feat(ktor-server): skip internal ContentNegotiation install when already configured#2174
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samuelAndalon merged 2 commits intoMay 18, 2026
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…ady configured When the host application has already installed ContentNegotiation at the application level — a common pattern when the app serves other JSON endpoints or uses StatusPages with JSON error responses — the existing unconditional route-scoped install in graphQLGetRoute and graphQLPostRoute caused Ktor to throw DuplicatePluginException. The install is now guarded by application.pluginOrNull(ContentNegotiation): if the plugin is present at the application level, the route-scoped install is skipped and the existing configuration is reused. When no global install exists, behaviour is unchanged. Added regression tests for both route helpers. Fixes ExpediaGroup#2025
samuelAndalon
approved these changes
May 18, 2026
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📝 Description
Route.graphQLGetRoute()andRoute.graphQLPostRoute()unconditionally installContentNegotiationon the route scope. When the host application has already installedContentNegotiationat the application level — a common pattern when the app serves other JSON endpoints or usesStatusPageswith JSON error responses — Ktor throwsDuplicatePluginException:This PR makes the internal install conditional on
application.pluginOrNull(ContentNegotiation):ContentNegotiationis already installed at the application level, the route-scoped install is skipped and the existing global configuration is reused.streamingResponseandjacksonConfiguration.When the global install wins,
streamingResponseandjacksonConfigurationare not applied, since the application-level configuration takes precedence; this trade-off is documented in the KDoc for both routes.No API change; fully backward compatible.
Added two regression tests in
GraphQLPluginTestcovering the globally-installed case for both the GET and POST routes.🔗 Related Issues
Fixes #2025