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encoding.go
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encoding.go
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// Package encoding defines the internal encoding that FTL uses to encode and
// decode messages. It is currently JSON.
package encoding
import (
"bytes"
"encoding/base64"
"encoding/json"
"fmt"
"io"
"reflect"
"strings"
"time"
"github.com/TBD54566975/ftl/backend/schema/strcase"
"github.com/TBD54566975/ftl/go-runtime/ftl/reflection"
)
var (
optionMarshaler = reflect.TypeFor[OptionMarshaler]()
optionUnmarshaler = reflect.TypeFor[OptionUnmarshaler]()
)
type OptionMarshaler interface {
Marshal(w *bytes.Buffer, encode func(v reflect.Value, w *bytes.Buffer) error) error
}
type OptionUnmarshaler interface {
Unmarshal(d *json.Decoder, isNull bool, decode func(d *json.Decoder, v reflect.Value) error) error
}
func Marshal(v any) ([]byte, error) {
w := &bytes.Buffer{}
err := encodeValue(reflect.ValueOf(v), w)
return w.Bytes(), err
}
func encodeValue(v reflect.Value, w *bytes.Buffer) error {
if !v.IsValid() {
w.WriteString("null")
return nil
}
if v.Kind() == reflect.Ptr {
return fmt.Errorf("pointer types are not supported: %s", v.Type())
}
t := v.Type()
// Special-cased types
switch {
case t == reflect.TypeFor[time.Time]():
data, err := json.Marshal(v.Interface())
if err != nil {
return err
}
w.Write(data)
return nil
case t.Implements(optionMarshaler):
enc := v.Interface().(OptionMarshaler) //nolint:forcetypeassert
return enc.Marshal(w, encodeValue)
// TODO(Issue #1439): remove this special case by removing all usage of
// json.RawMessage, which is not a type we support.
case t == reflect.TypeFor[json.RawMessage]():
data, err := json.Marshal(v.Interface())
if err != nil {
return err
}
w.Write(data)
return nil
}
switch v.Kind() {
case reflect.Struct:
return encodeStruct(v, w)
case reflect.Slice:
if v.Type().Elem().Kind() == reflect.Uint8 {
return encodeBytes(v, w)
}
return encodeSlice(v, w)
case reflect.Map:
return encodeMap(v, w)
case reflect.String:
return encodeString(v, w)
case reflect.Int:
return encodeInt(v, w)
case reflect.Float64:
return encodeFloat(v, w)
case reflect.Bool:
return encodeBool(v, w)
case reflect.Interface:
if t == reflect.TypeFor[any]() {
return encodeValue(v.Elem(), w)
}
if vName, ok := reflection.GetVariantByType(v.Type(), v.Elem().Type()).Get(); ok {
sumType := struct {
Name string
Value any
}{Name: vName, Value: v.Elem().Interface()}
return encodeValue(reflect.ValueOf(sumType), w)
}
return fmt.Errorf("the only supported interface types are enums or any, not %s", t)
default:
panic(fmt.Sprintf("unsupported type: %s", v.Type()))
}
}
func encodeStruct(v reflect.Value, w *bytes.Buffer) error {
w.WriteRune('{')
afterFirst := false
for i := range v.NumField() {
ft := v.Type().Field(i)
fv := v.Field(i)
// TODO: If these fields are skipped, the ingress encoder will not include
// them in the output. There should ideally be no relationship between
// the ingress encoder and the encoding package, but for now this is the
// simplest solution.
// t := ft.Type
// // Types that can be skipped if they're zero.
// if (t.Kind() == reflect.Slice && fv.Len() == 0) ||
// (t.Kind() == reflect.Map && fv.Len() == 0) ||
// (t.String() == "ftl.Unit" && fv.IsZero()) ||
// (strings.HasPrefix(t.String(), "ftl.Option[") && fv.IsZero()) ||
// (t == reflect.TypeOf((*any)(nil)).Elem() && fv.IsZero()) {
// continue
// }
if isTaggedOmitempty(v, i) && fv.IsZero() {
continue
}
if afterFirst {
w.WriteRune(',')
}
afterFirst = true
w.WriteString(`"` + strcase.ToLowerCamel(ft.Name) + `":`)
if err := encodeValue(fv, w); err != nil {
return err
}
}
w.WriteRune('}')
return nil
}
func isTaggedOmitempty(v reflect.Value, i int) bool {
tag := v.Type().Field(i).Tag
tagVals := strings.Split(tag.Get("json"), ",")
for _, tagVal := range tagVals {
if strings.TrimSpace(tagVal) == "omitempty" {
return true
}
}
return false
}
func encodeBytes(v reflect.Value, w *bytes.Buffer) error {
data := base64.StdEncoding.EncodeToString(v.Bytes())
fmt.Fprintf(w, "%q", data)
return nil
}
func encodeSlice(v reflect.Value, w *bytes.Buffer) error {
w.WriteRune('[')
for i := range v.Len() {
if i > 0 {
w.WriteRune(',')
}
if err := encodeValue(v.Index(i), w); err != nil {
return err
}
}
w.WriteRune(']')
return nil
}
func encodeMap(v reflect.Value, w *bytes.Buffer) error {
w.WriteRune('{')
for i, key := range v.MapKeys() {
if i > 0 {
w.WriteRune(',')
}
w.WriteRune('"')
w.WriteString(key.String())
w.WriteString(`":`)
if err := encodeValue(v.MapIndex(key), w); err != nil {
return err
}
}
w.WriteRune('}')
return nil
}
func encodeBool(v reflect.Value, w *bytes.Buffer) error {
if v.Bool() {
w.WriteString("true")
} else {
w.WriteString("false")
}
return nil
}
func encodeInt(v reflect.Value, w *bytes.Buffer) error {
fmt.Fprintf(w, "%d", v.Int())
return nil
}
func encodeFloat(v reflect.Value, w *bytes.Buffer) error {
fmt.Fprintf(w, "%g", v.Float())
return nil
}
func encodeString(v reflect.Value, w *bytes.Buffer) error {
fmt.Fprintf(w, "%q", v.String())
return nil
}
func Unmarshal(data []byte, v any) error {
rv := reflect.ValueOf(v)
if rv.Kind() != reflect.Ptr || rv.IsNil() {
return fmt.Errorf("unmarshal expects a non-nil pointer")
}
d := json.NewDecoder(bytes.NewReader(data))
return decodeValue(d, rv.Elem())
}
func decodeValue(d *json.Decoder, v reflect.Value) error {
if !v.CanSet() {
return fmt.Errorf("cannot set value: %s", v.Type())
}
if v.Kind() == reflect.Ptr {
return fmt.Errorf("pointer types are not supported: %s", v.Type())
}
t := v.Type()
// Special-case types
switch {
case t == reflect.TypeFor[time.Time]():
return d.Decode(v.Addr().Interface())
case v.CanAddr() && v.Addr().Type().Implements(optionUnmarshaler):
v = v.Addr()
fallthrough
case t.Implements(optionUnmarshaler):
if v.IsNil() {
v.Set(reflect.New(t.Elem()))
}
dec := v.Interface().(OptionUnmarshaler) //nolint:forcetypeassert
return handleIfNextTokenIsNull(d, func(d *json.Decoder) error {
return dec.Unmarshal(d, true, decodeValue)
}, func(d *json.Decoder) error {
return dec.Unmarshal(d, false, decodeValue)
})
}
switch v.Kind() {
case reflect.Struct:
return decodeStruct(d, v)
case reflect.Slice:
if v.Type().Elem().Kind() == reflect.Uint8 {
return decodeBytes(d, v)
}
return decodeSlice(d, v)
case reflect.Map:
return decodeMap(d, v)
case reflect.Interface:
if reflection.IsSumTypeDiscriminator(v.Type()) {
return decodeSumType(d, v)
}
if v.Type().NumMethod() != 0 {
return fmt.Errorf("the only supported interface types are enums or any, not %s", v.Type())
}
fallthrough
default:
return d.Decode(v.Addr().Interface())
}
}
func decodeStruct(d *json.Decoder, v reflect.Value) error {
if err := expectDelim(d, '{'); err != nil {
return err
}
for d.More() {
token, err := d.Token()
if err != nil {
return err
}
key, ok := token.(string)
if !ok {
return fmt.Errorf("expected string key, got %T", token)
}
field := v.FieldByNameFunc(func(s string) bool {
return strcase.ToLowerCamel(s) == key
})
if !field.IsValid() {
return fmt.Errorf("no field corresponding to key %s", key)
}
fieldTypeStr := field.Type().String()
switch {
case fieldTypeStr == "*Unit" || fieldTypeStr == "Unit":
if fieldTypeStr == "*Unit" && field.IsNil() {
field.Set(reflect.New(field.Type().Elem()))
}
default:
if err := decodeValue(d, field); err != nil {
return err
}
}
}
// consume the closing delimiter of the object
_, err := d.Token()
return err
}
func decodeBytes(d *json.Decoder, v reflect.Value) error {
var b []byte
if err := d.Decode(&b); err != nil {
return err
}
v.SetBytes(b)
return nil
}
func decodeSlice(d *json.Decoder, v reflect.Value) error {
if err := expectDelim(d, '['); err != nil {
return err
}
for d.More() {
newElem := reflect.New(v.Type().Elem()).Elem()
if err := decodeValue(d, newElem); err != nil {
return err
}
v.Set(reflect.Append(v, newElem))
}
// consume the closing delimiter of the slice
_, err := d.Token()
return err
}
func decodeMap(d *json.Decoder, v reflect.Value) error {
if err := expectDelim(d, '{'); err != nil {
return err
}
if v.IsNil() {
v.Set(reflect.MakeMap(v.Type()))
}
valType := v.Type().Elem()
for d.More() {
key, err := d.Token()
if err != nil {
return err
}
newElem := reflect.New(valType).Elem()
if err := decodeValue(d, newElem); err != nil {
return err
}
v.SetMapIndex(reflect.ValueOf(key), newElem)
}
// consume the closing delimiter of the map
_, err := d.Token()
return err
}
func decodeSumType(d *json.Decoder, v reflect.Value) error {
var sumType struct {
Name string
Value json.RawMessage
}
err := d.Decode(&sumType)
if err != nil {
return err
}
if sumType.Name == "" {
return fmt.Errorf("no name found for type enum variant")
}
if sumType.Value == nil {
return fmt.Errorf("no value found for type enum variant")
}
variantType, ok := reflection.GetVariantByName(v.Type(), sumType.Name).Get()
if !ok {
return fmt.Errorf("no enum variant found by name %s", sumType.Name)
}
out := reflect.New(variantType)
if err := decodeValue(json.NewDecoder(bytes.NewReader(sumType.Value)), out.Elem()); err != nil {
return err
}
if !out.Type().AssignableTo(v.Type()) {
return fmt.Errorf("cannot assign %s to %s", out.Type(), v.Type())
}
v.Set(out.Elem())
return nil
}
func expectDelim(d *json.Decoder, expected json.Delim) error {
token, err := d.Token()
if err != nil {
return err
}
delim, ok := token.(json.Delim)
if !ok || delim != expected {
return fmt.Errorf("expected delimiter %q, got %q", expected, token)
}
return nil
}
func handleIfNextTokenIsNull(d *json.Decoder, ifNullFn func(*json.Decoder) error, elseFn func(*json.Decoder) error) error {
isNull, err := isNextTokenNull(d)
if err != nil {
return err
}
if isNull {
err = ifNullFn(d)
if err != nil {
return err
}
// Consume the null token
_, err := d.Token()
if err != nil {
return err
}
return nil
}
return elseFn(d)
}
// isNextTokenNull implements a cheap/dirty version of `Peek()`, which json.Decoder does
// not support.
//
// It reads the buffered data and checks if the next token is "null" without actually consuming the token.
func isNextTokenNull(d *json.Decoder) (bool, error) {
s, err := io.ReadAll(d.Buffered())
if err != nil {
return false, err
}
remaining := s[bytes.IndexFunc(s, isDelim)+1:]
secondDelim := bytes.IndexFunc(remaining, isDelim)
if secondDelim == -1 {
secondDelim = len(remaining) // No delimiters found, read until the end
}
return strings.TrimSpace(string(remaining[:secondDelim])) == "null", nil
}
func isDelim(r rune) bool {
switch r {
case ',', ':', '{', '}', '[', ']':
return true
}
return false
}