From e5b59e3c15c24ca7a06726c482a35eb9b7844242 Mon Sep 17 00:00:00 2001
From: Sebastian Widmer <sebastian.widmer@vshn.net>
Date: Thu, 7 Dec 2023 11:21:10 +0100
Subject: [PATCH 1/2] Ensure client always sends empty array instead of JSON
 `null`

---
 pkg/odoo/odoo16.go      | 14 ++++++++++++--
 pkg/odoo/odoo16_test.go |  7 ++++---
 2 files changed, 16 insertions(+), 5 deletions(-)

diff --git a/pkg/odoo/odoo16.go b/pkg/odoo/odoo16.go
index 29a8b81..3fd2a7f 100644
--- a/pkg/odoo/odoo16.go
+++ b/pkg/odoo/odoo16.go
@@ -21,7 +21,7 @@ type OdooAPIClient struct {
 }
 
 type apiObject struct {
-	Data []OdooMeteredBillingRecord `json:"data"`
+	Data ensureJSONArray[OdooMeteredBillingRecord] `json:"data"`
 }
 
 type OdooMeteredBillingRecord struct {
@@ -72,7 +72,7 @@ func NewOdooAPIWithClient(odooURL string, client *http.Client, logger logr.Logge
 
 func (c OdooAPIClient) SendData(ctx context.Context, data []OdooMeteredBillingRecord) error {
 	apiObject := apiObject{
-		Data: data,
+		Data: ensureJSONArray[OdooMeteredBillingRecord](data),
 	}
 	str, err := json.Marshal(apiObject)
 	if err != nil {
@@ -92,3 +92,13 @@ func (c OdooAPIClient) SendData(ctx context.Context, data []OdooMeteredBillingRe
 
 	return nil
 }
+
+// ensureJSONArray is a wrapper around any slice that will marshal to an empty array instead of `null` if the array is nil.
+type ensureJSONArray[T any] []T
+
+func (a ensureJSONArray[T]) MarshalJSON() ([]byte, error) {
+	if a == nil {
+		return []byte("[]"), nil
+	}
+	return json.Marshal([]T(a))
+}
diff --git a/pkg/odoo/odoo16_test.go b/pkg/odoo/odoo16_test.go
index cdaf0d6..70c5753 100644
--- a/pkg/odoo/odoo16_test.go
+++ b/pkg/odoo/odoo16_test.go
@@ -44,10 +44,11 @@ func TestOdooRecordsSent(t *testing.T) {
 	logger := logr.New(logr.Discard().GetSink())
 	uut := odoo.NewOdooAPIWithClient("https://foo.bar/odoo16/", &client, logger)
 
-	err := uut.SendData(context.Background(), []odoo.OdooMeteredBillingRecord{getOdooRecord()})
-
-	require.NoError(t, err)
+	require.NoError(t, uut.SendData(context.Background(), []odoo.OdooMeteredBillingRecord{getOdooRecord()}))
 	require.Equal(t, `{"data":[{"product_id":"my-product","instance_id":"my-instance","item_description":"my-description","item_group_description":"my-group","sales_order_id":"SO00000","unit_id":"my-unit","consumed_units":11.1,"timerange":"2022-02-22T22:22:22Z/2022-02-22T23:22:22Z"}]}`, mrt.receivedContent)
+
+	require.NoError(t, uut.SendData(context.Background(), nil))
+	require.Equal(t, `{"data":[]}`, mrt.receivedContent, "client should ensure that the data field is always represented as an array")
 }
 
 func TestErrorHandling(t *testing.T) {

From 60e63cb2cf7db74e019923e5b484244ab55c30c2 Mon Sep 17 00:00:00 2001
From: Sebastian Widmer <sebastian.widmer@vshn.net>
Date: Thu, 7 Dec 2023 11:22:16 +0100
Subject: [PATCH 2/2] Initialize record array with assumed length

More or less cosmetic change with slight performance improvements possible.
---
 pkg/report/report.go | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/pkg/report/report.go b/pkg/report/report.go
index d3506bc..d6a980b 100644
--- a/pkg/report/report.go
+++ b/pkg/report/report.go
@@ -90,7 +90,7 @@ func runQuery(ctx context.Context, odooClient OdooClient, prom PromQuerier, args
 	}
 
 	var errs error
-	var records []odoo.OdooMeteredBillingRecord
+	records := make([]odoo.OdooMeteredBillingRecord, 0, len(samples))
 	for _, sample := range samples {
 		record, err := processSample(ctx, odooClient, args, from, sample)
 		if err != nil {