Setup logging after reading the config file

[dveeden]

What problem does this PR solve?

Issue Number: close #855

Problem Summary:

Logging is setup based with the generic NewConfig() and used during the initial parsing of the config file. Then later the watcher is correcting things where needed. However the encoder isn't changed. This results in the encoder from the config to be ignored.

What is changed and how it works:

1. Change the reading of the config to not use the logger at all. Messages might now go to stderr instead.
2. Delay the setup of logger until we have a config.
3. Print the config once we have the config and a logger.

As indicated for the changes in TestChecksum:

• With these changes the config isn't printed again when it changes
• The printing of the config is done in a different part of the code.

Check List

Tests

• Unit test
• Integration test
• Manual test (add detailed scripts or steps below)
• No code

Notable changes

• Has configuration change
• Has HTTP API interfaces change
• Has tiproxyctl change
• Other user behavior changes

Release note

Please refer to Release Notes Language Style Guide to write a quality release note.

Handling of the log encoder was corrected.

[ti-chi-bot]

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[ti-chi-bot]

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[dveeden]

/cc @djshow832

[dveeden]

This should probably get some more tests:

• With a logfile configured there should not be any output to stdout
• With a json encoder configured the output should parse as valid json

[dveeden]

$ ./bin/tiproxy --config=<(echo -en '[log]\nencoder = "json"\n') | head -1 | jq .
{
  "level": "INFO",
  "ts": "2025/09/04 10:00:58.199 +02:00",
  "logger": "main",
  "caller": "server/server.go:220",
  "msg": "Welcome to TiProxy.",
  "Release Version": "v1.4.0-beta.1-32-gd3f8304-dirty",
  "Git Commit Hash": "d3f830449f31e989e170340f6edc4627c0a09baa-dirty",
  "Git Branch": "main",
  "UTC Build Time": "2025-09-04 07:45:15",
  "GoVersion": "go1.24.6",
  "OS": "linux",
  "Arch": "amd64"
}

And with the current main branch:

dvaneeden@dve-carbon:~/dev/pingcap/tiproxy$ ./bin/tiproxy --config=<(echo -en '[log]\nencoder = "json"\n') | head -1 | jq .
jq: parse error: Invalid numeric literal at line 1, column 12
dvaneeden@dve-carbon:~/dev/pingcap/tiproxy$ ./bin/tiproxy --config=<(echo -en '[log]\nencoder = "json"\n') | head -1
[2025/09/04 10:02:05.431 +02:00] [INFO] [main.config] [config/config.go:71] [current config]  [cfg="{\"proxy\":{\"addr\":\"0.0.0.0:6000\",\"pd-addrs\":\"127.0.0.1:2379\",\"frontend-keepalive\":{\"enabled\":true},\"backend-healthy-keepalive\":{\"enabled\":true,\"idle\":60000000000,\"cnt\":5,\"intvl\":3000000000,\"timeout\":15000000000},\"backend-unhealthy-keepalive\":{\"enabled\":true,\"idle\":10000000000,\"cnt\":5,\"intvl\":1000000000,\"timeout\":5000000000},\"graceful-close-conn-timeout\":15},\"api\":{\"addr\":\"0.0.0.0:3080\"},\"workdir\":\"/home/dvaneeden/dev/pingcap/tiproxy/work\",\"security\":{\"server-tls\":{\"min-tls-version\":\"1.2\"},\"server-http-tls\":{\"min-tls-version\":\"1.2\"},\"cluster-tls\":{\"min-tls-version\":\"1.2\"},\"sql-tls\":{\"min-tls-version\":\"1.2\"}},\"log\":{\"encoder\":\"json\",\"level\":\"info\",\"log-file\":{\"max-size\":300,\"max-days\":3,\"max-backups\":3}},\"balance\":{\"policy\":\"resource\"},\"ha\":{},\"enable-traffic-replay\":true}"]

[codecov-commenter]

Codecov Report

❌ Patch coverage is 83.33333% with 2 lines in your changes missing coverage. Please review.
⚠️ Please upload report for BASE (main@d3f8304). Learn more about missing BASE report.

Files with missing lines	Patch %	Lines
pkg/server/server.go	80.00%	0 Missing and 2 partials ⚠️

Additional details and impacted files

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[djshow832]

It's crucial to print the config every time it changes. You can print it when the loggerManager watches a config change instead.