feat: wait for meilisearch index creation to succeed

In `search.meilisearch.create_indexes`, we were not waiting for the
index creation tasks to complete. This was causing a potential race
condition, where the `create_indexes` function would fail because it
took a few seconds for the index creation to succeed.

See the relevant conversation here:
openedx/edx-platform#35743 (comment)

edxsearch/__init__.py

@@ -1,3 +1,3 @@
 """ Container module for testing / demoing search """
 
-__version__ = '4.1.0'
+__version__ = '4.1.1'

search/meilisearch.py

@@ -115,9 +115,20 @@ class MeilisearchEngine(SearchEngine):
     compliant with edx-search's ElasticSearchEngine.
     """
 
-    def __init__(self, index=None):
+    def __init__(self, index=None) -> None:
         super().__init__(index=index)
-        self.meilisearch_index = get_meilisearch_index(self.index_name)
+        self._meilisearch_index: t.Optional[meilisearch.index.Index] = None
+
+    @property
+    def meilisearch_index(self) -> meilisearch.index.Index:
+        """
+        Lazy load meilisearch index.
+        """
+        if self._meilisearch_index is None:
+            meilisearch_index_name = get_meilisearch_index_name(self.index_name)
+            meilisearch_client = get_meilisearch_client()
+            self._meilisearch_index = meilisearch_client.index(meilisearch_index_name)
+        return self._meilisearch_index
 
     @property
     def meilisearch_index_name(self):
@@ -211,7 +222,7 @@ def print_failed_meilisearch_tasks(count: int = 10):
         print(result)
 
 
-def create_indexes(index_filterables: dict[str, list[str]] = None):
+def create_indexes(index_filterables: t.Optional[dict[str, list[str]]] = None):
     """
     This is an initialization function that creates indexes and makes sure that they
     support the right facetting.
@@ -225,38 +236,68 @@ def create_indexes(index_filterables: dict[str, list[str]] = None):
     client = get_meilisearch_client()
     for index_name, filterables in index_filterables.items():
         meilisearch_index_name = get_meilisearch_index_name(index_name)
-        try:
-            index = client.get_index(meilisearch_index_name)
-        except meilisearch.errors.MeilisearchApiError as e:
-            if e.code != "index_not_found":
-                raise
-            client.create_index(
-                meilisearch_index_name, {"primaryKey": PRIMARY_KEY_FIELD_NAME}
-            )
-            # Get the index again
-            index = client.get_index(meilisearch_index_name)
+        index = get_or_create_meilisearch_index(client, meilisearch_index_name)
+        update_index_filterables(client, index, filterables)
 
-        # Update filterables if there are some new elements
-        if filterables:
-            existing_filterables = set(index.get_filterable_attributes())
-            if not set(filterables).issubset(existing_filterables):
-                all_filterables = list(existing_filterables.union(filterables))
-                index.update_filterable_attributes(all_filterables)
 
+def get_or_create_meilisearch_index(
+    client: meilisearch.Client, index_name: str
+) -> meilisearch.index.Index:
+    """
+    Get an index. If it does not exist, create it.
 
-def get_meilisearch_index(index_name: str):
+    This will fail with a RuntimeError if we fail to create the index. It will fail with
+    a MeilisearchApiError in other failure cases.
     """
-    Return a meilisearch index.
+    try:
+        return client.get_index(index_name)
+    except meilisearch.errors.MeilisearchApiError as e:
+        if e.code != "index_not_found":
+            raise
+        task_info = client.create_index(
+            index_name, {"primaryKey": PRIMARY_KEY_FIELD_NAME}
+        )
+        wait_for_task_to_succeed(client, task_info)
+        # Get the index again
+        return client.get_index(index_name)
 
-    Note that the index may not exist, and it will be created on first insertion.
-    ideally, the initialisation function `create_indexes` should be run first.
+
+def update_index_filterables(
+    client: meilisearch.Client, index: meilisearch.index.Index, filterables: list[str]
+) -> None:
     """
-    meilisearch_client = get_meilisearch_client()
-    meilisearch_index_name = get_meilisearch_index_name(index_name)
-    return meilisearch_client.index(meilisearch_index_name)
+    Make sure that the filterable fields of an index include the given list of fields.
+
+    If existing fields are present, they are preserved.
+    """
+    if not filterables:
+        return
+    existing_filterables = set(index.get_filterable_attributes())
+    if set(filterables).issubset(existing_filterables):
+        # all filterables fields are already present
+        return
+    all_filterables = list(existing_filterables.union(filterables))
+    task_info = index.update_filterable_attributes(all_filterables)
+    wait_for_task_to_succeed(client, task_info)
+
+
+def wait_for_task_to_succeed(
+    client: meilisearch.Client,
+    task_info: meilisearch.task.TaskInfo,
+    timeout_in_ms: int = 5000,
+) -> None:
+    """
+    Wait for a Meilisearch task to succeed. If it does not, raise RuntimeError.
+    """
+    task = client.wait_for_task(task_info.task_uid, timeout_in_ms=timeout_in_ms)
+    if task.status != "succeeded":
+        raise RuntimeError(f"Failed meilisearch task: {task}")
 
 
 def get_meilisearch_client():
+    """
+    Return a Meilisearch client with the right settings.
+    """
     return meilisearch.Client(MEILISEARCH_URL, api_key=MEILISEARCH_API_KEY)
 
 
@@ -332,7 +373,7 @@ def get_search_params(
     Return a dictionary of parameters that should be passed to the Meilisearch client
     `.search()` method.
     """
-    params = {"showRankingScore": True}
+    params: dict[str, t.Any] = {"showRankingScore": True}
 
     # Aggregation
     if aggregation_terms:

search/tests/test_meilisearch.py

@@ -3,11 +3,13 @@
 """
 
 from datetime import datetime
-from unittest.mock import Mock
+from unittest.mock import Mock, patch
 
 import django.test
 from django.utils import timezone
+import meilisearch
 import pytest
+from requests import Response
 
 from search.utils import DateRange, ValueRange
 import search.meilisearch
@@ -294,20 +296,22 @@ def test_engine_index(self):
 
     def test_engine_search(self):
         engine = search.meilisearch.MeilisearchEngine(index="my_index")
-        engine.meilisearch_index.search = Mock(return_value={
-            "hits": [
-                {
-                    "pk": "f381d4f1914235c9532576c0861d09b484ade634",
-                    "id": "course-v1:OpenedX+DemoX+DemoCourse",
-                    "_rankingScore": 0.865,
-                },
-            ],
-            "query": "demo",
-            "processingTimeMs": 0,
-            "limit": 20,
-            "offset": 0,
-            "estimatedTotalHits": 1
-        })
+        engine.meilisearch_index.search = Mock(
+            return_value={
+                "hits": [
+                    {
+                        "pk": "f381d4f1914235c9532576c0861d09b484ade634",
+                        "id": "course-v1:OpenedX+DemoX+DemoCourse",
+                        "_rankingScore": 0.865,
+                    },
+                ],
+                "query": "demo",
+                "processingTimeMs": 0,
+                "limit": 20,
+                "offset": 0,
+                "estimatedTotalHits": 1,
+            }
+        )
 
         results = engine.search(
             query_string="abc",
@@ -321,15 +325,19 @@ def test_engine_search(self):
             log_search_params=True,
         )
 
-        engine.meilisearch_index.search.assert_called_with("abc", {
-            "showRankingScore": True,
-            "facets": ["org", "course"],
-            "filter": [
-                'course = "course-v1:testorg+test1+alpha"',
-                'org = "testorg"', 'key = "value" OR key NOT EXISTS',
-                'NOT _pk = "81fe8bfe87576c3ecb22426f8e57847382917acf"',
-            ]
-        })
+        engine.meilisearch_index.search.assert_called_with(
+            "abc",
+            {
+                "showRankingScore": True,
+                "facets": ["org", "course"],
+                "filter": [
+                    'course = "course-v1:testorg+test1+alpha"',
+                    'org = "testorg"',
+                    'key = "value" OR key NOT EXISTS',
+                    'NOT _pk = "81fe8bfe87576c3ecb22426f8e57847382917acf"',
+                ],
+            },
+        )
         assert results == {
             "aggs": {},
             "max_score": 0.865,
@@ -357,3 +365,32 @@ def test_engine_remove(self):
         doc_pk = "81fe8bfe87576c3ecb22426f8e57847382917acf"
         engine.remove(doc_ids=[doc_id])
         engine.meilisearch_index.delete_documents.assert_called_with([doc_pk])
+
+
+class UtilitiesTests(django.test.TestCase):
+    """
+    Tests associated to the utility functions of the meilisearch engine.
+    """
+
+    @patch.object(search.meilisearch, "wait_for_task_to_succeed")
+    def test_create_index(self, mock_wait_for_task_to_succeed) -> None:
+        class GetIndexMock:
+            number_of_calls = 0
+
+            def get_index(self, index_name):
+                """Mocked client.get_index method"""
+                self.number_of_calls += 1
+                if self.number_of_calls == 1:
+                    error = meilisearch.errors.MeilisearchApiError("", Response())
+                    error.code = "index_not_found"
+                    raise error
+                if self.number_of_calls == 2:
+                    return f"index created: {index_name}"
+                # We shouldn't be there
+                assert False
+
+        client = Mock()
+        client.get_index = Mock(side_effect=GetIndexMock().get_index)
+        result = search.meilisearch.get_or_create_meilisearch_index(client, "my_index")
+        assert result == "index created: my_index"
+        mock_wait_for_task_to_succeed.assert_called_once()