If max_returned_rows==page_size, increment max_returned_rows

Fixes #230, where if the two were equal pagination didn't work correctly.

datasette/app.py

@@ -176,10 +176,13 @@ def sql_operation_in_thread():
                 try:
                     cursor = conn.cursor()
                     cursor.execute(sql, params or {})
-                    if self.max_returned_rows and truncate:
-                        rows = cursor.fetchmany(self.max_returned_rows + 1)
-                        truncated = len(rows) > self.max_returned_rows
-                        rows = rows[:self.max_returned_rows]
+                    max_returned_rows = self.max_returned_rows
+                    if max_returned_rows == self.page_size:
+                        max_returned_rows += 1
+                    if max_returned_rows and truncate:
+                        rows = cursor.fetchmany(max_returned_rows + 1)
+                        truncated = len(rows) > max_returned_rows
+                        rows = rows[:max_returned_rows]
                     else:
                         rows = cursor.fetchall()
                         truncated = False

tests/fixtures.py

@@ -9,7 +9,7 @@
 import time
 
 
-def app_client(sql_time_limit_ms=None):
+def app_client(sql_time_limit_ms=None, max_returned_rows=None):
     with tempfile.TemporaryDirectory() as tmpdir:
         filepath = os.path.join(tmpdir, 'test_tables.db')
         conn = sqlite3.connect(filepath)
@@ -21,7 +21,7 @@ def app_client(sql_time_limit_ms=None):
         ds = Datasette(
             [filepath],
             page_size=50,
-            max_returned_rows=100,
+            max_returned_rows=max_returned_rows or 100,
             sql_time_limit_ms=sql_time_limit_ms or 20,
             metadata=METADATA,
             plugins_dir=plugins_dir,
@@ -38,6 +38,10 @@ def app_client_longer_time_limit():
     yield from app_client(200)
 
 
+def app_client_returend_rows_matches_page_size():
+    yield from app_client(max_returned_rows=50)
+
+
 def generate_compound_rows(num):
     for a, b, c in itertools.islice(
         itertools.product(string.ascii_lowercase, repeat=3), num

tests/test_api.py

@@ -1,6 +1,7 @@
 from .fixtures import (
     app_client,
     app_client_longer_time_limit,
+    app_client_returend_rows_matches_page_size,
     generate_compound_rows,
     generate_sortable_rows,
     METADATA,
@@ -9,6 +10,7 @@
 
 pytest.fixture(scope='module')(app_client)
 pytest.fixture(scope='module')(app_client_longer_time_limit)
+pytest.fixture(scope='module')(app_client_returend_rows_matches_page_size)
 
 
 def test_homepage(app_client):
@@ -691,3 +693,16 @@ def test_plugins_json(app_client):
         'static': False,
         'templates': False
     } in response.json
+
+
+def test_page_size_matching_max_returned_rows(app_client_returend_rows_matches_page_size):
+    fetched = []
+    path = '/test_tables/no_primary_key.json'
+    while path:
+        response = app_client_returend_rows_matches_page_size.get(
+            path, gather_request=False
+        )
+        fetched.extend(response.json['rows'])
+        assert len(response.json['rows']) in (1, 50)
+        path = response.json['next_url']
+    assert 201 == len(fetched)