tlv/record: adds various tlv record constructors

tlv/record.go

@@ -0,0 +1,153 @@
+package tlv
+
+import (
+	"io"
+
+	"github.com/btcsuite/btcd/btcec"
+)
+
+// Type is an 64-bit identifier for a TLV Record.
+type Type uint64
+
+// Encoder is a signature for methods that can encode TLV values. An error
+// should be returned if the Encoder cannot support the underlying type of val.
+// The provided scratch buffer must be non-nil.
+type Encoder func(w io.Writer, val interface{}, buf *[8]byte) error
+
+// Decoder is a signature for methods that can decode TLV values. An error
+// should be returned if the Decoder cannot support the underlying type of val.
+// The provided scratch buffer must be non-nil.
+type Decoder func(r io.Reader, val interface{}, buf *[8]byte, l uint64) error
+
+// ENOP is an encoder that doesn't modify the io.Writer and never fails.
+func ENOP(io.Writer, interface{}, *[8]byte) error { return nil }
+
+// DNOP is an encoder that doesn't modify the io.Reader and never fails.
+func DNOP(io.Reader, interface{}, *[8]byte, uint64) error { return nil }
+
+// SizeFunc is a function that can compute the length of a given field. Since
+// the size of the underlying field can change, this allows the size of the
+// field to be evaluated at the time of encoding.
+type SizeFunc func() uint64
+
+// SizeVarBytes returns a SizeFunc that can compute the length of a byte slice.
+func SizeVarBytes(e *[]byte) SizeFunc {
+	return func() uint64 {
+		return uint64(len(*e))
+	}
+}
+
+// Record holds the required information to encode or decode a TLV record.
+type Record struct {
+	value      interface{}
+	typ        Type
+	staticSize uint64
+	sizeFunc   SizeFunc
+	encoder    Encoder
+	decoder    Decoder
+}
+
+// Size returns the size of the Record's value. If no static size is known, the
+// dynamic size will be evaluated.
+func (f *Record) Size() uint64 {
+	if f.sizeFunc == nil {
+		return f.staticSize
+	}
+
+	return f.sizeFunc()
+}
+
+// MakePrimitiveRecord creates a record for common types.
+func MakePrimitiveRecord(typ Type, val interface{}) Record {
+	var (
+		staticSize uint64
+		sizeFunc   SizeFunc
+		encoder    Encoder
+		decoder    Decoder
+	)
+	switch e := val.(type) {
+	case *uint8:
+		staticSize = 1
+		encoder = EUint8
+		decoder = DUint8
+
+	case *uint16:
+		staticSize = 2
+		encoder = EUint16
+		decoder = DUint16
+
+	case *uint32:
+		staticSize = 4
+		encoder = EUint32
+		decoder = DUint32
+
+	case *uint64:
+		staticSize = 8
+		encoder = EUint64
+		decoder = DUint64
+
+	case *[32]byte:
+		staticSize = 32
+		encoder = EBytes32
+		decoder = DBytes32
+
+	case *[33]byte:
+		staticSize = 33
+		encoder = EBytes33
+		decoder = DBytes33
+
+	case **btcec.PublicKey:
+		staticSize = 33
+		encoder = EPubKey
+		decoder = DPubKey
+
+	case *[64]byte:
+		staticSize = 64
+		encoder = EBytes64
+		decoder = DBytes64
+
+	case *[]byte:
+		sizeFunc = SizeVarBytes(e)
+		encoder = EVarBytes
+		decoder = DVarBytes
+
+	default:
+		panic("unknown primitive type")
+	}
+
+	return Record{
+		value:      val,
+		typ:        typ,
+		staticSize: staticSize,
+		sizeFunc:   sizeFunc,
+		encoder:    encoder,
+		decoder:    decoder,
+	}
+}
+
+// MakeStaticRecord creates a record for a field of fixed-size
+func MakeStaticRecord(typ Type, val interface{}, size uint64, encoder Encoder,
+	decoder Decoder) Record {
+
+	return Record{
+		value:      val,
+		typ:        typ,
+		staticSize: size,
+		encoder:    encoder,
+		decoder:    decoder,
+	}
+}
+
+// MakeDynamicRecord creates a record whose size may vary, and will be
+// determined at the time of encoding via sizeFunc.
+func MakeDynamicRecord(typ Type, val interface{}, sizeFunc SizeFunc,
+	encoder Encoder, decoder Decoder) Record {
+
+	return Record{
+		value:    val,
+		typ:      typ,
+		sizeFunc: sizeFunc,
+		encoder:  encoder,
+		decoder:  decoder,
+	}
+}