From 4ceeba9e707330430c3e7638f6eca8222032dc4f Mon Sep 17 00:00:00 2001
From: Chris Lu <chris.lu@gmail.com>
Date: Sun, 16 Aug 2020 21:07:46 -0700
Subject: [PATCH] streaming reads

---
 weed/filer2/reader_at.go | 61 +++++++++++++++++-----------------------
 1 file changed, 26 insertions(+), 35 deletions(-)

diff --git a/weed/filer2/reader_at.go b/weed/filer2/reader_at.go
index b0702e03e..fc74ef2af 100644
--- a/weed/filer2/reader_at.go
+++ b/weed/filer2/reader_at.go
@@ -80,48 +80,39 @@ func (c *ChunkReadAt) ReadAt(p []byte, offset int64) (n int, err error) {
 
 func (c *ChunkReadAt) doReadAt(p []byte, offset int64) (n int, err error) {
 
-	var found bool
-	var chunkStart, chunkStop int64
-	var chunkView *ChunkView
+	var startOffset = offset
 	for _, chunk := range c.chunkViews {
+		if startOffset < min(chunk.LogicOffset, int64(len(p))+offset) {
+			gap := int(min(chunk.LogicOffset, int64(len(p))+offset) - startOffset)
+			glog.V(4).Infof("zero [%d,%d)", n, n+gap)
+			n += gap
+			startOffset = chunk.LogicOffset
+		}
 		// 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)))
-		chunkView = chunk
-		if chunkStart < chunkStop {
-			// fmt.Printf(">>> found [%d,%d), chunk %s [%d,%d)\n", chunkStart, chunkStop, chunk.FileId, chunk.LogicOffset, chunk.LogicOffset+int64(chunk.Size))
-			found = true
-			c.buffer, err = c.fetchWholeChunkData(chunk)
-			if err != nil {
-				glog.Errorf("fetching chunk %+v: %v\n", chunk, err)
-			}
-			c.bufferFileId = chunk.FileId
-			break
+		chunkStart, chunkStop := max(chunk.LogicOffset, offset), min(chunk.LogicOffset+int64(chunk.Size), offset+int64(len(p)))
+		if chunkStart >= chunkStop {
+			continue
+		}
+		glog.V(4).Infof("read [%d,%d), chunk %s [%d,%d)\n", chunkStart, chunkStop, chunk.FileId, chunk.LogicOffset-chunk.Offset, chunk.LogicOffset-chunk.Offset+int64(chunk.Size))
+		c.buffer, err = c.fetchWholeChunkData(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])
+		n += copied
+		startOffset += 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)
 
-	if err != nil {
-		return
+	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 found {
-		bufferOffset := chunkStart - chunkView.LogicOffset + chunkView.Offset
-		/*
-		skipped, copied := chunkStart-offset, chunkStop-chunkStart
-		fmt.Printf("+++ copy %d+%d=%d fill:[%d, %d) p[%d,%d) <- buffer:[%d,%d) buffer %s:%d\nchunkView:%+v\n\n",
-			skipped, copied, skipped+copied,
-			chunkStart, chunkStop,
-			chunkStart-offset, chunkStop-offset, bufferOffset, bufferOffset+chunkStop-chunkStart,
-			c.bufferFileId, len(c.buffer),
-			chunkView)
-		 */
-		n = int(chunkStart-offset) +
-			copy(p[chunkStart-offset:chunkStop-offset], c.buffer[bufferOffset:bufferOffset+chunkStop-chunkStart])
-		return
-	}
-
-	n = len(p)
 	if offset+int64(n) >= c.fileSize {
 		err = io.EOF
 	}
@@ -137,7 +128,7 @@ func (c *ChunkReadAt) fetchWholeChunkData(chunkView *ChunkView) (chunkData []byt
 
 	chunkData = c.chunkCache.GetChunk(chunkView.FileId, chunkView.ChunkSize)
 	if chunkData != nil {
-		glog.V(5).Infof("cache hit %s [%d,%d)", chunkView.FileId, chunkView.LogicOffset-chunkView.Offset, chunkView.LogicOffset-chunkView.Offset + int64(len(chunkData)))
+		glog.V(5).Infof("cache hit %s [%d,%d)", chunkView.FileId, chunkView.LogicOffset-chunkView.Offset, chunkView.LogicOffset-chunkView.Offset+int64(len(chunkData)))
 	} else {
 		chunkData, err = c.doFetchFullChunkData(chunkView.FileId, chunkView.CipherKey, chunkView.IsGzipped)
 		if err != nil {