How to call a server-side function from client-side?

It is possible to call server-side functions in client-side code using the ~% syntax. For security reasons, these functions must first be declared explicitely as "server functions" (with the type of their argument).

let f x = ...

let%client f_rpc = ~%(Eliom_client.server_function [%derive.json: int] f)

...

[%client ... f_rpc 4 ... ]

The server-side function (f in the example) needs to return an Lwt value.

Server functions are just syntactic sugar for pathless services returning OCaml values.

Note that you need to install ppx_deriving, and load our JSON ppx_deriving plugin in your project. The plugin is available as the Ocamlfind package js_of_ocaml.deriving.ppx.

If the function takes a more complex type, this type must have been declared with ppx_deriving. For example,

type t = int * string [@@deriving json]

Our infrastructure provides server-side data validation of the data sent, and prevents malformed data from crashing the server.