40 lines
980 B
Go
40 lines
980 B
Go
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package main
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import (
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"crypto/md5"
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"fmt"
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"io"
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"os"
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"path"
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"sync"
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)
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// Storage provides read and write access to items in the cache. In order to
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// avoid race conditions, adding and testing for entries in the cache are
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// protected by a mutex.
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type Storage struct {
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Directory string
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mutex sync.Mutex
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}
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// GetReader returns an io.Reader for the specified URL. If the file does not
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// exist, both a writer (for downloading the file) and a reader are created.
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func (s *Storage) GetReader(url string) (io.Reader, error) {
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var (
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hash = string(md5.Sum([]byte(url)))
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jsonFilename = path.Join(s.Directory, fmt.Sprintf("%s.json", hash))
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dataFilename = path.Join(s.Directory, fmt.Sprintf("%s.data", hash))
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)
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s.mutex.Lock()
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defer s.mutex.Unlock()
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i, err := os.Stat(jsonFilename)
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if err != nil {
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if os.IsNotExist(err) {
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NewWriter(url, jsonFilename, dataFilename)
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} else {
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return nil, err
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}
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}
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return NewReader(url, jsonFilename, dataFilename)
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}
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