interfaces are good

bit/decode.go

@@ -0,0 +1,47 @@
+package bit
+
+// ReadUbitVar reads a prefixed uint value. A prefix is 2 bits wide, followed
+// by the 4 least-significant bits, then a variable number of most-significant
+// bits based on the prefix.
+//
+// 00 - 4
+// 01 - 8
+// 10 - 12 (why 12? this really baffles me)
+// 11 - 32
+func ReadUBitVar(r Reader) uint64 {
+	switch b := r.ReadBits(6); b >> 4 {
+	case 0:
+		return b & 0xf
+	case 1:
+		return b&0xf | r.ReadBits(4)<<4
+	case 2:
+		return b&0xf | r.ReadBits(8)<<4
+	case 3:
+		return b&0xf | r.ReadBits(28)<<4
+	default:
+		panic("not reached")
+	}
+}
+
+// ReadVarInt reads a variable length int value as a uint64. This is the binary
+// representation used by Protobuf. Each byte contributes 7 bits to the value
+// in little-endian order. The most-significant bit of each byte represents a
+// continuation bit.
+func ReadVarInt(r Reader) uint64 {
+	var (
+		x     uint64
+		b     uint64
+		shift uint
+	)
+	for ; shift < 64; shift += 7 {
+		b = r.ReadBits(8)
+		if r.Err() != nil {
+			return 0
+		}
+		x |= b & 0x7f << shift
+		if b&0x80 == 0 {
+			return x
+		}
+	}
+	return x
+}

bit/reader.go

@@ -6,133 +6,26 @@ import (
 	"io"
 )
 
-// bit.Reader allows for bit-level reading of arbitrary source data. This is
+type Reader interface {
-// based on the bit reader found in the standard library's bzip2 package.
+	ReadBits(uint) uint64
-// https://golang.org/src/compress/bzip2/bit_reader.go
+	DiscardBits(int)
-type Reader struct {
+	ReadByte() (byte, error)
-	src  io.ByteReader // source of data
+	Read([]byte) (int, error)
-	n    uint64        // bit buffer
+	DiscardBytes(int)
-	bits uint          // number of valid bits in n
+	Err() error
-	err  error         // stored error
 }
 
 // NewReader creates a new bit.Reader for any arbitrary reader.
-func NewReader(r io.Reader) *Reader {
+func NewReader(r io.Reader) Reader {
 	br, ok := r.(io.ByteReader)
 	if !ok {
 		br = bufio.NewReader(r)
 	}
-	return &Reader{src: br}
+	return &streamReader{src: br}
 }
 
 // NewByteReader creates a bit.Reader for a static slice of bytes. It's just
 // using a bytes.Reader internally.
-func NewBytesReader(b []byte) *Reader {
+func NewBytesReader(b []byte) Reader {
 	return NewReader(bytes.NewReader(b))
 }
-
-// ReadBits reads the given number of bits and returns them in the
-// least-significant part of a uint64.
-func (r *Reader) ReadBits(bits uint) (n uint64) {
-	for bits > r.bits {
-		b, err := r.src.ReadByte()
-		if err != nil {
-			r.err = err
-			return 0
-		}
-		r.n |= uint64(b) << r.bits
-		r.bits += 8
-	}
-	n = r.n & (1<<bits - 1)
-	r.n >>= bits
-	r.bits -= bits
-	return
-}
-
-// discards up to bits bits. returns a bool indicating wheter any errors occured.
-func (r *Reader) DiscardBits(n int) {
-	r.ReadBits(uint(n))
-}
-
-// ReadByte reads a single byte, regardless of alignment.
-func (r *Reader) ReadByte() (byte, error) {
-	if r.bits == 0 {
-		return r.src.ReadByte()
-	}
-	b := byte(r.ReadBits(8))
-	if err := r.Err(); err != nil {
-		return 0, err
-	}
-	return b, nil
-}
-
-// Read reads like an io.Reader, taking care of alignment internally.
-func (r *Reader) Read(buf []byte) (int, error) {
-	for i := 0; i < len(buf); i++ {
-		b, err := r.ReadByte()
-		if err != nil {
-			return 0, err
-		}
-		buf[i] = b
-	}
-	return len(buf), nil
-}
-
-// discards N byte of data on the reader or until EOF
-func (r *Reader) DiscardBytes(n int) {
-	for i := 0; i < n; i++ {
-		_, err := r.ReadByte()
-		if err != nil {
-			r.err = err
-			return
-		}
-	}
-}
-
-func (r *Reader) Err() error { return r.err }
-
-// ReadUbitVar reads a prefixed uint value. A prefix is 2 bits wide, followed
-// by the 4 least-significant bits, then a variable number of most-significant
-// bits based on the prefix.
-//
-// 00 - 4
-// 01 - 8
-// 10 - 12 (why 12? this really baffles me)
-// 11 - 32
-func ReadUBitVar(r *Reader) uint64 {
-	switch b := r.ReadBits(6); b >> 4 {
-	case 0:
-		return b & 0xf
-	case 1:
-		return b&0xf | r.ReadBits(4)<<4
-	case 2:
-		return b&0xf | r.ReadBits(8)<<4
-	case 3:
-		return b&0xf | r.ReadBits(28)<<4
-	default:
-		panic("not reached")
-	}
-}
-
-// ReadVarInt reads a variable length int value as a uint64. This is the binary
-// representation used by Protobuf. Each byte contributes 7 bits to the value
-// in little-endian order. The most-significant bit of each byte represents a
-// continuation bit.
-func ReadVarInt(r *Reader) uint64 {
-	var (
-		x     uint64
-		b     uint64
-		shift uint
-	)
-	for ; shift < 64; shift += 7 {
-		b = r.ReadBits(8)
-		if r.Err() != nil {
-			return 0
-		}
-		x |= b & 0x7f << shift
-		if b&0x80 == 0 {
-			return x
-		}
-	}
-	return x
-}

bit/stream_reader.go

@@ -0,0 +1,75 @@
+package bit
+
+import (
+	"io"
+)
+
+// bit.Reader allows for bit-level reading of arbitrary source data. This is
+// based on the bit reader found in the standard library's bzip2 package.
+// https://golang.org/src/compress/bzip2/bit_reader.go
+type streamReader struct {
+	src  io.ByteReader // source of data
+	n    uint64        // bit buffer
+	bits uint          // number of valid bits in n
+	err  error         // stored error
+}
+
+// ReadBits reads the given number of bits and returns them in the
+// least-significant part of a uint64.
+func (r *streamReader) ReadBits(bits uint) (n uint64) {
+	for bits > r.bits {
+		b, err := r.src.ReadByte()
+		if err != nil {
+			r.err = err
+			return 0
+		}
+		r.n |= uint64(b) << r.bits
+		r.bits += 8
+	}
+	n = r.n & (1<<bits - 1)
+	r.n >>= bits
+	r.bits -= bits
+	return
+}
+
+// discards up to bits bits. returns a bool indicating wheter any errors occured.
+func (r *streamReader) DiscardBits(n int) {
+	r.ReadBits(uint(n))
+}
+
+// ReadByte reads a single byte, regardless of alignment.
+func (r *streamReader) ReadByte() (byte, error) {
+	if r.bits == 0 {
+		return r.src.ReadByte()
+	}
+	b := byte(r.ReadBits(8))
+	if err := r.Err(); err != nil {
+		return 0, err
+	}
+	return b, nil
+}
+
+// Read reads like an io.Reader, taking care of alignment internally.
+func (r *streamReader) Read(buf []byte) (int, error) {
+	for i := 0; i < len(buf); i++ {
+		b, err := r.ReadByte()
+		if err != nil {
+			return 0, err
+		}
+		buf[i] = b
+	}
+	return len(buf), nil
+}
+
+// discards N byte of data on the reader or until EOF
+func (r *streamReader) DiscardBytes(n int) {
+	for i := 0; i < n; i++ {
+		_, err := r.ReadByte()
+		if err != nil {
+			r.err = err
+			return
+		}
+	}
+}
+
+func (r *streamReader) Err() error { return r.err }