Jena integration – add support for content negotiation

build.sbt

@@ -23,7 +23,7 @@ sonatypeRepository := "https://s01.oss.sonatype.org/service/local"
 
 lazy val pekkoV = "1.1.2"
 lazy val pekkoGrpcV = "1.1.0"
-lazy val jenaV = "5.1.0"
+lazy val jenaV = "5.2.0"
 lazy val rdf4jV = "5.0.2"
 // !! When updating ScalaPB also change the version of the plugin in plugins.sbt
 lazy val scalapbV = "0.11.17"
@@ -104,6 +104,8 @@ lazy val jena = (project in file("jena"))
     libraryDependencies ++= Seq(
       "org.apache.jena" % "jena-core" % jenaV,
       "org.apache.jena" % "jena-arq" % jenaV,
+      // Integration with Fuseki is optional, so include this dep as "provided"
+      "org.apache.jena" % "jena-fuseki-main" % jenaV % "provided,test",
     ),
     commonSettings,
   )
@@ -120,6 +122,7 @@ lazy val jenaPlugin = (project in file("jena-plugin"))
       // Use the "provided" scope to not include the Jena dependencies in the plugin JAR
       "org.apache.jena" % "jena-core" % jenaV % "provided,test",
       "org.apache.jena" % "jena-arq" % jenaV % "provided,test",
+      "org.apache.jena" % "jena-fuseki-main" % jenaV % "provided,test",
     ),
     // Do not publish this to Maven – we will separately do sbt assembly and publish to GitHub
     publishArtifact := false,

docs/docs/getting-started-plugins.md

@@ -22,9 +22,11 @@ You can simply add Jelly format support to [Apache Jena](https://jena.apache.org
 
 !!! bug "Content negotiation in Fuseki"
 
-    Currently Apache Jena Fuseki will not properly handle content negotiation for the Jelly format, due to the supported content types being hardcoded in Fuseki (see [upstream issue](https://github.com/apache/jena/issues/2700)).
+    Content negotiation using the `application/x-jelly-rdf` media type in the `Accept` header works in Fuseki "Main" distribution since version 5.2.0. To get it working, you need to run Fuseki with the `--modules=true` command-line option. Content negotiation does not work in the "webapp" distribution with UI due to an [upstream bug](https://github.com/apache/jena/issues/2774).
+
+    In Fuseki 5.1.0 and older, content negotiation with Jelly does not work at all.
 
-    Until that is fixed, you can use Jelly with Fuseki endpoints by specifying the `output=application/x-jelly-rdf` parameter (either in the URL or in the URL-encoded form body) when querying the endpoint.
+    To work around these issues, you can specify the `output=application/x-jelly-rdf` parameter (either in the URL or in the URL-encoded form body) when querying the endpoint.
 
 
 ### Eclipse RDF4J

jena/src/main/resources/META-INF/services/org.apache.jena.fuseki.main.sys.FusekiAutoModule

@@ -0,0 +1 @@
+eu.ostrzyciel.jelly.convert.jena.fuseki.JellyFusekiModule

jena/src/main/scala/eu/ostrzyciel/jelly/convert/jena/JenaProtoEncoder.scala

@@ -2,9 +2,7 @@ package eu.ostrzyciel.jelly.convert.jena
 
 import eu.ostrzyciel.jelly.core.*
 import eu.ostrzyciel.jelly.core.proto.v1.{GraphTerm, RdfStreamOptions, SpoTerm}
-import org.apache.jena.JenaRuntime
 import org.apache.jena.datatypes.xsd.XSDDatatype
-import org.apache.jena.datatypes.xsd.impl.RDFLangString
 import org.apache.jena.graph.*
 import org.apache.jena.sparql.core.Quad
 

jena/src/main/scala/eu/ostrzyciel/jelly/convert/jena/fuseki/JellyFusekiModule.scala

@@ -0,0 +1,56 @@
+package eu.ostrzyciel.jelly.convert.jena.fuseki
+
+import eu.ostrzyciel.jelly.core.Constants
+import org.apache.jena.atlas.web.{AcceptList, MediaRange}
+import org.apache.jena.fuseki.{DEF, Fuseki}
+import org.apache.jena.fuseki.main.FusekiServer
+import org.apache.jena.fuseki.main.sys.FusekiAutoModule
+import org.apache.jena.rdf.model.Model
+import org.apache.jena.riot.WebContent
+
+import java.util
+
+object JellyFusekiModule:
+  val mediaRangeJelly: MediaRange = new MediaRange(Constants.jellyContentType)
+
+/**
+ * A Fuseki module that adds Jelly content type to the list of accepted content types.
+ *
+ * This allows users to use the Accept header set to application/x-jelly-rdf to request Jelly RDF responses.
+ * It works for SPARQL CONSTRUCT queries and for the Graph Store Protocol.
+ *
+ * More info on Fuseki modules: https://jena.apache.org/documentation/fuseki2/fuseki-modules.html
+ */
+final class JellyFusekiModule extends FusekiAutoModule:
+  import JellyFusekiModule.*
+
+  override def name(): String = "Jelly"
+
+  override def start(): Unit =
+    try {
+      maybeAddJellyToList(DEF.constructOffer).foreach(offer => DEF.constructOffer = offer)
+      maybeAddJellyToList(DEF.rdfOffer).foreach(offer => DEF.rdfOffer = offer)
+      maybeAddJellyToList(DEF.quadsOffer).foreach(offer => {
+        DEF.quadsOffer = offer
+        Fuseki.serverLog.info(s"Added ${Constants.jellyContentType} to the list of accepted content types")
+      })
+    } catch {
+      case e: IllegalAccessError => Fuseki.serverLog.warn(
+        s"Cannot register the ${Constants.jellyContentType} content type, because you are running an Apache Jena " +
+          s"Fuseki version that doesn't support content type registration. " +
+          s"Update to Fuseki 5.2.0 or newer for this to work."
+      )
+    }
+
+  /**
+   * Adds the Jelly content type to the list of accepted content types if it is not already present.
+   * @param list current list of accepted content types
+   * @return none or a new list with Jelly content type
+   */
+  private def maybeAddJellyToList(list: AcceptList): Option[AcceptList] =
+    if list.entries().contains(mediaRangeJelly) then
+      None
+    else
+      val newList = new util.Vector[MediaRange](list.entries())
+      newList.add(mediaRangeJelly)
+      Some(new AcceptList(newList))

jena/src/test/scala/eu/ostrzyciel/jelly/convert/jena/fuseki/JellyFusekiModuleSpec.scala

@@ -0,0 +1,47 @@
+package eu.ostrzyciel.jelly.convert.jena.fuseki
+
+import org.apache.jena.fuseki.DEF
+import org.scalatest.matchers.should.Matchers
+import org.scalatest.wordspec.AnyWordSpec
+
+import scala.jdk.CollectionConverters.*
+
+class JellyFusekiModuleSpec extends AnyWordSpec, Matchers:
+  "JellyFusekiModule" should {
+    "have a name" in {
+      JellyFusekiModule().name() should be ("Jelly")
+    }
+
+    "use the correct content type for Jelly" in {
+      JellyFusekiModule.mediaRangeJelly.getContentTypeStr should be ("application/x-jelly-rdf")
+    }
+
+    "register the Jelly content type in the lists of accepted content types" in {
+      val oldLists = List(DEF.constructOffer, DEF.rdfOffer, DEF.quadsOffer)
+      for list <- oldLists do
+        list.entries().asScala should not contain JellyFusekiModule.mediaRangeJelly
+      DEF.constructOffer.entries().asScala should not contain JellyFusekiModule.mediaRangeJelly
+      DEF.rdfOffer.entries().asScala should not contain JellyFusekiModule.mediaRangeJelly
+      DEF.quadsOffer.entries().asScala should not contain JellyFusekiModule.mediaRangeJelly
+
+      val module = JellyFusekiModule()
+      module.start()
+
+      val lists = List(DEF.constructOffer, DEF.rdfOffer, DEF.quadsOffer)
+      for (list, oldList) <- lists.zip(oldLists) do
+        list.entries().asScala should contain (JellyFusekiModule.mediaRangeJelly)
+        list.entries().size() should be (oldList.entries().size() + 1)
+    }
+
+    "not register the Jelly content type if it's already registered" in {
+      val module = JellyFusekiModule()
+      module.start()
+      DEF.rdfOffer.entries().asScala should contain (JellyFusekiModule.mediaRangeJelly)
+      val size1 = DEF.rdfOffer.entries().size()
+
+      module.start()
+      DEF.rdfOffer.entries().asScala should contain (JellyFusekiModule.mediaRangeJelly)
+      val size2 = DEF.rdfOffer.entries().size()
+      size2 should be (size1)
+    }
+  }