1 files changed, 273 insertions, 0 deletions
diff --git a/vendor/github.com/dsoprea/go-utility/v2/filesystem/bounceback.go b/vendor/github.com/dsoprea/go-utility/v2/filesystem/bounceback.go
new file mode 100644
index 000000000..1112a10ef
--- /dev/null
+++ b/vendor/github.com/dsoprea/go-utility/v2/filesystem/bounceback.go
@@ -0,0 +1,273 @@
+package rifs
+
+import (
+	"fmt"
+	"io"
+
+	"github.com/dsoprea/go-logging"
+)
+
+// BouncebackStats describes operation counts.
+type BouncebackStats struct {
+	reads  int
+	writes int
+	seeks  int
+	syncs  int
+}
+
+func (bbs BouncebackStats) String() string {
+	return fmt.Sprintf(
+		"BouncebackStats<READS=(%d) WRITES=(%d) SEEKS=(%d) SYNCS=(%d)>",
+		bbs.reads, bbs.writes, bbs.seeks, bbs.syncs)
+}
+
+type bouncebackBase struct {
+	currentPosition int64
+
+	stats BouncebackStats
+}
+
+// Position returns the position that we're supposed to be at.
+func (bb *bouncebackBase) Position() int64 {
+
+	// TODO(dustin): Add test
+
+	return bb.currentPosition
+}
+
+// StatsReads returns the number of reads that have been attempted.
+func (bb *bouncebackBase) StatsReads() int {
+
+	// TODO(dustin): Add test
+
+	return bb.stats.reads
+}
+
+// StatsWrites returns the number of write operations.
+func (bb *bouncebackBase) StatsWrites() int {
+
+	// TODO(dustin): Add test
+
+	return bb.stats.writes
+}
+
+// StatsSeeks returns the number of seeks.
+func (bb *bouncebackBase) StatsSeeks() int {
+
+	// TODO(dustin): Add test
+
+	return bb.stats.seeks
+}
+
+// StatsSyncs returns the number of corrective seeks ("bounce-backs").
+func (bb *bouncebackBase) StatsSyncs() int {
+
+	// TODO(dustin): Add test
+
+	return bb.stats.syncs
+}
+
+// Seek does a seek to an arbitrary place in the `io.ReadSeeker`.
+func (bb *bouncebackBase) seek(s io.Seeker, offset int64, whence int) (newPosition int64, err error) {
+	defer func() {
+		if state := recover(); state != nil {
+			err = log.Wrap(state.(error))
+		}
+	}()
+
+	// If the seek is relative, make sure we're where we're supposed to be *first*.
+	if whence != io.SeekStart {
+		err = bb.checkPosition(s)
+		log.PanicIf(err)
+	}
+
+	bb.stats.seeks++
+
+	newPosition, err = s.Seek(offset, whence)
+	log.PanicIf(err)
+
+	// Update our internal tracking.
+	bb.currentPosition = newPosition
+
+	return newPosition, nil
+}
+
+func (bb *bouncebackBase) checkPosition(s io.Seeker) (err error) {
+	defer func() {
+		if state := recover(); state != nil {
+			err = log.Wrap(state.(error))
+		}
+	}()
+
+	// Make sure we're where we're supposed to be.
+
+	// This should have no overhead, and enables us to collect stats.
+	realCurrentPosition, err := s.Seek(0, io.SeekCurrent)
+	log.PanicIf(err)
+
+	if realCurrentPosition != bb.currentPosition {
+		bb.stats.syncs++
+
+		_, err = s.Seek(bb.currentPosition, io.SeekStart)
+		log.PanicIf(err)
+	}
+
+	return nil
+}
+
+// BouncebackReader wraps a ReadSeeker, keeps track of our position, and
+// seeks back to it before writing. This allows an underlying ReadWriteSeeker
+// with an unstable position can still be used for a prolonged series of writes.
+type BouncebackReader struct {
+	rs io.ReadSeeker
+
+	bouncebackBase
+}
+
+// NewBouncebackReader returns a `*BouncebackReader` struct.
+func NewBouncebackReader(rs io.ReadSeeker) (br *BouncebackReader, err error) {
+	defer func() {
+		if state := recover(); state != nil {
+			err = log.Wrap(state.(error))
+		}
+	}()
+
+	initialPosition, err := rs.Seek(0, io.SeekCurrent)
+	log.PanicIf(err)
+
+	bb := bouncebackBase{
+		currentPosition: initialPosition,
+	}
+
+	br = &BouncebackReader{
+		rs:             rs,
+		bouncebackBase: bb,
+	}
+
+	return br, nil
+}
+
+// Seek does a seek to an arbitrary place in the `io.ReadSeeker`.
+func (br *BouncebackReader) Seek(offset int64, whence int) (newPosition int64, err error) {
+	defer func() {
+		if state := recover(); state != nil {
+			err = log.Wrap(state.(error))
+		}
+	}()
+
+	newPosition, err = br.bouncebackBase.seek(br.rs, offset, whence)
+	log.PanicIf(err)
+
+	return newPosition, nil
+}
+
+// Seek does a standard read.
+func (br *BouncebackReader) Read(p []byte) (n int, err error) {
+	defer func() {
+		if state := recover(); state != nil {
+			err = log.Wrap(state.(error))
+		}
+	}()
+
+	br.bouncebackBase.stats.reads++
+
+	err = br.bouncebackBase.checkPosition(br.rs)
+	log.PanicIf(err)
+
+	// Do read.
+
+	n, err = br.rs.Read(p)
+	if err != nil {
+		if err == io.EOF {
+			return 0, io.EOF
+		}
+
+		log.Panic(err)
+	}
+
+	// Update our internal tracking.
+	br.bouncebackBase.currentPosition += int64(n)
+
+	return n, nil
+}
+
+// BouncebackWriter wraps a WriteSeeker, keeps track of our position, and
+// seeks back to it before writing. This allows an underlying ReadWriteSeeker
+// with an unstable position can still be used for a prolonged series of writes.
+type BouncebackWriter struct {
+	ws io.WriteSeeker
+
+	bouncebackBase
+}
+
+// NewBouncebackWriter returns a new `BouncebackWriter` struct.
+func NewBouncebackWriter(ws io.WriteSeeker) (bw *BouncebackWriter, err error) {
+	defer func() {
+		if state := recover(); state != nil {
+			err = log.Wrap(state.(error))
+		}
+	}()
+
+	initialPosition, err := ws.Seek(0, io.SeekCurrent)
+	log.PanicIf(err)
+
+	bb := bouncebackBase{
+		currentPosition: initialPosition,
+	}
+
+	bw = &BouncebackWriter{
+		ws:             ws,
+		bouncebackBase: bb,
+	}
+
+	return bw, nil
+}
+
+// Seek puts us at a specific position in the internal writer for the next
+// write/seek.
+func (bw *BouncebackWriter) Seek(offset int64, whence int) (newPosition int64, err error) {
+	defer func() {
+		if state := recover(); state != nil {
+			err = log.Wrap(state.(error))
+		}
+	}()
+
+	newPosition, err = bw.bouncebackBase.seek(bw.ws, offset, whence)
+	log.PanicIf(err)
+
+	return newPosition, nil
+}
+
+// Write performs a write against the internal `WriteSeeker` starting at the
+// position that we're supposed to be at.
+func (bw *BouncebackWriter) Write(p []byte) (n int, err error) {
+	defer func() {
+		if state := recover(); state != nil {
+			err = log.Wrap(state.(error))
+		}
+	}()
+
+	bw.bouncebackBase.stats.writes++
+
+	// Make sure we're where we're supposed to be.
+
+	realCurrentPosition, err := bw.ws.Seek(0, io.SeekCurrent)
+	log.PanicIf(err)
+
+	if realCurrentPosition != bw.bouncebackBase.currentPosition {
+		bw.bouncebackBase.stats.seeks++
+
+		_, err = bw.ws.Seek(bw.bouncebackBase.currentPosition, io.SeekStart)
+		log.PanicIf(err)
+	}
+
+	// Do write.
+
+	n, err = bw.ws.Write(p)
+	log.PanicIf(err)
+
+	// Update our internal tracking.
+	bw.bouncebackBase.currentPosition += int64(n)
+
+	return n, nil
+}