GET /devices endpoint

implement a GET /devices endpoint which lists all of the user's devices.

It also returns the last IP where we saw that device, so there is some dancing
to fish that out of the user_ips table.

synapse/storage/client_ips.py

@@ -13,10 +13,13 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
+import logging
+
 from ._base import SQLBaseStore, Cache
 
 from twisted.internet import defer
 
+logger = logging.getLogger(__name__)
 
 # Number of msec of granularity to store the user IP 'last seen' time. Smaller
 # times give more inserts into the database even for readonly API hits
@@ -66,3 +69,72 @@ class ClientIpStore(SQLBaseStore):
             desc="insert_client_ip",
             lock=False,
         )
+
+    @defer.inlineCallbacks
+    def get_last_client_ip_by_device(self, devices):
+        """For each device_id listed, give the user_ip it was last seen on
+
+        Args:
+            devices (iterable[(str, str)]):  list of (user_id, device_id) pairs
+
+        Returns:
+            defer.Deferred: resolves to a dict, where the keys
+            are (user_id, device_id) tuples. The values are also dicts, with
+            keys giving the column names
+        """
+
+        res = yield self.runInteraction(
+            "get_last_client_ip_by_device",
+            self._get_last_client_ip_by_device_txn,
+            retcols=(
+                "user_id",
+                "access_token",
+                "ip",
+                "user_agent",
+                "device_id",
+                "last_seen",
+            ),
+            devices=devices
+        )
+
+        ret = {(d["user_id"], d["device_id"]): d for d in res}
+        defer.returnValue(ret)
+
+    @classmethod
+    def _get_last_client_ip_by_device_txn(cls, txn, devices, retcols):
+        def where_clause_for_device(d):
+                return
+
+        where_clauses = []
+        bindings = []
+        for (user_id, device_id) in devices:
+            if device_id is None:
+                where_clauses.append("(user_id = ? AND device_id IS NULL)")
+                bindings.extend((user_id, ))
+            else:
+                where_clauses.append("(user_id = ? AND device_id = ?)")
+                bindings.extend((user_id, device_id))
+
+        inner_select = (
+            "SELECT MAX(last_seen) mls, user_id, device_id FROM user_ips "
+            "WHERE %(where)s "
+            "GROUP BY user_id, device_id"
+        ) % {
+            "where": " OR ".join(where_clauses),
+        }
+
+        sql = (
+            "SELECT %(retcols)s FROM user_ips "
+            "JOIN (%(inner_select)s) ips ON"
+            "    user_ips.last_seen = ips.mls AND"
+            "    user_ips.user_id = ips.user_id AND"
+            "    (user_ips.device_id = ips.device_id OR"
+            "         (user_ips.device_id IS NULL AND ips.device_id IS NULL)"
+            "    )"
+        ) % {
+            "retcols": ",".join("user_ips." + c for c in retcols),
+            "inner_select": inner_select,
+        }
+
+        txn.execute(sql, bindings)
+        return cls.cursor_to_dict(txn)