libgo: update to go1.9

[official-gcc.git] / libgo / go / archive / tar / writer.go

// 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"
        "path"
        "sort"
        "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")
        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    block // buffer to use in writeHeader when writing a regular header
        paxHdrBuff block // 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
}

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(dsnet): 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

        // 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[:])

        // Wrappers around formatter that automatically sets paxHeaders if the
        // argument extends beyond the capacity of the input byte slice.
        var f formatter
        var formatString = func(b []byte, s string, paxKeyword string) {
                needsPaxHeader := paxKeyword != paxNone && len(s) > len(b) || !isASCII(s)
                if needsPaxHeader {
                        paxHeaders[paxKeyword] = s
                }

                // Write string in a best-effort manner to satisfy readers that expect
                // the field to be non-empty.
                s = toASCII(s)
                if len(s) > len(b) {
                        s = s[:len(b)]
                }
                f.formatString(b, s) // Should never error
        }
        var formatNumeric = func(b []byte, x int64, paxKeyword string) {
                // Try octal first.
                s := strconv.FormatInt(x, 8)
                if len(s) < len(b) {
                        f.formatOctal(b, x)
                        return
                }

                // If it is too long for octal, and PAX is preferred, use a PAX header.
                if paxKeyword != paxNone && tw.preferPax {
                        f.formatOctal(b, 0)
                        s := strconv.FormatInt(x, 10)
                        paxHeaders[paxKeyword] = s
                        return
                }

                tw.usedBinary = true
                f.formatNumeric(b, x)
        }

        // Handle out of range ModTime carefully.
        var modTime int64
        if !hdr.ModTime.Before(minTime) && !hdr.ModTime.After(maxTime) {
                modTime = hdr.ModTime.Unix()
        }

        v7 := header.V7()
        formatString(v7.Name(), hdr.Name, paxPath)
        // TODO(dsnet): The GNU format permits the mode field to be encoded in
        // base-256 format. Thus, we can use formatNumeric instead of formatOctal.
        f.formatOctal(v7.Mode(), hdr.Mode)
        formatNumeric(v7.UID(), int64(hdr.Uid), paxUid)
        formatNumeric(v7.GID(), int64(hdr.Gid), paxGid)
        formatNumeric(v7.Size(), hdr.Size, paxSize)
        // TODO(dsnet): Consider using PAX for finer time granularity.
        formatNumeric(v7.ModTime(), modTime, paxNone)
        v7.TypeFlag()[0] = hdr.Typeflag
        formatString(v7.LinkName(), hdr.Linkname, paxLinkpath)

        ustar := header.USTAR()
        formatString(ustar.UserName(), hdr.Uname, paxUname)
        formatString(ustar.GroupName(), hdr.Gname, paxGname)
        formatNumeric(ustar.DevMajor(), hdr.Devmajor, paxNone)
        formatNumeric(ustar.DevMinor(), hdr.Devminor, paxNone)

        // TODO(dsnet): The logic surrounding the prefix field is broken when trying
        // to encode the header as GNU format. The challenge with the current logic
        // is that we are unsure what format we are using at any given moment until
        // we have processed *all* of the fields. The problem is that by the time
        // all fields have been processed, some work has already been done to handle
        // each field under the assumption that it is for one given format or
        // another. In some situations, this causes the Writer to be confused and
        // encode a prefix field when the format being used is GNU. Thus, producing
        // an invalid tar file.
        //
        // As a short-term fix, we disable the logic to use the prefix field, which
        // will force the badly generated GNU files to become encoded as being
        // the PAX format.
        //
        // As an alternative fix, we could hard-code preferPax to be true. However,
        // this is problematic for the following reasons:
        //      * The preferPax functionality is not tested at all.
        //      * This can result in headers that try to use both the GNU and PAX
        //      features at the same time, which is also wrong.
        //
        // The proper fix for this is to use a two-pass method:
        //      * The first pass simply determines what set of formats can possibly
        //      encode the given header.
        //      * The second pass actually encodes the header as that given format
        //      without worrying about violating the format.
        //
        // See the following:
        //      https://golang.org/issue/12594
        //      https://golang.org/issue/17630
        //      https://golang.org/issue/9683
        const usePrefix = false

        // try to use a ustar header when only the name is too long
        _, paxPathUsed := paxHeaders[paxPath]
        if usePrefix && !tw.preferPax && len(paxHeaders) == 1 && paxPathUsed {
                prefix, suffix, ok := splitUSTARPath(hdr.Name)
                if ok {
                        // Since we can encode in USTAR format, disable PAX header.
                        delete(paxHeaders, paxPath)

                        // Update the path fields
                        formatString(v7.Name(), suffix, paxNone)
                        formatString(ustar.Prefix(), prefix, paxNone)
                }
        }

        if tw.usedBinary {
                header.SetFormat(formatGNU)
        } else {
                header.SetFormat(formatUSTAR)
        }

        // Check if there were any formatting errors.
        if f.err != nil {
                tw.err = f.err
                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 = hdr.Size
        tw.pad = (blockSize - (tw.nb % blockSize)) % blockSize

        _, tw.err = tw.w.Write(header[:])
        return tw.err
}

// splitUSTARPath splits a path according to USTAR prefix and suffix rules.
// If the path is not splittable, then it will return ("", "", false).
func splitUSTARPath(name string) (prefix, suffix string, ok bool) {
        length := len(name)
        if length <= nameSize || !isASCII(name) {
                return "", "", false
        } else if length > prefixSize+1 {
                length = prefixSize + 1
        } else if name[length-1] == '/' {
                length--
        }

        i := strings.LastIndex(name[:length], "/")
        nlen := len(name) - i - 1 // nlen is length of suffix
        plen := i                 // plen is length of prefix
        if i <= 0 || nlen > nameSize || nlen == 0 || plen > prefixSize {
                return "", "", false
        }
        return name[:i], name[i+1:], true
}

// 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. However, this results in differing outputs
        // for identical inputs. As such, the constant 0 is now used instead.
        // golang.org/issue/12358
        dir, file := path.Split(hdr.Name)
        fullName := path.Join(dir, "PaxHeaders.0", file)

        ascii := toASCII(fullName)
        if len(ascii) > nameSize {
                ascii = ascii[:nameSize]
        }
        ext.Name = ascii
        // Construct the body
        var buf bytes.Buffer

        // Keys are sorted before writing to body to allow deterministic output.
        keys := make([]string, 0, len(paxHeaders))
        for k := range paxHeaders {
                keys = append(keys, k)
        }
        sort.Strings(keys)

        for _, k := range keys {
                fmt.Fprint(&buf, formatPAXRecord(k, paxHeaders[k]))
        }

        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
}

// 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 = ErrWriteAfterClose
                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
}