tape: Implement dynamic decoding (untested)
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parent
1bc0788ff2
commit
9932abd6c4
237
tape/dynamic.go
237
tape/dynamic.go
@ -1,5 +1,11 @@
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package tape
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// dont smoke reflection, kids!!!!!!!!!
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// totally reflectric, reflectrified, etc. this is probably souper slow but
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// certainly no slower than the built in json encoder i'd imagine.
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// TODO: add support for struct tags: `tape:"0000"`, tape:"0001"` so they can get
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// transformed into tables with a defined schema
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import "fmt"
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import "reflect"
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@ -14,6 +20,7 @@ import "reflect"
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// - []<supported type>
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// - map[uint16]<supported type>
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func EncodeAny(encoder *Encoder, value any, tag Tag) (n int, err error) {
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// TODO use reflection for all of this to ignore type names
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// primitives
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switch value := value.(type) {
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case int: return encoder.WriteInt32(int32(value))
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@ -41,21 +48,128 @@ func EncodeAny(encoder *Encoder, value any, tag Tag) (n int, err error) {
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switch reflectType.Kind() {
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case reflect.Slice:
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return encodeAnySlice(encoder, value, tag)
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case reflect.Array:
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return encodeAnySlice(encoder, reflect.ValueOf(value).Slice(0, reflectType.Len()).Interface(), tag)
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// case reflect.Array:
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// return encodeAnySlice(encoder, reflect.ValueOf(value).Slice(0, reflectType.Len()).Interface(), tag)
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case reflect.Map:
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if reflectType.Key() == reflect.TypeOf(uint16(0)) {
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return encodeAnyMap(encoder, value, tag)
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}
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return 0, fmt.Errorf("cannot encode map key %T, key must be uint16", value)
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return n, fmt.Errorf("cannot encode map key %T, key must be uint16", value)
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}
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return 0, fmt.Errorf("cannot encode type %T", value)
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return n, fmt.Errorf("cannot encode type %T", value)
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}
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// DecodeAny decodes data and places it into destination, which must be a
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// pointer to a supported type. See [EncodeAny] for a list of supported types.
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func DecodeAny(decoder *Decoder, destination any, tag Tag) (n int, err error) {
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return decodeAny(decoder, reflect.ValueOf(destination), tag)
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}
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func decodeAny(decoder *Decoder, destination reflect.Value, tag Tag) (n int, err error) {
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errWrongDestinationType := func(expected string) error {
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return fmt.Errorf(
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"expected %s destination, not %v",
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expected, destination)
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}
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if destination.Kind() != reflect.Pointer {
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return n, errWrongDestinationType("pointer")
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}
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switch tag.WithoutCN() {
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case SI:
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// SI: (none)
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err = setIntPtr(destination, uint64(tag.CN()))
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if err != nil { return n, err }
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case LI:
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// LI: <value: IntN>
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nn, err := decodeAndSetIntPtr(decoder, destination, tag.CN() - 1)
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n += nn; if err != nil { return n, err }
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case FP:
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// FP: <value: FloatN>
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nn, err := decodeAndSetFloatPtr(decoder, destination, tag.CN() - 1)
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n += nn; if err != nil { return n, err }
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case SBA:
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// SBA: <data: U8>*
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destination, err := asByteArrayPtr(destination)
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if err != nil { return n, err }
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buffer := make([]byte, tag.CN())
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nn, err := decoder.Read(buffer)
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n += nn; if err != nil { return n, err }
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*destination = buffer
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case LBA:
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// LBA: <length: UN> <data: U8>*
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destination, err := asByteArrayPtr(destination)
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if err != nil { return n, err }
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length, nn, err := decoder.ReadUintN(tag.CN() - 1)
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n += nn; if err != nil { return n, err }
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buffer := make([]byte, length)
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nn, err = decoder.Read(buffer)
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n += nn; if err != nil { return n, err }
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*destination = buffer
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case OTA:
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// OTA: <length: UN> <elementTag: tape.Tag> <values>*
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length, nn, err := decoder.ReadUintN(tag.CN() - 1)
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n += nn; if err != nil { return n, err }
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oneTag, nn, err := decoder.ReadTag()
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n += nn; if err != nil { return n, err }
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var slice reflect.Value
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needSet := false
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elem := destination.Elem()
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if elem.Kind() == reflect.Struct && elem.Type().Name() == "unknownSlicePlaceholder" {
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needSet = true
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slice, err = skeletonValueSlice(oneTag, int(length))
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if err != nil { return n, err }
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} else {
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slice = elem
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if slice.Kind() != reflect.Slice {
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return n, errWrongDestinationType("slice")
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}
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slice.SetLen(int(length))
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}
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for index := range length {
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nn, err := decodeAny(decoder, slice.Index(int(index)), oneTag)
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n += nn; if err != nil { return n, err }
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}
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if needSet {
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destination.Elem().Set(slice)
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}
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case KTV:
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// KTV: <length: UN> (<key: U16> <tag: Tag> <value>)*
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table := destination.Elem()
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if table.Kind() != reflect.Map {
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return n, errWrongDestinationType("map")
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}
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typ := table.Type()
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if typ.Key().Kind() != reflect.Uint16 {
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return n, errWrongDestinationType("map[uint16]")
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}
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if typ.Elem() != reflect.TypeOf(any(nil)) {
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return n, errWrongDestinationType("map[uint16] any")
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}
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length, nn, err := decoder.ReadUintN(tag.CN() - 1)
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n += nn; if err != nil { return n, err }
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table.Clear()
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for _ = range length {
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key, nn, err := decoder.ReadUint16()
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n += nn; if err != nil { return n, err }
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itemTag, nn, err := decoder.ReadTag()
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n += nn; if err != nil { return n, err }
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value, err := skeletonValue(itemTag)
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if err != nil { return n, err }
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nn, err = decodeAny(decoder, value.Elem(), itemTag)
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n += nn; if err != nil { return n, err }
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table.SetMapIndex(reflect.ValueOf(key), value)
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}
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}
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return n, fmt.Errorf("unknown TN %d", tag.TN())
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}
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// TagAny returns the correct tag for an "any" value. Returns an error if the
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// underlying type is unsupported. See [EncodeAny] for a list of supported
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// types.
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func TagAny(value any) (Tag, error) {
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// TODO use reflection for all of this to ignore type names
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// primitives
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switch value := value.(type) {
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case int, uint: return LI.WithCN(3), nil
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@ -70,11 +184,11 @@ func TagAny(value any) (Tag, error) {
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// aggregates
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reflectType := reflect.TypeOf(value)
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switch reflectType.Kind() {
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case reflect.Slice: return OTA.WithCN(reflect.ValueOf(value).Len()), nil
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case reflect.Slice: return OTA.WithCN(reflect.ValueOf(value).Len() - 1), nil
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case reflect.Array: return OTA.WithCN(reflectType.Len()), nil
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case reflect.Map:
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if reflectType.Key() == reflect.TypeOf(uint16(0)) {
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return OTA.WithCN(reflect.ValueOf(value).Len()), nil
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return KTV.WithCN(IntBytes(uint64(reflect.ValueOf(value).Len())) - 1), nil
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}
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return 0, fmt.Errorf("cannot encode map key %T, key must be uint16", value)
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}
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@ -126,3 +240,114 @@ func encodeAnyMap(encoder *Encoder, value any, tag Tag) (n int, err error) {
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}
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return n, nil
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}
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func setIntPtr(destination reflect.Value, value uint64) error {
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elem := destination.Elem()
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if !elem.CanInt() {
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return fmt.Errorf("cannot assign integer to %T", elem.Interface())
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}
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elem.Set(reflect.ValueOf(value).Convert(elem.Type()))
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return nil
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}
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func setFloatPtr(destination reflect.Value, value float64) error {
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elem := destination.Elem()
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if !elem.CanFloat() {
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return fmt.Errorf("cannot assign float to %T", elem.Interface())
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}
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elem.Set(reflect.ValueOf(value).Convert(elem.Type()))
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return nil
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}
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func decodeAndSetIntPtr(decoder *Decoder, destination reflect.Value, bytes int) (n int, err error) {
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value, nn, err := decoder.ReadUintN(bytes)
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n += nn; if err != nil { return n, err }
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return n, setIntPtr(destination, value)
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}
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func decodeAndSetFloatPtr(decoder *Decoder, destination reflect.Value, bytes int) (n int, err error) {
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switch bytes {
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case 8:
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value, nn, err := decoder.ReadFloat64()
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n += nn; if err != nil { return n, err }
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return n, setFloatPtr(destination, float64(value))
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case 4:
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value, nn, err := decoder.ReadFloat32()
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n += nn; if err != nil { return n, err }
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return n, setFloatPtr(destination, float64(value))
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}
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return n, fmt.Errorf("cannot decode float%d", bytes * 8)
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}
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func asByteArrayPtr(value reflect.Value) (*[]byte, error) {
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typ := value.Type()
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if typ.Kind() != reflect.Pointer {
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return nil, fmt.Errorf("cannot convert %T to pointer", value)
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}
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if typ.Elem().Kind() != reflect.Slice {
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return nil, fmt.Errorf("cannot convert %T to slice pointer", value)
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}
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if typ.Elem().Elem() != reflect.TypeOf(byte(0)) {
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return nil, fmt.Errorf("cannot convert %T to *[]byte", value)
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}
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return value.Convert(reflect.PtrTo(reflect.SliceOf(reflect.TypeOf(byte(0))))).Interface().(*[]byte), nil
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}
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func skeletonValue(tag Tag) (reflect.Value, error) {
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switch tag.WithoutCN() {
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case SI:
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value := uint8(0)
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return reflect.ValueOf(&value), nil
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case LI:
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switch tag.CN() {
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case 0: value := uint8(0); return reflect.ValueOf(&value), nil
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case 1: value := uint16(0); return reflect.ValueOf(&value), nil
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case 3: value := uint32(0); return reflect.ValueOf(&value), nil
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case 7: value := uint64(0); return reflect.ValueOf(&value), nil
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}
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return reflect.Value { }, fmt.Errorf("unknown CN %d for LI", tag.CN())
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case FP:
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switch tag.CN() {
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case 3: value := float32(0); return reflect.ValueOf(&value), nil
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case 7: value := float64(0); return reflect.ValueOf(&value), nil
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}
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return reflect.Value { }, fmt.Errorf("unknown CN %d for FP", tag.CN())
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case SBA: value := []byte { }; return reflect.ValueOf(&value), nil
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case LBA: value := []byte { }; return reflect.ValueOf(&value), nil
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case OTA: value := unknownSlicePlaceholder { }; return reflect.ValueOf(&value), nil
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case KTV: value := map[uint16] any { }; return reflect.ValueOf(&value), nil
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}
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return reflect.Value { }, fmt.Errorf("unknown TN %d", tag.TN())
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}
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func skeletonValueSlice(tag Tag, length int) (reflect.Value, error) {
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switch tag.WithoutCN() {
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case SI:
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value := make([]uint8, length)
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return reflect.ValueOf(&value), nil
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case LI:
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switch tag.CN() {
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case 0: value := make([]uint8, length); return reflect.ValueOf(&value), nil
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case 1: value := make([]uint16, length); return reflect.ValueOf(&value), nil
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case 3: value := make([]uint32, length); return reflect.ValueOf(&value), nil
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case 7: value := make([]uint64, length); return reflect.ValueOf(&value), nil
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}
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return reflect.Value { }, fmt.Errorf("unknown CN %d for LI OTA", tag.CN())
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case FP:
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switch tag.CN() {
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case 3: value := make([]float32, length); return reflect.ValueOf(&value), nil
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case 7: value := make([]float64, length); return reflect.ValueOf(&value), nil
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}
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return reflect.Value { }, fmt.Errorf("unknown CN %d for FP OTA", tag.CN())
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case SBA: value := make([][]byte, length); return reflect.ValueOf(&value), nil
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case LBA: value := make([][]byte, length); return reflect.ValueOf(&value), nil
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case OTA: value := make([]any, length); return reflect.ValueOf(&value), nil
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case KTV: value := make([]map[uint16] any, length); return reflect.ValueOf(&value), nil
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}
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return reflect.Value { }, fmt.Errorf("unknown TN %d", tag.TN())
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}
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// unknownSlicePlaceholder is inserted by skeletonValue and informs the program
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// that the destination for the slice needs to be generated based on the item
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// tag in the OTA.
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type unknownSlicePlaceholder struct { }
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