vise/engine/engine.go

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package engine
import (
"context"
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"fmt"
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"io"
"log"
"git.defalsify.org/festive/cache"
"git.defalsify.org/festive/render"
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"git.defalsify.org/festive/resource"
"git.defalsify.org/festive/state"
"git.defalsify.org/festive/vm"
)
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// Config globally defines behavior of all components driven by the engine.
type Config struct {
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OutputSize uint32 // Maximum size of output from a single rendered page
}
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// Engine is an execution engine that handles top-level errors when running client inputs against code in the bytecode buffer.
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type Engine struct {
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st *state.State
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rs resource.Resource
ca cache.Memory
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vm *vm.Vm
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}
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// NewEngine creates a new Engine
func NewEngine(cfg Config, st *state.State, rs resource.Resource, ca cache.Memory) Engine {
var szr *render.Sizer
if cfg.OutputSize > 0 {
szr = render.NewSizer(cfg.OutputSize)
}
engine := Engine{
st: st,
rs: rs,
ca: ca,
vm: vm.NewVm(st, rs, ca, szr),
}
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return engine
}
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// Init must be explicitly called before using the Engine instance.
//
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// It loads and executes code for the start node.
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func(en *Engine) Init(sym string, ctx context.Context) error {
err := en.st.SetInput([]byte{})
if err != nil {
return err
}
b := vm.NewLine(nil, vm.MOVE, []string{sym}, nil, nil)
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b, err = en.vm.Run(b, ctx)
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if err != nil {
return err
}
en.st.SetCode(b)
return nil
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}
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// Exec processes user input against the current state of the virtual machine environment.
//
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// If successfully executed, output of the last execution is available using the WriteResult call.
//
// A bool return valus of false indicates that execution should be terminated. Calling Exec again has undefined effects.
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//
// Fails if:
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// - input is formally invalid (too long etc)
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// - no current bytecode is available
// - input processing against bytcode failed
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func (en *Engine) Exec(input []byte, ctx context.Context) (bool, error) {
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err := vm.ValidInput(input)
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if err != nil {
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return true, err
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}
err = en.st.SetInput(input)
if err != nil {
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return false, err
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}
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log.Printf("new execution with input '%s' (0x%x)", input, input)
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code, err := en.st.GetCode()
if err != nil {
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return false, err
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}
if len(code) == 0 {
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return false, fmt.Errorf("no code to execute")
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}
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code, err = en.vm.Run(code, ctx)
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if err != nil {
return false, err
}
v, err := en.st.MatchFlag(state.FLAG_TERMINATE, false)
if err != nil {
return false, err
}
if v {
if len(code) > 0 {
log.Printf("terminated with code remaining: %x", code)
}
return false, nil
}
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en.st.SetCode(code)
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if len(code) == 0 {
log.Printf("runner finished with no remaining code")
return false, nil
}
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return true, nil
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}
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// 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.
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func(en *Engine) WriteResult(w io.Writer, ctx context.Context) error {
r, err := en.vm.Render(ctx)
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if err != nil {
return err
}
_, err = io.WriteString(w, r)
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return err
}