Support late servlet content types for snippet injection by Copilot · Pull Request #20921 · open-telemetry/opentelemetry-java-instrumentation

Copilot · 2026-10-23T22:36:34Z

Allow servlet streams and writers to be acquired before the response becomes HTML, provided the content type is set before writing the head tag.

Fixes #8869.

ServletOutputStream out = response.getOutputStream();
response.setContentType("text/html");
out.print("<head>");

opentelemetry-pr-dashboard · 2026-10-23T22:37:32Z

Pull request dashboard status

Waiting on reviewers · refreshed 2026-10-24 05:32 UTC

Review the latest changes.

Status above doesn't look right?

Just replied or pushed? Anything around or after the refresh time above may not be picked up yet — give it a few minutes.
Anything look wrong? Report it with what you expected; it helps us improve the dashboard.

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

Copilot

🟡 Changes recommended

Bulk writer calls now repeat content-type lookups for every character until a head tag is found, adding avoidable work to the response-writing path.

1 open issue

Avoid repeated content-type lookups during bulk writes · New

What changed in this PR

This PR lets servlet streams and writers be acquired before an HTML content type is set, extending snippet injection support across both servlet namespaces.

Changes:

Check injection eligibility at write time and discard partial matches across non-HTML writes.
Preserve once-only injection and track content length before the content type is known.
Add regression coverage for late content types, split writes, reacquisition, and committed responses.

File	Description
instrumentation/servlet/servlet-common/javaagent/src/main/java/io/opentelemetry/javaagent/instrumentation/servlet/common/snippet/SnippetInjectingPrintWriter.java	Checks writer eligibility at write time.
instrumentation/servlet/servlet-common/javaagent/src/main/java/io/opentelemetry/javaagent/instrumentation/servlet/common/snippet/OutputStreamSnippetInjectionHelper.java	Checks stream eligibility at write time.
instrumentation/servlet/servlet-common/bootstrap/src/main/java/io/opentelemetry/javaagent/bootstrap/servlet/InjectionState.java	Centralizes eligibility and partial-match reset.
instrumentation/servlet/servlet-5.0/javaagent/src/main/java/io/opentelemetry/javaagent/instrumentation/servlet/v5_0/snippet/ServletOutputStreamInjectionState.java	Retains Jakarta stream state before HTML eligibility.
instrumentation/servlet/servlet-5.0/javaagent/src/main/java/io/opentelemetry/javaagent/instrumentation/servlet/v5_0/snippet/Servlet5SnippetInjectingResponseWrapper.java	Supports early writer acquisition and content-length tracking.
instrumentation/servlet/servlet-5.0/javaagent-unit-tests/src/test/java/io/opentelemetry/javaagent/instrumentation/servlet/v5_0/snippet/SnippetServletOutputStreamTest.java	Supplies HTML content type in existing fixtures.
instrumentation/servlet/servlet-5.0/javaagent-unit-tests/src/test/java/io/opentelemetry/javaagent/instrumentation/servlet/v5_0/snippet/LateContentTypeTest.java	Adds Jakarta late-content-type regression tests.
instrumentation/servlet/servlet-3.0/javaagent/src/main/java/io/opentelemetry/javaagent/instrumentation/servlet/v3_0/snippet/ServletOutputStreamInjectionState.java	Retains javax stream state before HTML eligibility.
instrumentation/servlet/servlet-3.0/javaagent/src/main/java/io/opentelemetry/javaagent/instrumentation/servlet/v3_0/snippet/Servlet3SnippetInjectingResponseWrapper.java	Supports early writer acquisition and content-length tracking.
instrumentation/servlet/servlet-3.0/javaagent-unit-tests/src/test/java/io/opentelemetry/javaagent/instrumentation/servlet/v3_0/snippet/SnippetServletOutputStreamTest.java	Supplies HTML content type in existing fixtures.
instrumentation/servlet/servlet-3.0/javaagent-unit-tests/src/test/java/io/opentelemetry/javaagent/instrumentation/servlet/v3_0/snippet/LateContentTypeTest.java	Adds javax late-content-type regression tests.

_{Review effort: Balanced}

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

Copilot

🟡 Changes recommended

Late-content-type behavior needs installed-agent integration coverage for transformed writes and real-container Content-Length handling.

1 open issue

Add integration coverage for late Content-Type injection · New

1 resolved since last review

Avoid repeated content-type lookups during bulk writes

_{Review effort: Balanced}

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

Copilot

🟢 Approval recommended

Only a minor test-organization convention issue remains, with no identified blocking correctness defects.

1 open issue

Add integration coverage for late Content-Type injection

1 previously missed issue

In code that hasn't changed since last review

Move standalone servlet tests to the javaagent unit-test suite

instrumentation/servlet/servlet-3.0/javaagent-unit-tests/src/test/java/io/opentelemetry/javaagent/instrumentation/servlet/v3_0/snippet/LateContentTypeTest.java:32

[Testing] This new class calls the wrapper and injection helper directly without requiring an installed agent, so its location does not follow .github/instructions/java-tests.instructions.md:22–25. Move it to the servlet-3.0 javaagent module's src/unitTests/java and register a unitTests JvmTestSuite; apply the same change to the new servlet-5.0/javaagent-unit-tests/src/test/java/io/opentelemetry/javaagent/instrumentation/servlet/v5_0/snippet/LateContentTypeTest.java:33. Existing standalone tests need not be migrated in this PR.

_{Review effort: Balanced}

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

Copilot

🟢 Approval recommended

The write-time eligibility changes are consistent across both servlet namespaces, with focused regression coverage and no unresolved blocking findings.

No open issues 🎉

1 resolved since last review

Add integration coverage for late Content-Type injection

_{Review effort: Balanced}

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

Copilot

🟢 Approval recommended

No unresolved blocking issues remain, and regression coverage addresses late content types and Content-Length adjustment in both servlet namespaces.

No open issues 🎉

_{Review effort: Balanced}

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

Copilot

🟢 Approval recommended

No unresolved defects were identified, and unit and installed-agent regression coverage addresses both servlet namespaces and output paths.

No open issues 🎉

_{Review effort: Balanced}

Initial plan

b710f68

Copilot AI assigned Copilot and trask Oct 23, 2026

Copilot started work on behalf of trask October 23, 2026 22:37

View session

opentelemetry-pr-dashboard Bot mentioned this pull request Oct 23, 2026

Pull Request Dashboard #18435

Open

Fix servlet snippet injection when content type is set after stream a…

ec581a4

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

Copilot AI changed the title ~~[WIP] Fix servlet output stream injection for content type HTML~~ Support late servlet content types for snippet injection Oct 23, 2026

Copilot finished work on behalf of trask October 23, 2026 22:49

Copilot AI requested a review from trask October 23, 2026 22:49

trask requested a balanced review from Copilot October 23, 2026 22:52

Copilot started reviewing on behalf of trask October 23, 2026 22:52

View session

Copilot AI reviewed Oct 23, 2026

View reviewed changes

Comment thread ...ntelemetry/javaagent/instrumentation/servlet/common/snippet/SnippetInjectingPrintWriter.java

trask reviewed Oct 23, 2026

View reviewed changes

Comment thread ...ntelemetry/javaagent/instrumentation/servlet/common/snippet/SnippetInjectingPrintWriter.java

Copilot started work on behalf of trask October 23, 2026 23:03

View session

Avoid repeated servlet writer type checks

c8648ff

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

Copilot finished work on behalf of trask October 23, 2026 23:10

Copilot AI requested a review from trask October 23, 2026 23:10

trask requested a balanced review from Copilot October 23, 2026 23:14

Copilot started reviewing on behalf of trask October 23, 2026 23:14

View session

Copilot AI reviewed Oct 23, 2026

View reviewed changes

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

trask reviewed Oct 23, 2026

View reviewed changes

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

Copilot started work on behalf of trask October 23, 2026 23:25

View session

Add late servlet content type integration coverage

e38e88a

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

Copilot finished work on behalf of trask October 23, 2026 23:46

Copilot AI requested a review from trask October 23, 2026 23:46

trask requested a balanced review from Copilot October 23, 2026 23:51

Copilot started reviewing on behalf of trask October 23, 2026 23:52

View session

Copilot AI reviewed Oct 23, 2026

View reviewed changes

trask reviewed Oct 24, 2026

View reviewed changes

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

Copilot started work on behalf of trask October 24, 2026 00:02

View session

Fix servlet late-type split-write coverage

dd99e69

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

Copilot finished work on behalf of trask October 24, 2026 00:23

Copilot AI requested a review from trask October 24, 2026 00:23

trask requested a balanced review from Copilot October 24, 2026 00:28

Copilot started reviewing on behalf of trask October 24, 2026 00:28

View session

Copilot AI reviewed Oct 24, 2026

View reviewed changes

trask reviewed Oct 24, 2026

View reviewed changes

Comment thread ...ava/io/opentelemetry/javaagent/instrumentation/servlet/v3_0/snippet/LateContentTypeTest.java

Copilot started work on behalf of trask October 24, 2026 03:49

View session

Simplify servlet late-type regression tests

98da8ed

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

Copilot finished work on behalf of trask October 24, 2026 04:06

Copilot AI requested a review from trask October 24, 2026 04:06

trask requested a balanced review from Copilot October 24, 2026 04:10

Copilot started reviewing on behalf of trask October 24, 2026 04:10

View session

Copilot AI reviewed Oct 24, 2026

View reviewed changes

trask reviewed Oct 24, 2026

View reviewed changes

Comment thread ...ava/io/opentelemetry/javaagent/instrumentation/servlet/v3_0/snippet/LateContentTypeTest.java

Copilot started work on behalf of trask October 24, 2026 04:16

View session

Test single-byte late servlet stream writes

5fea4aa

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

Copilot finished work on behalf of trask October 24, 2026 04:24

Copilot AI requested a review from trask October 24, 2026 04:24

trask requested a balanced review from Copilot October 24, 2026 04:27

Copilot started reviewing on behalf of trask October 24, 2026 04:28

View session

Copilot AI reviewed Oct 24, 2026

View reviewed changes

trask marked this pull request as ready for review October 24, 2026 04:34

trask requested a review from a team as a code owner October 24, 2026 04:34

trask approved these changes Oct 24, 2026

View reviewed changes

Navigation Menu

Repository navigation

Support late servlet content types for snippet injection - #20921

Support late servlet content types for snippet injection#20921
trask with Copilot wants to merge 7 commits into
mainfrom
copilot/fix-servlet-output-stream-injection

Copilot AI commented Oct 23, 2026 •

edited by trask

Loading

Uh oh!

opentelemetry-pr-dashboard Bot commented Oct 23, 2026 •

edited

Loading

Uh oh!

Copilot AI left a comment

Uh oh!

Uh oh!

Uh oh!

Copilot AI left a comment

Uh oh!

Uh oh!

Uh oh!

Copilot AI left a comment

Uh oh!

Uh oh!

Copilot AI left a comment

Uh oh!

Uh oh!

Copilot AI left a comment

Uh oh!

Uh oh!

Copilot AI left a comment

Uh oh!

This branch has not been deployed

Reviewers

Uh oh!

Assignees

Labels

Projects

Milestone

Development

Uh oh!

3 participants

Conversation

Copilot AI commented Oct 23, 2026 • edited by trask Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

Uh oh!

opentelemetry-pr-dashboard Bot commented Oct 23, 2026 • edited Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

Pull request dashboard status

Uh oh!

Copilot AI left a comment

Choose a reason for hiding this comment

🟡 Changes recommended

Uh oh!

Uh oh!

Uh oh!

Copilot AI left a comment

Choose a reason for hiding this comment

🟡 Changes recommended

Uh oh!

Uh oh!

Uh oh!

Copilot AI left a comment

Choose a reason for hiding this comment

🟢 Approval recommended

Uh oh!

Uh oh!

Copilot AI left a comment

Choose a reason for hiding this comment

🟢 Approval recommended

Uh oh!

Uh oh!

Copilot AI left a comment

Choose a reason for hiding this comment

🟢 Approval recommended

Uh oh!

Uh oh!

Copilot AI left a comment

Choose a reason for hiding this comment

🟢 Approval recommended

Uh oh!

This branch has not been deployed

Reviewers

Uh oh!

Assignees

Labels

Projects

Milestone

Development

Uh oh!

3 participants

Copilot AI commented Oct 23, 2026 •

edited by trask

Loading

opentelemetry-pr-dashboard Bot commented Oct 23, 2026 •

edited

Loading