fix(chunkenc): error out when reading unknown histogram schemas from chunks

Otherwise higher level code like PromQL needs to constantly check if it
can handle the samples.

Signed-off-by: György Krajcsovits <gyorgy.krajcsovits@grafana.com>

model/histogram/generic.go

@@ -54,6 +54,10 @@ func IsExponentialSchemaReserved(s int32) bool {
 	return s >= ExponentialSchemaMinReserved && s <= ExponentialSchemaMaxReserved
 }
 
+func IsValidSchema(s int32) bool {
+	return IsCustomBucketsSchema(s) || IsExponentialSchema(s)
+}
+
 // BucketCount is a type constraint for the count in a bucket, which can be
 // float64 (for type FloatHistogram) or uint64 (for type Histogram).
 type BucketCount interface {

tsdb/chunkenc/float_histogram.go

@@ -954,6 +954,12 @@ func (it *floatHistogramIterator) Next() ValueType {
 			it.err = err
 			return ValNone
 		}
+
+		if !histogram.IsValidSchema(schema) {
+			it.err = fmt.Errorf("invalid histogram schema %d", schema)
+			return ValNone
+		}
+
 		it.schema = schema
 		it.zThreshold = zeroThreshold
 		it.pSpans, it.nSpans = posSpans, negSpans

tsdb/chunkenc/float_histogram_test.go

@@ -14,6 +14,7 @@
 package chunkenc
 
 import (
+	"fmt"
 	"testing"
 
 	"github.com/stretchr/testify/require"
@@ -1462,3 +1463,32 @@ func TestFloatHistogramEmptyBucketsWithGaps(t *testing.T) {
 	require.Equal(t, ValNone, it.Next())
 	require.NoError(t, it.Err())
 }
+
+func TestFloatHistogramIteratorFailIfSchemaInValid(t *testing.T) {
+	for _, schema := range []int32{-101, 101} {
+		t.Run(fmt.Sprintf("schema %d", schema), func(t *testing.T) {
+			h := &histogram.FloatHistogram{
+				Schema:        schema,
+				Count:         10,
+				Sum:           15.0,
+				ZeroThreshold: 1e-100,
+				PositiveSpans: []histogram.Span{
+					{Offset: 0, Length: 2},
+					{Offset: 1, Length: 2},
+				},
+				PositiveBuckets: []float64{1, 2, 3, 4},
+			}
+
+			c := NewFloatHistogramChunk()
+			app, err := c.Appender()
+			require.NoError(t, err)
+
+			_, _, _, err = app.AppendFloatHistogram(nil, 1, h, false)
+			require.NoError(t, err)
+
+			it := c.Iterator(nil)
+			require.Equal(t, ValNone, it.Next())
+			require.EqualError(t, it.Err(), fmt.Sprintf("invalid histogram schema %d", schema))
+		})
+	}
+}

tsdb/chunkenc/histogram.go

@@ -1077,6 +1077,12 @@ func (it *histogramIterator) Next() ValueType {
 			it.err = err
 			return ValNone
 		}
+
+		if !histogram.IsValidSchema(schema) {
+			it.err = fmt.Errorf("invalid histogram schema %d", schema)
+			return ValNone
+		}
+
 		it.schema = schema
 		it.zThreshold = zeroThreshold
 		it.pSpans, it.nSpans = posSpans, negSpans

tsdb/chunkenc/histogram_test.go

@@ -14,6 +14,7 @@
 package chunkenc
 
 import (
+	"fmt"
 	"testing"
 
 	"github.com/stretchr/testify/require"
@@ -1818,3 +1819,32 @@ func TestIntHistogramEmptyBucketsWithGaps(t *testing.T) {
 	require.Equal(t, ValNone, it.Next())
 	require.NoError(t, it.Err())
 }
+
+func TestHistogramIteratorFailIfSchemaInValid(t *testing.T) {
+	for _, schema := range []int32{-101, 101} {
+		t.Run(fmt.Sprintf("schema %d", schema), func(t *testing.T) {
+			h := &histogram.Histogram{
+				Schema:        schema,
+				Count:         10,
+				Sum:           15.0,
+				ZeroThreshold: 1e-100,
+				PositiveSpans: []histogram.Span{
+					{Offset: 0, Length: 2},
+					{Offset: 1, Length: 2},
+				},
+				PositiveBuckets: []int64{1, 2, 3, 4},
+			}
+
+			c := NewHistogramChunk()
+			app, err := c.Appender()
+			require.NoError(t, err)
+
+			_, _, _, err = app.AppendHistogram(nil, 1, h, false)
+			require.NoError(t, err)
+
+			it := c.Iterator(nil)
+			require.Equal(t, ValNone, it.Next())
+			require.EqualError(t, it.Err(), fmt.Sprintf("invalid histogram schema %d", schema))
+		})
+	}
+}