Use relaxed JSON escaping for log bodies

[olsh]

Fixes #339.

Problem

The body formatter (LokiJsonTextFormatter) and the batch serializer build their Utf8JsonWriters with no options, so they use System.Text.Json's default HTML-safe JavaScriptEncoder. It escapes ", ', <, >, & and all non-ASCII as \uXXXX. Because Serilog quotes string property values by default, this makes most stored Loki lines unreadable — a regression from v8.x, which used Serilog's JsonValueFormatter (standard escaping). See #339 for details.

Fix

Construct the writers with JsonWriterOptions(Encoder = JavaScriptEncoder.UnsafeRelaxedJsonEscaping), applied at all three writer sites (formatter body, batch envelope, reused body buffer) via a shared value.

Before:

{"Message":"Initialize \u0022SAGO\u0022", ...}

After:

{"Message":"Initialize \"SAGO\"", ...}

Notes

• Output stays valid JSON and valid UTF-8, so consumers (including | json queries) are unaffected. "Unsafe" in the encoder name only refers to embedding JSON directly into HTML, which does not apply to Loki log bodies.
• Added a unit test asserting <, >, & and non-ASCII survive verbatim.
• dotnet test (UnitTests, net10.0): 122/122 pass.

Summary by CodeRabbit

• Bug Fixes
  • Improved Loki JSON formatting so quotes, markup characters, and non-ASCII text (e.g., Cyrillic) remain readable instead of being converted to escaped/unicode forms, while still producing valid JSON.
  • Ensured the same improved escaping behavior is applied consistently across log event serialization and the public formatter output.
• Tests
  • Added unit tests covering the public formatter path and promoted labels, verifying markup/non-ASCII remain verbatim and that quote escaping follows standard JSON rules.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Repository UI

Review profile: CHILL

Plan: Pro Plus

Run ID: 122161f2-6ff8-4d2e-8c1d-127b9c7386d7

📥 Commits

Reviewing files that changed from the base of the PR and between 39f3274 and bcb9a84.

📒 Files selected for processing (5)

• src/Serilog.Sinks.Grafana.Loki/Infrastructure/JsonWriterDefaults.fs
• src/Serilog.Sinks.Grafana.Loki/LokiJsonTextFormatter.fs
• src/Serilog.Sinks.Grafana.Loki/Serialization.fs
• src/Serilog.Sinks.Grafana.Loki/Serilog.Sinks.Grafana.Loki.fsproj
• tests/Serilog.Sinks.Grafana.Loki.UnitTests/WireFormatTests.fs

✅ Files skipped from review due to trivial changes (1)

• src/Serilog.Sinks.Grafana.Loki/Serilog.Sinks.Grafana.Loki.fsproj

🚧 Files skipped from review as they are similar to previous changes (1)

• src/Serilog.Sinks.Grafana.Loki/Serialization.fs

---

📝 Walkthrough

Walkthrough

The PR adds a shared JSON writer helper and switches formatter and payload serialization to use relaxed escaping. Unit tests verify that quotes, markup, and non-ASCII characters remain readable in the emitted output.

Changes

Relaxed JSON escaping update

Layer / File(s)	Summary
Shared relaxed writer defaults src/Serilog.Sinks.Grafana.Loki/Infrastructure/JsonWriterDefaults.fs, src/Serilog.Sinks.Grafana.Loki/Serilog.Sinks.Grafana.Loki.fsproj	Adds a shared internal writer factory with relaxed JSON escaping and includes it in the project build.
Formatter and payload serialization src/Serilog.Sinks.Grafana.Loki/LokiJsonTextFormatter.fs, src/Serilog.Sinks.Grafana.Loki/Serialization.fs	Routes the public formatter path and Loki payload serialization through the shared writer factory.
Wire format coverage tests/Serilog.Sinks.Grafana.Loki.UnitTests/WireFormatTests.fs	Adds tests covering readable body text, public formatter output, and promoted label values with markup and non-ASCII text.

Estimated code review effort

🎯 2 (Simple) | ⏱️ ~10 minutes

Poem

🐇 I nibble logs with a merry grin,
Less \u-tingle lets the true chars in.
Quotes stay tidy, glyphs stay bright,
Loki reads them clear and light.

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title is concise and accurately describes the main change: enabling relaxed JSON escaping for log bodies.
Linked Issues check	✅ Passed	The changes implement #339 by using relaxed JSON escaping for the Loki body writers and adding coverage for the intended output.
Out of Scope Changes check	✅ Passed	The added helper, project file update, and tests all support the escaping fix and do not introduce unrelated scope.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.

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✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests

---

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[coderabbitai]

Actionable comments posted: 1

🤖 Prompt for all review comments with AI agents

Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

Inline comments:
In `@tests/Serilog.Sinks.Grafana.Loki.UnitTests/WireFormatTests.fs`:
- Around line 255-267: The WireFormatTests ``body: quotes, markup and non-ASCII
are not unicode-escaped`` test currently checks angle brackets, ampersands, and
non-ASCII, but it never verifies quote handling. Update the assertions on
handler.LastBodyText to explicitly check that the quote character from mkInfo in
the payload is emitted as a literal quote and not escaped as \u0022, using the
existing test setup and the raw string checks already in place.

🪄 Autofix (Beta)

Fix all unresolved CodeRabbit comments on this PR:

• Push a commit to this branch (recommended)
• Create a new PR with the fixes

---

ℹ️ Review info

⚙️ Run configuration

Configuration used: Repository UI

Review profile: CHILL

Plan: Pro Plus

Run ID: 7bc04844-db9c-4a82-95f0-f3e0706a8169

📥 Commits

Reviewing files that changed from the base of the PR and between fa376ad and 375be12.

📒 Files selected for processing (3)

• src/Serilog.Sinks.Grafana.Loki/LokiJsonTextFormatter.fs
• src/Serilog.Sinks.Grafana.Loki/Serialization.fs
• tests/Serilog.Sinks.Grafana.Loki.UnitTests/WireFormatTests.fs