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environment.go
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environment.go
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package starkit
import (
"context"
"fmt"
"path/filepath"
"strings"
"github.com/pkg/errors"
"go.starlark.net/starlark"
)
// The main entrypoint to starkit.
// Execute a file with a set of starlark extensions.
func ExecFile(path string, extensions ...Extension) (Model, error) {
return newEnvironment(extensions...).start(path)
}
const argUnpackerKey = "starkit.ArgUnpacker"
const modelKey = "starkit.Model"
const ctxKey = "starkit.Ctx"
// Unpacks args, using the arg unpacker on the current thread.
func UnpackArgs(t *starlark.Thread, fnName string, args starlark.Tuple, kwargs []starlark.Tuple, pairs ...interface{}) error {
unpacker, ok := t.Local(argUnpackerKey).(ArgUnpacker)
if !ok {
return starlark.UnpackArgs(fnName, args, kwargs, pairs...)
}
return unpacker(fnName, args, kwargs, pairs...)
}
// A starlark execution environment.
type Environment struct {
ctx context.Context
unpackArgs ArgUnpacker
loadCache map[string]loadCacheEntry
predeclared starlark.StringDict
print func(thread *starlark.Thread, msg string)
extensions []Extension
fakeFileSystem map[string]string
loadInterceptors []LoadInterceptor
}
func newEnvironment(extensions ...Extension) *Environment {
return &Environment{
unpackArgs: starlark.UnpackArgs,
loadCache: make(map[string]loadCacheEntry),
extensions: append([]Extension{}, extensions...),
predeclared: starlark.StringDict{},
fakeFileSystem: nil,
}
}
func (e *Environment) AddLoadInterceptor(i LoadInterceptor) {
e.loadInterceptors = append(e.loadInterceptors, i)
}
func (e *Environment) SetArgUnpacker(unpackArgs ArgUnpacker) {
e.unpackArgs = unpackArgs
}
// Add a builtin to the environment.
//
// All builtins will be wrapped to invoke OnBuiltinCall on every extension.
//
// All builtins should use starkit.UnpackArgs to get instrumentation.
func (e *Environment) AddBuiltin(name string, f Function) error {
wrapped := starlark.NewBuiltin(name, func(thread *starlark.Thread, fn *starlark.Builtin, args starlark.Tuple, kwargs []starlark.Tuple) (starlark.Value, error) {
for _, ext := range e.extensions {
onBuiltinCallExt, ok := ext.(OnBuiltinCallExtension)
if ok {
onBuiltinCallExt.OnBuiltinCall(name, fn)
}
}
return f(thread, fn, args, kwargs)
})
return e.AddValue(name, wrapped)
}
func (e *Environment) AddValue(name string, val starlark.Value) error {
split := strings.Split(name, ".")
// Handle the simple case first.
if len(split) == 1 {
if _, ok := e.predeclared[name]; ok {
return fmt.Errorf("multiple values added named %s", name)
}
e.predeclared[name] = val
return nil
}
if len(split) == 2 {
var currentModule Module
predeclaredVal, ok := e.predeclared[split[0]]
if ok {
predeclaredDict, ok := predeclaredVal.(Module)
if !ok {
return fmt.Errorf("Module conflict at %s. Existing: %s", name, predeclaredVal)
}
currentModule = predeclaredDict
} else {
currentModule = Module{name: split[0], attrs: starlark.StringDict{}}
e.predeclared[split[0]] = currentModule
}
if _, ok := currentModule.attrs[split[1]]; ok {
return fmt.Errorf("multiple values added named %s", name)
}
currentModule.attrs[split[1]] = val
return nil
}
return fmt.Errorf("multi-level modules not supported yet")
}
func (e *Environment) SetPrint(print func(thread *starlark.Thread, msg string)) {
e.print = print
}
func (e *Environment) SetContext(ctx context.Context) {
e.ctx = ctx
}
// Set a fake file system so that we can write tests that don't
// touch the file system. Expressed as a map from paths to contents.
func (e *Environment) SetFakeFileSystem(files map[string]string) {
e.fakeFileSystem = files
}
func (e *Environment) start(path string) (Model, error) {
// NOTE(dmiller): we only call Abs here because it's the root of the stack
path, err := filepath.Abs(path)
if err != nil {
return Model{}, errors.Wrap(err, "environment#start")
}
model := NewModel()
for _, ext := range e.extensions {
sExt, isStateful := ext.(StatefulExtension)
if isStateful {
err := model.createInitState(sExt)
if err != nil {
return Model{}, err
}
}
}
for _, ext := range e.extensions {
err := ext.OnStart(e)
if err != nil {
return Model{}, errors.Wrapf(err, "internal error: %T", ext)
}
}
t := &starlark.Thread{
Print: e.print,
Load: e.load,
}
t.SetLocal(argUnpackerKey, e.unpackArgs)
t.SetLocal(modelKey, model)
t.SetLocal(ctxKey, e.ctx)
_, err = e.exec(t, path)
return model, err
}
func (e *Environment) load(t *starlark.Thread, path string) (starlark.StringDict, error) {
return e.exec(t, path)
}
func (e *Environment) exec(t *starlark.Thread, path string) (starlark.StringDict, error) {
localPath, err := e.getPath(t, path)
if err != nil {
e.loadCache[localPath] = loadCacheEntry{
status: loadStatusDone,
exports: starlark.StringDict{},
err: err,
}
return starlark.StringDict{}, err
}
entry := e.loadCache[localPath]
switch entry.status {
case loadStatusExecuting:
return starlark.StringDict{}, fmt.Errorf("Circular load: %s", localPath)
case loadStatusDone:
return entry.exports, entry.err
}
e.loadCache[localPath] = loadCacheEntry{
status: loadStatusExecuting,
}
exports, err := e.doLoad(t, localPath)
e.loadCache[localPath] = loadCacheEntry{
status: loadStatusDone,
exports: exports,
err: err,
}
return exports, err
}
func (e *Environment) getPath(t *starlark.Thread, path string) (string, error) {
for _, i := range e.loadInterceptors {
newPath, err := i.LocalPath(t, path)
if err != nil {
return "", err
}
if newPath != "" {
// we found an interceptor that does something with this path, return early
return newPath, nil
}
}
return AbsPath(t, path), nil
}
func (e *Environment) doLoad(t *starlark.Thread, localPath string) (starlark.StringDict, error) {
for _, ext := range e.extensions {
onExecExt, ok := ext.(OnExecExtension)
if ok {
err := onExecExt.OnExec(t, localPath)
if err != nil {
return starlark.StringDict{}, err
}
}
}
var contentBytes interface{} = nil
if e.fakeFileSystem != nil {
contents, ok := e.fakeFileSystem[localPath]
if !ok {
return starlark.StringDict{}, fmt.Errorf("Not in fake file system: %s", localPath)
}
contentBytes = []byte(contents)
}
return starlark.ExecFile(t, localPath, contentBytes, e.predeclared)
}
type ArgUnpacker func(fnName string, args starlark.Tuple, kwargs []starlark.Tuple, pairs ...interface{}) error
const (
loadStatusNone loadStatus = iota
loadStatusExecuting
loadStatusDone
)
type loadCacheEntry struct {
status loadStatus
exports starlark.StringDict
err error
}
type loadStatus int