ar.go

Documentation: github.com/bazelbuild/rules_go/go/tools/builders

     1  // Copyright 2018 The Bazel Authors. All rights reserved.
     2  //
     3  // Licensed under the Apache License, Version 2.0 (the "License");
     4  // you may not use this file except in compliance with the License.
     5  // You may obtain a copy of the License at
     6  //
     7  //    http://www.apache.org/licenses/LICENSE-2.0
     8  //
     9  // Unless required by applicable law or agreed to in writing, software
    10  // distributed under the License is distributed on an "AS IS" BASIS,
    11  // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
    12  // See the License for the specific language governing permissions and
    13  // limitations under the License.
    14  
    15  package main
    16  
    17  import (
    18  	"encoding/binary"
    19  	"fmt"
    20  	"io"
    21  	"os"
    22  	"strconv"
    23  	"strings"
    24  )
    25  
    26  const (
    27  	// arHeader appears at the beginning of archives created by "ar" and
    28  	// "go tool pack" on all platforms.
    29  	arHeader = "!<arch>\n"
    30  
    31  	// entryLength is the size in bytes of the metadata preceding each file
    32  	// in an archive.
    33  	entryLength = 60
    34  )
    35  
    36  var zeroBytes = []byte("0                    ")
    37  
    38  type header struct {
    39  	NameRaw     [16]byte
    40  	ModTimeRaw  [12]byte
    41  	OwnerIdRaw  [6]byte
    42  	GroupIdRaw  [6]byte
    43  	FileModeRaw [8]byte
    44  	FileSizeRaw [10]byte
    45  	EndRaw      [2]byte
    46  }
    47  
    48  func (h *header) name() string {
    49  	return strings.TrimRight(string(h.NameRaw[:]), " ")
    50  }
    51  
    52  func (h *header) size() int64 {
    53  	s, err := strconv.Atoi(strings.TrimRight(string(h.FileSizeRaw[:]), " "))
    54  	if err != nil {
    55  		panic(err)
    56  	}
    57  	return int64(s)
    58  }
    59  
    60  func (h *header) next() int64 {
    61  	size := h.size()
    62  	return size + size%2
    63  }
    64  
    65  func (h *header) deterministic() *header {
    66  	h2 := *h
    67  	copy(h2.ModTimeRaw[:], zeroBytes)
    68  	copy(h2.OwnerIdRaw[:], zeroBytes)
    69  	copy(h2.GroupIdRaw[:], zeroBytes)
    70  	copy(h2.FileModeRaw[:], zeroBytes) // GNU ar also clears this
    71  	return &h2
    72  }
    73  
    74  // stripArMetadata strips the archive metadata of non-deterministic data:
    75  // - Timestamps
    76  // - User IDs
    77  // - Group IDs
    78  // - File Modes
    79  // The archive is modified in place.
    80  func stripArMetadata(archivePath string) error {
    81  	archive, err := os.OpenFile(archivePath, os.O_RDWR, 0)
    82  	if err != nil {
    83  		return err
    84  	}
    85  	defer archive.Close()
    86  
    87  	magic := make([]byte, len(arHeader))
    88  	if _, err := io.ReadFull(archive, magic); err != nil {
    89  		return err
    90  	}
    91  
    92  	if string(magic) != arHeader {
    93  		return fmt.Errorf("%s is not an archive", archivePath)
    94  	}
    95  
    96  	for {
    97  		hdr := &header{}
    98  		if err := binary.Read(archive, binary.BigEndian, hdr); err == io.EOF {
    99  			return nil
   100  		} else if err != nil {
   101  			return err
   102  		}
   103  
   104  		// Seek back at the beginning of the header and overwrite it.
   105  		archive.Seek(-entryLength, os.SEEK_CUR)
   106  		if err := binary.Write(archive, binary.BigEndian, hdr.deterministic()); err != nil {
   107  			return err
   108  		}
   109  
   110  		if _, err := archive.Seek(hdr.next(), os.SEEK_CUR); err == io.EOF {
   111  			return nil
   112  		} else if err != nil {
   113  			return err
   114  		}
   115  	}
   116  }
   117
View as plain text