github.com/pdfcpu/pdfcpu@v0.11.1/pkg/filter/ascii85Decode.go (about)

     1  /*
     2  Copyright 2018 The pdfcpu Authors.
     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 filter
    18  
    19  import (
    20  	"bytes"
    21  	"encoding/ascii85"
    22  	"io"
    23  
    24  	"github.com/pkg/errors"
    25  )
    26  
    27  type ascii85Decode struct {
    28  	baseFilter
    29  }
    30  
    31  const eodASCII85 = "~>"
    32  
    33  // Encode implements encoding for an ASCII85Decode filter.
    34  func (f ascii85Decode) Encode(r io.Reader) (io.Reader, error) {
    35  
    36  	b2 := &bytes.Buffer{}
    37  	encoder := ascii85.NewEncoder(b2)
    38  	if _, err := io.Copy(encoder, r); err != nil {
    39  		return nil, err
    40  	}
    41  	encoder.Close()
    42  
    43  	// Add eod sequence
    44  	b2.WriteString(eodASCII85)
    45  
    46  	return b2, nil
    47  }
    48  
    49  // Decode implements decoding for an ASCII85Decode filter.
    50  func (f ascii85Decode) Decode(r io.Reader) (io.Reader, error) {
    51  	return f.DecodeLength(r, -1)
    52  }
    53  
    54  func (f ascii85Decode) DecodeLength(r io.Reader, maxLen int64) (io.Reader, error) {
    55  
    56  	bb, err := getReaderBytes(r)
    57  	if err != nil {
    58  		return nil, err
    59  	}
    60  
    61  	// fmt.Printf("dump:\n%s", hex.Dump(bb))
    62  
    63  	// Strip trailing whitespace (CR, LF, CRLF, etc.)
    64  	// Per PDF spec, whitespace should be ignored in ASCII85 encoding
    65  	bb = bytes.TrimRight(bb, "\r\n")
    66  
    67  	if !bytes.HasSuffix(bb, []byte(eodASCII85)) {
    68  		return nil, errors.New("pdfcpu: Decode: missing eod marker")
    69  	}
    70  
    71  	// Strip eod sequence: "~>"
    72  	bb = bb[:len(bb)-2]
    73  
    74  	decoder := ascii85.NewDecoder(bytes.NewReader(bb))
    75  
    76  	var b2 bytes.Buffer
    77  	if maxLen < 0 {
    78  		if _, err := io.Copy(&b2, decoder); err != nil {
    79  			return nil, err
    80  		}
    81  	} else {
    82  		if _, err := io.CopyN(&b2, decoder, maxLen); err != nil {
    83  			return nil, err
    84  		}
    85  	}
    86  
    87  	return &b2, nil
    88  }