tape: Implement dynamic decoding (untested)

tape/dynamic.go

@@ -1,5 +1,11 @@
 package tape
 
+// dont smoke reflection, kids!!!!!!!!!
+// totally reflectric, reflectrified, etc. this is probably souper slow but
+// certainly no slower than the built in json encoder i'd imagine.
+// TODO: add support for struct tags: `tape:"0000"`, tape:"0001"` so they can get
+// transformed into tables with a defined schema
+
 import "fmt"
 import "reflect"
 
@@ -14,6 +20,7 @@ import "reflect"
 //   - []<supported type>
 //   - map[uint16]<supported type>
 func EncodeAny(encoder *Encoder, value any, tag Tag) (n int, err error) {
+	// TODO use reflection for all of this to ignore type names
 	// primitives
 	switch value := value.(type) {
 	case int:    return encoder.WriteInt32(int32(value))
@@ -41,21 +48,128 @@ func EncodeAny(encoder *Encoder, value any, tag Tag) (n int, err error) {
 	switch reflectType.Kind() {
 	case reflect.Slice:
 		return encodeAnySlice(encoder, value, tag)
-	case reflect.Array:
+	// case reflect.Array:
-		return encodeAnySlice(encoder, reflect.ValueOf(value).Slice(0, reflectType.Len()).Interface(), tag)
+		// return encodeAnySlice(encoder, reflect.ValueOf(value).Slice(0, reflectType.Len()).Interface(), tag)
 	case reflect.Map:
 		if reflectType.Key() == reflect.TypeOf(uint16(0)) {
 			return encodeAnyMap(encoder, value, tag)
 		}
-		return 0, fmt.Errorf("cannot encode map key %T, key must be uint16", value)
+		return n, fmt.Errorf("cannot encode map key %T, key must be uint16", value)
 	}
-	return 0, fmt.Errorf("cannot encode type %T", value)
+	return n, fmt.Errorf("cannot encode type %T", value)
+}
+
+// DecodeAny decodes data and places it into destination, which must be a
+// pointer to a supported type. See [EncodeAny] for a list of supported types.
+func DecodeAny(decoder *Decoder, destination any, tag Tag) (n int, err error) {
+	return decodeAny(decoder, reflect.ValueOf(destination), tag)
+}
+
+func decodeAny(decoder *Decoder, destination reflect.Value, tag Tag) (n int, err error) {
+	errWrongDestinationType := func(expected string) error {
+		return fmt.Errorf(
+			"expected %s destination, not %v",
+			expected, destination)
+	}
+	
+	if destination.Kind() != reflect.Pointer {
+		return n, errWrongDestinationType("pointer")
+	}
+	
+	switch tag.WithoutCN() {
+	case SI:
+		// SI: (none)
+		err = setIntPtr(destination, uint64(tag.CN()))
+		if err != nil { return n, err }
+	case LI:
+		// LI: <value: IntN>
+		nn, err := decodeAndSetIntPtr(decoder, destination, tag.CN() - 1)
+		n += nn; if err != nil { return n, err }
+	case FP:
+		// FP: <value: FloatN>
+		nn, err := decodeAndSetFloatPtr(decoder, destination, tag.CN() - 1)
+		n += nn; if err != nil { return n, err }
+	case SBA:
+		// SBA: <data: U8>*
+		destination, err := asByteArrayPtr(destination)
+		if err != nil { return n, err }
+		buffer := make([]byte, tag.CN())
+		nn, err := decoder.Read(buffer)
+		n += nn; if err != nil { return n, err }
+		*destination = buffer
+	case LBA:
+		// LBA: <length: UN> <data: U8>*
+		destination, err := asByteArrayPtr(destination)
+		if err != nil { return n, err }
+		length, nn, err := decoder.ReadUintN(tag.CN() - 1)
+		n += nn; if err != nil { return n, err }
+		buffer := make([]byte, length)
+		nn, err = decoder.Read(buffer)
+		n += nn; if err != nil { return n, err }
+		*destination = buffer
+	case OTA:
+		// OTA: <length: UN> <elementTag: tape.Tag> <values>*
+		length, nn, err := decoder.ReadUintN(tag.CN() - 1)
+		n += nn; if err != nil { return n, err }
+		oneTag, nn, err := decoder.ReadTag()
+		n += nn; if err != nil { return n, err }
+		var slice reflect.Value
+		needSet := false
+		elem := destination.Elem()
+		if elem.Kind() == reflect.Struct && elem.Type().Name() == "unknownSlicePlaceholder" {
+			needSet = true
+			slice, err = skeletonValueSlice(oneTag, int(length))
+			if err != nil { return n, err }
+		} else {
+			slice = elem
+			if slice.Kind() != reflect.Slice {
+				return n, errWrongDestinationType("slice")
+			}
+			slice.SetLen(int(length))
+		}
+		for index := range length {
+			nn, err := decodeAny(decoder, slice.Index(int(index)), oneTag)
+			n += nn; if err != nil { return n, err }
+		}
+		if needSet {
+			destination.Elem().Set(slice)
+		}
+	case KTV:
+		// KTV: <length: UN> (<key: U16> <tag: Tag> <value>)*
+		table := destination.Elem()
+		if table.Kind() != reflect.Map {
+			return n, errWrongDestinationType("map")
+		}
+		typ := table.Type()
+		if typ.Key().Kind() != reflect.Uint16 {
+			return n, errWrongDestinationType("map[uint16]")
+		}
+		if typ.Elem() != reflect.TypeOf(any(nil)) {
+			return n, errWrongDestinationType("map[uint16] any")
+		}
+		length, nn, err := decoder.ReadUintN(tag.CN() - 1)
+		n += nn; if err != nil { return n, err }
+		table.Clear()
+		for _ = range length {
+			key, nn, err := decoder.ReadUint16()
+			n += nn; if err != nil { return n, err }
+			itemTag, nn, err := decoder.ReadTag()
+			n += nn; if err != nil { return n, err }
+			value, err := skeletonValue(itemTag)
+			if err != nil { return n, err }
+			nn, err = decodeAny(decoder, value.Elem(), itemTag)
+			n += nn; if err != nil { return n, err }
+			table.SetMapIndex(reflect.ValueOf(key), value)
+		}
+	}
+	return n, fmt.Errorf("unknown TN %d", tag.TN())
 }
 
 // TagAny returns the correct tag for an "any" value. Returns an error if the
 // underlying type is unsupported. See [EncodeAny] for a list of supported
 // types.
 func TagAny(value any) (Tag, error) {
+	// TODO use reflection for all of this to ignore type names
 	// primitives
 	switch value := value.(type) {
 	case int,   uint:   return LI.WithCN(3), nil
@@ -70,11 +184,11 @@ func TagAny(value any) (Tag, error) {
 	// aggregates
 	reflectType := reflect.TypeOf(value)
 	switch reflectType.Kind() {
-	case reflect.Slice: return OTA.WithCN(reflect.ValueOf(value).Len()), nil
+	case reflect.Slice: return OTA.WithCN(reflect.ValueOf(value).Len() - 1), nil
 	case reflect.Array: return OTA.WithCN(reflectType.Len()), nil
 	case reflect.Map:
 		if reflectType.Key() == reflect.TypeOf(uint16(0)) {
-			return OTA.WithCN(reflect.ValueOf(value).Len()), nil
+			return KTV.WithCN(IntBytes(uint64(reflect.ValueOf(value).Len())) - 1), nil
 		}
 		return 0, fmt.Errorf("cannot encode map key %T, key must be uint16", value)
 	}
@@ -126,3 +240,114 @@ func encodeAnyMap(encoder *Encoder, value any, tag Tag) (n int, err error) {
 	}
 	return n, nil
 }
+
+func setIntPtr(destination reflect.Value, value uint64) error {
+	elem := destination.Elem()
+	if !elem.CanInt() {
+		return fmt.Errorf("cannot assign integer to %T", elem.Interface())
+	}
+	elem.Set(reflect.ValueOf(value).Convert(elem.Type()))
+	return nil
+}
+
+func setFloatPtr(destination reflect.Value, value float64) error {
+	elem := destination.Elem()
+	if !elem.CanFloat() {
+		return fmt.Errorf("cannot assign float to %T", elem.Interface())
+	}
+	elem.Set(reflect.ValueOf(value).Convert(elem.Type()))
+	return nil
+}
+
+func decodeAndSetIntPtr(decoder *Decoder, destination reflect.Value, bytes int) (n int, err error) {
+	value, nn, err := decoder.ReadUintN(bytes)
+	n += nn; if err != nil { return n, err }
+	return n, setIntPtr(destination, value)
+}
+
+func decodeAndSetFloatPtr(decoder *Decoder, destination reflect.Value, bytes int) (n int, err error) {
+	switch bytes {
+	case 8:
+		value, nn, err := decoder.ReadFloat64()
+		n += nn; if err != nil { return n, err }
+		return n, setFloatPtr(destination, float64(value))
+	case 4:
+		value, nn, err := decoder.ReadFloat32()
+		n += nn; if err != nil { return n, err }
+		return n, setFloatPtr(destination, float64(value))
+	}
+	return n, fmt.Errorf("cannot decode float%d", bytes * 8)
+}
+
+func asByteArrayPtr(value reflect.Value) (*[]byte, error) {
+	typ := value.Type()
+	if typ.Kind() != reflect.Pointer {
+		return nil, fmt.Errorf("cannot convert %T to pointer", value)
+	}
+	if typ.Elem().Kind() != reflect.Slice {
+		return nil, fmt.Errorf("cannot convert %T to slice pointer", value)
+	}
+	if typ.Elem().Elem() != reflect.TypeOf(byte(0)) {
+		return nil, fmt.Errorf("cannot convert %T to *[]byte", value)
+	}
+	return value.Convert(reflect.PtrTo(reflect.SliceOf(reflect.TypeOf(byte(0))))).Interface().(*[]byte), nil
+}
+
+func skeletonValue(tag Tag) (reflect.Value, error) {
+	switch tag.WithoutCN() {
+	case SI:
+		value := uint8(0)
+		return reflect.ValueOf(&value), nil
+	case LI:
+		switch tag.CN() {
+		case 0: value := uint8(0); return reflect.ValueOf(&value), nil
+		case 1: value := uint16(0); return reflect.ValueOf(&value), nil
+		case 3: value := uint32(0); return reflect.ValueOf(&value), nil
+		case 7: value := uint64(0); return reflect.ValueOf(&value), nil
+		}
+		return reflect.Value { }, fmt.Errorf("unknown CN %d for LI", tag.CN())
+	case FP:
+		switch tag.CN() {
+		case 3: value := float32(0); return reflect.ValueOf(&value), nil
+		case 7: value := float64(0); return reflect.ValueOf(&value), nil
+		}
+		return reflect.Value { }, fmt.Errorf("unknown CN %d for FP", tag.CN())
+	case SBA: value := []byte { }; return reflect.ValueOf(&value), nil
+	case LBA: value := []byte { }; return reflect.ValueOf(&value), nil
+	case OTA: value := unknownSlicePlaceholder { }; return reflect.ValueOf(&value), nil
+	case KTV: value := map[uint16] any { }; return reflect.ValueOf(&value), nil
+	}
+	return reflect.Value { }, fmt.Errorf("unknown TN %d", tag.TN())
+}
+
+func skeletonValueSlice(tag Tag, length int) (reflect.Value, error) {
+	switch tag.WithoutCN() {
+	case SI:
+		value := make([]uint8, length)
+		return reflect.ValueOf(&value), nil
+	case LI:
+		switch tag.CN() {
+		case 0: value := make([]uint8, length); return reflect.ValueOf(&value), nil
+		case 1: value := make([]uint16, length); return reflect.ValueOf(&value), nil
+		case 3: value := make([]uint32, length); return reflect.ValueOf(&value), nil
+		case 7: value := make([]uint64, length); return reflect.ValueOf(&value), nil
+		}
+		return reflect.Value { }, fmt.Errorf("unknown CN %d for LI OTA", tag.CN())
+	case FP:
+		switch tag.CN() {
+		case 3: value := make([]float32, length); return reflect.ValueOf(&value), nil
+		case 7: value := make([]float64, length); return reflect.ValueOf(&value), nil
+		}
+		return reflect.Value { }, fmt.Errorf("unknown CN %d for FP OTA", tag.CN())
+	case SBA: value := make([][]byte, length); return reflect.ValueOf(&value), nil
+	case LBA: value := make([][]byte, length); return reflect.ValueOf(&value), nil
+	case OTA: value := make([]any, length); return reflect.ValueOf(&value), nil
+	case KTV: value := make([]map[uint16] any, length); return reflect.ValueOf(&value), nil
+	}
+	return reflect.Value { }, fmt.Errorf("unknown TN %d", tag.TN())
+}
+
+// unknownSlicePlaceholder is inserted by skeletonValue and informs the program
+// that the destination for the slice needs to be generated based on the item
+// tag in the OTA.
+type unknownSlicePlaceholder struct { }