Add ability to emit plain data messages in SSE by 1cg · Pull Request #2578 · javalin/javalin

1cg · 2026-04-07T23:22:04Z

This PR makes it possible to emit plain data SSE messages:

  client.sendData("Hello World");

See https://developer.mozilla.org/en-US/docs/Web/API/Server-sent_events/Using_server-sent_events#examples for more info on this.

This is useful for libraries like htmx where raw data messages are used to transmit HTML to the client.

…essages.

tipsy · 2026-04-15T19:40:30Z

augment review

augmentcode · 2026-04-15T19:43:20Z

🤖 Augment PR Summary

Summary: Adds support for emitting “plain data” Server-Sent Events (SSE) messages (no explicit event: field), which browsers surface as the default message event.

Changes:

Allow Emitter.emit to accept a nullable event name and omit the event: line when absent
Add SseClient.sendData(...) to send data-only SSE messages (optionally with an id)
Refactor shared emission logic into a private helper in SseClient
Add test coverage for plain data (string/json/input stream, with/without id, multiline)

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codecov · 2026-04-15T19:59:21Z

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 86.30%. Comparing base (152f7b3) to head (71805ca).
⚠️ Report is 4 commits behind head on master.

Additional details and impacted files

@@             Coverage Diff              @@
##             master    #2578      +/-   ##
============================================
+ Coverage     86.27%   86.30%   +0.02%     
- Complexity     1539     1542       +3     
============================================
  Files           157      157              
  Lines          4437     4439       +2     
  Branches        539      540       +1     
============================================
+ Hits           3828     3831       +3     
  Misses          374      374              
+ Partials        235      234       -1

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tipsy · 2026-04-15T19:59:29Z

Thanks @1cg !

Bumps `javalin.version` from 7.1.0 to 7.2.0. Updates `io.javalin:javalin-bundle` from 7.1.0 to 7.2.0 Release notes *Sourced from [io.javalin:javalin-bundle's releases](https://github.com/javalin/javalin/releases).* > 7.2.0 > ----- > > What's Changed > -------------- > > * [performance] Replace Stream API with List and reduce per-request allocations by [`@tipsy`](https://github.com/tipsy) in [javalin/javalin#2567](https://redirect.github.com/javalin/javalin/pull/2567) > * feat: introduce `JavalinJackson3` as an optional `JsonMapper` implementation for Jackson 3 by [`@yvasyliev`](https://github.com/yvasyliev) in [javalin/javalin#2548](https://redirect.github.com/javalin/javalin/pull/2548) > * [workflow]: Bump codecov/codecov-action from 5.5.2 to 5.5.3 in the dependencies group by [`@dependabot`](https://github.com/dependabot)[bot] in [javalin/javalin#2569](https://redirect.github.com/javalin/javalin/pull/2569) > * Add path role inheritance by [`@AoElite`](https://github.com/AoElite) in [javalin/javalin#2553](https://redirect.github.com/javalin/javalin/pull/2553) > * [deps]: Bump the dependencies group across 1 directory with 23 updates by [`@dependabot`](https://github.com/dependabot)[bot] in [javalin/javalin#2575](https://redirect.github.com/javalin/javalin/pull/2575) > * [workflow]: Bump codecov/codecov-action from 5.5.3 to 6.0.0 in the dependencies group across 1 directory by [`@dependabot`](https://github.com/dependabot)[bot] in [javalin/javalin#2570](https://redirect.github.com/javalin/javalin/pull/2570) > * [workflow]: Bump actions/github-script from 8 to 9 in the dependencies group by [`@dependabot`](https://github.com/dependabot)[bot] in [javalin/javalin#2581](https://redirect.github.com/javalin/javalin/pull/2581) > * [cleanup] Remove JavalinTest.class by [`@vorburger`](https://github.com/vorburger) in [javalin/javalin#2584](https://redirect.github.com/javalin/javalin/pull/2584) > * [deps] Bump Jetty from 12.1.7 to 12.1.8 by [`@vorburger`](https://github.com/vorburger) in [javalin/javalin#2585](https://redirect.github.com/javalin/javalin/pull/2585) > * Add ability to emit plain data messages in SSE by [`@1cg`](https://github.com/1cg) in [javalin/javalin#2578](https://redirect.github.com/javalin/javalin/pull/2578) > * fix: sanitize newlines in SSE event and id fields by [`@eddieran`](https://github.com/eddieran) in [javalin/javalin#2580](https://redirect.github.com/javalin/javalin/pull/2580) > * [deps] Bump stable deps and sync OptionalDependency.kt by [`@tipsy`](https://github.com/tipsy) in [javalin/javalin#2588](https://redirect.github.com/javalin/javalin/pull/2588) > > New Contributors > ---------------- > > * [`@AoElite`](https://github.com/AoElite) made their first contribution in [javalin/javalin#2553](https://redirect.github.com/javalin/javalin/pull/2553) > * [`@vorburger`](https://github.com/vorburger) made their first contribution in [javalin/javalin#2584](https://redirect.github.com/javalin/javalin/pull/2584) > * [`@1cg`](https://github.com/1cg) made their first contribution in [javalin/javalin#2578](https://redirect.github.com/javalin/javalin/pull/2578) > * [`@eddieran`](https://github.com/eddieran) made their first contribution in [javalin/javalin#2580](https://redirect.github.com/javalin/javalin/pull/2580) > > **Full Changelog**: <javalin/javalin@javalin-parent-7.1.0...javalin-parent-7.2.0> Commits * [`c67b118`](javalin/javalin@c67b118) [maven-release-plugin] prepare release javalin-parent-7.2.0 * [`b89fdf7`](javalin/javalin@b89fdf7) [deps] Bump stable deps and sync OptionalDependency.kt ([#2588](https://redirect.github.com/javalin/javalin/issues/2588)) * [`a3ad657`](javalin/javalin@a3ad657) [sse] Sanitize newlines in event and id fields * [`e0f5458`](javalin/javalin@e0f5458) [sse] Add ability to emit plain data messages * [`fa51869`](javalin/javalin@fa51869) [deps] Bump Jetty from 12.1.7 to 12.1.8 ([#2585](https://redirect.github.com/javalin/javalin/issues/2585)) * [`4bc70e9`](javalin/javalin@4bc70e9) [cleanup] Remove JavalinTest.class ([#2584](https://redirect.github.com/javalin/javalin/issues/2584)) * [`1901feb`](javalin/javalin@1901feb) [workflow]: Bump actions/github-script in the dependencies group ([#2581](https://redirect.github.com/javalin/javalin/issues/2581)) * [`152f7b3`](javalin/javalin@152f7b3) [workflow]: Bump codecov/codecov-action in the dependencies group ([#2570](https://redirect.github.com/javalin/javalin/issues/2570)) * [`2c4d1ef`](javalin/javalin@2c4d1ef) [deps]: Bump the dependencies group across 1 directory with 23 updates ([#2575](https://redirect.github.com/javalin/javalin/issues/2575)) * [`64f3a75`](javalin/javalin@64f3a75) [apibuilder] Refactor role-scoping internals to Kotlin * Additional commits viewable in [compare view](javalin/javalin@7.1.0...javalin-parent-7.2.0) Updates `io.javalin.community.openapi:javalin-openapi-plugin` from 7.1.0 to 7.2.0 Release notes *Sourced from [io.javalin.community.openapi:javalin-openapi-plugin's releases](https://github.com/javalin/javalin-openapi/releases).* > 7.2.0 > ----- > > **Changes** > > * Bumped Javalin to 7.2.0 > > **Sponsors** > Thanks to everyone who supported me this month 💜 > > **Minimal requirements** > > * Java 17+ / Kotlin 2.3+ > * Javalin 7.2.0 > > 7.1.1-rc.1 > ---------- > > **Changes** > > * [javalin/javalin-openapi#275](https://redirect.github.com/javalin/javalin-openapi/issues/275) [Make ClassLoader used for loading resources configurable](javalin/javalin-openapi@de1b6b7) > > **Sponsors** > Thanks to everyone who supported me this month 💜 ... (truncated) Commits * [`123e727`](javalin/javalin-openapi@123e727) [GH-279](https://redirect.github.com/javalin/javalin-openapi/issues/279) Adjust to Javalin's breaking changed in InternalRouter * [`3ea0e98`](javalin/javalin-openapi@3ea0e98) [GH-279](https://redirect.github.com/javalin/javalin-openapi/issues/279) Release 7.2.0 (Resolves [#279](https://redirect.github.com/javalin/javalin-openapi/issues/279)) * [`0471f8a`](javalin/javalin-openapi@0471f8a) [GH-277](https://redirect.github.com/javalin/javalin-openapi/issues/277) Release 7.1.1-rc.2 * [`3831f78`](javalin/javalin-openapi@3831f78) [GH-277](https://redirect.github.com/javalin/javalin-openapi/issues/277) Cover handling of complex types in query parameters (Resolves [#277](https://redirect.github.com/javalin/javalin-openapi/issues/277)) * See full diff in [compare view](javalin/javalin-openapi@7.1.0...7.2.0) Updates `io.javalin.community.openapi:javalin-swagger-plugin` from 7.1.0 to 7.2.0 Release notes *Sourced from [io.javalin.community.openapi:javalin-swagger-plugin's releases](https://github.com/javalin/javalin-openapi/releases).* > 7.2.0 > ----- > > **Changes** > > * Bumped Javalin to 7.2.0 > > **Sponsors** > Thanks to everyone who supported me this month 💜 > > **Minimal requirements** > > * Java 17+ / Kotlin 2.3+ > * Javalin 7.2.0 > > 7.1.1-rc.1 > ---------- > > **Changes** > > * [javalin/javalin-openapi#275](https://redirect.github.com/javalin/javalin-openapi/issues/275) [Make ClassLoader used for loading resources configurable](javalin/javalin-openapi@de1b6b7) > > **Sponsors** > Thanks to everyone who supported me this month 💜 ... (truncated) Commits * [`123e727`](javalin/javalin-openapi@123e727) [GH-279](https://redirect.github.com/javalin/javalin-openapi/issues/279) Adjust to Javalin's breaking changed in InternalRouter * [`3ea0e98`](javalin/javalin-openapi@3ea0e98) [GH-279](https://redirect.github.com/javalin/javalin-openapi/issues/279) Release 7.2.0 (Resolves [#279](https://redirect.github.com/javalin/javalin-openapi/issues/279)) * [`0471f8a`](javalin/javalin-openapi@0471f8a) [GH-277](https://redirect.github.com/javalin/javalin-openapi/issues/277) Release 7.1.1-rc.2 * [`3831f78`](javalin/javalin-openapi@3831f78) [GH-277](https://redirect.github.com/javalin/javalin-openapi/issues/277) Cover handling of complex types in query parameters (Resolves [#277](https://redirect.github.com/javalin/javalin-openapi/issues/277)) * See full diff in [compare view](javalin/javalin-openapi@7.1.0...7.2.0) Updates `io.javalin:javalin-micrometer` from 7.1.0 to 7.2.0 Release notes *Sourced from [io.javalin:javalin-micrometer's releases](https://github.com/javalin/javalin/releases).* > 7.2.0 > ----- > > What's Changed > -------------- > > * [performance] Replace Stream API with List and reduce per-request allocations by [`@tipsy`](https://github.com/tipsy) in [javalin/javalin#2567](https://redirect.github.com/javalin/javalin/pull/2567) > * feat: introduce `JavalinJackson3` as an optional `JsonMapper` implementation for Jackson 3 by [`@yvasyliev`](https://github.com/yvasyliev) in [javalin/javalin#2548](https://redirect.github.com/javalin/javalin/pull/2548) > * [workflow]: Bump codecov/codecov-action from 5.5.2 to 5.5.3 in the dependencies group by [`@dependabot`](https://github.com/dependabot)[bot] in [javalin/javalin#2569](https://redirect.github.com/javalin/javalin/pull/2569) > * Add path role inheritance by [`@AoElite`](https://github.com/AoElite) in [javalin/javalin#2553](https://redirect.github.com/javalin/javalin/pull/2553) > * [deps]: Bump the dependencies group across 1 directory with 23 updates by [`@dependabot`](https://github.com/dependabot)[bot] in [javalin/javalin#2575](https://redirect.github.com/javalin/javalin/pull/2575) > * [workflow]: Bump codecov/codecov-action from 5.5.3 to 6.0.0 in the dependencies group across 1 directory by [`@dependabot`](https://github.com/dependabot)[bot] in [javalin/javalin#2570](https://redirect.github.com/javalin/javalin/pull/2570) > * [workflow]: Bump actions/github-script from 8 to 9 in the dependencies group by [`@dependabot`](https://github.com/dependabot)[bot] in [javalin/javalin#2581](https://redirect.github.com/javalin/javalin/pull/2581) > * [cleanup] Remove JavalinTest.class by [`@vorburger`](https://github.com/vorburger) in [javalin/javalin#2584](https://redirect.github.com/javalin/javalin/pull/2584) > * [deps] Bump Jetty from 12.1.7 to 12.1.8 by [`@vorburger`](https://github.com/vorburger) in [javalin/javalin#2585](https://redirect.github.com/javalin/javalin/pull/2585) > * Add ability to emit plain data messages in SSE by [`@1cg`](https://github.com/1cg) in [javalin/javalin#2578](https://redirect.github.com/javalin/javalin/pull/2578) > * fix: sanitize newlines in SSE event and id fields by [`@eddieran`](https://github.com/eddieran) in [javalin/javalin#2580](https://redirect.github.com/javalin/javalin/pull/2580) > * [deps] Bump stable deps and sync OptionalDependency.kt by [`@tipsy`](https://github.com/tipsy) in [javalin/javalin#2588](https://redirect.github.com/javalin/javalin/pull/2588) > > New Contributors > ---------------- > > * [`@AoElite`](https://github.com/AoElite) made their first contribution in [javalin/javalin#2553](https://redirect.github.com/javalin/javalin/pull/2553) > * [`@vorburger`](https://github.com/vorburger) made their first contribution in [javalin/javalin#2584](https://redirect.github.com/javalin/javalin/pull/2584) > * [`@1cg`](https://github.com/1cg) made their first contribution in [javalin/javalin#2578](https://redirect.github.com/javalin/javalin/pull/2578) > * [`@eddieran`](https://github.com/eddieran) made their first contribution in [javalin/javalin#2580](https://redirect.github.com/javalin/javalin/pull/2580) > > **Full Changelog**: <javalin/javalin@javalin-parent-7.1.0...javalin-parent-7.2.0> Commits * [`c67b118`](javalin/javalin@c67b118) [maven-release-plugin] prepare release javalin-parent-7.2.0 * [`b89fdf7`](javalin/javalin@b89fdf7) [deps] Bump stable deps and sync OptionalDependency.kt ([#2588](https://redirect.github.com/javalin/javalin/issues/2588)) * [`a3ad657`](javalin/javalin@a3ad657) [sse] Sanitize newlines in event and id fields * [`e0f5458`](javalin/javalin@e0f5458) [sse] Add ability to emit plain data messages * [`fa51869`](javalin/javalin@fa51869) [deps] Bump Jetty from 12.1.7 to 12.1.8 ([#2585](https://redirect.github.com/javalin/javalin/issues/2585)) * [`4bc70e9`](javalin/javalin@4bc70e9) [cleanup] Remove JavalinTest.class ([#2584](https://redirect.github.com/javalin/javalin/issues/2584)) * [`1901feb`](javalin/javalin@1901feb) [workflow]: Bump actions/github-script in the dependencies group ([#2581](https://redirect.github.com/javalin/javalin/issues/2581)) * [`152f7b3`](javalin/javalin@152f7b3) [workflow]: Bump codecov/codecov-action in the dependencies group ([#2570](https://redirect.github.com/javalin/javalin/issues/2570)) * [`2c4d1ef`](javalin/javalin@2c4d1ef) [deps]: Bump the dependencies group across 1 directory with 23 updates ([#2575](https://redirect.github.com/javalin/javalin/issues/2575)) * [`64f3a75`](javalin/javalin@64f3a75) [apibuilder] Refactor role-scoping internals to Kotlin * Additional commits viewable in [compare view](javalin/javalin@7.1.0...javalin-parent-7.2.0) Updates `io.javalin:javalin-testtools` from 7.1.0 to 7.2.0 Release notes *Sourced from [io.javalin:javalin-testtools's releases](https://github.com/javalin/javalin/releases).* > 7.2.0 > ----- > > What's Changed > -------------- > > * [performance] Replace Stream API with List and reduce per-request allocations by [`@tipsy`](https://github.com/tipsy) in [javalin/javalin#2567](https://redirect.github.com/javalin/javalin/pull/2567) > * feat: introduce `JavalinJackson3` as an optional `JsonMapper` implementation for Jackson 3 by [`@yvasyliev`](https://github.com/yvasyliev) in [javalin/javalin#2548](https://redirect.github.com/javalin/javalin/pull/2548) > * [workflow]: Bump codecov/codecov-action from 5.5.2 to 5.5.3 in the dependencies group by [`@dependabot`](https://github.com/dependabot)[bot] in [javalin/javalin#2569](https://redirect.github.com/javalin/javalin/pull/2569) > * Add path role inheritance by [`@AoElite`](https://github.com/AoElite) in [javalin/javalin#2553](https://redirect.github.com/javalin/javalin/pull/2553) > * [deps]: Bump the dependencies group across 1 directory with 23 updates by [`@dependabot`](https://github.com/dependabot)[bot] in [javalin/javalin#2575](https://redirect.github.com/javalin/javalin/pull/2575) > * [workflow]: Bump codecov/codecov-action from 5.5.3 to 6.0.0 in the dependencies group across 1 directory by [`@dependabot`](https://github.com/dependabot)[bot] in [javalin/javalin#2570](https://redirect.github.com/javalin/javalin/pull/2570) > * [workflow]: Bump actions/github-script from 8 to 9 in the dependencies group by [`@dependabot`](https://github.com/dependabot)[bot] in [javalin/javalin#2581](https://redirect.github.com/javalin/javalin/pull/2581) > * [cleanup] Remove JavalinTest.class by [`@vorburger`](https://github.com/vorburger) in [javalin/javalin#2584](https://redirect.github.com/javalin/javalin/pull/2584) > * [deps] Bump Jetty from 12.1.7 to 12.1.8 by [`@vorburger`](https://github.com/vorburger) in [javalin/javalin#2585](https://redirect.github.com/javalin/javalin/pull/2585) > * Add ability to emit plain data messages in SSE by [`@1cg`](https://github.com/1cg) in [javalin/javalin#2578](https://redirect.github.com/javalin/javalin/pull/2578) > * fix: sanitize newlines in SSE event and id fields by [`@eddieran`](https://github.com/eddieran) in [javalin/javalin#2580](https://redirect.github.com/javalin/javalin/pull/2580) > * [deps] Bump stable deps and sync OptionalDependency.kt by [`@tipsy`](https://github.com/tipsy) in [javalin/javalin#2588](https://redirect.github.com/javalin/javalin/pull/2588) > > New Contributors > ---------------- > > * [`@AoElite`](https://github.com/AoElite) made their first contribution in [javalin/javalin#2553](https://redirect.github.com/javalin/javalin/pull/2553) > * [`@vorburger`](https://github.com/vorburger) made their first contribution in [javalin/javalin#2584](https://redirect.github.com/javalin/javalin/pull/2584) > * [`@1cg`](https://github.com/1cg) made their first contribution in [javalin/javalin#2578](https://redirect.github.com/javalin/javalin/pull/2578) > * [`@eddieran`](https://github.com/eddieran) made their first contribution in [javalin/javalin#2580](https://redirect.github.com/javalin/javalin/pull/2580) > > **Full Changelog**: <javalin/javalin@javalin-parent-7.1.0...javalin-parent-7.2.0> Commits * [`c67b118`](javalin/javalin@c67b118) [maven-release-plugin] prepare release javalin-parent-7.2.0 * [`b89fdf7`](javalin/javalin@b89fdf7) [deps] Bump stable deps and sync OptionalDependency.kt ([#2588](https://redirect.github.com/javalin/javalin/issues/2588)) * [`a3ad657`](javalin/javalin@a3ad657) [sse] Sanitize newlines in event and id fields * [`e0f5458`](javalin/javalin@e0f5458) [sse] Add ability to emit plain data messages * [`fa51869`](javalin/javalin@fa51869) [deps] Bump Jetty from 12.1.7 to 12.1.8 ([#2585](https://redirect.github.com/javalin/javalin/issues/2585)) * [`4bc70e9`](javalin/javalin@4bc70e9) [cleanup] Remove JavalinTest.class ([#2584](https://redirect.github.com/javalin/javalin/issues/2584)) * [`1901feb`](javalin/javalin@1901feb) [workflow]: Bump actions/github-script in the dependencies group ([#2581](https://redirect.github.com/javalin/javalin/issues/2581)) * [`152f7b3`](javalin/javalin@152f7b3) [workflow]: Bump codecov/codecov-action in the dependencies group ([#2570](https://redirect.github.com/javalin/javalin/issues/2570)) * [`2c4d1ef`](javalin/javalin@2c4d1ef) [deps]: Bump the dependencies group across 1 directory with 23 updates ([#2575](https://redirect.github.com/javalin/javalin/issues/2575)) * [`64f3a75`](javalin/javalin@64f3a75) [apibuilder] Refactor role-scoping internals to Kotlin * Additional commits viewable in [compare view](javalin/javalin@7.1.0...javalin-parent-7.2.0)

Add ability to emit plain data messages in SSE in addition to named m…

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tipsy merged commit e0f5458 into javalin:master Apr 15, 2026
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Add ability to emit plain data messages in SSE #2578

Add ability to emit plain data messages in SSE #2578
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