forked from TrueCloudLab/distribution
135 lines
3.2 KiB
Go
135 lines
3.2 KiB
Go
package storage
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import (
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"bytes"
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"fmt"
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"io"
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"os"
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"github.com/docker/distribution/context"
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storagedriver "github.com/docker/distribution/registry/storage/driver"
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)
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// fileWriter implements a remote file writer backed by a storage driver.
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type fileWriter struct {
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driver storagedriver.StorageDriver
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ctx context.Context
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// identifying fields
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path string
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// mutable fields
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size int64 // size of the file, aka the current end
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offset int64 // offset is the current write offset
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err error // terminal error, if set, reader is closed
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}
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// fileWriterInterface makes the desired io compliant interface that the
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// filewriter should implement.
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type fileWriterInterface interface {
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io.WriteSeeker
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io.ReaderFrom
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io.Closer
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}
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var _ fileWriterInterface = &fileWriter{}
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// newFileWriter returns a prepared fileWriter for the driver and path. This
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// could be considered similar to an "open" call on a regular filesystem.
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func newFileWriter(ctx context.Context, driver storagedriver.StorageDriver, path string) (*fileWriter, error) {
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fw := fileWriter{
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driver: driver,
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path: path,
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ctx: ctx,
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}
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if fi, err := driver.Stat(ctx, path); err != nil {
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switch err := err.(type) {
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case storagedriver.PathNotFoundError:
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// ignore, offset is zero
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default:
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return nil, err
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}
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} else {
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if fi.IsDir() {
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return nil, fmt.Errorf("cannot write to a directory")
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}
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fw.size = fi.Size()
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}
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return &fw, nil
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}
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// Write writes the buffer p at the current write offset.
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func (fw *fileWriter) Write(p []byte) (n int, err error) {
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nn, err := fw.ReadFrom(bytes.NewReader(p))
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return int(nn), err
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}
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// ReadFrom reads reader r until io.EOF writing the contents at the current
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// offset.
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func (fw *fileWriter) ReadFrom(r io.Reader) (n int64, err error) {
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if fw.err != nil {
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return 0, fw.err
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}
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nn, err := fw.driver.WriteStream(fw.ctx, fw.path, fw.offset, r)
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// We should forward the offset, whether or not there was an error.
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// Basically, we keep the filewriter in sync with the reader's head. If an
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// error is encountered, the whole thing should be retried but we proceed
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// from an expected offset, even if the data didn't make it to the
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// backend.
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fw.offset += nn
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if fw.offset > fw.size {
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fw.size = fw.offset
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}
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return nn, err
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}
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// Seek moves the write position do the requested offest based on the whence
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// argument, which can be os.SEEK_CUR, os.SEEK_END, or os.SEEK_SET.
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func (fw *fileWriter) Seek(offset int64, whence int) (int64, error) {
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if fw.err != nil {
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return 0, fw.err
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}
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var err error
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newOffset := fw.offset
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switch whence {
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case os.SEEK_CUR:
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newOffset += int64(offset)
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case os.SEEK_END:
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newOffset = fw.size + int64(offset)
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case os.SEEK_SET:
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newOffset = int64(offset)
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}
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if newOffset < 0 {
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err = fmt.Errorf("cannot seek to negative position")
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} else {
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// No problems, set the offset.
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fw.offset = newOffset
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}
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return fw.offset, err
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}
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// Close closes the fileWriter for writing.
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// Calling it once is valid and correct and it will
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// return a nil error. Calling it subsequent times will
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// detect that fw.err has been set and will return the error.
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func (fw *fileWriter) Close() error {
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if fw.err != nil {
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return fw.err
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}
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fw.err = fmt.Errorf("filewriter@%v: closed", fw.path)
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return nil
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}
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