Handle servlet response lifecycle boundaries during RUM injection

[amarziali]

What Does This Do

Preserves servlet response semantics when RUM injection encounters flush, reset, error, or redirect boundaries.

The injecting streams retain a small look-behind buffer while searching for </head>. Previously, that buffered state could survive lifecycle operations, causing delayed output, matching across committed
boundaries, or content from a reset response to be written later.

This PR:

• Drains buffered content and resets partial marker matching on flush() and commit().
• Adds a discard operation for content removed by the servlet container.
• Handles flushBuffer(), resetBuffer(), reset(), sendError(), and sendRedirect().
• Re-arms injection after resetBuffer().
• Retires old wrappers and restores fresh injection state after reset().
• Applies equivalent behavior to javax Servlet 3 and Jakarta Servlet 5.

Motivation

Additional Notes

Contributor Checklist

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• Assign the type: and (comp: or inst:) labels in addition to any other useful labels
• Avoid using close, fix, or any linking keywords when referencing an issue
  Use solves instead, and assign the PR milestone to the issue
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• Update public documentation with any new configuration flags or behaviors
• Once approved, use merge queue to merge the PR

Jira ticket: [PROJ-IDENT]

[chatgpt-codex-connector]

Codex Review Summary

This comment shows the latest Codex review activity on this pull request.

Review	Status	Commit	Review trigger
📝 Code Review	✅ Completed 2026-09-15T14:03:50.702130Z	c07186b	Manual request
🔒 Security Review	✅ Completed 2026-09-15T14:02:22.761885Z	c07186b	Manual request

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[datadog-official]

An asynchronous reset can start old response wrappers again. Each wrapper can then add the RUM script, so one response can contain the script more than once.

_{Open Bits AI session}

_{🤖 Datadog Autotest · Commit 57f6c18 · What is Autotest? · @DataDog review to ask questions · Any feedback? Reach out in #autotest}

[dd-octo-sts]

🟢 Java Benchmark SLOs — All performance SLOs passed

Suite	Status
Startup	🟢 pass

SLO thresholds are defined here based on automatically generated metrics. A warning is raised when results are within 5% of the threshold.

PR vs. master results

Scenario	Candidate	master	Δ (95% CI of mean)
startup:insecure-bank:iast:Agent	13.93 s	13.96 s	[-0.9%; +0.5%] (no difference)
startup:insecure-bank:tracing:Agent	12.92 s	13.00 s	[-1.2%; +0.0%] (no difference)
startup:petclinic:appsec:Agent	17.05 s	16.93 s	[-0.1%; +1.6%] (no difference)
startup:petclinic:iast:Agent	16.92 s	16.43 s	[-1.5%; +7.4%] (no difference)
startup:petclinic:profiling:Agent	16.60 s	16.84 s	[-2.6%; -0.3%] (maybe better)
startup:petclinic:sca:Agent	16.95 s	16.67 s	[+0.6%; +2.8%] (maybe worse)
startup:petclinic:tracing:Agent	16.18 s	16.10 s	[-0.3%; +1.3%] (no difference)

Commit: c07186bf · CI Pipeline · Benchmarking Platform UI

---

Load and DaCapo benchmarks can be triggered manually in the GitLab pipeline. Results will appear in the Benchmarking Platform UI after completion.

[amarziali]

@DataDog review

[datadog-official]

More details

The change drains buffered output at flush boundaries. It discards buffered output at reset, error, and redirect boundaries, and it keeps injection state aligned in both servlet versions.

Was this helpful? React 👍 or 👎

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_{🤖 Datadog Autotest · Commit 1b514ff · What is Autotest? · @DataDog review to ask questions · Any feedback? Reach out in #autotest}

[amarziali]

@codex review

[chatgpt-codex-connector]

🛡️ Codex Security Review · Automatically triggered

Security review completed. No security issues were found in this pull request.

Reviewed commit: 1b514ff0de

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[chatgpt-codex-connector]

💡 Codex Review

Here are some automated review suggestions for this pull request.

Reviewed commit: 1b514ff0de

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[amarziali]

@codex review

[chatgpt-codex-connector]

🛡️ Codex Security Review · Automatically triggered

Security review completed. No security issues were found in this pull request.

Reviewed commit: 52946eff9e

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ℹ️ About Codex security reviews in GitHub

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[chatgpt-codex-connector]

💡 Codex Review

Here are some automated review suggestions for this pull request.

Reviewed commit: 52946eff9e

ℹ️ About Codex in GitHub

Your team has set up Codex to review pull requests in this repo. Reviews are triggered when you

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If Codex has suggestions, it will comment; otherwise it will react with 👍.

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[amarziali]

@codex review

[chatgpt-codex-connector]

🛡️ Codex Security Review · Automatically triggered

Security review completed. No security issues were found in this pull request.

Reviewed commit: c07186bfc7

View security finding report

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ℹ️ About Codex security reviews in GitHub

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Once complete, Codex will leave suggestions, or a comment if no findings are found.

[chatgpt-codex-connector]

Codex Review: Didn't find any major issues. What shall we delve into next?

Reviewed commit: c07186bfc7

ℹ️ About Codex in GitHub

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