.removedStdModules[name] {
+			stdModules[name] = true
+		}
+	}
+
+	globals = make([]*objects.Object, runtime.GlobalsSize, runtime.GlobalsSize)
+
+	for idx, name := range names {
+		symbol := symbolTable.Define(name)
+		if symbol.Index != idx {
+			panic(fmt.Errorf("wrong symbol index: %d != %d", idx, symbol.Index))
+		}
+
+		globals[symbol.Index] = s.variables[name].value
+	}
+
+	return
+}
+
+func (s *Script) copyVariables() map[string]*Variable {
+	vars := make(map[string]*Variable)
+	for n, v := range s.variables {
+		vars[n] = v
+	}
+
+	return vars
+}

vendor/github.com/d5/tengo/script/variable.go

@@ -0,0 +1,149 @@
+package script
+
+import (
+	"errors"
+
+	"github.com/d5/tengo/objects"
+)
+
+// Variable is a user-defined variable for the script.
+type Variable struct {
+	name  string
+	value *objects.Object
+}
+
+// NewVariable creates a Variable.
+func NewVariable(name string, value interface{}) (*Variable, error) {
+	obj, err := objects.FromInterface(value)
+	if err != nil {
+		return nil, err
+	}
+
+	return &Variable{
+		name:  name,
+		value: &obj,
+	}, nil
+}
+
+// Name returns the name of the variable.
+func (v *Variable) Name() string {
+	return v.name
+}
+
+// Value returns an empty interface of the variable value.
+func (v *Variable) Value() interface{} {
+	return objectToInterface(*v.value)
+}
+
+// ValueType returns the name of the value type.
+func (v *Variable) ValueType() string {
+	return (*v.value).TypeName()
+}
+
+// Int returns int value of the variable value.
+// It returns 0 if the value is not convertible to int.
+func (v *Variable) Int() int {
+	c, _ := objects.ToInt(*v.value)
+
+	return c
+}
+
+// Int64 returns int64 value of the variable value.
+// It returns 0 if the value is not convertible to int64.
+func (v *Variable) Int64() int64 {
+	c, _ := objects.ToInt64(*v.value)
+
+	return c
+}
+
+// Float returns float64 value of the variable value.
+// It returns 0.0 if the value is not convertible to float64.
+func (v *Variable) Float() float64 {
+	c, _ := objects.ToFloat64(*v.value)
+
+	return c
+}
+
+// Char returns rune value of the variable value.
+// It returns 0 if the value is not convertible to rune.
+func (v *Variable) Char() rune {
+	c, _ := objects.ToRune(*v.value)
+
+	return c
+}
+
+// Bool returns bool value of the variable value.
+// It returns 0 if the value is not convertible to bool.
+func (v *Variable) Bool() bool {
+	c, _ := objects.ToBool(*v.value)
+
+	return c
+}
+
+// Array returns []interface value of the variable value.
+// It returns 0 if the value is not convertible to []interface.
+func (v *Variable) Array() []interface{} {
+	switch val := (*v.value).(type) {
+	case *objects.Array:
+		var arr []interface{}
+		for _, e := range val.Value {
+			arr = append(arr, objectToInterface(e))
+		}
+		return arr
+	}
+
+	return nil
+}
+
+// Map returns map[string]interface{} value of the variable value.
+// It returns 0 if the value is not convertible to map[string]interface{}.
+func (v *Variable) Map() map[string]interface{} {
+	switch val := (*v.value).(type) {
+	case *objects.Map:
+		kv := make(map[string]interface{})
+		for mk, mv := range val.Value {
+			kv[mk] = objectToInterface(mv)
+		}
+		return kv
+	}
+
+	return nil
+}
+
+// String returns string value of the variable value.
+// It returns 0 if the value is not convertible to string.
+func (v *Variable) String() string {
+	c, _ := objects.ToString(*v.value)
+
+	return c
+}
+
+// Bytes returns a byte slice of the variable value.
+// It returns nil if the value is not convertible to byte slice.
+func (v *Variable) Bytes() []byte {
+	c, _ := objects.ToByteSlice(*v.value)
+
+	return c
+}
+
+// Error returns an error if the underlying value is error object.
+// If not, this returns nil.
+func (v *Variable) Error() error {
+	err, ok := (*v.value).(*objects.Error)
+	if ok {
+		return errors.New(err.String())
+	}
+
+	return nil
+}
+
+// Object returns an underlying Object of the variable value.
+// Note that returned Object is a copy of an actual Object used in the script.
+func (v *Variable) Object() objects.Object {
+	return *v.value
+}
+
+// IsUndefined returns true if the underlying value is undefined.
+func (v *Variable) IsUndefined() bool {
+	return *v.value == objects.UndefinedValue
+}