uploads: Add a method to copy attachment contents out.

zerver/lib/upload/__init__.py

@@ -3,7 +3,7 @@ import logging
 import urllib
 from datetime import datetime
 from mimetypes import guess_type
-from typing import IO, Any, Callable, Iterator, List, Optional, Tuple
+from typing import IO, Any, BinaryIO, Callable, Iterator, List, Optional, Tuple
 from urllib.parse import urljoin
 
 from django.conf import settings
@@ -107,6 +107,10 @@ def upload_message_attachment_from_request(
     )
 
 
+def save_attachment_contents(path_id: str, filehandle: BinaryIO) -> None:
+    return upload_backend.save_attachment_contents(path_id, filehandle)
+
+
 def delete_message_attachment(path_id: str) -> bool:
     return upload_backend.delete_message_attachment(path_id)
 

zerver/lib/upload/base.py

@@ -3,7 +3,7 @@ import os
 import re
 import unicodedata
 from datetime import datetime
-from typing import IO, Any, Callable, Iterator, List, Optional, Tuple
+from typing import IO, Any, BinaryIO, Callable, Iterator, List, Optional, Tuple
 
 from django.utils.translation import gettext as _
 from PIL import GifImagePlugin, Image, ImageOps, PngImagePlugin
@@ -198,6 +198,9 @@ class ZulipUploadBackend:
     ) -> str:
         raise NotImplementedError
 
+    def save_attachment_contents(self, path_id: str, filehandle: BinaryIO) -> None:
+        raise NotImplementedError
+
     def delete_message_attachment(self, path_id: str) -> bool:
         raise NotImplementedError
 

zerver/lib/upload/local.py

@@ -4,7 +4,7 @@ import random
 import secrets
 import shutil
 from datetime import datetime
-from typing import IO, Any, Callable, Iterator, Literal, Optional, Tuple
+from typing import IO, Any, BinaryIO, Callable, Iterator, Literal, Optional, Tuple
 
 from django.conf import settings
 
@@ -98,6 +98,9 @@ class LocalUploadBackend(ZulipUploadBackend):
         create_attachment(uploaded_file_name, path, user_profile, target_realm, uploaded_file_size)
         return "/user_uploads/" + path
 
+    def save_attachment_contents(self, path_id: str, filehandle: BinaryIO) -> None:
+        filehandle.write(read_local_file("files", path_id))
+
     def delete_message_attachment(self, path_id: str) -> bool:
         return delete_local_file("files", path_id)
 

zerver/lib/upload/s3.py

@@ -4,7 +4,7 @@ import secrets
 import urllib
 from datetime import datetime
 from mimetypes import guess_type
-from typing import IO, Any, Callable, Iterator, List, Optional, Tuple
+from typing import IO, Any, BinaryIO, Callable, Iterator, List, Optional, Tuple
 
 import boto3
 import botocore
@@ -231,6 +231,10 @@ class S3UploadBackend(ZulipUploadBackend):
         )
         return url
 
+    def save_attachment_contents(self, path_id: str, filehandle: BinaryIO) -> None:
+        for chunk in self.uploads_bucket.Object(path_id).get()["Body"]:
+            filehandle.write(chunk)
+
     def delete_message_attachment(self, path_id: str) -> bool:
         return self.delete_file_from_s3(path_id, self.uploads_bucket)
 

zerver/tests/test_upload_local.py

@@ -1,7 +1,7 @@
 import os
 import re
 import urllib
-from io import StringIO
+from io import BytesIO, StringIO
 from urllib.parse import urlparse
 
 from django.conf import settings
@@ -20,6 +20,7 @@ from zerver.lib.upload import (
     delete_export_tarball,
     delete_message_attachment,
     delete_message_attachments,
+    save_attachment_contents,
     upload_emoji_image,
     upload_export_tarball,
     upload_message_attachment,
@@ -56,6 +57,17 @@ class LocalStorageTest(UploadSerializeMixin, ZulipTestCase):
         uploaded_file = Attachment.objects.get(owner=user_profile, path_id=path_id)
         self.assert_length(b"zulip!", uploaded_file.size)
 
+    def test_save_attachment_contents(self) -> None:
+        user_profile = self.example_user("hamlet")
+        uri = upload_message_attachment(
+            "dummy.txt", len(b"zulip!"), "text/plain", b"zulip!", user_profile
+        )
+
+        path_id = re.sub("/user_uploads/", "", uri)
+        output = BytesIO()
+        save_attachment_contents(path_id, output)
+        self.assertEqual(output.getvalue(), b"zulip!")
+
     def test_upload_message_attachment_local_cross_realm_path(self) -> None:
         """
         Verifies that the path of a file uploaded by a cross-realm bot to another

zerver/tests/test_upload_s3.py

@@ -2,7 +2,7 @@ import io
 import os
 import re
 import urllib
-from io import StringIO
+from io import BytesIO, StringIO
 from unittest.mock import patch
 
 import botocore.exceptions
@@ -25,6 +25,7 @@ from zerver.lib.upload import (
     delete_export_tarball,
     delete_message_attachment,
     delete_message_attachments,
+    save_attachment_contents,
     upload_export_tarball,
     upload_message_attachment,
 )
@@ -67,6 +68,19 @@ class S3Test(ZulipTestCase):
         body = f"First message ...[zulip.txt](http://{user_profile.realm.host}{uri})"
         self.send_stream_message(self.example_user("hamlet"), "Denmark", body, "test")
 
+    @use_s3_backend
+    def test_save_attachment_contents(self) -> None:
+        create_s3_buckets(settings.S3_AUTH_UPLOADS_BUCKET)
+        user_profile = self.example_user("hamlet")
+        uri = upload_message_attachment(
+            "dummy.txt", len(b"zulip!"), "text/plain", b"zulip!", user_profile
+        )
+
+        path_id = re.sub("/user_uploads/", "", uri)
+        output = BytesIO()
+        save_attachment_contents(path_id, output)
+        self.assertEqual(output.getvalue(), b"zulip!")
+
     @use_s3_backend
     def test_upload_message_attachment_s3_cross_realm_path(self) -> None:
         """