github.com/uber/kraken@v0.1.4/lib/torrent/storage/piecereader/file.go (about)

     1  // Copyright (c) 2016-2019 Uber Technologies, Inc.
     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  package piecereader
    15  
    16  import (
    17  	"fmt"
    18  	"io"
    19  	"os"
    20  
    21  	"github.com/uber/kraken/lib/store"
    22  )
    23  
    24  // Opener opens files.
    25  type Opener interface {
    26  	Open() (store.FileReader, error)
    27  }
    28  
    29  // FileReader is a storage.PieceReader which reads a piece from a file.
    30  type FileReader struct {
    31  	offset int64
    32  	length int64
    33  
    34  	opener Opener
    35  	closer io.Closer
    36  	reader io.Reader
    37  }
    38  
    39  // NewFileReader creates a FileReader which reads a piece from f. f should not
    40  // be used once it is given to a FileReader.
    41  func NewFileReader(offset, length int64, opener Opener) *FileReader {
    42  	return &FileReader{
    43  		offset: offset,
    44  		length: length,
    45  		opener: opener,
    46  	}
    47  }
    48  
    49  // Read reads a piece in p.
    50  func (r *FileReader) Read(p []byte) (int, error) {
    51  	if r.reader == nil {
    52  		f, err := r.opener.Open()
    53  		if err != nil {
    54  			return 0, fmt.Errorf("open: %s", err)
    55  		}
    56  		if _, err := f.Seek(r.offset, os.SEEK_SET); err != nil {
    57  			return 0, fmt.Errorf("seek: %s", err)
    58  		}
    59  		r.reader = io.LimitReader(f, r.length)
    60  		r.closer = f
    61  	}
    62  	return r.reader.Read(p)
    63  }
    64  
    65  // Close closes the underlying file.
    66  func (r *FileReader) Close() error {
    67  	if r.closer == nil {
    68  		return nil
    69  	}
    70  	return r.closer.Close()
    71  }
    72  
    73  // Length returns the length of the piece.
    74  func (r *FileReader) Length() int {
    75  	return int(r.length)
    76  }