Handle zero chunk size (#265)

Backport of #263 +
#270

---------

Co-authored-by: Abhinav Dangeti <[email protected]>

chunk.go

@@ -15,6 +15,7 @@
 package zap
 
 import (
+	"errors"
 	"fmt"
 )
 
@@ -26,8 +27,18 @@ var LegacyChunkMode uint32 = 1024
 // be used by default.
 var DefaultChunkMode uint32 = 1026
 
+var ErrChunkSizeZero = errors.New("chunk size is zero")
+
+// getChunkSize returns the chunk size for the given chunkMode, cardinality, and
+// maxDocs.
+//
+// In error cases, the returned chunk size will be 0. Caller can differentiate
+// between a valid chunk size of 0 and an error by checking for ErrChunkSizeZero.
 func getChunkSize(chunkMode uint32, cardinality uint64, maxDocs uint64) (uint64, error) {
 	switch {
+	case chunkMode == 0:
+		return 0, ErrChunkSizeZero
+
 	// any chunkMode <= 1024 will always chunk with chunkSize=chunkMode
 	case chunkMode <= 1024:
 		// legacy chunk size
@@ -46,6 +57,9 @@ func getChunkSize(chunkMode uint32, cardinality uint64, maxDocs uint64) (uint64,
 		// chunk-size items.
 		// no attempt is made to tweak any other case
 		if cardinality <= 1024 {
+			if maxDocs == 0 {
+				return 0, ErrChunkSizeZero
+			}
 			return maxDocs, nil
 		}
 		return 1024, nil
@@ -61,6 +75,9 @@ func getChunkSize(chunkMode uint32, cardinality uint64, maxDocs uint64) (uint64,
 		// 2.  convert to chunkSize, dividing into maxDocs
 		numChunks := (cardinality / 1024) + 1
 		chunkSize := maxDocs / numChunks
+		if chunkSize == 0 {
+			return 0, ErrChunkSizeZero
+		}
 		return chunkSize, nil
 	}
 	return 0, fmt.Errorf("unknown chunk mode %d", chunkMode)

posting.go

@@ -305,10 +305,7 @@ func (rv *PostingsList) read(postingsOffset uint64, d *Dictionary) error {
 	chunkSize, err := getChunkSize(d.sb.chunkMode,
 		rv.postings.GetCardinality(), d.sb.numDocs)
 	if err != nil {
-		return err
-	} else if chunkSize == 0 {
-		return fmt.Errorf("chunk size is zero, chunkMode: %v, numDocs: %v",
-			d.sb.chunkMode, d.sb.numDocs)
+		return fmt.Errorf("failed to get chunk size: %v", err)
 	}
 
 	rv.chunkSize = chunkSize
@@ -632,6 +629,10 @@ func (i *PostingsIterator) nextDocNumAtOrAfter(atOrAfter uint64) (uint64, bool,
 		return i.nextDocNumAtOrAfterClean(atOrAfter)
 	}
 
+	if i.postings.chunkSize == 0 {
+		return 0, false, ErrChunkSizeZero
+	}
+
 	i.Actual.AdvanceIfNeeded(uint32(atOrAfter))
 
 	if !i.Actual.HasNext() || !i.all.HasNext() {
@@ -741,6 +742,10 @@ func (i *PostingsIterator) nextDocNumAtOrAfterClean(
 		return uint64(i.Actual.Next()), true, nil
 	}
 
+	if i.postings != nil && i.postings.chunkSize == 0 {
+		return 0, false, ErrChunkSizeZero
+	}
+
 	// freq-norm's needed, so maintain freq-norm chunk reader
 	sameChunkNexts := 0 // # of times we called Next() in the same chunk
 	n := i.Actual.Next()