github.com/cayleygraph/cayley@v0.7.7/internal/decompressor/decompressor.go (about)

     1  // Copyright 2014 The Cayley 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 decompressor
    16  
    17  import (
    18  	"bufio"
    19  	"bytes"
    20  	"compress/bzip2"
    21  	"compress/gzip"
    22  	"io"
    23  )
    24  
    25  const (
    26  	gzipMagic  = "\x1f\x8b"
    27  	b2zipMagic = "BZh"
    28  )
    29  
    30  // New detects the file type of an io.Reader between
    31  // bzip, gzip, or raw quad file.
    32  func New(r io.Reader) (io.Reader, error) {
    33  	br := bufio.NewReader(r)
    34  	buf, err := br.Peek(3)
    35  	if err != nil {
    36  		return nil, err
    37  	}
    38  	switch {
    39  	case bytes.Compare(buf[:2], []byte(gzipMagic)) == 0:
    40  		return gzip.NewReader(br)
    41  	case bytes.Compare(buf[:3], []byte(b2zipMagic)) == 0:
    42  		return bzip2.NewReader(br), nil
    43  	default:
    44  		return br, nil
    45  	}
    46  }