62 lines
2.1 KiB
Python
62 lines
2.1 KiB
Python
# This file is part of the Glowtables software
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# Copyright (C) 2023 Valentin Lorentz
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#
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# This program is free software: you can redistribute it and/or modify it under the
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# terms of the GNU Affero General Public License version 3, as published by the
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# Free Software Foundation.
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#
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# This program is distributed in the hope that it will be useful, but WITHOUT ANY
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# WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A
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# PARTICULAR PURPOSE. See the GNU Affero General Public License for more details.
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#
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# You should have received a copy of the GNU Affero General Public License along with
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# this program. If not, see <http://www.gnu.org/licenses/>.
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"""Abstraction over SPARQL backends, primarily meant to be mocked by tests."""
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import abc
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import json
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from typing import Iterable
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import requests
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from .cache import Cache
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class SparqlBackend(abc.ABC):
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"""Abstract class for SPARQL clients"""
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@abc.abstractmethod
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def query(self, query: str) -> Iterable[tuple]:
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"""Sends a SPARQL query, and returns an iterable of results."""
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class RemoteSparqlBackend(SparqlBackend):
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"""Queries a SPARQL API over HTTP."""
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def __init__(self, url: str, agent: str, cache: Cache):
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"""
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:param url: Base URL of the endpoint
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:param agent: User-Agent to use in HTTP requests
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"""
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self._url = url
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self._session = requests.Session()
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self._session.headers["User-Agent"] = agent
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self._cache = cache
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def query(self, query: str) -> Iterable[tuple]:
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headers = {
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"Content-Type": "application/sparql-query",
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"Accept": "application/json",
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}
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resp_text = self._cache.get(self._url, query)
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if not resp_text:
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resp_text = self._session.post(self._url, headers=headers, data=query).text
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self._cache.set(self._url, query, resp_text)
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resp = json.loads(resp_text)
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variables = resp["head"]["vars"]
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for result in resp["results"]["bindings"]:
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yield tuple(result.get(variable) for variable in variables)
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