94 lines
2.1 KiB
Go
94 lines
2.1 KiB
Go
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package cache
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import (
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"github.com/fsnotify/fsnotify"
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"io"
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"os"
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)
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// liveReader reads a file from disk, synchronizing reads with a downloader.
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type liveReader struct {
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downloader *downloader
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file *os.File
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watcher *fsnotify.Watcher
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entry *Entry
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done chan error
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err error
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eof bool
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}
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// newLiveReader creates a reader from the provided downloader and data
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// file. fsnotify is used to watch for writes to the file to avoid using a
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// spinloop. Invoking this function assumes the existence of the data file.
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func newLiveReader(d *downloader, dataFilename string) (*liveReader, error) {
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f, err := os.Open(dataFilename)
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if err != nil {
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return nil, err
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}
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w, err := fsnotify.NewWatcher()
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if err != nil {
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return nil, err
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}
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if err = w.Add(dataFilename); err != nil {
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return nil, err
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}
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l := &liveReader{
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downloader: d,
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file: f,
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watcher: w,
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done: make(chan error),
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}
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go func() {
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defer close(l.done)
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l.done <- d.WaitForDone()
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}()
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return l, err
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}
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// Read attempts to read as much data as possible into the provided buffer.
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// Since data is being downloaded as data is being read, fsnotify is used to
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// monitor writes to the file. This function blocks until the requested amount
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// of data is read, an error occurs, or EOF is encountered.
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func (l *liveReader) Read(p []byte) (int, error) {
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if l.err != nil {
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return 0, l.err
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}
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bytesRead := 0
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loop:
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for bytesRead < len(p) {
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n, err := l.file.Read(p[bytesRead:])
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bytesRead += n
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if err != nil {
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if err != io.EOF || l.eof {
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l.err = err
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break loop
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}
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for {
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select {
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case e := <-l.watcher.Events:
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if e.Op&fsnotify.Write != fsnotify.Write {
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continue
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}
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case err = <-l.done:
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l.err = err
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l.eof = true
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}
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continue loop
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}
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}
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}
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return bytesRead, l.err
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}
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// Close attempts to close the data file (if opened).
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func (l *liveReader) Close() error {
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return l.file.Close()
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}
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// GetEntry returns the Entry associated with the file, blocking until either
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// the data is available or an error occurs.
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func (l *liveReader) GetEntry() (*Entry, error) {
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return l.downloader.GetEntry()
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}
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