dateTime param illegal

[matt-beanland]

Elixir and Erlang/OTP versions

Erlang/OTP 28 [erts-16.2] [source] [64-bit] [smp:12:12] [ds:12:12:10] [async-threads:1] [jit]

Elixir 1.19.5 (compiled with Erlang/OTP 28)

Operating system

macOS 26.4

Neo4j version

community 5.26.22

Bolty version

0.0.9

Current behavior

when creating a cypher node with a %DateTime{} parameter, such as

 %{ "utcDatetimeUsec" => ~U[2025-05-11 07:45:41.429903Z] }

Bolty.query(conn, query, params) raises

              %Bolty.Error{
                __exception__: true,
                bolt: %{code: "Neo.ClientError.Request.Invalid", message: "Illegal value for field \"params\": Unexpected struct tag: 0x66"},
                code: :request_invalid,
                module: Bolty.BoltProtocol.Message.RunMessage,
                packstream: nil
              }

Expected behavior

We expected the create to succeed with the utcDateTimeUsec property having at the appropriate neo4j localdatetime value.

[matt-beanland]

The problem is that with bolt 5.x DateTime is packed to legacy structures that aren't handled. A fix will either need to dynamically use the bolt_version and/or break bolt 4.x compatibility. Not ready to go there yet so will leave this open.

[matt-beanland]

What should happen is that bolty should behave differently according to the negotiated Bolt protocol version for that connection.

Bolt 4.x uses the legacy datetime structs (0x66, 0x46) and Bolt 5.x uses the new ones (0x69, 0x49). Currently Bolty has both markers defined but presumably picks one path regardless. A version-aware connection would dispatch correctly, the version would need to be available to pack stream/unpack stream.

DBConnection owns the process, it returns a state struct from connect/1 - whatever you return from that callback is threaded through every subsequent callback as the last argument. So if you capture the negotiated version during handshake and put it in the state struct, it's available in every handle_execute/4, handle_begin/3 etc. call without any process messaging.

Something like:

defstruct [:socket, :protocol_version, ...]

def connect(opts) do
  # ... handshake ...
  {:ok, %__MODULE__{socket: socket, protocol_version: version, ...}}
end

def handle_execute(query, params, _opts, %{protocol_version: version} = state) do
  # version available here
end

The state is bolty's to define — DBConnection just passes it back to you each time.