Add download_attachment() method (#381)

README.rst

@@ -418,7 +418,11 @@ The history of a bucket can also be purged with:
 Attachments
 -----------
 
-If the `kinto-attachment plugin <https://github.com/Kinto/kinto-attachment/>`_ is enabled, it is possible to add attachments on records:
+If the `kinto-attachment plugin <https://github.com/Kinto/kinto-attachment/>`_ is enabled, it is possible to fetch, add, or remove attachments on records:
+
+.. code-block:: python
+
+    filepath = client.download_attachment(record_obj)
 
 .. code-block:: python
 

src/kinto_http/client.py

@@ -880,6 +880,33 @@ def purge_history(self, *, bucket=None, safe=True, if_match=None) -> List[Dict]:
         resp, _ = self.session.request("delete", endpoint, headers=headers)
         return resp["data"]
 
+    @retry_timeout
+    def download_attachment(
+        self,
+        record,
+        filepath=None,
+        chunk_size=8 * 1024,
+    ):
+        if "attachment" not in record:
+            raise ValueError("Specified record has no attachment")
+
+        server_info = self.server_info()
+        base_url = server_info["capabilities"]["attachments"]["base_url"]
+        location = record["attachment"]["location"]
+        url = base_url + location
+
+        if filepath is None:
+            filepath = record["attachment"]["filename"]
+        elif os.path.isdir(filepath):
+            filepath = os.path.join(filepath, record["attachment"]["filename"])
+
+        with open(filepath, "wb") as f:
+            with requests.get(url, stream=True) as r:
+                r.raise_for_status()
+                for chunk in r.iter_content(chunk_size=chunk_size):
+                    f.write(chunk)
+        return filepath
+
     @retry_timeout
     def add_attachment(
         self,

tests/test_client.py

@@ -1,3 +1,4 @@
+import os
 import re
 
 import pytest
@@ -1394,6 +1395,34 @@ def test_purging_of_history(client_setup: Client):
     client.session.request.assert_called_with("delete", url, headers=None)
 
 
+def test_download_attachment(client_setup: Client, mocker: MockerFixture):
+    client = client_setup
+
+    client.session.request.return_value = (
+        {"capabilities": {"attachments": {"base_url": "https://cdn/"}}},
+        {},
+    )
+
+    mock_requests_get = mocker.patch("kinto_http.requests.get")
+    mock_response = mocker.MagicMock()
+    mock_response.iter_content = mocker.MagicMock(return_value=[b"chunk1", b"chunk2", b"chunk3"])
+    mock_response.raise_for_status = mocker.MagicMock()
+    mock_requests_get.return_value.__enter__.return_value = mock_response
+
+    with pytest.raises(ValueError):
+        client.download_attachment({})
+
+    record = {"attachment": {"location": "file.bin", "filename": "local.bin"}}
+
+    path = client.download_attachment(record)
+    assert path == "local.bin"
+    with open(path) as f:
+        assert f.read() == "chunk1chunk2chunk3"
+
+    path = client.download_attachment(record, filepath="/tmp")
+    assert os.path.exists("/tmp/local.bin")
+
+
 def test_add_attachment_guesses_mimetype(record_setup: Client, tmp_path):
     client = record_setup
     mock_response(client.session)