This uses the orjson library to serialize annotations.

The orjson library is substantially faster than the built in python
library at he expense of being less flexible.  Here, we strip out the
access control dictionaries from each annotation, convert the mongo id
to a string, then use orjson to serialize.  Further, rather than load
the entire set of annotations into memory and serialize them in one
shot, we stream them from the database and serialize them individually.
When there are enough of them for efficiency, we yield them to the
output function.  This allows the data to start being returned before
the database finishes, and, if the connection is interrupted, to stop
pulling from the database when it is no longer useful.

orjson is included as part of large_image, so we don't need to add it to
the dependencies.

devops/girder/plugins/AnnotationPlugin/upenncontrast_annotation/server/api/annotation.py

@@ -1,8 +1,12 @@
+import json
+import orjson
+
 from girder.api import access
 from girder.api.describe import Description, describeRoute, autoDescribeRoute
-from girder.api.rest import Resource, loadmodel
+from girder.api.rest import Resource, loadmodel, setResponseHeader
 from girder.constants import AccessType
 from girder.exceptions import AccessException, RestException
+from girder.utility import JsonEncoder
 from ..helpers.proxiedModel import recordable, memoizeBodyJson
 from ..models.annotation import Annotation as AnnotationModel
 
@@ -209,14 +213,41 @@ def find(self, params):
             query["shape"] = params["shape"]
         if params["tags"] is not None and len(params["tags"]) > 0:
             query["tags"] = {"$all": params["tags"]}
-        return self._annotationModel.findWithPermissions(
-            query,
-            sort=sort,
-            user=self.getCurrentUser(),
-            level=AccessType.READ,
-            limit=limit,
-            offset=offset,
-        )
+
+        def generateResult():
+            cursor = self._annotationModel.findWithPermissions(
+                query,
+                sort=sort,
+                user=self.getCurrentUser(),
+                level=AccessType.READ,
+                limit=limit,
+                offset=offset,
+            )
+            chunk = [b"["]
+            first = True
+            for annotation in cursor:
+                if not first:
+                    chunk.append(b",")
+                # orjson and base json won't serialize ObjectIds
+                annotation["_id"] = str(annotation["_id"])
+                # We don't need to transmit the access control for
+                # annotations
+                annotation.pop("access")
+                # Otherwise, we can use json
+                # chunk.append(json.dumps(annotation, allow_nan=False, cls=JsonEncoder, separators=(",", ":")).encode())
+                # If we got rid of ObjectIds, using the json defaults is faster
+                # chunk.append(json.dumps(annotation).encode())
+                # But orjson is faster yet
+                chunk.append(orjson.dumps(annotation))
+                first = False
+                if len(chunk) > 1000:
+                    yield b"".join(chunk)
+                    chunk = []
+            chunk.append(b"]")
+            yield b"".join(chunk)
+
+        setResponseHeader("Content-Type", "application/json")
+        return generateResult
 
     @access.user
     @describeRoute(