xl/utils: getPartSizeFromIdx should return error. (#3669)

cmd/xl-v1-utils.go

@@ -17,6 +17,7 @@
 package cmd
 
 import (
+	"errors"
 	"hash/crc32"
 	"path"
 	"sync"
@@ -344,29 +345,35 @@ func getOrderedDisks(distribution []int, disks []StorageAPI) (orderedDisks []Sto
 	return orderedDisks
 }
 
+// Errors specifically generated by getPartSizeFromIdx function.
+var (
+	errPartSizeZero  = errors.New("Part size cannot be zero")
+	errPartSizeIndex = errors.New("Part index cannot be smaller than 1")
+)
+
 // getPartSizeFromIdx predicts the part size according to its index. It also
 // returns -1 when totalSize is also -1.
-func getPartSizeFromIdx(totalSize int64, partSize int64, partIndex int) int64 {
+func getPartSizeFromIdx(totalSize int64, partSize int64, partIndex int) (int64, error) {
 	if partSize == 0 {
-		panic("Part size cannot be nil.")
+		return 0, traceError(errPartSizeZero)
 	}
 	if partIndex < 1 {
-		panic("Part index should be greater than 1.")
+		return 0, traceError(errPartSizeIndex)
 	}
 	switch totalSize {
 	case -1, 0:
-		return totalSize
+		return totalSize, nil
 	}
 	// Compute the total count of parts
 	partsCount := totalSize/partSize + 1
 	// Return the part's size
 	switch {
 	case int64(partIndex) < partsCount:
-		return partSize
+		return partSize, nil
 	case int64(partIndex) == partsCount:
 		// Size of last part
-		return totalSize % partSize
+		return totalSize % partSize, nil
 	default:
-		return 0
+		return 0, nil
 	}
 }