store: add issue 6545 repro

Add repro for issue 6545.

Signed-off-by: Giedrius Statkevičius <[email protected]>

pkg/store/postings_codec_test.go

@@ -7,8 +7,10 @@ import (
 	"bytes"
 	"context"
 	crand "crypto/rand"
+	"io"
 	"math"
 	"math/rand"
+	"os"
 	"sort"
 	"strconv"
 	"testing"
@@ -338,3 +340,26 @@ func FuzzSnappyStreamEncoding(f *testing.F) {
 		testutil.Ok(t, err)
 	})
 }
+
+func TestDiffVarintDecodingIssue6545(t *testing.T) {
+	f, err := os.Open("issue6545_repro")
+	testutil.Ok(t, err)
+	t.Cleanup(func() { f.Close() })
+
+	in, err := io.ReadAll(f)
+	testutil.Ok(t, err)
+
+	postings, err := newStreamedDiffVarintPostings(in, false)
+	testutil.Ok(t, err)
+
+	t.Cleanup(postings.close)
+
+	var p storage.SeriesRef
+	for postings.Next() {
+		curp := postings.At()
+		testutil.Assert(t, curp > p)
+		p = curp
+	}
+
+	testutil.Ok(t, postings.Err())
+}