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archive/tar: add RawBytes()

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Plumbing a means to access the raw bytes of a tar archive apart from the
file payload itself.
This commit is contained in:
Vincent Batts 2015-02-19 16:49:06 -05:00
parent 3ae6151165
commit 7cc3f4b289
1 changed files with 100 additions and 0 deletions
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100
archive/tar/reader.go
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@ -34,6 +34,29 @@ type Reader struct {
pad int64 // amount of padding (ignored) after current file entry
curr numBytesReader // reader for current file entry
hdrBuff [blockSize]byte // buffer to use in readHeader
RawAccounting bool // Whether to enable the access needed to reassemble the tar from raw bytes. Some performance/memory hit for this.
rawBytes *bytes.Buffer // last raw bits
}
// RawBytes accesses the raw bytes of the archive, apart from the file payload itself.
// This includes the header and padding.
//
// This call resets the current rawbytes buffer
//
// Only when RawAccounting is enabled, otherwise this returns nil
func (tr *Reader) RawBytes() []byte {
if !tr.RawAccounting {
return nil
}
if tr.rawBytes == nil {
tr.rawBytes = bytes.NewBuffer(nil)
}
defer func() {
// if we've read them, then flush them.
tr.rawBytes.Reset()
}()
return tr.rawBytes.Bytes()
}
// A numBytesReader is an io.Reader with a numBytes method, returning the number
@ -89,6 +112,13 @@ func NewReader(r io.Reader) *Reader { return &Reader{r: r} }
// io.EOF is returned at the end of the input.
func (tr *Reader) Next() (*Header, error) {
var hdr *Header
if tr.RawAccounting {
if tr.rawBytes == nil {
tr.rawBytes = bytes.NewBuffer(nil)
} else {
tr.rawBytes.Reset()
}
}
if tr.err == nil {
tr.skipUnread()
}
@ -131,7 +161,20 @@ func (tr *Reader) Next() (*Header, error) {
if err != nil {
return nil, err
}
var b []byte
if tr.RawAccounting {
if _, err = tr.rawBytes.Write(realname); err != nil {
return nil, err
}
b = tr.RawBytes()
}
hdr, err := tr.Next()
// since the above call to Next() resets the buffer, we need to throw the bytes over
if tr.RawAccounting {
if _, err = tr.rawBytes.Write(b); err != nil {
return nil, err
}
}
hdr.Name = cString(realname)
return hdr, err
case TypeGNULongLink:
@ -140,7 +183,20 @@ func (tr *Reader) Next() (*Header, error) {
if err != nil {
return nil, err
}
var b []byte
if tr.RawAccounting {
if _, err = tr.rawBytes.Write(realname); err != nil {
return nil, err
}
b = tr.RawBytes()
}
hdr, err := tr.Next()
// since the above call to Next() resets the buffer, we need to throw the bytes over
if tr.RawAccounting {
if _, err = tr.rawBytes.Write(b); err != nil {
return nil, err
}
}
hdr.Linkname = cString(realname)
return hdr, err
}
@ -315,6 +371,12 @@ func parsePAX(r io.Reader) (map[string]string, error) {
if err != nil {
return nil, err
}
// leaving this function for io.Reader makes it more testable
if tr, ok := r.(*Reader); ok && tr.RawAccounting {
if _, err = tr.rawBytes.Write(buf); err != nil {
return nil, err
}
}
// For GNU PAX sparse format 0.0 support.
// This function transforms the sparse format 0.0 headers into sparse format 0.1 headers.
@ -410,6 +472,10 @@ func (tr *Reader) octal(b []byte) int64 {
func (tr *Reader) skipUnread() {
nr := tr.numBytes() + tr.pad // number of bytes to skip
tr.curr, tr.pad = nil, 0
if tr.RawAccounting {
_, tr.err = io.CopyN(tr.rawBytes, tr.r, nr)
return
}
if sr, ok := tr.r.(io.Seeker); ok {
if _, err := sr.Seek(nr, os.SEEK_CUR); err == nil {
return
@ -433,14 +499,36 @@ func (tr *Reader) readHeader() *Header {
copy(header, zeroBlock)
if _, tr.err = io.ReadFull(tr.r, header); tr.err != nil {
// because it could read some of the block, but reach EOF first
if tr.err == io.EOF && tr.RawAccounting {
if _, tr.err = tr.rawBytes.Write(header); tr.err != nil {
return nil
}
}
return nil
}
if tr.RawAccounting {
if _, tr.err = tr.rawBytes.Write(header); tr.err != nil {
return nil
}
}
// Two blocks of zero bytes marks the end of the archive.
if bytes.Equal(header, zeroBlock[0:blockSize]) {
if _, tr.err = io.ReadFull(tr.r, header); tr.err != nil {
// because it could read some of the block, but reach EOF first
if tr.err == io.EOF && tr.RawAccounting {
if _, tr.err = tr.rawBytes.Write(header); tr.err != nil {
return nil
}
}
return nil
}
if tr.RawAccounting {
if _, tr.err = tr.rawBytes.Write(header); tr.err != nil {
return nil
}
}
if bytes.Equal(header, zeroBlock[0:blockSize]) {
tr.err = io.EOF
} else {
@ -627,6 +715,12 @@ func readGNUSparseMap1x0(r io.Reader) ([]sparseEntry, error) {
if _, err := io.ReadFull(r, sparseHeader[oldLen:newLen]); err != nil {
return 0, err
}
// leaving this function for io.Reader makes it more testable
if tr, ok := r.(*Reader); ok && tr.RawAccounting {
if _, err := tr.rawBytes.Write(sparseHeader[oldLen:newLen]); err != nil {
return 0, err
}
}
// Look for a newline in the new data
nl = bytes.IndexByte(sparseHeader[oldLen:newLen], '\n')
@ -651,6 +745,12 @@ func readGNUSparseMap1x0(r io.Reader) ([]sparseEntry, error) {
if _, err := io.ReadFull(r, sparseHeader); err != nil {
return nil, err
}
// leaving this function for io.Reader makes it more testable
if tr, ok := r.(*Reader); ok && tr.RawAccounting {
if _, err := tr.rawBytes.Write(sparseHeader); err != nil {
return nil, err
}
}
// The first line contains the number of entries
numEntries, err := readDecimal()