fix postings offset reader and npe

Signed-off-by: Ben Ye <[email protected]>

pkg/block/indexheader/binary_reader.go

@@ -889,6 +889,10 @@ func (r *BinaryReader) postingsOffset(name string, values ...string) ([]index.Ra
 			}
 
 			if valueIndex != len(values) && wantedValue <= e.offsets[i+1].value {
+				// Increment i when wanted value is same as next offset.
+				if wantedValue == e.offsets[i+1].value {
+					i++
+				}
 				// wantedValue is smaller or same as the next offset we know about, let's iterate further to add those.
 				continue
 			}

pkg/store/bucket.go

@@ -987,6 +987,7 @@ func (b *blockSeriesClient) ExpandPostings(
 		return errors.Wrap(err, "expanded matching posting")
 	}
 
+	b.lazyPostings = ps
 	if len(ps.postings) == 0 {
 		return nil
 	}
@@ -995,7 +996,6 @@ func (b *blockSeriesClient) ExpandPostings(
 		return httpgrpc.Errorf(int(codes.ResourceExhausted), "exceeded series limit: %s", err)
 	}
 
-	b.lazyPostings = ps
 	if b.batchSize > len(ps.postings) {
 		b.batchSize = len(ps.postings)
 	}
@@ -1044,7 +1044,7 @@ func (b *blockSeriesClient) nextBatch() error {
 		if b.lazyPostings.lazyExpanded() {
 			v, err := b.indexr.IndexVersion()
 			if err != nil {
-				errors.Wrap(err, "get index version")
+				return errors.Wrap(err, "get index version")
 			}
 			if v >= 2 {
 				for i := range b.expandedPostings {
@@ -2264,7 +2264,7 @@ func (r *bucketIndexReader) ExpandedPostings(ctx context.Context, ms []*labels.M
 	// Shortcut the case of `len(postingGroups) == 0`. It will only happen when no
 	// matchers specified, and we don't need to fetch expanded postings from cache.
 	if len(ms) == 0 {
-		return nil, nil
+		return emptyLazyPostings, nil
 	}
 
 	hit, postings, err := r.fetchExpandedPostingsFromCache(ctx, ms, bytesLimiter)
@@ -2297,7 +2297,7 @@ func (r *bucketIndexReader) ExpandedPostings(ctx context.Context, ms []*labels.M
 		// E.g. label="non-existing-value" returns empty group.
 		if !pg.addAll && len(pg.addKeys) == 0 {
 			r.storeExpandedPostingsToCache(ms, index.EmptyPostings(), 0)
-			return nil, nil
+			return emptyLazyPostings, nil
 		}
 
 		allRequested = allRequested || pg.addAll

pkg/store/lazy_postings.go

@@ -1,3 +1,6 @@
+// Copyright (c) The Thanos Authors.
+// Licensed under the Apache License 2.0.
+
 package store
 
 import (
@@ -10,6 +13,8 @@ import (
 	"github.com/prometheus/prometheus/tsdb/index"
 )
 
+var emptyLazyPostings = &lazyExpandedPostings{postings: nil, matchers: nil}
+
 type lazyExpandedPostings struct {
 	postings []storage.SeriesRef
 	matchers []*labels.Matcher