Use sets more widely in the schema.

docs/proposed/http-storage-node-protocol.rst

@@ -350,6 +350,9 @@ Because of the simple types used throughout
 and the equivalence described in `RFC 7049`_
 these examples should be representative regardless of which of these two encodings is chosen.
 
+For CBOR messages, any sequence that is semantically a set (i.e. no repeated values allowed, order doesn't matter, and is hashable in Python) should be sent as a set.
+Tag 6.258 is used to indicate sets in CBOR.
+
 HTTP Design
 ~~~~~~~~~~~
 

src/allmydata/storage/http_client.py

@@ -39,8 +39,9 @@ class ClientException(Exception):
 
 # Schemas for server responses.
 #
-# TODO usage of sets is inconsistent. Either use everywhere (and document in
-# spec document) or use nowhere.
+# Tags are of the form #6.nnn, where the number is documented at
+# https://www.iana.org/assignments/cbor-tags/cbor-tags.xhtml. Notably, #6.258
+# indicates a set.
 _SCHEMAS = {
     "get_version": Schema(
         """
@@ -74,7 +75,7 @@ _SCHEMAS = {
     ),
     "list_shares": Schema(
         """
-    message = [* uint]
+    message = #6.258([* uint])
     """
     ),
 }

src/allmydata/storage/http_server.py

@@ -436,7 +436,7 @@ class HTTPServer(object):
         """
         List shares for the given storage index.
         """
-        share_numbers = list(self._storage_server.get_buckets(storage_index).keys())
+        share_numbers = set(self._storage_server.get_buckets(storage_index).keys())
         return self._send_encoded(request, share_numbers)
 
     @_authorized_route(