Bring Reader into conformance with other resumable decoders

nsv/reader.py

@@ -1,23 +1,26 @@
 class Reader:
     def __init__(self, file_obj):
         self._file_obj = file_obj
+        self._line_parts = []
+        self._row_buffer = []
 
     def __iter__(self):
         return self
 
     def __next__(self):
-        acc = []
         for line in self._file_obj:
+            if line[-1] != '\n':  # missing newline = EOF mid-line
+                self._line_parts.append(line)
+                continue
+            if self._line_parts:
+                self._line_parts.append(line)
+                line = ''.join(self._line_parts)
+                self._line_parts = []
             if line == '\n':
-                return acc
-            if line[-1] == '\n':  # so as not to chop if missing newline at EOF
-                line = line[:-1]
-            acc.append(Reader.unescape(line))  # bruh
-        # at the end of the file
-        if acc:
-            return acc
-        else:  # an empty row would self-report in the cycle body
-            raise StopIteration
+                row, self._row_buffer = self._row_buffer, []
+                return row
+            self._row_buffer.append(Reader.unescape(line[:-1]))  # bruh
+        raise StopIteration
 
     @staticmethod
     def unescape(s: str) -> str:

tests/test_incremental.py

@@ -1,4 +1,5 @@
 import unittest
+import io
 import os
 import tempfile
 import nsv
@@ -17,13 +18,43 @@ def test_incremental_reading(self):
             second = next(reader)
             self.assertEqual(second, ["d", "e", "f"])
 
-            # third = next(reader)
-            # self.assertEqual(third, ["last1", "last2"])
-
             # Should be at end of the file
             with self.assertRaises(StopIteration):
                 next(reader)
 
+    def test_incomplete_trailing_row_buffered(self):
+        """A resumable Reader buffers an incomplete trailing row instead of emitting it."""
+        reader = nsv.Reader(io.StringIO('a\nb\n\nc\nd'))
+        self.assertEqual(next(reader), ['a', 'b'])
+        with self.assertRaises(StopIteration):
+            next(reader)
+
+        reader = nsv.Reader(io.StringIO('a\nb\n\nc\nd\n'))
+        self.assertEqual(next(reader), ['a', 'b'])
+        with self.assertRaises(StopIteration):
+            next(reader)
+
+    def test_reading_resumes_after_eof(self):
+        """Reading continues across EOF once more data is appended (tailing)."""
+        with tempfile.TemporaryDirectory() as output_dir:
+            file_path = os.path.join(output_dir, 'tail.nsv')
+            with open(file_path, 'w') as f:
+                f.write('a\nb')
+                f.flush()
+
+                with open(file_path, 'r') as rf:
+                    reader = nsv.Reader(rf)
+                    with self.assertRaises(StopIteration):
+                        next(reader)
+
+                    f.write('c\nd\n\n')
+                    f.flush()
+                    self.assertEqual(next(reader), ['a', 'bc', 'd'])
+
+    def test_load_emits_incomplete_trailing_row(self):
+        """Non-resumable loads keeps emitting the incomplete tail."""
+        self.assertEqual(nsv.loads('a\nb\n\nc\nd'), [['a', 'b'], ['c', 'd']])
+
     def test_incremental_writing(self):
         """Test writing elements incrementally."""
         data = [["field1", "field2"], ["value1", "value2"], ["last1", "last2"]]