Source file schema.ml
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module J = Yojson.Safe
type atomic_type =
| Null
| Bool
| Int32
| Int64
| Float32
| Float64
| Bytes
| String
type top_type =
| Atomic of atomic_type
| Named of string
| Array of top_type
| Str_map of top_type
| Union of top_type list
| Fixed of {
name: string;
namespace: string option;
doc: string option;
size: int;
}
| Enum of {
name: string;
namespace: string option;
symbols: string list;
doc: string option;
aliases: string list option;
}
| Record of {
name: string;
namespace: string option;
fields: record_field list;
doc: string option;
aliases: string list option;
}
and record_field = {
name: string;
doc: string option;
ty: top_type;
}
(** A toplevel schema. *)
type t = top_type
let json_of_atomic (self:atomic_type) : J.t =
match self with
| Null -> `String "null"
| Bool -> `String "boolean"
| Int32 -> `String "int"
| Int64 -> `String "long"
| Float32 -> `String "float"
| Float64 -> `String "double"
| Bytes -> `String "bytes"
| String -> `String "string"
let rec to_json (self:t) : J.t =
let module JU = J.Util in
match self with
| Atomic i -> json_of_atomic i
| Named s -> `String s
| Union l -> `List (List.map to_json l)
| Array ty ->
`Assoc ["type", `String "array"; "items", to_json ty]
| Str_map ty ->
`Assoc ["type", `String "map"; "values", to_json ty]
| Fixed { name; doc; namespace; size; } ->
`Assoc (Util.list_keep_some [
Some ("type", `String "fixed");
Some ("name", `String name);
Some ("size", `Int size);
Util.map_opt doc ~f:(fun s -> "doc", `String s);
Util.map_opt namespace ~f:(fun s -> "namespace", `String s);
])
| Enum { name; doc; symbols; namespace; aliases; } ->
`Assoc (Util.list_keep_some [
Some ("type", `String "enum");
Some ("name", `String name);
Some ("symbols", `List (List.map (fun s -> `String s) symbols));
Util.map_opt doc ~f:(fun s -> "doc", `String s);
Util.map_opt namespace ~f:(fun s -> "namespace", `String s);
Util.map_opt aliases ~f:(fun l -> "aliases", `List (List.map (fun s->`String s) l));
])
| Record { name; doc; fields; namespace; aliases; } ->
`Assoc (Util.list_keep_some [
Some ("type", `String "record");
Some ("name", `String name);
Some ("fields", `List (List.map json_of_field fields));
Util.map_opt doc ~f:(fun s -> "doc", `String s);
Util.map_opt aliases ~f:(fun l -> "aliases", `List (List.map (fun s->`String s) l));
Util.map_opt namespace ~f:(fun s -> "namespace", `String s);
])
and json_of_field (f:record_field) : J.t =
let {doc; name; ty; } = f in
`Assoc (Util.list_keep_some [
Some ("type", to_json ty);
Some ("name", `String name);
Util.map_opt doc ~f:(fun s -> "type", `String s);
])
let of_json (j:J.t) : (t, string) result =
let exception E of string in
let module JU = J.Util in
let spf = Printf.sprintf in
let assoc k l =
try List.assoc k l
with Not_found -> raise (E (spf "cannot find key %S" k))
in
let rec loop j : t =
match j with
| `String "null" -> Atomic Null
| `String "boolean" -> Atomic Bool
| `String "int" -> Atomic Int32
| `String "long" -> Atomic Int64
| `String "float" -> Atomic Float32
| `String "double" -> Atomic Float64
| `String "string" -> Atomic String
| `String "bytes" -> Atomic Bytes
| `String n -> Named n
| `List ([] | [_]) -> failwith "union needs >= 2 elements"
| `List l -> Union (List.map loop l)
| `Assoc l ->
begin try
begin match assoc "type" l |> JU.to_string with
| "array" ->
let items = assoc "items" l |> loop in
Array items
| "map" ->
let values = assoc "values" l |> loop in
Str_map values
| "fixed" ->
let name = assoc "name" l |> JU.to_string in
let namespace = None in
let doc = List.assoc_opt "doc" l |> Util.map_opt ~f:JU.to_string in
let size = assoc "size" l |> JU.to_int in
Fixed {name; doc; namespace; size}
| "record" ->
let name = assoc "name" l |> JU.to_string in
let namespace = None in
let aliases = List.assoc_opt "aliases" l |> Util.map_opt ~f:(fun x -> JU.to_list x |> List.map JU.to_string) in
let doc = List.assoc_opt "doc" l |> Util.map_opt ~f:JU.to_string in
let fields = assoc "fields" l |> JU.to_list |> List.map loop_field in
Record {name; namespace; doc; fields; aliases }
| "enum" ->
let name = assoc "name" l |> JU.to_string in
let namespace = None in
let aliases = List.assoc_opt "aliases" l |> Util.map_opt ~f:(fun x -> JU.to_list x |> List.map JU.to_string) in
let doc = List.assoc_opt "doc" l |> Util.map_opt ~f:JU.to_string in
let symbols = assoc "symbols" l |> JU.to_list |> List.map JU.to_string in
Enum {name; namespace; doc; aliases; symbols }
| s -> raise (E (spf "unknown schema type %S" s))
end
with e ->
raise (E (spf "error %s\nwhile decoding %s" (Printexc.to_string e) (J.to_string j)))
end
| _ -> raise (E (spf "unknown json schema %s" (J.to_string j)))
and loop_field j : record_field =
let l = JU.to_assoc j in
let name = assoc "name" l |> JU.to_string in
let ty = assoc "type" l |> loop in
let doc = List.assoc_opt "doc" l |> Util.map_opt ~f:JU.to_string in
{ name; ty; doc; }
in
try Ok (loop j)
with E e -> Error e
let pp out (self:t) = J.pretty_print out (to_json self)
let to_string (self:t) : string = J.to_string (to_json self)
let parse_string (str:string) : (t, string) result =
match J.from_string str with
| j -> of_json j
| exception _ -> Error "cannot parse json"
let parse_file (file:string) : (t, string) result =
match J.from_file file with
| j -> of_json j
| exception _ -> Error (Printf.sprintf "cannot parse json from file %S" file)