handle consecutive empty lines correctly

src/main/java/de/landsh/opendata/catalogproxy/FilterInvalidRDF.java

@@ -84,12 +84,6 @@ public class FilterInvalidRDF extends InputStream {
             return -1;
         }
 
-        // insert a newline character at the end of each line
-        if (index == currentLine.length) {
-            index++;
-            return '\n';
-        }
-
         if (index > currentLine.length) {
             readNextLine();
         }
@@ -97,6 +91,11 @@ public class FilterInvalidRDF extends InputStream {
         if (currentLine == null) {
             return -1;
         }
+        // insert a newline character at the end of each line
+        if (index == currentLine.length) {
+            index++;
+            return '\n';
+        }
         
         byte result = currentLine[index];
         index++;

src/test/java/de/landsh/opendata/catalogproxy/FilterInvalidRDFTest.java

@@ -3,6 +3,7 @@ package de.landsh.opendata.catalogproxy;
 import org.apache.commons.io.IOUtils;
 import org.junit.jupiter.api.Test;
 
+import java.io.ByteArrayInputStream;
 import java.io.IOException;
 import java.io.InputStream;
 import java.nio.charset.StandardCharsets;
@@ -21,6 +22,32 @@ public class FilterInvalidRDFTest {
         assertEquals(expectedResult, result);
     }
 
+    @Test
+    public void read_empty_stream() throws IOException {
+        InputStream inputStream = new FilterInvalidRDF(new ByteArrayInputStream(new byte[0]));
+        assertEquals(-1, inputStream.read());
+    }
+
+    @Test
+    public void read_empty_line() throws IOException {
+        InputStream inputStream = new FilterInvalidRDF(new ByteArrayInputStream("\n".getBytes()));
+        String result = IOUtils.toString(inputStream, StandardCharsets.UTF_8);
+        assertEquals("\n", result);
+    }
+    @Test
+    public void read_empty_lines() throws IOException {
+        InputStream inputStream = new FilterInvalidRDF(new ByteArrayInputStream("\n\n\n".getBytes()));
+        String result = IOUtils.toString(inputStream, StandardCharsets.UTF_8);
+        assertEquals("\n\n\n", result);
+    }
+
+    @Test
+    public void read_no_newline() throws IOException {
+        InputStream inputStream = new FilterInvalidRDF(new ByteArrayInputStream("OK".getBytes()));
+        String result = IOUtils.toString(inputStream, StandardCharsets.UTF_8);
+        assertEquals("OK\n", result);
+    }
+
     @Test
     public void read_iri_with_space() throws IOException {
         final String invalidIRI = "\"https://opendata.schleswig-holstein.de/dataset/automatische-zahlstelle-neustadt i. h.-süd-2012\"";
@@ -59,6 +86,5 @@ public class FilterInvalidRDFTest {
     @Test
     public void filterLine_invalid_xml_entity() {
         assertEquals("?nn=1819516&cms_detail=1105&cms_map=0", FilterInvalidRDF.filterLine("?nn=1819516&cms_detail=1105&cms_map=0"));
-
     }
 }