* Returns the trailers if they're immediately available.
   */
  @Throws(IOException::class)
  fun peekTrailers(): Headers? {
    withLock {
      if (source.finished && source.receiveBuffer.exhausted() && source.readBuffer.exhausted()) {
        return source.trailers ?: Headers.EMPTY
      }
      if (errorCode != null) {
        throw errorException ?: StreamResetException(errorCode!!)
      }
      return null
    }

  }

  private EndpointPairIterator(BaseGraph<N> graph) {
    this.graph = graph;
    this.nodeIterator = graph.nodes().iterator();
  }

  /**
   * Called after {@link #successorIterator} is exhausted. Advances {@link #node} to the next node
   * and updates {@link #successorIterator} to iterate through the successors of {@link #node}.
   */
  final boolean advance() {
    checkState(!successorIterator.hasNext());

        // End of iteration behavior
        assertFalse(it.hasNext(), "No more elements expected");
        assertNull(it.next(), "next() returns null when exhausted in this implementation");
    }

    @Test
    @DisplayName("With filter: only accepted entries are returned and filter is invoked per entry")

        String url = "http://example.com/large-dataset";
        String message = "Crawling failed due to memory exhaustion";
        OutOfMemoryError error = new OutOfMemoryError("Heap space exhausted");

        DataStoreCrawlingException exception = new DataStoreCrawlingException(url, message, error);

        assertEquals(url, exception.getUrl());
        assertEquals(message, exception.getMessage());

      assertTrue(
          "index " + i + " expected <" + expected + "., actual is exhausted",
          actualIterator.hasNext());

      Object actual = actualIterator.next();
      assertEquals("index " + i, expected, actual);
      i++;
    }
    if (actualIterator.hasNext()) {
      fail("index " + i + ", expected is exhausted, actual <" + actualIterator.next() + ">");
    }
  }

  /**

 * bookkeeping easier for the caller: releasing the allocation as soon as the terminal stream has
 * been found. But only complete the stream once its data stream has been exhausted.
 */
interface Connection {
  /** Returns the route used by this connection. */
  fun route(): Route

  /**
   * Returns the socket that this connection is using. Returns an

    }

    /**
     * Returns a value in [0..maxByteCount] with the number of bytes that can be read from [source]
     * in the current part. If this returns 0 the current part is exhausted; otherwise it has at
     * least one byte left to read.
     */
    private fun currentPartBytesRemaining(maxByteCount: Long): Long {
      val toIndex = minOf(source.buffer.size, maxByteCount) + 1L

          currentLabelByteIndex++
          if (publicSuffixByteIndex == publicSuffixLength) break

          if (labels[currentLabelIndex].size == currentLabelByteIndex) {
            // We've exhausted our current label. Either there are more labels to compare, in which
            // case we expect a dot as the next character. Otherwise, we've checked all our labels.
            if (currentLabelIndex == labels.size - 1) {

          maskCursor.seek(messageFrameBuffer.size - frameLength)
          toggleMask(maskCursor, maskKey!!)
          maskCursor.close()
        }
      }

      if (isFinalFrame) break // We are exhausted and have no continuations.

      readUntilNonControlFrame()
      if (opcode != OPCODE_CONTINUATION) {
        throw ProtocolException("Expected continuation opcode. Got: ${opcode.toHexString()}")
      }
    }

                return;
              } else {
                // Increment the run counter to avoid the ABA problem of a submitter marking the
                // thread as QUEUED after it already ran and exhausted the queue before returning
                // from execute().
                workerRunCount++;
                workerRunningState = RUNNING;
                hasSetRunning = true;
              }
            }