From 44e7602ad2f11f78f9703ac8bd06ff827f4e4d16 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?G=C3=A1bor=20Farkas?= <gabor.farkas@gmail.com>
Date: Thu, 12 May 2022 08:56:09 +0200
Subject: [PATCH] loki: backend-mode: add "limit" dataframe meta attribute
 (#48894)

---
 .../loki/backendResultTransformer.test.ts     | 31 +++++++++++++++++++
 .../loki/backendResultTransformer.ts          |  1 +
 2 files changed, 32 insertions(+)

diff --git a/public/app/plugins/datasource/loki/backendResultTransformer.test.ts b/public/app/plugins/datasource/loki/backendResultTransformer.test.ts
index 1b713005141..098b7d276c3 100644
--- a/public/app/plugins/datasource/loki/backendResultTransformer.test.ts
+++ b/public/app/plugins/datasource/loki/backendResultTransformer.test.ts
@@ -91,6 +91,37 @@ describe('loki backendResultTransformer', () => {
     expect(result).toEqual(expected);
   });
 
+  it('applies maxLines correctly', () => {
+    const response: DataQueryResponse = { data: [cloneDeep(inputFrame)] };
+
+    const frame1: DataFrame = transformBackendResult(
+      response,
+      [
+        {
+          refId: 'A',
+          expr: LOKI_EXPR,
+        },
+      ],
+      []
+    ).data[0];
+
+    expect(frame1.meta?.limit).toBeUndefined();
+
+    const frame2 = transformBackendResult(
+      response,
+      [
+        {
+          refId: 'A',
+          expr: LOKI_EXPR,
+          maxLines: 42,
+        },
+      ],
+      []
+    ).data[0];
+
+    expect(frame2.meta?.limit).toBe(42);
+  });
+
   it('processed derived fields correctly', () => {
     const input: DataFrame = {
       length: 1,
diff --git a/public/app/plugins/datasource/loki/backendResultTransformer.ts b/public/app/plugins/datasource/loki/backendResultTransformer.ts
index 93504c1caef..29c9b7a0f3b 100644
--- a/public/app/plugins/datasource/loki/backendResultTransformer.ts
+++ b/public/app/plugins/datasource/loki/backendResultTransformer.ts
@@ -27,6 +27,7 @@ function processStreamFrame(
 ): DataFrame {
   const meta: QueryResultMeta = {
     preferredVisualisationType: 'logs',
+    limit: query?.maxLines,
     searchWords: query !== undefined ? getHighlighterExpressionsFromQuery(formatQuery(query.expr)) : undefined,
     custom: {
       // used by logs_model