github.com/ajguerrer/rules_go@v0.20.3/go/tools/builders/ar.go (about)

     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  type header struct {
    27  	NameRaw     [16]byte
    28  	ModTimeRaw  [12]byte
    29  	OwnerIdRaw  [6]byte
    30  	GroupIdRaw  [6]byte
    31  	FileModeRaw [8]byte
    32  	FileSizeRaw [10]byte
    33  	EndRaw      [2]byte
    34  }
    35  
    36  func (h *header) name() string {
    37  	return strings.TrimRight(string(h.NameRaw[:]), " ")
    38  }
    39  
    40  func (h *header) size() int64 {
    41  	s, err := strconv.Atoi(strings.TrimRight(string(h.FileSizeRaw[:]), " "))
    42  	if err != nil {
    43  		panic(err)
    44  	}
    45  	return int64(s)
    46  }
    47  
    48  func (h *header) next() int64 {
    49  	size := h.size()
    50  	return size + size%2
    51  }
    52  
    53  func (h *header) deterministic() *header {
    54  	h2 := *h
    55  	copy(h2.ModTimeRaw[:], zeroBytes)
    56  	copy(h2.OwnerIdRaw[:], zeroBytes)
    57  	copy(h2.GroupIdRaw[:], zeroBytes)
    58  	copy(h2.FileModeRaw[:], zeroBytes) // GNU ar also clears this
    59  	return &h2
    60  }
    61  
    62  // stripArMetadata strips the archive metadata of non-deterministic data:
    63  // - Timestamps
    64  // - User IDs
    65  // - Group IDs
    66  // - File Modes
    67  // The archive is modified in place.
    68  func stripArMetadata(archivePath string) error {
    69  	archive, err := os.OpenFile(archivePath, os.O_RDWR, 0)
    70  	if err != nil {
    71  		return err
    72  	}
    73  	defer archive.Close()
    74  
    75  	magic := make([]byte, len(arHeader))
    76  	if _, err := io.ReadFull(archive, magic); err != nil {
    77  		return err
    78  	}
    79  
    80  	if string(magic) != arHeader {
    81  		return fmt.Errorf("%s is not an archive", archivePath)
    82  	}
    83  
    84  	for {
    85  		hdr := &header{}
    86  		if err := binary.Read(archive, binary.BigEndian, hdr); err == io.EOF {
    87  			return nil
    88  		} else if err != nil {
    89  			return err
    90  		}
    91  
    92  		// Seek back at the beginning of the header and overwrite it.
    93  		archive.Seek(-entryLength, os.SEEK_CUR)
    94  		if err := binary.Write(archive, binary.BigEndian, hdr.deterministic()); err != nil {
    95  			return err
    96  		}
    97  
    98  		if _, err := archive.Seek(hdr.next(), os.SEEK_CUR); err == io.EOF {
    99  			return nil
   100  		} else if err != nil {
   101  			return err
   102  		}
   103  	}
   104  }