183 lines
6.7 KiB
Markdown
183 lines
6.7 KiB
Markdown
# Interoperability
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## Table of Contents
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- [Using Scripts](#using-scripts)
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- [Type Conversion Table](#type-conversion-table)
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- [User Types](#user-types)
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- [Sandbox Environments](#sandbox-environments)
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- [Compiler and VM](#compiler-and-vm)
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## Using Scripts
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Embedding and executing the Tengo code in Go is very easy. At a high level, this process is like:
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- create a [Script](https://godoc.org/github.com/d5/tengo/script#Script) instance with your code,
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- _optionally_ add some [Script Variables](https://godoc.org/github.com/d5/tengo/script#Variable) to Script,
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- compile or directly run the script,
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- retrieve _output_ values from the [Compiled](https://godoc.org/github.com/d5/tengo/script#Compiled) instance.
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The following is an example where a Tengo script is compiled and run with no input/output variables.
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```golang
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import "github.com/d5/tengo/script"
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var code = `
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reduce := func(seq, fn) {
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s := 0
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for x in seq { fn(x, s) }
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return s
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}
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print(reduce([1, 2, 3], func(x, s) { s += x }))
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`
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func main() {
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s := script.New([]byte(code))
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if _, err := s.Run(); err != nil {
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panic(err)
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}
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}
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```
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Here's another example where an input variable is added to the script, and, an output variable is accessed through [Variable.Int](https://godoc.org/github.com/d5/tengo/script#Variable.Int) function:
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```golang
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import (
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"fmt"
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"github.com/d5/tengo/script"
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)
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func main() {
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s := script.New([]byte(`a := b + 20`))
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// define variable 'b'
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_ = s.Add("b", 10)
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// compile the source
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c, err := s.Compile()
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if err != nil {
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panic(err)
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}
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// run the compiled bytecode
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// a compiled bytecode 'c' can be executed multiple times without re-compiling it
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if err := c.Run(); err != nil {
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panic(err)
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}
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// retrieve value of 'a'
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a := c.Get("a")
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fmt.Println(a.Int()) // prints "30"
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// re-run after replacing value of 'b'
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if err := c.Set("b", 20); err != nil {
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panic(err)
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}
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if err := c.Run(); err != nil {
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panic(err)
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}
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fmt.Println(c.Get("a").Int()) // prints "40"
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}
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```
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A variable `b` is defined by the user before compilation using [Script.Add](https://godoc.org/github.com/d5/tengo/script#Script.Add) function. Then a compiled bytecode `c` is used to execute the bytecode and get the value of global variables. In this example, the value of global variable `a` is read using [Compiled.Get](https://godoc.org/github.com/d5/tengo/script#Compiled.Get) function. See [documentation](https://godoc.org/github.com/d5/tengo/script#Variable) for the full list of variable value functions.
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Value of the global variables can be replaced using [Compiled.Set](https://godoc.org/github.com/d5/tengo/script#Compiled.Set) function. But it will return an error if you try to set the value of un-defined global variables _(e.g. trying to set the value of `x` in the example)_.
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### Type Conversion Table
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When adding a Variable _([Script.Add](https://godoc.org/github.com/d5/tengo/script#Script.Add))_, Script converts Go values into Tengo values based on the following conversion table.
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| Go Type | Tengo Type | Note |
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| :--- | :--- | :--- |
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|`nil`|`Undefined`||
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|`string`|`String`||
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|`int64`|`Int`||
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|`int`|`Int`||
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|`bool`|`Bool`||
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|`rune`|`Char`||
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|`byte`|`Char`||
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|`float64`|`Float`||
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|`[]byte`|`Bytes`||
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|`time.Time`|`Time`||
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|`error`|`Error{String}`|use `error.Error()` as String value|
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|`map[string]Object`|`Map`||
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|`map[string]interface{}`|`Map`|individual elements converted to Tengo objects|
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|`[]Object`|`Array`||
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|`[]interface{}`|`Array`|individual elements converted to Tengo objects|
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|`Object`|`Object`|_(no type conversion performed)_|
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### User Types
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Users can add and use a custom user type in Tengo code by implementing [Object](https://godoc.org/github.com/d5/tengo/objects#Object) interface. Tengo runtime will treat the user types in the same way it does to the runtime types with no performance overhead. See [Object Types](https://github.com/d5/tengo/blob/master/docs/objects.md) for more details.
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## Sandbox Environments
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To securely compile and execute _potentially_ unsafe script code, you can use the following Script functions.
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#### Script.SetBuiltinFunctions(funcs []*objects.BuiltinFunction)
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SetBuiltinFunctions resets all builtin functions in the compiler to the ones provided in the input parameter. Compiler will report a compile-time error if the a function not set is referenced. Passing `nil` will disable all builtin functions. All builtin functions **are included by default** unless `SetBuiltinFunctions` is called.
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```golang
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s := script.New([]byte(`print([1, 2, 3])`))
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_, err := s.Run() // prints [1, 2, 3]
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s.SetBuiltinFunctions(nil)
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_, err := s.Run() // compile error
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s.SetBuiltinFunctions([]*objects.BuiltinFunction{&objects.Builtins[0]})
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_, err := s.Run() // prints [1, 2, 3]
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```
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#### Script.SetBuiltinModules(modules map[string]*objects.ImmutableMap)
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SetBuiltinModules adds builtin modules provided in the input parameter. This can be used to add [standard library](https://github.com/d5/tengo/blob/master/docs/stdlib.md) modules into the compiler and VM. Compiler will report a compile-time error if the code tries to import a module that hasn't been included. Passing `nil` will disable all builtin modules. No standard library modules are included by default unless `SetBuiltinModules` is called.
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```golang
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s := script.New([]byte(`math := import("math"); a := math.abs(-19.84)`))
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_, err := s.Run() // compile error
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s.SetBuiltinModules(stdlib.Modules)
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_, err := s.Run() // a = 19.84
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s.SetBuiltinModules(nil)
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_, err := s.Run() // compile error
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s.SetBuiltinModules(map[string]*objects.ImmutableMap{"math": stdlib.Modules["math"]})
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_, err := s.Run() // a = 19.84
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```
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#### Script.SetUserModuleLoader(loader compiler.ModuleLoader)
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SetUserModuleLoader replaces the default user-module loader of the compiler, which tries to read the source from a local file.
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```golang
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s := script.New([]byte(`math := import("mod1"); a := math.foo()`))
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s.SetUserModuleLoader(func(moduleName string) ([]byte, error) {
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if moduleName == "mod1" {
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return []byte(`foo := func() { return 5 }`), nil
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}
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return nil, errors.New("module not found")
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})
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```
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Note that when a script is being added to another script as a module (via `Script.AddModule`), it does not inherit the module loader from the main script.
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## Compiler and VM
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Although it's not recommended, you can directly create and run the Tengo [Parser](https://godoc.org/github.com/d5/tengo/compiler/parser#Parser), [Compiler](https://godoc.org/github.com/d5/tengo/compiler#Compiler), and [VM](https://godoc.org/github.com/d5/tengo/runtime#VM) for yourself instead of using Scripts and Script Variables. It's a bit more involved as you have to manage the symbol tables and global variables between them, but, basically that's what Script and Script Variable is doing internally.
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_TODO: add more information here_
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