Serialization seems to fail for query param `serial_consistency`

[Gowtham Kaki]

serial_consistency is one of the query params whose default value is set to None in src/scylla.ml. I added consistency and serial_consistency as optional arguments to Scylla.query in my fork so that non-default values can be passed. Unfortunately, query serialization seems to fail when I pass Scylla.Protocol.Serial as value for serial_consistency query param. This param is necessary for Scylla's conditional writes (lightweight transactions).

The following script reproduces the error:

(*
 * Assumes scylla is running on localhost at 9042 port.
 *
 * Before you run this script, set up the db as following:
 *    create keyspace if not exists keyspace1 with replication={'class':'SimpleStrategy', 'replication_factor':3}
 *    create table if not exists keyspace1.employee(id int primary key, name text)
 *    insert into keyspace1.employee(id,name) VALUES(1, 'anderson')
 *)
let conn = Scylla.connect ~ip:"127.0.0.1" ~port:9042 |> Result.get_ok

let () = Printf.printf "Opened connection.\n"

let keyspace = "keyspace1"

let table = "employee"

let update_query = Printf.sprintf
  "update %s.%s set name = ? where id = ? if name = ?"
  keyspace table

let big_of_string s = Bigstringaf.of_string s ~off:0 ~len:(String.length s);;

let res = Scylla.query conn
          ~query:update_query
          ~values:[| Scylla.Protocol.Varchar (big_of_string "smith"); 
                     Scylla.Protocol.Int 1l;
                     Scylla.Protocol.Varchar (big_of_string "anderson")
                  |] 
          ~consistency: Scylla.Protocol.One
          ~serial_consistency: Scylla.Protocol.Serial () in
begin
  match res with
  | Ok _ -> Ok ()
  | Error s -> failwith s
end

Here is the dune file you need to compile:

(executable
  (name scylla_test)
  (libraries scylla))

The error we get is as follows:

error code 10
error msg truncated frame: expected 2 bytes, length is 0
Fatal error: exception Failure("query did not succeed")

Any idea what's going on?

[Anmol]

Hi @gowthamk,I can take a look in a couple of days. Would that be okay?

[Anmol]

I have pushed some changes, which should fix the issue. Let me know if it works for you.

[Gowtham Kaki]

The fix works. Thanks!