Allow for a Jelly stream that starts with empty frames

src/main/scala/eu/neverblink/jelly/cli/command/rdf/RdfValidate.scala

@@ -14,6 +14,7 @@ import org.apache.jena.riot.RDFParser
 import org.apache.jena.riot.system.StreamRDFLib
 import org.apache.jena.sparql.core.Quad
 
+import scala.annotation.tailrec
 import scala.util.Using
 
 object RdfValidatePrint extends RdfCommandPrintUtil[RdfFormat.Jena]:
@@ -91,7 +92,7 @@ object RdfValidate extends JellyCommand[RdfValidateOptions]:
     // Step 1: Validate delimiting
     validateDelimiting(delimiting, delimited)
     // Step 2: Validate basic stream structure & the stream options
-    val framesSeq = frameIterator.toSeq
+    val framesSeq = skipEmptyFrames(frameIterator.toSeq)
     validateOptions(framesSeq)
     // Step 3: Validate the content
     validateContent(framesSeq, frameIndices, rdfComparison)
@@ -109,10 +110,6 @@ object RdfValidate extends JellyCommand[RdfValidateOptions]:
         throw CriticalException("Expected undelimited input, but the file was delimited")
 
   private def validateOptions(frames: Seq[RdfStreamFrame]): Unit =
-    // Validate basic stream structure
-    if frames.isEmpty then throw CriticalException("Empty input stream")
-    if frames.head.rows.isEmpty then
-      throw CriticalException("First frame in the input stream is empty")
     if !frames.head.rows.head.row.isOptions then
       throw CriticalException("First row in the input stream does not contain stream options")
     val streamOptions = frames.head.rows.head.row.options
@@ -192,6 +189,24 @@ object RdfValidate extends JellyCommand[RdfValidateOptions]:
       comparator.compare(rdfComparison, actual)
     }
 
+  /** Skip empty frames in the stream. If the first frame is empty, we skip it and continue with the
+    * next one. If the first row is empty, we throw an exception
+    * @param frames
+    *   frames to check
+    * @return
+    *   frames after empty frames
+    */
+  @tailrec
+  private def skipEmptyFrames(
+      frames: Seq[RdfStreamFrame],
+  ): Seq[RdfStreamFrame] =
+    if frames.isEmpty then throw CriticalException("Empty input stream")
+    else if frames.head.rows.isEmpty then
+      // We want to accept empty frames in the stream, but not empty streams
+      if frames.tail.isEmpty then throw CriticalException("All frames are empty")
+      skipEmptyFrames(frames.tail)
+    else frames
+
   /** Reads the RDF file for comparison and returns a StreamRdfCollector
     * @param fileName
     *   filename to read

src/test/scala/eu/neverblink/jelly/cli/command/helpers/TestFixtureHelper.scala

@@ -10,7 +10,7 @@ import org.scalatest.BeforeAndAfterAll
 import org.scalatest.wordspec.AnyWordSpec
 
 import java.io.FileOutputStream
-import java.nio.file.{Files, Path}
+import java.nio.file.{Files, Path, Paths}
 import java.util.UUID.randomUUID
 import scala.util.Using
 
@@ -24,6 +24,7 @@ trait TestFixtureHelper extends BeforeAndAfterAll:
     CliRiot.initialize()
   }
 
+  private val specificTestDir: Path = Paths.get("src", "test", "resources")
   private val tmpDir: Path = Files.createTempDirectory("jelly-cli")
 
   /** The number of triples to generate for the tests
@@ -85,6 +86,16 @@ trait TestFixtureHelper extends BeforeAndAfterAll:
       testCode(tempFile.toString)
     } finally { tempFile.toFile.delete() }
 
+  def withSpecificJellyFile(
+      testCode: (String) => Any,
+      fileName: String,
+  ): Unit = {
+    val filePath = specificTestDir.resolve(fileName)
+    if !Files.exists(filePath) then
+      throw new IllegalArgumentException(s"File $fileName does not exist in $specificTestDir")
+    else testCode(filePath.toString)
+  }
+
   def withFullJellyFile(testCode: (String) => Any, frameSize: Int = 256): Unit =
     val extension = getFileExtension(JellyLanguage.JELLY)
     val tempFile = Files.createTempFile(tmpDir, randomUUID.toString, f".${extension}")

src/test/scala/eu/neverblink/jelly/cli/command/rdf/RdfValidateSpec.scala

@@ -23,9 +23,25 @@ class RdfValidateSpec extends AnyWordSpec, Matchers, TestFixtureHelper:
         RdfValidate.runTestCommand(List("rdf", "validate"))
       }
       e.cause.get shouldBe a[CriticalException]
-      e.cause.get.getMessage should include("First frame in the input stream is empty")
+      e.cause.get.getMessage should include("All frames are empty")
     }
 
+    "accept empty frame before stream options" in withSpecificJellyFile(
+      testCode = { jellyF =>
+        val (out, err) = RdfValidate.runTestCommand(List("rdf", "validate", jellyF))
+        out shouldBe empty
+      },
+      fileName = "firstEmptyFrame.jelly",
+    )
+
+    "accept three first empty frames" in withSpecificJellyFile(
+      testCode = { jellyF =>
+        val (out, err) = RdfValidate.runTestCommand(List("rdf", "validate", jellyF))
+        out shouldBe empty
+      },
+      fileName = "threeFirstEmptyFrames.jelly",
+    )
+
     "validate delimiting" when {
       val frame = RdfStreamFrame(
         Seq(