feat: implement strategies for SPARQL query functionality

Currently, rdfproxy relies on SPARQLWrapper for querying triplestores;
this is not always ideal, since SPARQLWrapper occasionally gets
blacklisted e.g. by wikidata and caused severe performance issues in
the past.

The change introduces SPARQLQuery strategies for better control over
what query functionality should run in RDFProxy. The default strategy,
SPARQLWrapperStrategy, implements exactly the previous SPARQLWrapper behavior.
An HttpxStrategy implements the query functionality required by
RDFProxy using raw httpx instead of SPARQLWrapper.

rdfproxy/adapter.py

@@ -4,15 +4,14 @@
 import math
 from typing import Generic
 
-from SPARQLWrapper import JSON, SPARQLWrapper
 from rdfproxy.mapper import ModelBindingsMapper
+from rdfproxy.sparql_strategies import SPARQLStrategy, SPARQLWrapperStrategy
 from rdfproxy.utils._types import _TModelInstance
 from rdfproxy.utils.models import Page, QueryParameters
 from rdfproxy.utils.sparql_utils import (
     calculate_offset,
     construct_count_query,
     construct_items_query,
-    query_with_wrapper,
 )
 
 
@@ -32,15 +31,16 @@ class SPARQLModelAdapter(Generic[_TModelInstance]):
     """
 
     def __init__(
-        self, target: str | SPARQLWrapper, query: str, model: type[_TModelInstance]
+        self,
+        target: str,
+        query: str,
+        model: type[_TModelInstance],
+        sparql_strategy: SPARQLStrategy = SPARQLWrapperStrategy,
     ) -> None:
         self._query = query
         self._model = model
 
-        self.sparql_wrapper: SPARQLWrapper = (
-            SPARQLWrapper(target) if isinstance(target, str) else target
-        )
-        self.sparql_wrapper.setReturnFormat(JSON)
+        self.sparql_strategy = sparql_strategy(target)
 
     def query(self, query_parameters: QueryParameters) -> Page[_TModelInstance]:
         """Run a query against an endpoint and return a Page model object."""
@@ -52,9 +52,7 @@ def query(self, query_parameters: QueryParameters) -> Page[_TModelInstance]:
             offset=calculate_offset(query_parameters.page, query_parameters.size),
         )
 
-        items_query_bindings: Iterator[dict] = query_with_wrapper(
-            query=items_query, sparql_wrapper=self.sparql_wrapper
-        )
+        items_query_bindings: Iterator[dict] = self.sparql_strategy.query(items_query)
 
         mapper = ModelBindingsMapper(self._model, *items_query_bindings)
 
@@ -75,7 +73,5 @@ def _get_count(self, query: str) -> int:
 
         Helper for SPARQLModelAdapter.query.
         """
-        result: Iterator[dict] = query_with_wrapper(
-            query=query, sparql_wrapper=self.sparql_wrapper
-        )
+        result: Iterator[dict] = self.sparql_strategy.query(query)
         return int(next(result)["cnt"])

rdfproxy/sparql_strategies.py

@@ -0,0 +1,64 @@
+"""Strategy classes for SPARQL query functionality."""
+
+import abc
+from collections.abc import Iterator
+
+from SPARQLWrapper import JSON, QueryResult, SPARQLWrapper
+import httpx
+
+
+class SPARQLStrategy(abc.ABC):
+    def __init__(self, endpoint: str):
+        self.endpoint = endpoint
+
+    @abc.abstractmethod
+    def query(self, sparql_query: str) -> Iterator[dict[str, str]]:
+        raise NotImplementedError
+
+    @staticmethod
+    def _get_bindings_from_bindings_dict(bindings_dict: dict) -> Iterator[dict]:
+        bindings = map(
+            lambda binding: {k: v["value"] for k, v in binding.items()},
+            bindings_dict["results"]["bindings"],
+        )
+        return bindings
+
+
+class SPARQLWrapperStrategy(SPARQLStrategy):
+    def __init__(self, *args, **kwargs):
+        super().__init__(*args, **kwargs)
+
+        self._sparql_wrapper = SPARQLWrapper(self.endpoint)
+        self._sparql_wrapper.setReturnFormat(JSON)
+
+    def query(self, sparql_query: str) -> Iterator[dict[str, str]]:
+        self._sparql_wrapper.setQuery(sparql_query)
+
+        result: QueryResult = self._sparql_wrapper.query()
+        return self._get_bindings_from_bindings_dict(result.convert())
+
+
+class HttpxStrategy(SPARQLStrategy):
+    def query(self, sparql_query: str) -> Iterator[dict[str, str]]:
+        result: httpx.Response = self._httpx_run_sparql_query(sparql_query)
+        return self._get_bindings_from_bindings_dict(result.json())
+
+    def _httpx_run_sparql_query(
+        self, query: str, headers: dict | None = None
+    ) -> httpx.Response:
+        data = {"output": "json", "query": query}
+        headers = (
+            {
+                "Accept": "application/sparql-results+json",
+            }
+            if headers is None
+            else headers
+        )
+
+        response = httpx.post(
+            self.endpoint,
+            headers=headers,
+            data=data,
+        )
+
+        return response