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305183e6c5
- Tests all passing. - Zip and squashfs archivers working. - Lazily loads and caches squashfs Squashfs - see archive.go for more FIXMEs
125 lines
3.2 KiB
Go
125 lines
3.2 KiB
Go
package squashfs
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// Could just be using bare object Open with RangeRequest which
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// would transfer the minimum amount of data but may be slower.
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import (
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"errors"
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"fmt"
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"os"
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"sync"
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"github.com/rclone/rclone/vfs"
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)
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// Cache file handles for accessing the file
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type cache struct {
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node vfs.Node
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fhsMu sync.Mutex
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fhs []cacheHandle
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}
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// A cached file handle
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type cacheHandle struct {
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offset int64
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fh vfs.Handle
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}
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// Make a new cache
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func newCache(node vfs.Node) *cache {
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return &cache{
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node: node,
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}
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}
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// Get a vfs.Handle from the pool or open one
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//
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// This tries to find an open file handle which doesn't require seeking.
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func (c *cache) open(off int64) (fh vfs.Handle, err error) {
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c.fhsMu.Lock()
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defer c.fhsMu.Unlock()
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if len(c.fhs) > 0 {
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// Look for exact match first
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for i, cfh := range c.fhs {
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if cfh.offset == off {
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// fs.Debugf(nil, "CACHE MATCH")
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c.fhs = append(c.fhs[:i], c.fhs[i+1:]...)
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return cfh.fh, nil
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}
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}
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// fs.Debugf(nil, "CACHE MISS")
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// Just take the first one if not found
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cfh := c.fhs[0]
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c.fhs = c.fhs[1:]
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return cfh.fh, nil
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}
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fh, err = c.node.Open(os.O_RDONLY)
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if err != nil {
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return nil, fmt.Errorf("failed to open squashfs archive: %w", err)
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}
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return fh, nil
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}
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// Close a vfs.Handle or return it to the pool
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//
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// off should be the offset the file handle would read from without seeking
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func (c *cache) close(fh vfs.Handle, off int64) {
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c.fhsMu.Lock()
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defer c.fhsMu.Unlock()
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c.fhs = append(c.fhs, cacheHandle{
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offset: off,
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fh: fh,
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})
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}
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// ReadAt reads len(p) bytes into p starting at offset off in the underlying
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// input source. It returns the number of bytes read (0 <= n <= len(p)) and any
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// error encountered.
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//
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// When ReadAt returns n < len(p), it returns a non-nil error explaining why
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// more bytes were not returned. In this respect, ReadAt is stricter than Read.
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//
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// Even if ReadAt returns n < len(p), it may use all of p as scratch
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// space during the call. If some data is available but not len(p) bytes,
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// ReadAt blocks until either all the data is available or an error occurs.
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// In this respect ReadAt is different from Read.
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//
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// If the n = len(p) bytes returned by ReadAt are at the end of the input
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// source, ReadAt may return either err == EOF or err == nil.
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//
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// If ReadAt is reading from an input source with a seek offset, ReadAt should
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// not affect nor be affected by the underlying seek offset.
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//
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// Clients of ReadAt can execute parallel ReadAt calls on the same input
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// source.
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//
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// Implementations must not retain p.
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func (c *cache) ReadAt(p []byte, off int64) (n int, err error) {
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fh, err := c.open(off)
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if err != nil {
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return n, err
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}
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defer func() {
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c.close(fh, off+int64(len(p)))
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}()
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// fs.Debugf(nil, "ReadAt(p[%d], off=%d, fh=%p)", len(p), off, fh)
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return fh.ReadAt(p, off)
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}
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var errCacheNotImplemented = errors.New("internal error: squashfs cache doesn't implement method")
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// WriteAt method dummy stub to satisfy interface
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func (c *cache) WriteAt(p []byte, off int64) (n int, err error) {
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return 0, errCacheNotImplemented
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}
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// Seek method dummy stub to satisfy interface
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func (c *cache) Seek(offset int64, whence int) (int64, error) {
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return 0, errCacheNotImplemented
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}
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