// Package binary implements sintax-sugar functions on top of the standard
// library binary package
package binary
import (
"bufio"
"encoding/binary"
"io"
"gopkg.in/src-d/go-git.v4/plumbing"
)
// Read reads structured binary data from r into data. Bytes are read and
// decoded in BigEndian order
// https://golang.org/pkg/encoding/binary/#Read
func Read(r io.Reader, data ...interface{}) error {
for _, v := range data {
if err := binary.Read(r, binary.BigEndian, v); err != nil {
return err
}
}
return nil
}
// ReadUntil reads from r untin delim is found
func ReadUntil(r io.Reader, delim byte) ([]byte, error) {
var buf [1]byte
value := make([]byte, 0, 16)
for {
if _, err := io.ReadFull(r, buf[:]); err != nil {
if err == io.EOF {
return nil, err
}
return nil, err
}
if buf[0] == delim {
return value, nil
}
value = append(value, buf[0])
}
}
// ReadVariableWidthInt reads and returns an int in Git VLQ special format:
//
// Ordinary VLQ has some redundancies, example: the number 358 can be
// encoded as the 2-octet VLQ 0x8166 or the 3-octet VLQ 0x808166 or the
// 4-octet VLQ 0x80808166 and so forth.
//
// To avoid these redundancies, the VLQ format used in Git removes this
// prepending redundancy and extends the representable range of shorter
// VLQs by adding an offset to VLQs of 2 or more octets in such a way
// that the lowest possible value for such an (N+1)-octet VLQ becomes
// exactly one more than the maximum possible value for an N-octet VLQ.
// In particular, since a 1-octet VLQ can store a maximum value of 127,
// the minimum 2-octet VLQ (0x8000) is assigned the value 128 instead of
// 0. Conversely, the maximum value of such a 2-octet VLQ (0xff7f) is
// 16511 instead of just 16383. Similarly, the minimum 3-octet VLQ
// (0x808000) has a value of 16512 instead of zero, which means
// that the maximum 3-octet VLQ (0xffff7f) is 2113663 instead of
// just 2097151. And so forth.
//
// This is how the offset is saved in C:
//
// dheader[pos] = ofs & 127;
// while (ofs >>= 7)
// dheader[--pos] = 128 | (--ofs & 127);
//
func ReadVariableWidthInt(r io.Reader) (int64, error) {
var c byte
if err := Read(r, &c); err != nil {
return 0, err
}
var v = int64(c & maskLength)
for c&maskContinue > 0 {
v++
if err := Read(r, &c); err != nil {
return 0, err
}
v = (v << lengthBits) + int64(c&maskLength)
}
return v, nil
}
const (
maskContinue = uint8(128) // 1000 000
maskLength = uint8(127) // 0111 1111
lengthBits = uint8(7) // subsequent bytes has 7 bits to store the length
)
// ReadUint32 reads 4 bytes and returns them as a Big ndian uint32
func ReadUint32(r io.Reader) (uint32, error) {
var v uint32
if err := binary.Read(r, binary.BigEndian, &v); err != nil {
return 0, err
}
return v, nil
}
// ReadUint16 reads 2 bytes and returns them as a BigEndian uint16
func ReadUint16(r io.Reader) (uint16, error) {
var v uint16
if err := binary.Read(r, binary.BigEndian, &v); err != nil {
return 0, err
}
return v, nil
}
// ReadHash reads a plumbing.Hash from r
func ReadHash(r io.Reader) (plumbing.Hash, error) {
var h plumbing.Hash
if err := binary.Read(r, binary.BigEndian, h[:]); err != nil {
return plumbing.ZeroHash, err
}
return h, nil
}
const sniffLen = 8000
// IsBinary detects if data is a binary value based on:
// http://git.kernel.org/cgit/git/git.git/tree/xdiff-interface.c?id=HEAD#n198
func IsBinary(r io.Reader) (bool, error) {
reader := bufio.NewReader(r)
c := 0
for {
if c == sniffLen {
break
}
b, err := reader.ReadByte()
if err == io.EOF {
break
}
if err != nil {
return false, err
}
if b == byte(0) {
return true, nil
}
c++
}
return false, nil
}
