lib/logstorage: properly search for the surrounding logs in stream_context pipe

The set of log fields in the found logs may differ from the set of log fields present in the log stream.
So compare only the log fields in the found logs when searching for the matching log entry in the log stream.

While at it, return _stream field in the delimiter log entry, since this field is used by VictoriaLogs Web UI
for grouping logs by log streams.

docs/VictoriaLogs/CHANGELOG.md

@@ -19,6 +19,8 @@ according to [these docs](https://docs.victoriametrics.com/victorialogs/quicksta
 
 ## tip
 
+* BUGFIX: return the proper surrounding logs for [`stream_context` pipe](https://docs.victoriametrics.com/victorialogs/logsql/#stream_context-pipe) when additional [pipes](https://docs.victoriametrics.com/victorialogs/logsql/#pipes) are put after the `stream_context` pipe. This has been broken in [v0.26.0](https://github.com/VictoriaMetrics/VictoriaMetrics/releases/tag/v0.26.0-victorialogs).
+
 ## [v0.26.0](https://github.com/VictoriaMetrics/VictoriaMetrics/releases/tag/v0.26.0-victorialogs)
 
 Released at 2024-07-01

lib/logstorage/pipe_stream_context.go

@@ -364,6 +364,10 @@ func (wctx *pipeStreamContextWriteContext) writeStreamContextRows(streamID strin
 					Name:  "_stream_id",
 					Value: streamID,
 				},
+				{
+					Name:  "_stream",
+					Value: getFieldValue(r.fields, "_stream"),
+				},
 				{
 					Name:  "_msg",
 					Value: "---",
@@ -402,20 +406,30 @@ func getStreamContextRowIdx(rows []streamContextRow, r *streamContextRow) int {
 	if n == len(rows) {
 		return -1
 	}
-	if rows[n].timestamp != r.timestamp {
-		return -1
+
+	equalFields := func(fields []Field) bool {
+		for _, f := range r.fields {
+			if f.Value != getFieldValue(fields, f.Name) {
+				return false
+			}
+		}
+		return true
 	}
-	for rows[n].timestamp == r.timestamp && !equalFields(rows[n].fields, r.fields) {
+
+	for rows[n].timestamp == r.timestamp && !equalFields(rows[n].fields) {
 		n++
 		if n >= len(rows) {
 			return -1
 		}
 	}
+	if rows[n].timestamp != r.timestamp {
+		return -1
+	}
 	return n
 }
 
 func sortStreamContextRows(rows []streamContextRow) {
-	sort.SliceStable(rows, func(i, j int) bool {
+	sort.Slice(rows, func(i, j int) bool {
 		return rows[i].timestamp < rows[j].timestamp
 	})
 }

lib/logstorage/rows.go

@@ -79,20 +79,13 @@ func (f *Field) marshalToLogfmt(dst []byte) []byte {
 	return dst
 }
 
-func equalFields(a, b []Field) bool {
-	if len(a) != len(b) {
-		return false
-	}
-	for i, x := range a {
-		y := b[i]
-		if x.Name != y.Name {
-			return false
-		}
-		if x.Value != y.Value {
-			return false
+func getFieldValue(fields []Field, name string) string {
+	for _, f := range fields {
+		if f.Name == name {
+			return f.Value
 		}
 	}
-	return true
+	return ""
 }
 
 func needLogfmtQuoting(s string) bool {

lib/logstorage/storage_search_test.go

@@ -707,7 +707,7 @@ func TestStorageRunQuery(t *testing.T) {
 			| stream_context before 1000
 			| stats count() rows`, [][]Field{
 			{
-				{"rows", "858"},
+				{"rows", "825"},
 			},
 		})
 	})
@@ -716,7 +716,7 @@ func TestStorageRunQuery(t *testing.T) {
 			| stream_context after 1000
 			| stats count() rows`, [][]Field{
 			{
-				{"rows", "462"},
+				{"rows", "495"},
 			},
 		})
 	})