From 0625e63648e8c4a2c4bc9dfe5b8d6011014518ce Mon Sep 17 00:00:00 2001
From: Chris Lu <chris.lu@gmail.com>
Date: Mon, 17 Aug 2020 20:14:40 -0700
Subject: [PATCH] count 0 as part of the reads

---
 weed/filer2/reader_at.go | 49 ++++++++++++++++++++--------------------
 1 file changed, 24 insertions(+), 25 deletions(-)

diff --git a/weed/filer2/reader_at.go b/weed/filer2/reader_at.go
index 600788f9c..75a0a0655 100644
--- a/weed/filer2/reader_at.go
+++ b/weed/filer2/reader_at.go
@@ -15,8 +15,6 @@ import (
 type ChunkReadAt struct {
 	masterClient *wdclient.MasterClient
 	chunkViews   []*ChunkView
-	buffer       []byte
-	bufferFileId string
 	lookupFileId func(fileId string) (targetUrl string, err error)
 	readerLock   sync.Mutex
 	fileSize     int64
@@ -71,49 +69,50 @@ func (c *ChunkReadAt) ReadAt(p []byte, offset int64) (n int, err error) {
 	defer c.readerLock.Unlock()
 
 	glog.V(4).Infof("ReadAt [%d,%d) of total file size %d bytes %d chunk views", offset, offset+int64(len(p)), c.fileSize, len(c.chunkViews))
-	for n < len(p) && err == nil {
-		readCount, readErr := c.doReadAt(p[n:], offset+int64(n))
-		n += readCount
-		err = readErr
-	}
-	return
+	return c.doReadAt(p[n:], offset+int64(n))
 }
 
 func (c *ChunkReadAt) doReadAt(p []byte, offset int64) (n int, err error) {
 
-	var startOffset = offset
+	var buffer []byte
+	startOffset, remaining := offset, int64(len(p))
 	for i, chunk := range c.chunkViews {
-		if startOffset < min(chunk.LogicOffset, int64(len(p))+offset) {
-			gap := int(min(chunk.LogicOffset, int64(len(p))+offset) - startOffset)
+		if remaining <= 0 {
+			break
+		}
+		if startOffset < chunk.LogicOffset {
+			gap := int(chunk.LogicOffset - startOffset)
 			glog.V(4).Infof("zero [%d,%d)", n, n+gap)
 			n += gap
-			startOffset = chunk.LogicOffset
+			startOffset, remaining = chunk.LogicOffset, remaining-int64(gap)
+			if remaining <= 0 {
+				break
+			}
 		}
 		// fmt.Printf(">>> doReadAt [%d,%d), chunk[%d,%d)\n", offset, offset+int64(len(p)), chunk.LogicOffset, chunk.LogicOffset+int64(chunk.Size))
-		chunkStart, chunkStop := max(chunk.LogicOffset, offset), min(chunk.LogicOffset+int64(chunk.Size), offset+int64(len(p)))
+		chunkStart, chunkStop := max(chunk.LogicOffset, startOffset), min(chunk.LogicOffset+int64(chunk.Size), startOffset+remaining)
 		if chunkStart >= chunkStop {
 			continue
 		}
-		glog.V(4).Infof("read [%d,%d), %d chunk %s [%d,%d)", chunkStart, chunkStop, i, chunk.FileId, chunk.LogicOffset-chunk.Offset, chunk.LogicOffset-chunk.Offset+int64(chunk.Size))
-		c.buffer, err = c.fetchWholeChunkData(chunk)
+		glog.V(4).Infof("read [%d,%d), %d/%d chunk %s [%d,%d)", chunkStart, chunkStop, i, len(c.chunkViews), chunk.FileId, chunk.LogicOffset-chunk.Offset, chunk.LogicOffset-chunk.Offset+int64(chunk.Size))
+		buffer, err = c.readFromWholeChunkData(chunk)
 		if err != nil {
 			glog.Errorf("fetching chunk %+v: %v\n", chunk, err)
 			return
 		}
-		c.bufferFileId = chunk.FileId
 		bufferOffset := chunkStart - chunk.LogicOffset + chunk.Offset
-		copied := copy(p[chunkStart-offset:chunkStop-offset], c.buffer[bufferOffset:bufferOffset+chunkStop-chunkStart])
+		copied := copy(p[chunkStart-startOffset:chunkStop-startOffset], buffer[bufferOffset:bufferOffset+chunkStop-chunkStart])
 		n += copied
-		startOffset += int64(copied)
+		startOffset, remaining = startOffset + int64(copied), remaining-int64(copied)
 	}
 
-	// fmt.Printf("> doReadAt [%d,%d), buffer %s:%d, found:%v, err:%v\n", offset, offset+int64(len(p)), c.bufferFileId, int64(len(c.buffer)), found, err)
+	glog.V(4).Infof("doReadAt [%d,%d), n:%v, err:%v", offset, offset+int64(len(p)), n, err)
 
-	if startOffset < min(c.fileSize, int64(len(p))+offset) {
-		gap := int(min(c.fileSize, int64(len(p))+offset) - startOffset)
-		glog.V(4).Infof("zero2 [%d,%d)", n, n+gap)
-		n += gap
+	if remaining > 0 {
+		glog.V(4).Infof("zero2 [%d,%d)", n, n+int(remaining))
+		n += int(remaining)
 	}
+
 	if offset+int64(n) >= c.fileSize {
 		err = io.EOF
 	}
@@ -123,9 +122,9 @@ func (c *ChunkReadAt) doReadAt(p []byte, offset int64) (n int, err error) {
 
 }
 
-func (c *ChunkReadAt) fetchWholeChunkData(chunkView *ChunkView) (chunkData []byte, err error) {
+func (c *ChunkReadAt) readFromWholeChunkData(chunkView *ChunkView) (chunkData []byte, err error) {
 
-	glog.V(4).Infof("fetchWholeChunkData %s offset %d [%d,%d) size at least %d", chunkView.FileId, chunkView.Offset, chunkView.LogicOffset, chunkView.LogicOffset+int64(chunkView.Size), chunkView.ChunkSize)
+	glog.V(4).Infof("readFromWholeChunkData %s offset %d [%d,%d) size at least %d", chunkView.FileId, chunkView.Offset, chunkView.LogicOffset, chunkView.LogicOffset+int64(chunkView.Size), chunkView.ChunkSize)
 
 	chunkData = c.chunkCache.GetChunk(chunkView.FileId, chunkView.ChunkSize)
 	if chunkData != nil {