vise/go/engine/engine.go
2023-04-01 15:04:44 +01:00

101 lines
2.7 KiB
Go

package engine
import (
"context"
"fmt"
"io"
"log"
"git.defalsify.org/festive/resource"
"git.defalsify.org/festive/state"
"git.defalsify.org/festive/vm"
)
//
//type Config struct {
// FlagCount uint32
// CacheSize uint32
//}
// Engine is an execution engine that handles top-level errors when running user inputs against currently exposed bytecode.
type Engine struct {
st *state.State
rs resource.Resource
}
// NewEngine creates a new Engine
func NewEngine(st *state.State, rs resource.Resource) Engine {
engine := Engine{st, rs}
return engine
}
// Init must be explicitly called before using the Engine instance.
//
// It makes sure bootstrapping code has been executed, and that the exposed bytecode is ready for user input.
func(en *Engine) Init(ctx context.Context) error {
b := vm.NewLine([]byte{}, vm.MOVE, []string{"root"}, nil, nil)
var err error
_, err = vm.Run(b, en.st, en.rs, ctx)
if err != nil {
return err
}
location := en.st.Where()
code, err := en.rs.GetCode(location)
if err != nil {
return err
}
return en.st.AppendCode(code)
}
// Exec processes user input against the current state of the virtual machine environment.
//
// If successfully executed:
// - output of the last execution is available using the WriteResult(...) call
// - Exec(...) may be called again with new input
//
// This implementation is in alpha state. That means that any error emitted may have left the system in an undefined state.
//
// TODO: Disambiguate errors as critical and resumable errors.
//
// Fails if:
// - input is objectively invalid (too long etc)
// - no current bytecode is available
// - input processing against bytcode failed
func (en *Engine) Exec(input []byte, ctx context.Context) error {
l := uint8(len(input))
if l > 255 {
return fmt.Errorf("input too long (%v)", l)
}
input = append([]byte{l}, input...)
code, err := en.st.GetCode()
if err != nil {
return err
}
if len(code) == 0 {
return fmt.Errorf("no code to execute")
}
code, err = vm.Apply(input, code, en.st, en.rs, ctx)
en.st.SetCode(code)
return err
}
// WriteResult writes the output of the last vm execution to the given writer.
//
// Fails if
// - required data inputs to the template are not available.
// - the template for the given node point is note available for retrieval using the resource.Resource implementer.
// - the supplied writer fails to process the writes.
func(en *Engine) WriteResult(w io.Writer) error {
location := en.st.Where()
v, err := en.st.Get()
if err != nil {
return err
}
r, err := en.rs.RenderTemplate(location, v)
if err != nil {
return err
}
c, err := io.WriteString(w, r)
log.Printf("%v bytes written as result for %v", c, location)
return err
}