feat!: list_databases returns an iterator (#4442)

CatalogConnection.list_databases should return an iterator so that users
don't have to manually re-implement pagination. For those who do want
more control over pagination, add num_page_results and page_token to the
Iterator object, and also allow the iterator object to be created at a
specific page token.

python/python/tests/test_catalog.py

@@ -55,7 +55,7 @@ def test_catalog_sync_scope_and_serialization(catalog_server):
             (200, {}),
             (200, {"tables": []}),
             (200, {"tables": []}),
-            (200, {"namespaces": ["team/search"], "page_token": "next"}),
+            (200, {"namespaces": ["team/search"]}),
             (204, None),
         ]
     )
@@ -85,13 +85,12 @@ def test_catalog_sync_scope_and_serialization(catalog_server):
         with pytest.raises(ValueError, match="sql_host_override must use"):
             connection.execute_query_async("SELECT 1")
     assert restored.table_names() == []
-    page = catalog.list_databases(limit=1, page_token="a/b")
-    assert page == lancedb.ListDatabasesResponse(["team/search"], "next")
+    assert list(catalog.list_databases()) == ["team/search"]
     catalog.drop_database("team/search", ignore_missing=True)
     assert requests[0][0] == "/v1/namespace/team%2Fsearch/create"
     assert requests[0][2] == {"mode": "ExistOk"}
     assert requests[1][0] == "/v1/namespace/team%2Fsearch/describe"
-    assert requests[4][0] == "/v1/namespace/$/list?limit=1&page_token=a%2Fb"
+    assert requests[4][0] == "/v1/namespace/$/list"
     assert requests[5][2] == {"mode": "Skip", "behavior": "Restrict"}
     for i, (_, headers, _) in enumerate(requests):
         headers = {key.lower(): value for key, value in headers.items()}
@@ -138,3 +137,129 @@ async def test_catalog_async_and_errors(catalog_server):
 def test_catalog_requires_remote_endpoint(endpoint):
     with pytest.raises(ValueError, match="endpoint"):
         lancedb.connect_catalog(endpoint)
+
+
+@pytest.mark.parametrize("asynchronous", [False, True])
+@pytest.mark.asyncio
+@pytest.mark.parametrize("page_token,page_limit", [(None, None), ("start/token", 2)])
+async def test_database_names_iteration(
+    catalog_server, asynchronous, page_token, page_limit
+):
+    endpoint, requests, responses = catalog_server
+    responses.extend(
+        [
+            (200, {"namespaces": ["first", "second"], "page_token": "a/b"}),
+            (200, {"namespaces": [], "page_token": "next"}),
+            (200, {"namespaces": ["last", "final"], "page_token": ""}),
+        ]
+    )
+    catalog = (
+        await lancedb.connect_catalog_async(endpoint)
+        if asynchronous
+        else lancedb.connect_catalog(endpoint)
+    )
+    names = catalog.list_databases(page_token=page_token, page_limit=page_limit)
+    assert requests == []
+    assert names.num_page_results() == 0
+    assert names.page_token() == page_token
+    for cached, expected in [(1, "first"), (0, "second")]:
+        assert (await names.__anext__() if asynchronous else next(names)) == expected
+        assert names.num_page_results() == cached
+        assert names.page_token() == "a/b"
+        assert len(requests) == 1
+    assert (await names.__anext__() if asynchronous else next(names)) == "last"
+    assert names.num_page_results() == 1
+    assert names.page_token() is None
+    assert (await names.__anext__() if asynchronous else next(names)) == "final"
+    assert names.num_page_results() == 0
+    assert names.page_token() is None
+    for _ in range(2):
+        with pytest.raises(StopAsyncIteration if asynchronous else StopIteration):
+            if asynchronous:
+                await names.__anext__()
+            else:
+                next(names)
+    from urllib.parse import parse_qs, urlsplit
+
+    for request, token in zip(requests, [page_token, "a/b", "next"]):
+        url = urlsplit(request[0])
+        assert url.path == "/v1/namespace/$/list"
+        expected = {}
+        if token is not None:
+            expected["page_token"] = [token]
+        if page_limit is not None:
+            expected["limit"] = [str(page_limit)]
+        assert parse_qs(url.query) == expected
+
+
+@pytest.mark.parametrize("asynchronous", [False, True])
+@pytest.mark.parametrize("fail", [False, True])
+@pytest.mark.asyncio
+async def test_database_names_empty_or_error(catalog_server, asynchronous, fail):
+    endpoint, requests, responses = catalog_server
+    responses.append(
+        (401, {"error": "unauthorized"}) if fail else (200, {"namespaces": []})
+    )
+    catalog = (
+        await lancedb.connect_catalog_async(endpoint)
+        if asynchronous
+        else lancedb.connect_catalog(endpoint)
+    )
+    names = catalog.list_databases()
+    if fail:
+        with pytest.raises(HttpError):
+            if asynchronous:
+                await names.__anext__()
+            else:
+                next(names)
+    assert ([name async for name in names] if asynchronous else list(names)) == []
+    assert len(requests) == 1
+
+
+@pytest.mark.parametrize("asynchronous", [False, True])
+@pytest.mark.asyncio
+async def test_database_names_resume(catalog_server, asynchronous):
+    endpoint, requests, responses = catalog_server
+    responses.extend(
+        [
+            (200, {"namespaces": ["first"], "page_token": "resume/token"}),
+            (200, {"namespaces": ["second"]}),
+        ]
+    )
+    catalog = (
+        await lancedb.connect_catalog_async(endpoint)
+        if asynchronous
+        else lancedb.connect_catalog(endpoint)
+    )
+    names = catalog.list_databases(page_limit=1)
+    assert (await names.__anext__() if asynchronous else next(names)) == "first"
+    assert names.num_page_results() == 0
+    resumed = catalog.list_databases(page_token=names.page_token(), page_limit=1)
+    assert resumed.page_token() == "resume/token"
+    assert len(requests) == 1
+    assert ([name async for name in resumed] if asynchronous else list(resumed)) == [
+        "second"
+    ]
+    assert resumed.page_token() is None
+    assert resumed.num_page_results() == 0
+    assert requests[1][0] == "/v1/namespace/$/list?limit=1&page_token=resume%2Ftoken"
+
+
+@pytest.mark.parametrize("asynchronous", [False, True])
+@pytest.mark.parametrize("page_limit", [0, 2**32 - 1])
+@pytest.mark.asyncio
+async def test_database_names_invalid_limit(catalog_server, asynchronous, page_limit):
+    endpoint, requests, _ = catalog_server
+    catalog = (
+        await lancedb.connect_catalog_async(endpoint)
+        if asynchronous
+        else lancedb.connect_catalog(endpoint)
+    )
+    names = catalog.list_databases(page_limit=page_limit)
+    with pytest.raises(ValueError, match="limit"):
+        if asynchronous:
+            await names.__anext__()
+        else:
+            next(names)
+    assert names.num_page_results() == 0
+    assert requests == []