Check if observations sorted before taking median

relayer/pkg/chainlink/ocr2/medianreport/report.go

@@ -90,6 +90,7 @@ func (c ReportCodec) MedianFromReport(report types.Report) (*big.Int, error) {
 		return nil, errors.New("invalid report length")
 	}
 
+	// Decode the number of observations
 	numBig := junotypes.BytesToFelt(report[(timestampSizeBytes + observersSizeBytes):prefixSizeBytes]).Big()
 	if !numBig.IsUint64() {
 		return nil, errors.New("length of observations is invalid")
@@ -102,22 +103,34 @@ func (c ReportCodec) MedianFromReport(report types.Report) (*big.Int, error) {
 		return nil, errors.New("length of observations is invalid")
 	}
 
+	// Check if the report is big enough
 	n := int(n64)
-
-	if rLen < prefixSizeBytes+(observationSizeBytes*n)+juelsPerFeeCoinSizeBytes {
-		return nil, errors.New("report does not contain enough observations or is missing juels/feeCoin observation")
+	expectedLen := prefixSizeBytes + (observationSizeBytes * n) + juelsPerFeeCoinSizeBytes
+	if rLen < expectedLen {
+		return nil, errors.New("invalid report length, missing main or juelsPerFeeCoin observations")
 	}
 
-	var observations []*big.Int
+	// Decode observations
+	var oo []*big.Int
 	for i := 0; i < n; i++ {
 		start := prefixSizeBytes + observationSizeBytes*i
 		end := start + observationSizeBytes
-		o := junotypes.BytesToFelt(report[start:end]).Big()
-		o = starknet.FeltToSignedBig(&caigotypes.Felt{Int: o})
-		observations = append(observations, o)
+		o := starknet.FeltToSignedBig(&caigotypes.Felt{
+			Int: junotypes.BytesToFelt(report[start:end]).Big(),
+		})
+		oo = append(oo, o)
+	}
+
+	// Check if the report contains sorted observations
+	_less := func(i, j int) bool {
+		return oo[i].Cmp(oo[j]) < 0
+	}
+	sorted := sort.SliceIsSorted(oo, _less)
+	if !sorted {
+		return nil, errors.New("observations not sorted")
 	}
 
-	return observations[n/2], nil
+	return oo[n/2], nil
 }
 
 func (c ReportCodec) MaxReportLength(n int) int {
@@ -127,7 +140,7 @@ func (c ReportCodec) MaxReportLength(n int) int {
 func SplitReport(report types.Report) ([][]byte, error) {
 	chunkSize := junotypes.FeltLength
 	if len(report)%chunkSize != 0 {
-		return [][]byte{}, errors.New("invalid length of the report")
+		return [][]byte{}, errors.New("invalid report length")
 	}
 
 	// order is guaranteed by buildReport: