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reader.go
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/
reader.go
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package ar
import (
"io"
"io/ioutil"
"os"
"strconv"
"time"
)
// Provides read access to an ar archive.
// Call next to skip files
//
// Example:
// reader := NewReader(f)
// var buf bytes.Buffer
// for {
// _, err := reader.Next()
// if err == io.EOF {
// break
// }
// if err != nil {
// t.Errorf(err.Error())
// }
// io.Copy(&buf, reader)
// }
type Reader struct {
r io.Reader
nb int64
pad int64
}
// Copies read data to r. Strips the global ar header.
func NewReader(r io.Reader) *Reader {
io.CopyN(ioutil.Discard, r, 8) // Discard global header
return &Reader{r: r}
}
func (rd *Reader) string(b []byte) string {
i := len(b)-1
for i > 0 && b[i] == 32 {
i--
}
return string(b[0:i+1])
}
func (rd *Reader) numeric(b []byte) int64 {
i := len(b)-1
for i > 0 && b[i] == 32 {
i--
}
n, _ := strconv.ParseInt(string(b[0:i+1]), 10, 64)
return n
}
func (rd *Reader) octal(b []byte) int64 {
i := len(b)-1
for i > 0 && b[i] == 32 {
i--
}
n, _ := strconv.ParseInt(string(b[3:i+1]), 8, 64)
return n
}
func (rd *Reader) skipUnread() error {
skip := rd.nb + rd.pad
rd.nb, rd.pad = 0, 0
if seeker, ok := rd.r.(io.Seeker); ok {
_, err := seeker.Seek(skip, os.SEEK_CUR)
return err
}
_, err := io.CopyN(ioutil.Discard, rd.r, skip)
return err
}
func (rd *Reader) readHeader() (*Header, error) {
headerBuf := make([]byte, HEADER_BYTE_SIZE)
if _, err := io.ReadFull(rd.r, headerBuf); err != nil {
return nil, err
}
header := new(Header)
s := slicer(headerBuf)
header.Name = rd.string(s.next(16))
header.ModTime = time.Unix(rd.numeric(s.next(12)), 0)
header.Uid = int(rd.numeric(s.next(6)))
header.Gid = int(rd.numeric(s.next(6)))
header.Mode = rd.octal(s.next(8))
header.Size = rd.numeric(s.next(10))
rd.nb = int64(header.Size)
if header.Size%2 == 1 {
rd.pad = 1
} else {
rd.pad = 0
}
return header, nil
}
// Call Next() to skip to the next file in the archive file.
// Returns a Header which contains the metadata about the
// file in the archive.
func (rd *Reader) Next() (*Header, error) {
err := rd.skipUnread()
if err != nil {
return nil, err
}
return rd.readHeader()
}
// Read data from the current entry in the archive.
func (rd *Reader) Read(b []byte) (n int, err error) {
if rd.nb == 0 {
return 0, io.EOF
}
if int64(len(b)) > rd.nb {
b = b[0:rd.nb]
}
n, err = rd.r.Read(b)
rd.nb -= int64(n)
return
}