2018-11-27 14:52:20 -07:00
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// Package binary implements sintax-sugar functions on top of the standard
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// library binary package
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package binary
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import (
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"bufio"
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"encoding/binary"
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"io"
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"gopkg.in/src-d/go-git.v4/plumbing"
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)
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// Read reads structured binary data from r into data. Bytes are read and
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// decoded in BigEndian order
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// https://golang.org/pkg/encoding/binary/#Read
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func Read(r io.Reader, data ...interface{}) error {
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for _, v := range data {
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if err := binary.Read(r, binary.BigEndian, v); err != nil {
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return err
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}
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}
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return nil
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}
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// ReadUntil reads from r untin delim is found
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func ReadUntil(r io.Reader, delim byte) ([]byte, error) {
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2019-06-18 20:14:15 -06:00
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if bufr, ok := r.(*bufio.Reader); ok {
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return ReadUntilFromBufioReader(bufr, delim)
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}
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2018-11-27 14:52:20 -07:00
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var buf [1]byte
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value := make([]byte, 0, 16)
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for {
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if _, err := io.ReadFull(r, buf[:]); err != nil {
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if err == io.EOF {
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return nil, err
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}
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return nil, err
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}
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if buf[0] == delim {
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return value, nil
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}
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value = append(value, buf[0])
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}
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}
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2019-06-18 20:14:15 -06:00
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// ReadUntilFromBufioReader is like bufio.ReadBytes but drops the delimiter
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// from the result.
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func ReadUntilFromBufioReader(r *bufio.Reader, delim byte) ([]byte, error) {
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value, err := r.ReadBytes(delim)
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if err != nil || len(value) == 0 {
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return nil, err
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}
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return value[:len(value)-1], nil
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}
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2018-11-27 14:52:20 -07:00
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// ReadVariableWidthInt reads and returns an int in Git VLQ special format:
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//
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// Ordinary VLQ has some redundancies, example: the number 358 can be
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// encoded as the 2-octet VLQ 0x8166 or the 3-octet VLQ 0x808166 or the
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// 4-octet VLQ 0x80808166 and so forth.
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//
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// To avoid these redundancies, the VLQ format used in Git removes this
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// prepending redundancy and extends the representable range of shorter
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// VLQs by adding an offset to VLQs of 2 or more octets in such a way
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// that the lowest possible value for such an (N+1)-octet VLQ becomes
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// exactly one more than the maximum possible value for an N-octet VLQ.
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// In particular, since a 1-octet VLQ can store a maximum value of 127,
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// the minimum 2-octet VLQ (0x8000) is assigned the value 128 instead of
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// 0. Conversely, the maximum value of such a 2-octet VLQ (0xff7f) is
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// 16511 instead of just 16383. Similarly, the minimum 3-octet VLQ
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// (0x808000) has a value of 16512 instead of zero, which means
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// that the maximum 3-octet VLQ (0xffff7f) is 2113663 instead of
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// just 2097151. And so forth.
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//
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// This is how the offset is saved in C:
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//
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// dheader[pos] = ofs & 127;
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// while (ofs >>= 7)
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// dheader[--pos] = 128 | (--ofs & 127);
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//
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func ReadVariableWidthInt(r io.Reader) (int64, error) {
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var c byte
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if err := Read(r, &c); err != nil {
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return 0, err
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}
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var v = int64(c & maskLength)
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for c&maskContinue > 0 {
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v++
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if err := Read(r, &c); err != nil {
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return 0, err
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}
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v = (v << lengthBits) + int64(c&maskLength)
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}
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return v, nil
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}
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const (
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maskContinue = uint8(128) // 1000 000
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maskLength = uint8(127) // 0111 1111
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lengthBits = uint8(7) // subsequent bytes has 7 bits to store the length
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)
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// ReadUint64 reads 8 bytes and returns them as a BigEndian uint32
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func ReadUint64(r io.Reader) (uint64, error) {
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var v uint64
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if err := binary.Read(r, binary.BigEndian, &v); err != nil {
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return 0, err
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}
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return v, nil
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}
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// ReadUint32 reads 4 bytes and returns them as a BigEndian uint32
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func ReadUint32(r io.Reader) (uint32, error) {
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var v uint32
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if err := binary.Read(r, binary.BigEndian, &v); err != nil {
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return 0, err
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}
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return v, nil
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}
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// ReadUint16 reads 2 bytes and returns them as a BigEndian uint16
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func ReadUint16(r io.Reader) (uint16, error) {
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var v uint16
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if err := binary.Read(r, binary.BigEndian, &v); err != nil {
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return 0, err
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}
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return v, nil
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}
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// ReadHash reads a plumbing.Hash from r
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func ReadHash(r io.Reader) (plumbing.Hash, error) {
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var h plumbing.Hash
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if err := binary.Read(r, binary.BigEndian, h[:]); err != nil {
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return plumbing.ZeroHash, err
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}
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return h, nil
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}
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const sniffLen = 8000
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// IsBinary detects if data is a binary value based on:
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// http://git.kernel.org/cgit/git/git.git/tree/xdiff-interface.c?id=HEAD#n198
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func IsBinary(r io.Reader) (bool, error) {
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reader := bufio.NewReader(r)
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c := 0
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for {
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if c == sniffLen {
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break
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}
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b, err := reader.ReadByte()
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if err == io.EOF {
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break
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}
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if err != nil {
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return false, err
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}
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if b == byte(0) {
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return true, nil
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}
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c++
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}
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return false, nil
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}
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