tarzip.go

Documentation: github.com/sassoftware/relic/lib/zipslicer

     1  //
     2  // Copyright (c) SAS Institute Inc.
     3  //
     4  // Licensed under the Apache License, Version 2.0 (the "License");
     5  // you may not use this file except in compliance with the License.
     6  // You may obtain a copy of the License at
     7  //
     8  //     http://www.apache.org/licenses/LICENSE-2.0
     9  //
    10  // Unless required by applicable law or agreed to in writing, software
    11  // distributed under the License is distributed on an "AS IS" BASIS,
    12  // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
    13  // See the License for the specific language governing permissions and
    14  // limitations under the License.
    15  //
    16  
    17  package zipslicer
    18  
    19  import (
    20  	"archive/tar"
    21  	"errors"
    22  	"fmt"
    23  	"io"
    24  	"io/ioutil"
    25  	"os"
    26  )
    27  
    28  const (
    29  	TarMemberCD  = "zipdir.bin"
    30  	TarMemberZip = "contents.zip"
    31  )
    32  
    33  // Make a tar archive with two members:
    34  // - the central directory of the zip file
    35  // - the complete zip file
    36  // This lets us process the zip in one pass, which normally isn't possible with
    37  // the directory at the end.
    38  func ZipToTar(r *os.File, w io.Writer) error {
    39  	size, err := r.Seek(0, io.SeekEnd)
    40  	if err != nil {
    41  		return err
    42  	}
    43  	dirLoc, err := FindDirectory(r, size)
    44  	if err != nil {
    45  		return err
    46  	}
    47  	tw := tar.NewWriter(w)
    48  	r.Seek(dirLoc, 0)
    49  	if err := tarAddStream(tw, r, TarMemberCD, size-dirLoc); err != nil {
    50  		return err
    51  	}
    52  	r.Seek(0, 0)
    53  	if err := tarAddStream(tw, r, TarMemberZip, size); err != nil {
    54  		return err
    55  	}
    56  	return tw.Close()
    57  }
    58  
    59  func tarAddStream(tw *tar.Writer, r io.Reader, name string, size int64) error {
    60  	hdr := &tar.Header{Name: name, Mode: 0644, Size: size}
    61  	if err := tw.WriteHeader(hdr); err != nil {
    62  		return err
    63  	}
    64  	if _, err := io.CopyN(tw, r, size); err != nil {
    65  		return err
    66  	}
    67  	return nil
    68  }
    69  
    70  // Read a tar stream produced by ZipToTar and return the zip directory. Files
    71  // must be read from the zip in order or an error will be raised.
    72  func ReadZipTar(r io.Reader) (*Directory, error) {
    73  	tr := tar.NewReader(r)
    74  	hdr, err := tr.Next()
    75  	if err != nil {
    76  		return nil, fmt.Errorf("error reading tar: %s", err)
    77  	} else if hdr.Name != TarMemberCD {
    78  		return nil, errors.New("invalid tarzip")
    79  	}
    80  	zipdir, err := ioutil.ReadAll(tr)
    81  	if err != nil {
    82  		return nil, fmt.Errorf("error reading tar: %s", err)
    83  	}
    84  	hdr, err = tr.Next()
    85  	if err != nil {
    86  		return nil, err
    87  	} else if hdr.Name != TarMemberZip {
    88  		return nil, errors.New("invalid tarzip")
    89  	}
    90  	zr := &zipTarReader{tr: tr}
    91  	return ReadStream(zr, hdr.Size, zipdir)
    92  }
    93  
    94  type zipTarReader struct {
    95  	tr *tar.Reader
    96  }
    97  
    98  func (z *zipTarReader) Read(d []byte) (int, error) {
    99  	if z.tr == nil {
   100  		return 0, io.EOF
   101  	}
   102  	n, err := z.tr.Read(d)
   103  	if err == io.EOF {
   104  		_, err2 := z.tr.Next()
   105  		if err2 == nil {
   106  			err = errors.New("invalid tarzip")
   107  		} else if err2 != io.EOF {
   108  			err = err2
   109  		}
   110  		z.tr = nil
   111  	}
   112  	return n, err
   113  }
   114
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