From a4219137a5bfcf2a6f44780ecdbf475c1129e461 Mon Sep 17 00:00:00 2001
From: Jim Fulton <jim@jimfulton.info>
Date: Wed, 2 Jun 2021 12:24:38 -0400
Subject: [PATCH] =?UTF-8?q?feat:=20HTTPIterator=20now=20accepts=20a=20page?=
 =?UTF-8?q?=5Fsize=20parameter=20to=20control=20page=20=E2=80=A6=20(#197)?=
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Content-Transfer-Encoding: 8bit

---
 google/api_core/page_iterator.py | 19 ++++++++--
 tests/unit/test_page_iterator.py | 62 ++++++++++++++++++++++++++++++++
 2 files changed, 78 insertions(+), 3 deletions(-)

diff --git a/google/api_core/page_iterator.py b/google/api_core/page_iterator.py
index 11a92d38..fff3b556 100644
--- a/google/api_core/page_iterator.py
+++ b/google/api_core/page_iterator.py
@@ -179,7 +179,7 @@ def __init__(
             single item.
         """
         self.max_results = max_results
-        """int: The maximum number of results to fetch."""
+        """int: The maximum number of results to fetch"""
 
         # The attributes below will change over the life of the iterator.
         self.page_number = 0
@@ -298,7 +298,8 @@ class HTTPIterator(Iterator):
             can be found.
         page_token (str): A token identifying a page in a result set to start
             fetching results from.
-        max_results (int): The maximum number of results to fetch.
+        page_size (int): The maximum number of results to fetch per page
+        max_results (int): The maximum number of results to fetch
         extra_params (dict): Extra query string parameters for the
             API call.
         page_start (Callable[
@@ -329,6 +330,7 @@ def __init__(
         item_to_value,
         items_key=_DEFAULT_ITEMS_KEY,
         page_token=None,
+        page_size=None,
         max_results=None,
         extra_params=None,
         page_start=_do_nothing_page_start,
@@ -341,6 +343,7 @@ def __init__(
         self.path = path
         self._items_key = items_key
         self.extra_params = extra_params
+        self._page_size = page_size
         self._page_start = page_start
         self._next_token = next_token
         # Verify inputs / provide defaults.
@@ -399,8 +402,18 @@ def _get_query_params(self):
         result = {}
         if self.next_page_token is not None:
             result[self._PAGE_TOKEN] = self.next_page_token
+
+        page_size = None
         if self.max_results is not None:
-            result[self._MAX_RESULTS] = self.max_results - self.num_results
+            page_size = self.max_results - self.num_results
+            if self._page_size is not None:
+                page_size = min(page_size, self._page_size)
+        elif self._page_size is not None:
+            page_size = self._page_size
+
+        if page_size is not None:
+            result[self._MAX_RESULTS] = page_size
+
         result.update(self.extra_params)
         return result
 
diff --git a/tests/unit/test_page_iterator.py b/tests/unit/test_page_iterator.py
index 2bf74249..83595376 100644
--- a/tests/unit/test_page_iterator.py
+++ b/tests/unit/test_page_iterator.py
@@ -12,6 +12,7 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
+import math
 import types
 
 import mock
@@ -235,6 +236,7 @@ def test_constructor(self):
         assert iterator.page_number == 0
         assert iterator.next_page_token is None
         assert iterator.num_results == 0
+        assert iterator._page_size is None
 
     def test_constructor_w_extra_param_collision(self):
         extra_params = {"pageToken": "val"}
@@ -432,6 +434,66 @@ def test__get_next_page_bad_http_method(self):
         with pytest.raises(ValueError):
             iterator._get_next_page_response()
 
+    @pytest.mark.parametrize(
+        "page_size,max_results,pages",
+        [(3, None, False), (3, 8, False), (3, None, True), (3, 8, True)])
+    def test_page_size_items(self, page_size, max_results, pages):
+        path = "/foo"
+        NITEMS = 10
+
+        n = [0]  # blast you python 2!
+
+        def api_request(*args, **kw):
+            assert not args
+            query_params = dict(
+                maxResults=(
+                    page_size if max_results is None
+                    else min(page_size, max_results - n[0]))
+            )
+            if n[0]:
+                query_params.update(pageToken='test')
+            assert kw == {'method': 'GET', 'path': '/foo',
+                          'query_params': query_params}
+            n_items = min(kw['query_params']['maxResults'], NITEMS - n[0])
+            items = [dict(name=str(i + n[0])) for i in range(n_items)]
+            n[0] += n_items
+            result = dict(items=items)
+            if n[0] < NITEMS:
+                result.update(nextPageToken='test')
+            return result
+
+        iterator = page_iterator.HTTPIterator(
+            mock.sentinel.client,
+            api_request,
+            path=path,
+            item_to_value=page_iterator._item_to_value_identity,
+            page_size=page_size,
+            max_results=max_results,
+        )
+
+        assert iterator.num_results == 0
+
+        n_results = max_results if max_results is not None else NITEMS
+        if pages:
+            items_iter = iter(iterator.pages)
+            npages = int(math.ceil(float(n_results) / page_size))
+            for ipage in range(npages):
+                assert (
+                    list(six.next(items_iter)) == [
+                        dict(name=str(i))
+                        for i in range(ipage * page_size,
+                                       min((ipage + 1) * page_size, n_results),
+                                       )
+                    ])
+        else:
+            items_iter = iter(iterator)
+            for i in range(n_results):
+                assert six.next(items_iter) == dict(name=str(i))
+                assert iterator.num_results == i + 1
+
+        with pytest.raises(StopIteration):
+            six.next(items_iter)
+
 
 class TestGRPCIterator(object):
     def test_constructor(self):