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// Copyright (c) 2011 Mikkel Krautz
// The use of this source code is goverened by a BSD-style
// license that can be found in the LICENSE-file.
package ar
import (
"io"
"strconv"
)
// A Writer provides sequential writing of an ar archive in BSD format. It does not support
// writing in the GNU format, since the GNU-style extended filenames cannot be written sequentially.
// The BSD ar format is widely compatible with most modern ar readers out there.
//
// An ar 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.
//
// Example:
// aw := ar.NewWriter(w)
// hdr := new(ar.Header)
// hdr.Size = length of data in bytes
// // populate other hdr fields as desired
// if err := aw.WriteHeader(hdr); err != nil {
// // handle error
// }
// io.Copy(tw, data)
// tw.Close()
type Writer struct {
w io.Writer
offset int64
dataRemain int64
closed bool
}
// NewWriter creates a new Writer writing to w.
func NewWriter(w io.Writer) *Writer {
return &Writer{w, 0, 0, false}
}
// Closes the ar achive, flushing any unwritten data to the underlying writer.
func (aw *Writer) Close() error {
err := aw.Flush()
if err != nil {
return err
}
aw.closed = true
return nil
}
// Flush finishes writing the current file (optional).
func (aw *Writer) Flush() error {
if aw.closed {
return ErrWriteAfterClose
}
if aw.offset%2 != 0 {
_, err := io.WriteString(aw.w, "\n")
aw.offset += int64(1)
if err != nil {
return err
}
}
return nil
}
// Write writes the current entry in the ar archive. Write returns the error ErrWriteTooLong
// if more than hdr.Size bytes are written following a call to WriteHeader.
func (aw *Writer) Write(b []byte) (n int, err error) {
if aw.closed {
return 0, ErrWriteAfterClose
}
// Overflow check
tooLong := false
if int64(len(b)) > aw.dataRemain {
b = b[0:aw.dataRemain]
tooLong = true
}
n, err = aw.w.Write(b)
aw.dataRemain -= int64(n)
// Warn if the write would have overflowed the
// space set aside for the provided data.
if err == nil && tooLong {
err = ErrWriteTooLong
return
}
return
}
// WriteHeader writes hdr and prepares to accept the file's content. WriteHeader calls Flush to
// correctly pad the last written file. Calling after WriteHeader a Close will return ErrWriteAfterClose.
func (aw *Writer) WriteHeader(hdr *Header) (err error) {
if aw.closed {
return ErrWriteAfterClose
}
// Flush previous data write
err = aw.Flush()
if err != nil {
return err
}
// If we're at the beginning of the writer, write
// the global header.
if aw.offset == 0 {
nwritten, err := io.WriteString(aw.w, globalHeader)
aw.offset += int64(nwritten)
if err != nil {
return err
}
}
var (
newName string
newSize int64
)
longFn := len(hdr.Name) > 15
if longFn {
newName = bsdLongFileNamePrefix + strconv.Itoa(len(hdr.Name))
newSize = hdr.Size + int64(len(hdr.Name))
} else {
newName = hdr.Name
newSize = hdr.Size
}
nwritten, err := io.WriteString(aw.w, encodeArString(newName, 16))
aw.offset += int64(nwritten)
if err != nil {
return err
}
nwritten, err = io.WriteString(aw.w, encodeArString(strconv.FormatInt(hdr.Mtime, 10), 12))
aw.offset += int64(nwritten)
if err != nil {
return err
}
nwritten, err = io.WriteString(aw.w, encodeArString(strconv.Itoa(hdr.Uid), 6))
aw.offset += int64(nwritten)
if err != nil {
return err
}
nwritten, err = io.WriteString(aw.w, encodeArString(strconv.Itoa(hdr.Gid), 6))
aw.offset += int64(nwritten)
if err != nil {
return err
}
nwritten, err = io.WriteString(aw.w, encodeArString(strconv.FormatInt(hdr.Mode, 8), 8))
aw.offset += int64(nwritten)
if err != nil {
return err
}
nwritten, err = io.WriteString(aw.w, encodeArString(strconv.FormatInt(newSize, 10), 10))
aw.offset += int64(nwritten)
if err != nil {
return err
}
nwritten, err = io.WriteString(aw.w, fileHeaderMagic)
aw.offset += int64(nwritten)
if err != nil {
return err
}
if longFn {
nwritten, err = io.WriteString(aw.w, hdr.Name)
aw.offset += int64(nwritten)
aw.dataRemain = newSize - int64(nwritten)
if err != nil {
return err
}
} else {
aw.dataRemain = newSize
}
return nil
}
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