client: fix Paginate's arguments validation

Check both page and defLimit against negative values.

Follow up of #6205

client/utils.go

@@ -2,15 +2,22 @@ package client
 
 // Paginate returns the correct starting and ending index for a paginated query,
 // given that client provides a desired page and limit of objects and the handler
-// provides the total number of objects. If the start page is invalid, non-positive
-// values are returned signaling the request is invalid.
-//
-// NOTE: The start page is assumed to be 1-indexed.
+// provides the total number of objects. The start page is assumed to be 1-indexed.
+// If the start page is invalid, non-positive values are returned signaling the
+// request is invalid; it returns non-positive values if limit is non-positive and
+// defLimit is negative.
 func Paginate(numObjs, page, limit, defLimit int) (start, end int) {
-	if page == 0 {
+	if page <= 0 {
 		// invalid start page
 		return -1, -1
-	} else if limit == 0 {
+	}
+
+	// fallback to default limit if supplied limit is invalid
+	if limit <= 0 {
+		if defLimit < 0 {
+			// invalid default limit
+			return -1, -1
+		}
 		limit = defLimit
 	}
 

client/utils_test.go

@@ -39,6 +39,11 @@ func TestPaginate(t *testing.T) {
 			75, 2, 50, 100,
 			50, 75,
 		},
+		{
+			"fallback to default limit",
+			75, 5, 0, 10,
+			40, 50,
+		},
 		{
 			"invalid start page",
 			75, 4, 25, 100,
@@ -49,6 +54,16 @@ func TestPaginate(t *testing.T) {
 			75, 0, 25, 100,
 			-1, -1,
 		},
+		{
+			"invalid negative start page",
+			75, -1, 25, 100,
+			-1, -1,
+		},
+		{
+			"invalid default limit",
+			75, 2, 0, -10,
+			-1, -1,
+		},
 	}
 
 	for i, tc := range testCases {