diff options
Diffstat (limited to 'src/archive/tar/writer.go')
| -rw-r--r-- | src/archive/tar/writer.go | 396 |
1 files changed, 396 insertions, 0 deletions
diff --git a/src/archive/tar/writer.go b/src/archive/tar/writer.go new file mode 100644 index 000000000..dafb2cabf --- /dev/null +++ b/src/archive/tar/writer.go @@ -0,0 +1,396 @@ +// Copyright 2009 The Go Authors. All rights reserved. +// Use of this source code is governed by a BSD-style +// license that can be found in the LICENSE file. + +package tar + +// TODO(dsymonds): +// - catch more errors (no first header, etc.) + +import ( + "bytes" + "errors" + "fmt" + "io" + "os" + "path" + "strconv" + "strings" + "time" +) + +var ( + ErrWriteTooLong = errors.New("archive/tar: write too long") + ErrFieldTooLong = errors.New("archive/tar: header field too long") + ErrWriteAfterClose = errors.New("archive/tar: write after close") + errNameTooLong = errors.New("archive/tar: name too long") + errInvalidHeader = errors.New("archive/tar: header field too long or contains invalid values") +) + +// A Writer provides sequential writing of a tar archive in POSIX.1 format. +// A tar archive consists of a sequence of files. +// Call WriteHeader to begin a new file, and then call Write to supply that file's data, +// writing at most hdr.Size bytes in total. +type Writer struct { + w io.Writer + err error + nb int64 // number of unwritten bytes for current file entry + pad int64 // amount of padding to write after current file entry + closed bool + usedBinary bool // whether the binary numeric field extension was used + preferPax bool // use pax header instead of binary numeric header + hdrBuff [blockSize]byte // buffer to use in writeHeader when writing a regular header + paxHdrBuff [blockSize]byte // buffer to use in writeHeader when writing a pax header +} + +// NewWriter creates a new Writer writing to w. +func NewWriter(w io.Writer) *Writer { return &Writer{w: w} } + +// Flush finishes writing the current file (optional). +func (tw *Writer) Flush() error { + if tw.nb > 0 { + tw.err = fmt.Errorf("archive/tar: missed writing %d bytes", tw.nb) + return tw.err + } + + n := tw.nb + tw.pad + for n > 0 && tw.err == nil { + nr := n + if nr > blockSize { + nr = blockSize + } + var nw int + nw, tw.err = tw.w.Write(zeroBlock[0:nr]) + n -= int64(nw) + } + tw.nb = 0 + tw.pad = 0 + return tw.err +} + +// Write s into b, terminating it with a NUL if there is room. +// If the value is too long for the field and allowPax is true add a paxheader record instead +func (tw *Writer) cString(b []byte, s string, allowPax bool, paxKeyword string, paxHeaders map[string]string) { + needsPaxHeader := allowPax && len(s) > len(b) || !isASCII(s) + if needsPaxHeader { + paxHeaders[paxKeyword] = s + return + } + if len(s) > len(b) { + if tw.err == nil { + tw.err = ErrFieldTooLong + } + return + } + ascii := toASCII(s) + copy(b, ascii) + if len(ascii) < len(b) { + b[len(ascii)] = 0 + } +} + +// Encode x as an octal ASCII string and write it into b with leading zeros. +func (tw *Writer) octal(b []byte, x int64) { + s := strconv.FormatInt(x, 8) + // leading zeros, but leave room for a NUL. + for len(s)+1 < len(b) { + s = "0" + s + } + tw.cString(b, s, false, paxNone, nil) +} + +// Write x into b, either as octal or as binary (GNUtar/star extension). +// If the value is too long for the field and writingPax is enabled both for the field and the add a paxheader record instead +func (tw *Writer) numeric(b []byte, x int64, allowPax bool, paxKeyword string, paxHeaders map[string]string) { + // Try octal first. + s := strconv.FormatInt(x, 8) + if len(s) < len(b) { + tw.octal(b, x) + return + } + + // If it is too long for octal, and pax is preferred, use a pax header + if allowPax && tw.preferPax { + tw.octal(b, 0) + s := strconv.FormatInt(x, 10) + paxHeaders[paxKeyword] = s + return + } + + // Too big: use binary (big-endian). + tw.usedBinary = true + for i := len(b) - 1; x > 0 && i >= 0; i-- { + b[i] = byte(x) + x >>= 8 + } + b[0] |= 0x80 // highest bit indicates binary format +} + +var ( + minTime = time.Unix(0, 0) + // There is room for 11 octal digits (33 bits) of mtime. + maxTime = minTime.Add((1<<33 - 1) * time.Second) +) + +// WriteHeader writes hdr and prepares to accept the file's contents. +// WriteHeader calls Flush if it is not the first header. +// Calling after a Close will return ErrWriteAfterClose. +func (tw *Writer) WriteHeader(hdr *Header) error { + return tw.writeHeader(hdr, true) +} + +// WriteHeader writes hdr and prepares to accept the file's contents. +// WriteHeader calls Flush if it is not the first header. +// Calling after a Close will return ErrWriteAfterClose. +// As this method is called internally by writePax header to allow it to +// suppress writing the pax header. +func (tw *Writer) writeHeader(hdr *Header, allowPax bool) error { + if tw.closed { + return ErrWriteAfterClose + } + if tw.err == nil { + tw.Flush() + } + if tw.err != nil { + return tw.err + } + + // a map to hold pax header records, if any are needed + paxHeaders := make(map[string]string) + + // TODO(shanemhansen): we might want to use PAX headers for + // subsecond time resolution, but for now let's just capture + // too long fields or non ascii characters + + var header []byte + + // We need to select which scratch buffer to use carefully, + // since this method is called recursively to write PAX headers. + // If allowPax is true, this is the non-recursive call, and we will use hdrBuff. + // If allowPax is false, we are being called by writePAXHeader, and hdrBuff is + // already being used by the non-recursive call, so we must use paxHdrBuff. + header = tw.hdrBuff[:] + if !allowPax { + header = tw.paxHdrBuff[:] + } + copy(header, zeroBlock) + s := slicer(header) + + // keep a reference to the filename to allow to overwrite it later if we detect that we can use ustar longnames instead of pax + pathHeaderBytes := s.next(fileNameSize) + + tw.cString(pathHeaderBytes, hdr.Name, true, paxPath, paxHeaders) + + // Handle out of range ModTime carefully. + var modTime int64 + if !hdr.ModTime.Before(minTime) && !hdr.ModTime.After(maxTime) { + modTime = hdr.ModTime.Unix() + } + + tw.octal(s.next(8), hdr.Mode) // 100:108 + tw.numeric(s.next(8), int64(hdr.Uid), true, paxUid, paxHeaders) // 108:116 + tw.numeric(s.next(8), int64(hdr.Gid), true, paxGid, paxHeaders) // 116:124 + tw.numeric(s.next(12), hdr.Size, true, paxSize, paxHeaders) // 124:136 + tw.numeric(s.next(12), modTime, false, paxNone, nil) // 136:148 --- consider using pax for finer granularity + s.next(8) // chksum (148:156) + s.next(1)[0] = hdr.Typeflag // 156:157 + + tw.cString(s.next(100), hdr.Linkname, true, paxLinkpath, paxHeaders) + + copy(s.next(8), []byte("ustar\x0000")) // 257:265 + tw.cString(s.next(32), hdr.Uname, true, paxUname, paxHeaders) // 265:297 + tw.cString(s.next(32), hdr.Gname, true, paxGname, paxHeaders) // 297:329 + tw.numeric(s.next(8), hdr.Devmajor, false, paxNone, nil) // 329:337 + tw.numeric(s.next(8), hdr.Devminor, false, paxNone, nil) // 337:345 + + // keep a reference to the prefix to allow to overwrite it later if we detect that we can use ustar longnames instead of pax + prefixHeaderBytes := s.next(155) + tw.cString(prefixHeaderBytes, "", false, paxNone, nil) // 345:500 prefix + + // Use the GNU magic instead of POSIX magic if we used any GNU extensions. + if tw.usedBinary { + copy(header[257:265], []byte("ustar \x00")) + } + + _, paxPathUsed := paxHeaders[paxPath] + // try to use a ustar header when only the name is too long + if !tw.preferPax && len(paxHeaders) == 1 && paxPathUsed { + suffix := hdr.Name + prefix := "" + if len(hdr.Name) > fileNameSize && isASCII(hdr.Name) { + var err error + prefix, suffix, err = tw.splitUSTARLongName(hdr.Name) + if err == nil { + // ok we can use a ustar long name instead of pax, now correct the fields + + // remove the path field from the pax header. this will suppress the pax header + delete(paxHeaders, paxPath) + + // update the path fields + tw.cString(pathHeaderBytes, suffix, false, paxNone, nil) + tw.cString(prefixHeaderBytes, prefix, false, paxNone, nil) + + // Use the ustar magic if we used ustar long names. + if len(prefix) > 0 && !tw.usedBinary { + copy(header[257:265], []byte("ustar\x00")) + } + } + } + } + + // The chksum field is terminated by a NUL and a space. + // This is different from the other octal fields. + chksum, _ := checksum(header) + tw.octal(header[148:155], chksum) + header[155] = ' ' + + if tw.err != nil { + // problem with header; probably integer too big for a field. + return tw.err + } + + if allowPax { + for k, v := range hdr.Xattrs { + paxHeaders[paxXattr+k] = v + } + } + + if len(paxHeaders) > 0 { + if !allowPax { + return errInvalidHeader + } + if err := tw.writePAXHeader(hdr, paxHeaders); err != nil { + return err + } + } + tw.nb = int64(hdr.Size) + tw.pad = (blockSize - (tw.nb % blockSize)) % blockSize + + _, tw.err = tw.w.Write(header) + return tw.err +} + +// writeUSTARLongName splits a USTAR long name hdr.Name. +// name must be < 256 characters. errNameTooLong is returned +// if hdr.Name can't be split. The splitting heuristic +// is compatible with gnu tar. +func (tw *Writer) splitUSTARLongName(name string) (prefix, suffix string, err error) { + length := len(name) + if length > fileNamePrefixSize+1 { + length = fileNamePrefixSize + 1 + } else if name[length-1] == '/' { + length-- + } + i := strings.LastIndex(name[:length], "/") + // nlen contains the resulting length in the name field. + // plen contains the resulting length in the prefix field. + nlen := len(name) - i - 1 + plen := i + if i <= 0 || nlen > fileNameSize || nlen == 0 || plen > fileNamePrefixSize { + err = errNameTooLong + return + } + prefix, suffix = name[:i], name[i+1:] + return +} + +// writePaxHeader writes an extended pax header to the +// archive. +func (tw *Writer) writePAXHeader(hdr *Header, paxHeaders map[string]string) error { + // Prepare extended header + ext := new(Header) + ext.Typeflag = TypeXHeader + // Setting ModTime is required for reader parsing to + // succeed, and seems harmless enough. + ext.ModTime = hdr.ModTime + // The spec asks that we namespace our pseudo files + // with the current pid. + pid := os.Getpid() + dir, file := path.Split(hdr.Name) + fullName := path.Join(dir, + fmt.Sprintf("PaxHeaders.%d", pid), file) + + ascii := toASCII(fullName) + if len(ascii) > 100 { + ascii = ascii[:100] + } + ext.Name = ascii + // Construct the body + var buf bytes.Buffer + + for k, v := range paxHeaders { + fmt.Fprint(&buf, paxHeader(k+"="+v)) + } + + ext.Size = int64(len(buf.Bytes())) + if err := tw.writeHeader(ext, false); err != nil { + return err + } + if _, err := tw.Write(buf.Bytes()); err != nil { + return err + } + if err := tw.Flush(); err != nil { + return err + } + return nil +} + +// paxHeader formats a single pax record, prefixing it with the appropriate length +func paxHeader(msg string) string { + const padding = 2 // Extra padding for space and newline + size := len(msg) + padding + size += len(strconv.Itoa(size)) + record := fmt.Sprintf("%d %s\n", size, msg) + if len(record) != size { + // Final adjustment if adding size increased + // the number of digits in size + size = len(record) + record = fmt.Sprintf("%d %s\n", size, msg) + } + return record +} + +// Write writes to the current entry in the tar archive. +// Write returns the error ErrWriteTooLong if more than +// hdr.Size bytes are written after WriteHeader. +func (tw *Writer) Write(b []byte) (n int, err error) { + if tw.closed { + err = ErrWriteTooLong + return + } + overwrite := false + if int64(len(b)) > tw.nb { + b = b[0:tw.nb] + overwrite = true + } + n, err = tw.w.Write(b) + tw.nb -= int64(n) + if err == nil && overwrite { + err = ErrWriteTooLong + return + } + tw.err = err + return +} + +// Close closes the tar archive, flushing any unwritten +// data to the underlying writer. +func (tw *Writer) Close() error { + if tw.err != nil || tw.closed { + return tw.err + } + tw.Flush() + tw.closed = true + if tw.err != nil { + return tw.err + } + + // trailer: two zero blocks + for i := 0; i < 2; i++ { + _, tw.err = tw.w.Write(zeroBlock) + if tw.err != nil { + break + } + } + return tw.err +} |