From 75bd1831bb694e9c598ea34bab2afe91ccdf13f4 Mon Sep 17 00:00:00 2001
From: Yury Molodov <yurymolodov@gmail.com>
Date: Wed, 22 May 2024 21:44:13 +0200
Subject: [PATCH] vmui/logs: fix parsing long `_msg` values  (#6310)

This PR fixes an issue where parsing long `_msg` values caused errors,
resulting in some log records not being displayed.

The error occurred due to partial processing of strings. In some cases,
a long record could be split into multiple chunks, causing only part of
the record to be processed instead of the entire entry.

#6281

Co-authored-by: Aliaksandr Valialkin <valyala@victoriametrics.com>
---
 .../pages/ExploreLogs/hooks/useFetchLogs.ts   | 38 +++----------------
 docs/VictoriaLogs/CHANGELOG.md                |  1 +
 2 files changed, 6 insertions(+), 33 deletions(-)

diff --git a/app/vmui/packages/vmui/src/pages/ExploreLogs/hooks/useFetchLogs.ts b/app/vmui/packages/vmui/src/pages/ExploreLogs/hooks/useFetchLogs.ts
index a9b8eaca7..21f63449c 100644
--- a/app/vmui/packages/vmui/src/pages/ExploreLogs/hooks/useFetchLogs.ts
+++ b/app/vmui/packages/vmui/src/pages/ExploreLogs/hooks/useFetchLogs.ts
@@ -35,49 +35,22 @@ export const useFetchLogs = (server: string, query: string, limit: number) => {
   };
 
   const fetchLogs = useCallback(async () => {
-    const limit = Number(options.body.get("limit")) + 1;
+    const limit = Number(options.body.get("limit"));
     setIsLoading(true);
     setError(undefined);
     try {
       const response = await fetch(url, options);
+      const text = await response.text();
 
       if (!response.ok || !response.body) {
-        const errorText = await response.text();
-        setError(errorText);
+        setError(text);
         setLogs([]);
         setIsLoading(false);
         return;
       }
 
-      const reader = response.body.getReader();
-      const decoder = new TextDecoder("utf-8");
-      const result = [];
-
-      while (reader) {
-        const { done, value } = await reader.read();
-
-        if (done) {
-          // "Stream finished, no more data."
-          break;
-        }
-
-        const lines = decoder.decode(value, { stream: true }).split("\n");
-        result.push(...lines);
-
-        // Trim result to limit
-        // This will lose its meaning with these changes:
-        // https://github.com/VictoriaMetrics/VictoriaMetrics/pull/5778
-        if (result.length > limit) {
-          result.splice(0, result.length - limit);
-        }
-
-        if (result.length >= limit) {
-          // Reached the maximum line limit
-          reader.cancel();
-          break;
-        }
-      }
-      const data = result.map(parseLineToJSON).filter(line => line) as Logs[];
+      const lines = text.split("\n").filter(line => line).slice(0, limit);
+      const data = lines.map(parseLineToJSON).filter(line => line) as Logs[];
       setLogs(data);
     } catch (e) {
       console.error(e);
@@ -96,4 +69,3 @@ export const useFetchLogs = (server: string, query: string, limit: number) => {
     fetchLogs,
   };
 };
-
diff --git a/docs/VictoriaLogs/CHANGELOG.md b/docs/VictoriaLogs/CHANGELOG.md
index 9f0a8f49f..2fcab1a4d 100644
--- a/docs/VictoriaLogs/CHANGELOG.md
+++ b/docs/VictoriaLogs/CHANGELOG.md
@@ -33,6 +33,7 @@ according to [these docs](https://docs.victoriametrics.com/VictoriaLogs/QuickSta
 * FEATURE: [web UI](https://docs.victoriametrics.com/VictoriaLogs/querying/#web-ui): change time range limitation from `_time` in the expression to `start` and `end` query args.
 
 * BUGFIX: fix `invalid memory address or nil pointer dereference` panic when using [`extract`](https://docs.victoriametrics.com/victorialogs/logsql/#extract-pipe), [`unpack_json`](https://docs.victoriametrics.com/victorialogs/logsql/#unpack_json-pipe) or [`unpack_logfmt`](https://docs.victoriametrics.com/victorialogs/logsql/#unpack_logfmt-pipe) pipes. See [this issue](https://github.com/VictoriaMetrics/VictoriaMetrics/issues/6306).
+* BUGFIX: [web UI](https://docs.victoriametrics.com/VictoriaLogs/querying/#web-ui): fix an issue where logs with long `_msg` values might not display. See [this issue](https://github.com/VictoriaMetrics/VictoriaMetrics/issues/6281).
 
 ## [v0.8.0](https://github.com/VictoriaMetrics/VictoriaMetrics/releases/tag/v0.8.0-victorialogs)