Prevent servlet snippet injection from corrupting recycled responses by Copilot · Pull Request #21104 · open-telemetry/opentelemetry-java-instrumentation

Copilot · 2026-10-31T18:17:08Z

Prevent recycled Jetty output streams from carrying stale snippet state into later requests. A cached five-byte Content-Length could truncate a 228-byte JSP to 37 bytes.

Scope stream state to the request lifetime in both javax and jakarta instrumentation, while keeping stream and writer matching independent and preserving late content-type support.

Fixes #21096.

opentelemetry-pr-dashboard · 2026-10-31T18:17:40Z

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…etime Co-authored-by: trask <218610+trask@users.noreply.github.com>

Co-authored-by: trask <218610+trask@users.noreply.github.com>

Copilot

🔵 Needs a closer look

Mock lifetime and synchronous keep-alive tests do not establish shared-body lifecycle behavior when forwards or async code reset the raw container response, so installed-agent validation is needed.

No open issues 🎉

What changed in this PR

This PR fixes servlet snippet injection state leaking across recycled responses, preventing stale Content-Length values from truncating later responses in both javax and jakarta instrumentation.

Changes:

Bind injection state to the request and response body while preserving async redispatch and late-content-type support.
Share writer and stream tracking, and reset abandoned body state without double-adjusting Content-Length.
Add lifecycle regression tests and a Jetty smoke test that reuses one HTTP/1.1 connection.

File	Description
`smoke-tests/src/test/java/io/opentelemetry/smoketest/appserver/JettySmokeTest.java`	Tests complete JSP output after a non-HTML response on the same connection.
`instrumentation/servlet/servlet-common/javaagent/src/main/java/io/opentelemetry/javaagent/instrumentation/servlet/common/snippet/SnippetInjectingPrintWriter.java`	Accepts shared injection state and marks writer ownership.
`instrumentation/servlet/servlet-common/javaagent/src/main/java/io/opentelemetry/javaagent/instrumentation/servlet/common/snippet/OutputStreamSnippetInjectionHelper.java`	Skips stream injection when the writer owns injection.
`instrumentation/servlet/servlet-common/bootstrap/src/main/java/io/opentelemetry/javaagent/bootstrap/servlet/InjectionState.java`	Tracks request lifetime, output ownership, resets, and Content-Length adjustments.
`instrumentation/servlet/servlet-5.0/javaagent/src/unitTests/java/io/opentelemetry/javaagent/instrumentation/servlet/v5_0/snippet/InjectionStateLifetimeTest.java`	Covers jakarta response reuse, redispatch, errors, and resets.
`instrumentation/servlet/servlet-5.0/javaagent/src/main/java/io/opentelemetry/javaagent/instrumentation/servlet/v5_0/snippet/ServletOutputStreamInjectionState.java`	Shares body state and clears expired jakarta stream ownership.
`instrumentation/servlet/servlet-5.0/javaagent/src/main/java/io/opentelemetry/javaagent/instrumentation/servlet/v5_0/snippet/Servlet5SnippetInjectingResponseWrapper.java`	Manages request-bound state and body resets for jakarta responses.
`instrumentation/servlet/servlet-5.0/javaagent/src/main/java/io/opentelemetry/javaagent/instrumentation/servlet/v5_0/service/JakartaServletServiceAdvice.java`	Passes the request into the jakarta response wrapper.
`instrumentation/servlet/servlet-3.0/javaagent/src/unitTests/java/io/opentelemetry/javaagent/instrumentation/servlet/v3_0/snippet/InjectionStateLifetimeTest.java`	Covers javax response reuse, redispatch, errors, and resets.
`instrumentation/servlet/servlet-3.0/javaagent/src/main/java/io/opentelemetry/javaagent/instrumentation/servlet/v3_0/snippet/ServletOutputStreamInjectionState.java`	Shares body state and clears expired javax stream ownership.
`instrumentation/servlet/servlet-3.0/javaagent/src/main/java/io/opentelemetry/javaagent/instrumentation/servlet/v3_0/snippet/Servlet3SnippetInjectingResponseWrapper.java`	Manages request-bound state and body resets for javax responses.
`instrumentation/servlet/servlet-3.0/javaagent/src/main/java/io/opentelemetry/javaagent/instrumentation/servlet/v3_0/Servlet3Advice.java`	Passes the request into the javax response wrapper.

_{Review effort: Balanced}

Co-authored-by: trask <218610+trask@users.noreply.github.com>

Copilot

🟡 Changes recommended

Both servlet response wrappers disable stream injection before writer creation succeeds, causing snippet injection to be lost when callers catch a getWriter() failure and continue using the output stream.

1 open issue

Preserve stream injection when writer creation fails · New

_{Review effort: Balanced}

Co-authored-by: trask <218610+trask@users.noreply.github.com>

Copilot

🔵 Needs a closer look

The ERROR-dispatch behavior lacks installed-agent regression coverage for Servlet 3 and Servlet 5, leaving wrapper-guard and reset-advice interactions, replacement-body completeness, single-snippet injection, and Content-Length consistency unverified.

No open issues 🎉

1 previously missed issue

In code that hasn't changed since last review

Add installed-agent regression for ERROR-dispatch response replacement

instrumentation/servlet/servlet-3.0/javaagent/src/main/java/io/opentelemetry/javaagent/instrumentation/servlet/v3_0/snippet/Servlet3SnippetInjectingResponseWrapper.java:74

[Testing] The new ERROR-dispatch behavior lacks an installed-agent regression: the unit test constructs the wrapper directly, leaving its interaction with the existing-wrapper guard and reset advice untested. Add a regression for both Servlet 3 and Servlet 5 that writes an uncommitted fixed-length body, dispatches to an HTML error servlet, and checks the complete replacement body, exactly one snippet, and matching Content-Length when present. The same gap applies to Servlet5SnippetInjectingResponseWrapper.java:66.

1 resolved since last review

Preserve stream injection when writer creation fails

_{Review effort: Balanced}

Copilot

🔵 Needs a closer look

An unpublished finding about stale cached writers after raw async response resets warrants human assessment because it can bypass container ownership checks and disable active-stream injection.

No open issues 🎉

_{Review effort: Balanced}

Co-authored-by: trask <218610+trask@users.noreply.github.com>

Copilot

🔵 Needs a closer look

Human assessment is needed because an unpublished finding identifies an asynchronous span-export race that may contaminate subsequent tests and undermine their assertions.

No open issues 🎉

_{Review effort: Balanced}

Co-authored-by: trask <218610+trask@users.noreply.github.com>

Copilot

🟡 Changes recommended

Both servlet versions unnecessarily clear an already-empty virtual field on every output-stream write, adding volatile-write overhead even when snippet injection is disabled.

1 open issue

Avoid clearing the empty virtual field on every output write · New

_{Review effort: Balanced}

Co-authored-by: trask <218610+trask@users.noreply.github.com>

Copilot

🟢 Approval recommended

No active review issues are reported for the changes tying servlet snippet-injection state to the request lifetime.

No open issues 🎉

1 resolved since last review

Avoid clearing the empty virtual field on every output write

_{Review effort: Balanced}

Initial plan

90b2273

Copilot AI assigned Copilot and trask Oct 31, 2026

opentelemetry-pr-dashboard Bot mentioned this pull request Oct 31, 2026

Pull Request Dashboard #18435

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Copilot started work on behalf of trask October 31, 2026 18:17

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Copilot AI and others added 2 commits October 31, 2026 18:32

Bind servlet snippet injection state to request and response body lif…

9e5e2e8

…etime Co-authored-by: trask <218610+trask@users.noreply.github.com>

Handle response resets and release expired servlet snippet state

ab4b2d6

Co-authored-by: trask <218610+trask@users.noreply.github.com>

Copilot AI changed the title ~~[WIP] Fix advice failure with snippet injection in Jetty smoke tests~~ Prevent servlet snippet injection from corrupting recycled responses Oct 31, 2026

Copilot finished work on behalf of trask October 31, 2026 18:48

Copilot AI requested a review from trask October 31, 2026 18:48

trask requested a balanced review from Copilot October 31, 2026 18:55

Copilot started reviewing on behalf of trask October 31, 2026 18:56

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Comment thread .../javaagent/instrumentation/servlet/v3_0/snippet/Servlet3SnippetInjectingResponseWrapper.java Resolved

Copilot started work on behalf of trask October 31, 2026 19:12

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Reset servlet snippet state on raw body discard

5dcfc5e

Co-authored-by: trask <218610+trask@users.noreply.github.com>

Copilot finished work on behalf of trask October 31, 2026 19:53

Copilot AI requested a review from trask October 31, 2026 19:53

trask requested a balanced review from Copilot October 31, 2026 20:02

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Comment thread .../javaagent/instrumentation/servlet/v3_0/snippet/Servlet3SnippetInjectingResponseWrapper.java Resolved

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Comment thread ...mon/bootstrap/src/main/java/io/opentelemetry/javaagent/bootstrap/servlet/InjectionState.java Resolved

Copilot started work on behalf of trask October 31, 2026 20:24

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Fix servlet snippet state across forwards

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Co-authored-by: trask <218610+trask@users.noreply.github.com>

Copilot finished work on behalf of trask October 31, 2026 20:50

Copilot AI requested a review from trask October 31, 2026 20:51

trask requested a balanced review from Copilot October 31, 2026 20:59

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trask requested a balanced review from Copilot October 31, 2026 22:03

Copilot started reviewing on behalf of trask October 31, 2026 22:03

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github-advanced-security Bot found potential problems Oct 31, 2026

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Comment thread .../javaagent/instrumentation/servlet/v3_0/snippet/Servlet3SnippetInjectingResponseWrapper.java Resolved

Copilot started work on behalf of trask October 31, 2026 22:27

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Validate cached servlet writers against native response ownership

319dde0

Co-authored-by: trask <218610+trask@users.noreply.github.com>

Copilot finished work on behalf of trask October 31, 2026 22:53

Copilot AI requested a review from trask October 31, 2026 22:53

trask requested a balanced review from Copilot October 31, 2026 23:00

Copilot started reviewing on behalf of trask October 31, 2026 23:01

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Comment thread .../javaagent/instrumentation/servlet/v3_0/snippet/Servlet3SnippetInjectingResponseWrapper.java Resolved

Copilot started work on behalf of trask November 2, 2026 05:49

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Scope servlet snippet fix to recycled streams

61ae5b4

Co-authored-by: trask <218610+trask@users.noreply.github.com>

Copilot finished work on behalf of trask November 2, 2026 06:16

Copilot AI requested a review from trask November 2, 2026 06:16

trask requested a balanced review from Copilot November 2, 2026 06:19

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Comment thread ...emetry/javaagent/instrumentation/servlet/v3_0/snippet/ServletOutputStreamInjectionState.java Resolved

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Comment thread ...emetry/javaagent/instrumentation/servlet/v3_0/snippet/ServletOutputStreamInjectionState.java Resolved

Copilot started work on behalf of trask November 2, 2026 06:26

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Restore recycled servlet stream assertions

aec0441

Co-authored-by: trask <218610+trask@users.noreply.github.com>

Copilot finished work on behalf of trask November 2, 2026 06:48

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trask requested a balanced review from Copilot November 2, 2026 06:51

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trask added this pull request to stack #21134 November 2, 2026 06:57

Copilot AI mentioned this pull request Nov 2, 2026

Preserve shared servlet snippet state across response-body reuse #21133

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Copilot AI commented Oct 31, 2026 •

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