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// Copyright (c) 2017, Google Inc.
//
// Permission to use, copy, modify, and/or distribute this software for any
// purpose with or without fee is hereby granted, provided that the above
// copyright notice and this permission notice appear in all copies.
//
// THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
// WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
// MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY
// SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
// WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION
// OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN
// CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE. */
// ar.go contains functions for parsing .a archive files.
package main
import (
"bytes"
"errors"
"io"
"strconv"
"strings"
)
// ParseAR parses an archive file from r and returns a map from filename to
// contents, or else an error.
func ParseAR(r io.Reader) (map[string][]byte, error) {
// See https://en.wikipedia.org/wiki/Ar_(Unix)#File_format_details
const expectedMagic = "!<arch>\n"
var magic [len(expectedMagic)]byte
if _, err := io.ReadFull(r, magic[:]); err != nil {
return nil, err
}
if string(magic[:]) != expectedMagic {
return nil, errors.New("ar: not an archive file")
}
const filenameTableName = "//"
const symbolTableName = "/"
var longFilenameTable []byte
ret := make(map[string][]byte)
for {
var header [60]byte
if _, err := io.ReadFull(r, header[:]); err != nil {
if err == io.EOF {
break
}
return nil, errors.New("ar: error reading file header: " + err.Error())
}
name := strings.TrimRight(string(header[:16]), " ")
sizeStr := strings.TrimRight(string(header[48:58]), "\x00 ")
size, err := strconv.ParseUint(sizeStr, 10, 64)
if err != nil {
return nil, errors.New("ar: failed to parse file size: " + err.Error())
}
// File contents are padded to a multiple of two bytes
storedSize := size
if storedSize%2 == 1 {
storedSize++
}
contents := make([]byte, storedSize)
if _, err := io.ReadFull(r, contents); err != nil {
return nil, errors.New("ar: error reading file contents: " + err.Error())
}
contents = contents[:size]
switch {
case name == filenameTableName:
if longFilenameTable != nil {
return nil, errors.New("ar: two filename tables found")
}
longFilenameTable = contents
continue
case name == symbolTableName:
continue
case len(name) > 1 && name[0] == '/':
if longFilenameTable == nil {
return nil, errors.New("ar: long filename reference found before filename table")
}
// A long filename is stored as "/" followed by a
// base-10 offset in the filename table.
offset, err := strconv.ParseUint(name[1:], 10, 64)
if err != nil {
return nil, errors.New("ar: failed to parse filename offset: " + err.Error())
}
if offset > uint64((^uint(0))>>1) {
return nil, errors.New("ar: filename offset overflow")
}
if int(offset) > len(longFilenameTable) {
return nil, errors.New("ar: filename offset out of bounds")
}
filename := longFilenameTable[offset:]
if i := bytes.IndexByte(filename, '/'); i < 0 {
return nil, errors.New("ar: unterminated filename in table")
} else {
filename = filename[:i]
}
name = string(filename)
default:
name = strings.TrimRight(name, "/")
}
ret[name] = contents
}
return ret, nil
}
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