Merge codec and tape packages

tape/decode.go

@@ -0,0 +1,127 @@
+package tape
+
+import "io"
+
+// Decodable is any type that can decode itself from a decoder.
+type Decodable interface {
+	// Decode reads data from decoder, replacing the data of the object. It
+	// returns the amount of bytes written, and an error if the write
+	// stopped early.
+	Decode(decoder *Decoder) (n int, err error)
+}
+
+// Decoder wraps an [io.Reader] and decodes data from it.
+type Decoder struct {
+	io.Reader
+}
+
+// ReadFull calls [io.ReadFull] on the reader.
+func (this *Decoder) ReadFull(buffer []byte) (n int, err error) {
+	return io.ReadFull(this, buffer)
+}
+
+// ReadByte decodes a single byte from the input reader.
+func (this *Decoder) ReadByte() (value byte, n int, err error) {
+	uncasted, n, err := this.ReadUint8()
+	return byte(uncasted), n, err
+}
+
+// ReadInt8 decodes an 8-bit signed integer from the input reader.
+func (this *Decoder) ReadInt8() (value int8, n int, err error) {
+	uncasted, n, err := this.ReadUint8()
+	return int8(uncasted), n, err
+}
+
+// ReadUint8 decodes an 8-bit unsigned integer from the input reader.
+func (this *Decoder) ReadUint8() (value uint8, n int, err error) {
+	buffer := [1]byte { }
+	n, err = this.ReadFull(buffer[:])
+	return uint8(buffer[0]), n, err
+}
+
+// ReadInt16 decodes an 16-bit signed integer from the input reader.
+func (this *Decoder) ReadInt16() (value int16, n int, err error) {
+	uncasted, n, err := this.ReadUint16()
+	return int16(uncasted), n, err
+}
+
+// ReadUint16 decodes an 16-bit unsigned integer from the input reader.
+func (this *Decoder) ReadUint16() (value uint16, n int, err error) {
+	buffer := [2]byte { }
+	n, err = this.ReadFull(buffer[:])
+	return uint16(buffer[0]) << 8 |
+		uint16(buffer[1]), n, err
+}
+
+// ReadInt32 decodes an 32-bit signed integer from the input reader.
+func (this *Decoder) ReadInt32() (value int32, n int, err error) {
+	uncasted, n, err := this.ReadUint32()
+	return int32(uncasted), n, err
+}
+
+// ReadUint32 decodes an 32-bit unsigned integer from the input reader.
+func (this *Decoder) ReadUint32() (value uint32, n int, err error) {
+	buffer := [4]byte { }
+	n, err = this.ReadFull(buffer[:])
+	return uint32(buffer[0]) << 24 |
+		uint32(buffer[1]) << 16 |
+		uint32(buffer[2]) << 8 |
+		uint32(buffer[3]), n, err
+}
+
+// ReadInt64 decodes an 64-bit signed integer from the input reader.
+func (this *Decoder) ReadInt64() (value int64, n int, err error) {
+	uncasted, n, err := this.ReadUint64()
+	return int64(uncasted), n, err
+}
+
+// ReadUint64 decodes an 64-bit unsigned integer from the input reader.
+func (this *Decoder) ReadUint64() (value uint64, n int, err error) {
+	buffer := [8]byte { }
+	n, err = this.ReadFull(buffer[:])
+	return uint64(buffer[0]) << 56 |
+		uint64(buffer[1]) << 48 |
+		uint64(buffer[2]) << 40 |
+		uint64(buffer[3]) << 32 |
+		uint64(buffer[4]) << 24 |
+		uint64(buffer[5]) << 16 |
+		uint64(buffer[6]) << 8 |
+		uint64(buffer[7]), n, err
+}
+
+// ReadIntN decodes an N-byte signed integer from the input reader.
+func (this *Decoder) ReadIntN(bytes int) (value int64, n int, err error) {
+	uncasted, n, err := this.ReadUintN(bytes)
+	return int64(uncasted), n, err
+}
+
+// ReadUintN decodes an N-byte unsigned integer from the input reader.
+func (this *Decoder) ReadUintN(bytes int) (value uint64, n int, err error) {
+	// TODO: don't make multiple read calls (without allocating)
+	buffer := [1]byte { }
+	for bytesLeft := bytes; bytesLeft > 0; bytesLeft -- {
+		nn, err := this.ReadFull(buffer[:])
+		n += nn; if err != nil { return 0, n, err }
+		value |= uint64(buffer[0]) << ((bytesLeft - 1) * 8)
+	}
+	// *read* integers too big, but don't return them.
+	if bytes > 8 { value = 0 }
+	return value, n, nil
+}
+
+// ReadGBEU decodes a growing unsigned integer of up to 64 bits from the input
+// reader.
+func (this *Decoder) ReadGBEU() (value uint64, n int, err error) {
+	var fullValue uint64
+	for {
+		chunk, nn, err := this.ReadByte()
+		n += nn; if err != nil { return 0, n, err }
+		
+		fullValue *= 0x80
+		fullValue += uint64(chunk & 0x7F)
+		ccb := chunk >> 7
+		if ccb == 0 {
+			return fullValue, n, nil
+		}
+	}
+}