chore(model): Reject reading multiple YAML documents per file

Resolves #6873.

Signed-off-by: Sebastian Schuberth <sebastian@doubleopen.org>

model/src/main/kotlin/FileFormat.kt

@@ -22,9 +22,10 @@ package org.ossreviewtoolkit.model
 import com.fasterxml.jackson.databind.JsonNode
 import com.fasterxml.jackson.databind.ObjectMapper
 import com.fasterxml.jackson.module.kotlin.convertValue
-import com.fasterxml.jackson.module.kotlin.readValue
+import com.fasterxml.jackson.module.kotlin.readValues
 
 import java.io.File
+import java.io.IOException
 
 import org.ossreviewtoolkit.utils.common.safeMkdirs
 
@@ -94,9 +95,20 @@ fun File.mapper() = FileFormat.forFile(this).mapper
 fun File.readTree(): JsonNode = mapper().readTree(this)
 
 /**
- * Use the Jackson mapper returned from [File.mapper] to read an object of type [T] from this file.
+ * Use the Jackson mapper returned from [File.mapper] to read a single object of type [T] from this file. Throw an
+ * [IOException] if not exactly one value is contained in the file, e.g. in case of multiple YAML documents per file.
  */
-inline fun <reified T : Any> File.readValue(): T = mapper().readValue(this)
+inline fun <reified T : Any> File.readValue(): T {
+    val mapper = mapper()
+    val parser = mapper.factory.createParser(this)
+
+    val values = mapper.readValues<T>(parser).readAll().also {
+        if (it.isEmpty()) throw IOException("No object found in file '$this'.")
+        if (it.size > 1) throw IOException("Multiple top-level objects found in file '$this'.")
+    }
+
+    return values.first()
+}
 
 /**
  * Use the Jackson mapper returned from [File.mapper] to read an object of type [T] from this file, or return null if

model/src/test/kotlin/FileFormatTest.kt

@@ -22,6 +22,7 @@ package org.ossreviewtoolkit.model
 import com.fasterxml.jackson.core.JsonParseException
 
 import io.kotest.assertions.throwables.shouldThrow
+import io.kotest.assertions.throwables.shouldThrowWithMessage
 import io.kotest.core.spec.style.WordSpec
 import io.kotest.engine.spec.tempfile
 import io.kotest.matchers.file.shouldHaveFileSize
@@ -58,6 +59,28 @@ class FileFormatTest : WordSpec({
                 file.readValue()
             }
         }
+
+        "refuse to read multiple documents per file" {
+            val file = tempfile(null, ".yml").apply {
+                @Suppress("MaxLineLength")
+                writeText(
+                    """
+                    ---
+                    id: "Maven:dom4j:dom4j:1.6.1"
+                    source_artifact_url: "https://repo.maven.apache.org/maven2/dom4j/dom4j/1.6.1/dom4j-1.6.1-sources.jar"
+                    ---
+                    id: "Maven:dom4j:dom4j:1.6.1"
+                    source_artifact_url: "<INTERNAL_ARTIFACTORY>/dom4j-1.6.1-sources.jar"
+                    """.trimIndent()
+                )
+            }
+
+            shouldThrowWithMessage<IOException>(
+                "Multiple top-level objects found in file '$file'."
+            ) {
+                file.readValue()
+            }
+        }
     }
 
     "File.readValueOrNull()" should {