Fix crash on long lines

polynote-kernel/src/main/scala/polynote/kernel/interpreter/CellExecutor.scala

@@ -2,9 +2,8 @@ package polynote.kernel.interpreter
 
 import java.io.{OutputStream, PrintStream}
 import java.lang.reflect.InvocationHandler
-
 import polynote.kernel.environment.{CurrentRuntime, CurrentTask, PublishResult, PublishStatus}
-import polynote.kernel.util.ResultOutputStream
+import polynote.kernel.util.{ResultOutputStream, ResultPrintStream}
 import polynote.kernel.{BaseEnv, ExecutionStatus, InterpreterEnv, Output, Result, ScalaCompiler, withContextClassLoader}
 import polynote.messages.CellID
 import polynote.runtime.KernelRuntime
@@ -26,7 +25,7 @@ class CellExecutor(publishSync: Result => Unit, classLoader: ClassLoader, blocki
     blockingExecutor.submit {
       new Runnable {
         def run(): Unit = {
-          val console = new PrintStream(new ResultOutputStream(publishSync), true)
+          val console = new ResultPrintStream(publishSync)()
           withContextClassLoader(classLoader) {
             try {
               Console.withOut(console) {

polynote-kernel/src/main/scala/polynote/kernel/util/ResultOutputStream.scala

@@ -1,13 +1,12 @@
 package polynote.kernel.util
 
-import java.io.OutputStream
+import java.io.{OutputStream, PrintStream}
 import java.nio.ByteBuffer
 import java.nio.charset.StandardCharsets
 import java.util.concurrent.atomic.AtomicBoolean
-
 import polynote.kernel.{Output, Result}
 
-class ResultOutputStream(publishSync: Result => Unit, bufSize: Int = 1024) extends OutputStream {
+class ResultOutputStream(publishSync: Result => Unit, bufSize: Int = 65536) extends OutputStream {
   private val buf: ByteBuffer = ByteBuffer.allocate(bufSize)
   private val closed = new AtomicBoolean(false)
 
@@ -21,15 +20,17 @@ class ResultOutputStream(publishSync: Result => Unit, bufSize: Int = 1024) exten
 
   override def flush(): Unit = {
     super.flush()
-    buf.synchronized {
-      val len = buf.position()
-      if (len > 0) {
-        val b = ByteBuffer.allocate(buf.position())
-        val arr = new Array[Byte](buf.position())
-        buf.rewind()
-        buf.get(arr)
-        publishSync(Output("text/plain; rel=stdout", new String(arr, StandardCharsets.UTF_8)))
-        buf.rewind()
+    if (buf.hasRemaining) {
+      buf.synchronized {
+        val len = buf.position()
+        if (len > 0) {
+          val b = ByteBuffer.allocate(buf.position())
+          val arr = new Array[Byte](buf.position())
+          buf.rewind()
+          buf.get(arr)
+          publishSync(Output("text/plain; rel=stdout", new String(arr, StandardCharsets.UTF_8)))
+          buf.rewind()
+        }
       }
     }
   }
@@ -42,3 +43,17 @@ class ResultOutputStream(publishSync: Result => Unit, bufSize: Int = 1024) exten
   }
 
 }
+
+class ResultPrintStream(publishSync: Result => Unit, bufSize: Int = 65536)(private val outputStream: OutputStream = new ResultOutputStream(publishSync, bufSize)) extends PrintStream(outputStream, true, "UTF-8") {
+  override def println(value: String): Unit = {
+    outputStream.flush()
+    publishSync(Output("text/plain; rel=stdout", value + "\n"))
+  }
+
+  override def print(s: String): Unit = {
+    outputStream.flush()
+    publishSync(Output("text/plain; rel=stdout", s))
+  }
+
+  override def println(x: AnyRef): Unit = println(String.valueOf(x))
+}