fix: Fix panic on requesting out-of-order Pattern samples (#13010)

pkg/pattern/drain/chunk.go

@@ -66,6 +66,11 @@ func (c Chunk) ForRange(start, end, step model.Time) []logproto.PatternSample {
 			return c.Samples[i].Timestamp >= end
 		})
 	}
+
+	if c.Samples[lo].Timestamp > c.Samples[hi-1].Timestamp {
+		return nil
+	}
+
 	if step == TimeResolution {
 		return c.Samples[lo:hi]
 	}
@@ -110,6 +115,9 @@ func (c *Chunks) Add(ts model.Time) {
 		*c = append(*c, newChunk(t))
 		return
 	}
+	if ts.Before(last.Samples[len(last.Samples)-1].Timestamp) {
+		return
+	}
 	last.Samples = append(last.Samples, logproto.PatternSample{
 		Timestamp: t,
 		Value:     1,

pkg/pattern/drain/chunk_test.go

@@ -21,6 +21,9 @@ func TestAdd(t *testing.T) {
 	cks.Add(model.TimeFromUnixNano(time.Hour.Nanoseconds()) + TimeResolution + 1)
 	require.Equal(t, 2, len(cks))
 	require.Equal(t, 1, len(cks[1].Samples))
+	cks.Add(model.TimeFromUnixNano(time.Hour.Nanoseconds()) - TimeResolution)
+	require.Equal(t, 2, len(cks))
+	require.Equalf(t, 1, len(cks[1].Samples), "Older samples should not be added if they arrive out of order")
 }
 
 func TestIterator(t *testing.T) {
@@ -52,6 +55,7 @@ func TestForRange(t *testing.T) {
 		c        *Chunk
 		start    model.Time
 		end      model.Time
+		step     model.Time
 		expected []logproto.PatternSample
 	}{
 		{
@@ -180,6 +184,28 @@ func TestForRange(t *testing.T) {
 				{Timestamp: 4, Value: 10},
 			},
 		},
+		{
+			name: "Out-of-order samples generate nil result",
+			c: &Chunk{Samples: []logproto.PatternSample{
+				{Timestamp: 5, Value: 2},
+				{Timestamp: 3, Value: 2},
+			}},
+			start:    4,
+			end:      6,
+			expected: nil,
+		},
+		{
+			name: "Internally out-of-order samples generate nil result",
+			c: &Chunk{Samples: []logproto.PatternSample{
+				{Timestamp: 1, Value: 2},
+				{Timestamp: 5, Value: 2},
+				{Timestamp: 3, Value: 2},
+				{Timestamp: 7, Value: 2},
+			}},
+			start:    2,
+			end:      6,
+			expected: nil,
+		},
 	}
 
 	for _, tc := range testCases {