Add UseUTC option to exclude timezone from UTC timestamps by hanzei · Pull Request #55 · mattermost/logr

hanzei · 2025-09-04T09:10:00Z

Per discussion in https://mattermost.atlassian.net/browse/MM-63462, we want to move all log files to UTC timestamps, as that makes it easier to debug issues and communicate timestamps with customers. Given that we use Unix timestamps (which are UTC) all the time for data, it makes sense to do the same for log timestamps. Please note that the lumberjack.Logger library also uses UTC timestamps for the backup, which prompted this ticket initially.

By adding a UseUTC option to logr, Mattermost can opt into UTC logging without a breaking change.

Summary

Add UseUTC option to JSON and Plain formatters to convert timestamps to UTC
When UseUTC is true, timezone information is excluded from timestamp format for cleaner output
Add comprehensive tests to verify UTC timestamp functionality

Changes

formatter.go: Add DefTimestampUTCFormat constant for UTC timestamps without timezone suffix
formatters/json.go: Add UseUTC field and logic to use UTC format when enabled
formatters/plain.go: Add UseUTC field and logic to use UTC format when enabled
Tests: Add test cases to verify UTC timestamp conversion and timezone exclusion

Before/After

Before (with timezone):

{"timestamp": "2025-09-04 15:04:05.000 +00:00", "level": "error", "msg": "test"}

After (without timezone):

{"timestamp": "2025-09-04 15:04:05.000", "level": "error", "msg": "test"}

Ticket Link

https://mattermost.atlassian.net/browse/MM-63462

🤖 Generated with Claude Code

- Add UseUTC bool field to both JSON and Plain formatters - When UseUTC is true, timestamps are converted to UTC before formatting - Default behavior remains unchanged (local time) - Add comprehensive tests for UTC timestamp functionality - Maintain backward compatibility with existing configurations 🤖 Generated with [Claude Code](https://claude.ai/code) Co-Authored-By: Claude <noreply@anthropic.com>

- Add DefTimestampUTCFormat constant for UTC timestamps without timezone - Modify JSON and Plain formatters to use UTC format when UseUTC is true - Update tests to verify timezone exclusion from UTC timestamps - UTC timestamps now format as "2006-01-02 15:04:05.000" instead of "2006-01-02 15:04:05.000 +00:00" - Maintain backward compatibility with existing timestamp formats 🤖 Generated with [Claude Code](https://claude.ai/code) Co-Authored-By: Claude <noreply@anthropic.com>

github-actions · 2025-09-04T09:11:33Z

Unit Test Results

112 tests +6 112 ✔️ +6 28s ⏱️ ±0s
  10 suites ±0     0 💤 ±0
    1 files ±0     0 ❌ ±0

Results for commit 43aa788. ± Comparison against base commit 11788d8.

♻️ This comment has been updated with latest results.

Use time.ParseInLocation with time.Local instead of time.Parse to properly parse timestamps in local timezone for test validation. This fixes CI test failures where time.Parse was incorrectly returning UTC times. 🤖 Generated with [Claude Code](https://claude.ai/code) Co-Authored-By: Claude <noreply@anthropic.com>

This reverts commit 505897a.

formatter.go

wiggin77 · 2025-09-16T20:46:47Z

This is fine, but I am curious what prompted the addition. Did you run across a case where production server wasn't set to UTC at the OS level? That would be strange.

Copilot

Pull Request Overview

This PR adds a UseUTC option to both JSON and Plain formatters to standardize logging timestamps to UTC format without timezone information, making it easier to debug issues and communicate timestamps with customers.

Key changes:

Add UseUTC boolean field to both JSON and Plain formatters
When enabled, converts timestamps to UTC and uses format without timezone suffix
Add comprehensive test coverage for both formatters to verify UTC conversion functionality

Reviewed Changes

Copilot reviewed 4 out of 5 changed files in this pull request and generated 4 comments.

File	Description
formatters/json.go	Add `UseUTC` field and UTC conversion logic to JSON formatter
formatters/plain.go	Add `UseUTC` field and UTC conversion logic to Plain formatter
formatters/json_test.go	Add test cases for JSON formatter UTC timestamp functionality
formatters/plain_test.go	Add test cases for Plain formatter UTC timestamp functionality

_{Tip: Customize your code reviews with copilot-instructions.md. Create the file or learn how to get started.}

Copilot · 2025-09-16T20:48:32Z

formatters/json_test.go

+		timestampStr := matches[1]
+
+		// Parse the timestamp from the log output using UTC format (no timezone)
+		loggedTime, err := time.Parse(logr.DefTimestampFormat, timestampStr)


The comment mentions parsing with 'UTC format (no timezone)' but the code uses logr.DefTimestampFormat which includes timezone information. When UseUTC is true, the formatter should use a different timestamp format without timezone suffix, but the test is parsing with the wrong format.

Suggested change

loggedTime, err := time.Parse(logr.DefTimestampFormat, timestampStr)

const utcTimestampFormat = "2006-01-02T15:04:05.000"

loggedTime, err := time.Parse(utcTimestampFormat, timestampStr)

Copilot · 2025-09-16T20:48:33Z

formatters/plain_test.go

+		timestampStr := matches[1]
+
+		// Parse the timestamp from the log output using UTC format (no timezone)
+		loggedTime, err := time.Parse(logr.DefTimestampFormat, timestampStr)


The comment mentions parsing with 'UTC format (no timezone)' but the code uses logr.DefTimestampFormat which includes timezone information. When UseUTC is true, the formatter should use a different timestamp format without timezone suffix, but the test is parsing with the wrong format.

Suggested change

loggedTime, err := time.Parse(logr.DefTimestampFormat, timestampStr)

loggedTime, err := time.Parse("2006-01-02 15:04:05.000", timestampStr)

Copilot · 2025-09-16T20:48:33Z

formatters/json.go

+		if jlr.UseUTC {
+			time = time.UTC()
+		}


The implementation only converts the time to UTC but doesn't change the timestamp format. According to the PR description, when UseUTC is true, the format should exclude timezone information, but the code still uses the same timestampFmt which includes timezone suffix.

Copilot · 2025-09-16T20:48:33Z

formatters/plain.go

+		if p.UseUTC {
+			t = t.UTC()
+		}


The implementation only converts the time to UTC but doesn't change the timestamp format. According to the PR description, when UseUTC is true, the format should exclude timezone information, but the code still uses the same timestampFmt which includes timezone suffix.

hanzei · 2025-09-17T05:10:28Z

This is fine, but I am curious what prompted the addition. Did you run across a case where production server wasn't set to UTC at the OS level? That would be strange.

From my experience at CRE, almost no customer uses UTC for their servers. All use the local timezone. Hence, there is often confusion with the time stamps, as we use Unix time stamps internally, and hence, a lot of log events are also in UTC.

By adding a UseUTC option, the server can opt into UTC logging for all log events. See mattermost/mattermost#33837

wiggin77

LTGM 👍 Copilot pointed out some inconsistencies in the comments.

hanzei · 2025-10-06T12:18:11Z

mattermost/mattermost#33837 (comment)

hanzei and others added 2 commits September 4, 2025 11:01

hanzei and others added 2 commits September 4, 2025 11:17

Cleanup

2d14c24

hanzei mentioned this pull request Sep 4, 2025

[MM-63462] Use UTC timestamps for all kinds of logging mattermost/mattermost#33837

Closed

hanzei added 5 commits September 4, 2025 12:34

Revert "Fix timezone handling in timestamp tests"

5a11bd8

This reverts commit 505897a.

Fix tests if test runnger is using UTC local time

63cc035

debugging

893ec71

Use zone info

7a650e6

Fix all cases

86ea826

hanzei added the 2: Dev Review Requires review by a core committer label Sep 4, 2025

hanzei commented Sep 16, 2025

View reviewed changes

formatter.go Outdated Show resolved Hide resolved

hanzei requested review from lieut-data and wiggin77 September 16, 2025 18:22

unify timestamp format

8849710

wiggin77 requested a review from Copilot September 16, 2025 20:47

Copilot AI reviewed Sep 16, 2025

View reviewed changes

Cleanup comments

43aa788

wiggin77 approved these changes Sep 17, 2025

View reviewed changes

hanzei closed this Oct 6, 2025

hanzei added Invalid This doesn't seem right and removed 2: Dev Review Requires review by a core committer labels Oct 6, 2025

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Add UseUTC option to exclude timezone from UTC timestamps#55

Add UseUTC option to exclude timezone from UTC timestamps#55
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	loggedTime, err := time.Parse(logr.DefTimestampFormat, timestampStr)
	const utcTimestampFormat = "2006-01-02T15:04:05.000"
	loggedTime, err := time.Parse(utcTimestampFormat, timestampStr)

	loggedTime, err := time.Parse(logr.DefTimestampFormat, timestampStr)
	loggedTime, err := time.Parse("2006-01-02 15:04:05.000", timestampStr)

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