From cc783c157f31e7e713c8b83be67449b1859dac27 Mon Sep 17 00:00:00 2001
From: Marc Coquand <marc@mccd.space>
Date: Wed, 20 Dec 2023 20:43:25 -0600
Subject: Initial commit

---
 lib/activitypub/activitypub.ml |   5 +
 lib/activitypub/common.ml      |  47 ++++++
 lib/activitypub/constants.ml   |  49 ++++++
 lib/activitypub/decode.ml      | 352 +++++++++++++++++++++++++++++++++++++++++
 lib/activitypub/dune           |   3 +
 lib/activitypub/encode.ml      | 303 +++++++++++++++++++++++++++++++++++
 lib/activitypub/readme.md      |   5 +
 lib/activitypub/types.ml       | 245 ++++++++++++++++++++++++++++
 8 files changed, 1009 insertions(+)
 create mode 100644 lib/activitypub/activitypub.ml
 create mode 100644 lib/activitypub/common.ml
 create mode 100644 lib/activitypub/constants.ml
 create mode 100644 lib/activitypub/decode.ml
 create mode 100644 lib/activitypub/dune
 create mode 100644 lib/activitypub/encode.ml
 create mode 100644 lib/activitypub/readme.md
 create mode 100644 lib/activitypub/types.ml

(limited to 'lib/activitypub')

diff --git a/lib/activitypub/activitypub.ml b/lib/activitypub/activitypub.ml
new file mode 100644
index 0000000..511b4a3
--- /dev/null
+++ b/lib/activitypub/activitypub.ml
@@ -0,0 +1,5 @@
+module Common = Common
+module Constants = Constants
+module Types = Types
+module Encode = Encode
+module Decode = Decode
diff --git a/lib/activitypub/common.ml b/lib/activitypub/common.ml
new file mode 100644
index 0000000..59c7099
--- /dev/null
+++ b/lib/activitypub/common.ml
@@ -0,0 +1,47 @@
+module D = Decoders_yojson.Safe.Decode
+
+let timestamp =
+  let open D in
+  let* time = string in
+  match Ptime.of_rfc3339 time |> Ptime.rfc3339_error_to_msg with
+  | Ok (t, _, _) -> succeed t
+  | Error `Msg err -> fail err
+
+let singleton_or_list dec =
+  D.(one_of ["singleton", (dec >|= fun v -> [v]);
+             "list", list dec;
+             "null", null >|= fun () -> []])  
+
+let lossy_list_of dec =
+  let open D in
+  list (one_of ["known", (dec >|= fun v -> `Value v); "unknown", value >|= fun v -> `Raw v])
+
+
+let constant ?msg target =
+  let open D in
+  let* str = string in
+  if String.equal str target
+  then succeed ()
+  else match msg with
+    | None -> fail (Printf.sprintf "expected %s received %s" target str)
+    | Some msg -> fail (Printf.sprintf msg str)
+
+let field_or_default field' decoder default =
+  let open D in
+  let+ field = field_opt field' decoder in
+  Option.value ~default field
+
+let list_ignoring_unknown ty =
+  let open D in
+  list (maybe ty) >|= fun v -> List.filter_map Fun.id v
+
+let items obj =
+  let open D in
+  one_of [
+    ("ordered items",
+     let* items = field "orderedItems" (list obj) in
+     succeed (true, items));
+    "items",
+    let* items = field "items" (list obj) in
+    succeed (false, items)
+  ]
diff --git a/lib/activitypub/constants.ml b/lib/activitypub/constants.ml
new file mode 100644
index 0000000..0488335
--- /dev/null
+++ b/lib/activitypub/constants.ml
@@ -0,0 +1,49 @@
+open Containers
+
+module ContentType = struct
+  let ld_json_activity_streams = "application/ld+json; profile=\"https://www.w3.org/ns/activitystreams\""
+
+  let xrd_xml = "application/xrd+xml"
+  let ld_json = "application/ld+json"
+  let activity_json = "application/activity+json"
+  let plain_json = "application/json"
+  let html = "text/html"
+  let any = "*/*"
+
+  let content_types = [
+    ld_json_activity_streams, `JSON;
+    ld_json, `JSON;
+    activity_json, `JSON;
+    plain_json, `JSON;
+    html, `HTML;
+    any, `HTML;
+  ]
+
+  let of_string content_type =
+    List.find_opt
+      (fun (str, _) ->
+         String.prefix ~pre:str content_type) content_types
+    |> Option.map snd
+
+
+end
+
+module Webfinger = struct
+  let json_rd = "application/jrd+json"
+
+  let self_rel = "self"
+  let ostatus_rel = "http://ostatus.org/schema/1.0/subscribe"
+  let profile_page = "http://webfinger.net/rel/profile-page"
+end
+
+module ActivityStreams = struct
+
+  let public = "https://www.w3.org/ns/activitystreams#Public"
+
+  let context : string * Yojson.Safe.t =
+    "@context", `List [
+      `String "https://www.w3.org/ns/activitystreams";
+      `String "https://w3id.org/security/v1"
+    ]
+
+end
diff --git a/lib/activitypub/decode.ml b/lib/activitypub/decode.ml
new file mode 100644
index 0000000..4074e68
--- /dev/null
+++ b/lib/activitypub/decode.ml
@@ -0,0 +1,352 @@
+open Containers
+open Common
+
+let decode_string enc vl = D.decode_string enc vl |> Result.map_err D.string_of_error
+
+let id = D.(one_of ["string", string; "id", field "id" string])
+
+let ordered_collection_page obj =
+  let open D in
+  let* () = field "type" @@ constant ~msg:"Expected OrderedCollectionPage (received %s)" "OrderedCollectionPage"
+  and* id = field "id" string
+  and* next = field_opt "next" id
+  and* prev = field_opt "prev" id
+  and* part_of = field_opt "partOf" string
+  and* total_items = field_opt "totalItems" int
+  and* (is_ordered, items) = items obj in
+  succeed ({id; next; prev; part_of; total_items; is_ordered; items}: _ Types.ordered_collection_page)
+
+let ordered_collection obj =
+  let open D in
+  let* () = field "type" @@ constant ~msg:"Expected OrderedCollection (received %s)" "OrderedCollection"
+  and* id = field_opt "id" string
+  and* total_items = field "totalItems" int
+  and* contents =
+    one_of [
+      "items", map (fun v -> `Items v) (items obj);
+      "first", map (fun v -> `First v) (field "first" (ordered_collection_page obj))
+    ] in
+  succeed ({id; total_items; contents}: _ Types.ordered_collection)
+
+let mention =
+  let open D in
+  let* () = field "type" @@ constant ~msg:"expected Mention (received %s)" "Mention"
+  and* href = field "href" string
+  and* name = field "name" string in
+  succeed ({ty=`Mention; href;name} : Types.tag)
+
+let hashtag =
+  let open D in
+  let* () = field "type" @@ constant ~msg:"expected Hashtag (received %s)" "Hashtag"
+  and* href = field "href" string
+  and* name = field "name" string in
+  succeed ({ty=`Hashtag; href;name}: Types.tag)
+
+let tag =
+  let open D in
+  let* ty = field "type" string in
+  match ty with
+  | "Mention" -> mention
+  | "Hashtag" -> hashtag
+  | _ -> fail (Printf.sprintf "unknown tag %s" ty)
+
+let undo obj =
+  let open D in
+  let* () = field "type" @@ constant ~msg:"expected Undo (received %s)" "Undo"
+  and* id = field "id" string
+  and* actor = field "actor" id
+  and* published = field_opt "published" timestamp
+  and* obj = field "object" obj
+  and* raw = value in
+  succeed ({id;published;actor;obj;raw}: _ Types.undo)
+
+let like =
+  let open D in
+  let* () = field "type" @@ constant ~msg:"expected Like (received %s)" "Like"
+  and* id = field "id" string
+  and* actor = field "actor" id
+  and* published = field_opt "published" timestamp
+  and* obj = field "object" id
+  and* raw = value in
+  succeed ({id; actor; published; obj; raw}: Types.like)
+
+let tombstone =
+  let open D in
+  let* () = field "type" @@ constant ~msg:"expected Tombstone (received %s)" "Tombstone"
+  and* id = field "id" string in
+  succeed id
+
+let delete obj =
+  let open D in
+  let* () = field "type" @@ constant ~msg:"expected Delete (received %s)" "Delete"
+  and* id = field "id" string
+  and* actor = field "actor" id
+  and* published = field_opt "published" timestamp
+  and* obj = field "object" obj
+  and* raw = value in
+  succeed ({id;published;actor;obj;raw}: _ Types.delete)
+
+let block =
+  let open D in
+  let* () = field "type" @@ constant ~msg:"expected Block (received %s)" "Block"
+  and* id = field "id" string
+  and* obj = field "object" string
+  and* published = field_opt "published" timestamp
+  and* actor = field "actor" id
+  and* raw = value in
+  succeed ({id;published;obj;actor;raw}: Types.block)
+
+let accept obj =
+  let open D in
+  let* () = field "type" @@ constant ~msg:"expected Accept (received %s)" "Accept"
+  and* id = field "id" string
+  and* actor = field "actor" id
+  and* published = field_opt "published" timestamp
+  and* obj = field "object" obj
+  and* raw = value in
+  succeed ({id;published;actor;obj;raw}: _ Types.accept)
+
+let public_key =
+  let open D in
+  let* id = field "id" string
+  and* owner = field "owner" string
+  and* pem = field "publicKeyPem" string in
+  succeed ({id;owner;pem}: Types.public_key)
+
+let attachment =
+  let open D in
+  let* media_type = field_opt "mediaType" string
+  and* name = field_opt "name" string
+  and* type_ = field_opt "type" string
+  and* url = field "url" string in
+  succeed ({media_type;name;type_;url}: Types.attachment)
+
+
+let person =
+  let open D in
+  let* () = field "type" @@ constant ~msg:"expected Person (received %s)" "Person"
+  and* id = field "id" string
+  and* name = field_opt "name" string
+  and* url = field_or_default "url" (nullable string) None
+  and* preferred_username = field_opt "preferredUsername" string
+  and* inbox = field "inbox" string
+  and* outbox = field "outbox" string
+  and* summary = field_opt "summary" string
+  and* public_key = field "publicKey" public_key
+  and* manually_approves_followers =
+    field_or_default "manuallyApprovesFollowers" bool false
+  and* discoverable = field_or_default "discoverable" bool false
+  and* followers = field_opt "followers" string
+  and* following = field_opt "following" string
+  and* icon = maybe (at ["icon";"url"] string)
+  and* raw = value in
+  succeed ({
+    id;
+    name;
+    url;
+
+    preferred_username;
+
+    inbox;
+    outbox;
+
+    summary;
+
+    public_key;
+
+    manually_approves_followers;
+
+    discoverable;
+    followers;
+    following;
+    icon;
+    raw;
+  }: Types.person)
+
+let note = 
+  let open D in
+  let* () = field "type" @@ constant ~msg:"expected Note (received %s)" "Note"
+  and* id = field "id" string
+  and* actor = one_of ["actor", field "actor" id; "attributed_to", field "attributedTo" id]
+  and* attachment = field_or_default "attachment" (singleton_or_list attachment) []
+  and* to_ = field "to" (singleton_or_list string)
+  and* in_reply_to = field_or_default "inReplyTo" (nullable string) None
+  and* cc = field_or_default "cc" (singleton_or_list string) []
+  and* content = field "content" string
+  and* source = field_opt "source"
+                  (one_of ["string", string; "multi-encode", field "content" string])
+  and* summary = field_or_default "summary" (nullable string) None
+  and* sensitive = field_or_default "sensitive" (nullable bool) None
+  and* published = field_opt "published" timestamp
+  and* tags = field_or_default "tag" (lossy_list_of tag) []
+  and* raw = value in
+  succeed ({ id; actor; attachment; in_reply_to; to_; cc;
+             sensitive=Option.value ~default:false sensitive;
+             content; source; summary; tags; published; raw }: Types.note)
+
+let follow =
+  let open D in
+  let* () = field "type" @@ constant ~msg:"expected create object (received %s)" "Follow"
+  and* actor = field "actor" id
+  and* cc = field_or_default "cc" (singleton_or_list string) []
+  and* to_ = field_or_default "to" (singleton_or_list string) []
+  and* id = field "id" string
+  and* object_ = field "object" id
+  and* state = field_opt "state" (string >>= function "pending" -> succeed `Pending
+                                                    | "cancelled" -> succeed `Cancelled
+                                                    | _ -> fail "unknown status")
+  and* raw = value in
+  succeed ({actor; cc; to_; id; object_; state; raw}: Types.follow)
+
+let announce obj =
+  let open D in
+  let* () = field "type" @@ constant ~msg:"expected create object (received %s)" "Announce"
+  and* actor = field "actor" id
+  and* id = field "id" string
+  and* published = field_opt "published" timestamp
+  and* to_ = field "to" (singleton_or_list string)
+  and* cc = field_or_default "cc" (singleton_or_list string) []
+  and* obj = field "object" obj
+  and* raw = value in
+  succeed ({id; published; actor; to_; cc; obj; raw}: _ Types.announce)
+
+let create obj =
+  let open D in
+  let* () = field "type" @@ constant ~msg:"expected create object (received %s)" "Create"
+  and* id = field "id" string
+  and* actor = field "actor" id
+  and* direct_message = field_or_default "direct" bool false
+  and* published = field_opt "published" timestamp
+  and* to_ = field_or_default "to" (singleton_or_list string) []
+  and* cc = field_or_default "cc" (singleton_or_list string) []
+  and* obj = field "object" obj
+  and* raw = value in
+
+  succeed ({
+    id; actor; published;
+    to_; cc;
+    direct_message;
+    obj;
+    raw;
+  }: _ Types.create)
+
+let core_obj () =
+  let open D in
+  let* ty = field_opt "type" string in
+  match ty with
+  | Some "Person" -> person >|= fun v -> `Person v
+  | Some "Follow" -> follow >|= fun v -> `Follow v
+  | Some "Note" -> note >|= fun v -> `Note v
+  | Some "Block" -> block >|= fun v -> `Block v
+  | Some "Like" -> like >|= fun v -> `Like v
+  | None -> string >|= fun v -> `Link v
+  | Some ev -> fail ("unsupported event" ^ ev)
+
+let core_obj = core_obj ()
+
+let event (enc: Types.core_obj D.decoder) : Types.obj D.decoder =
+  let open D in
+  let* ty = field "type" string in
+  match ty with
+  | "Create" -> create enc >|= fun v -> `Create v
+  | "Accept" -> accept enc >|= fun v -> `Accept v
+  | "Undo" -> undo enc >|= fun v -> `Undo v
+  | "Delete" -> delete enc >|= fun v -> `Delete v
+  | "Announce" -> announce enc >|= fun v -> `Announce v
+  | _ -> fail "unsupported event"
+
+let obj : Types.obj D.decoder =
+  D.one_of [
+    "core_obj", core_obj;
+    "core_obj event", (event core_obj)
+  ]
+
+module Webfinger = struct
+
+  let ty =
+    let open D in
+    string >>= function
+    | str when String.prefix ~pre:Constants.ContentType.html str ->
+      succeed `Html
+    | str when String.prefix ~pre:Constants.ContentType.plain_json str ->
+      succeed `Json
+    | str when String.prefix ~pre:Constants.ContentType.activity_json str ->
+      succeed `ActivityJson
+    | str when String.prefix ~pre:Constants.ContentType.ld_json_activity_streams str ->
+      succeed `ActivityJsonLd
+    | _ ->
+      fail "unsupported self link type"
+
+  let self =
+    let open D in
+    let* ty = field "type" ty
+    and* href = field "href" string in
+    succeed @@ Types.Webfinger.Self (ty, href)
+
+  let profile_page =
+    let open D in
+    let* ty = field "type" ty
+    and* href = field "href" string in
+    succeed @@ Types.Webfinger.ProfilePage (ty, href)
+
+  let ostatus_subscribe =
+    let open D in
+    let* template = field "template" string in
+    succeed @@ Types.Webfinger.OStatusSubscribe template
+
+  let link =
+    let open D in
+    let* rel = field "rel" string in
+    match rel with
+    | "self" -> self
+    | str when String.equal str Constants.Webfinger.ostatus_rel ->
+      ostatus_subscribe
+    | str when String.equal str Constants.Webfinger.profile_page ->
+      profile_page
+    | _ -> fail "unsupported link relation"
+
+  let query_result =
+    let open D in
+    let* subject = field "subject" string
+    and* aliases = field "aliases" (list string)
+    and* links = field "links" (list_ignoring_unknown link) in
+
+    succeed Types.Webfinger.{subject;aliases;links}
+
+end
+
+module Nodeinfo = struct
+
+  let software =
+    let open D in
+    let* name = field "name" string
+    and* version = field "version" string in
+    succeed @@ Types.Nodeinfo.{name;version}
+
+  let usage_users =
+    let open D in
+    let* total = field_or_default "total" int 0
+    and* active_month = field_or_default "activeMonth" int 0
+    and* active_half_year = field_or_default "activeHalfyear" int 0 in
+    succeed @@ Types.Nodeinfo.{total; active_month; active_half_year}
+
+  let usage =
+    let open D in
+    let* users = field "users" usage_users 
+    and* local_posts = field_or_default "localPosts" int 0 in
+    succeed @@ Types.Nodeinfo.{users; local_posts}
+
+  let t =
+    let open D in
+    let* software = field "software" software
+    and* protocols = field_or_default "protocols" (list string) []
+    and* inbound_services = field_or_default "services" (field_or_default "inbound" (list string) []) []
+    and* outbound_services = field_or_default "services" (field_or_default "outbound" (list string) []) []
+    and* usage = field "usage" usage
+    and* open_registrations = field_or_default "openRegistrations" bool false 
+    and* metadata = field_opt "metadata" value
+    and* raw = value in
+    succeed @@ Types.Nodeinfo.{software;protocols;inbound_services;outbound_services;usage;open_registrations;metadata;raw}
+
+
+end
diff --git a/lib/activitypub/dune b/lib/activitypub/dune
new file mode 100644
index 0000000..9222a82
--- /dev/null
+++ b/lib/activitypub/dune
@@ -0,0 +1,3 @@
+(library (name activitypub)
+ (preprocess (pps ppx_deriving.std))
+ (libraries containers uri yojson decoders decoders-yojson ptime))
diff --git a/lib/activitypub/encode.ml b/lib/activitypub/encode.ml
new file mode 100644
index 0000000..2b64e76
--- /dev/null
+++ b/lib/activitypub/encode.ml
@@ -0,0 +1,303 @@
+module E = Decoders_yojson.Safe.Encode
+
+
+let (<:) = function
+  | (_, None) -> fun _ -> []
+  | (field, Some vl) -> fun ty -> [field, ty vl]
+let (@) field vl = (field, Some vl)
+let (@?) field vl = (field, vl)
+
+let ptime time = E.string (Ptime.to_rfc3339 ~tz_offset_s:0 time)
+let obj ls = E.obj @@ List.flatten ls
+let ap_obj ty ls =
+  E.obj (Constants.ActivityStreams.context :: ("type", E.string ty) :: List.flatten ls)
+
+let or_raw conv = function
+  | `Raw v -> v
+  | `Value v -> conv v
+
+(** * Collections  *)
+let ordered_collection_page enc
+      ({ id; prev; next; is_ordered; items; part_of; total_items }:
+         _ Types.ordered_collection_page) =
+  ap_obj "OrderedCollectionPage" [
+    "id" @ id <: E.string;
+    "next" @? next <: E.string;
+    "prev" @? prev <: E.string;
+    "partOf" @? part_of <: E.string;
+    "totalItems" @? total_items <: E.int;
+    (match is_ordered with
+     | true -> "orderedItems"
+     | false -> "items")  @ items <: E.list enc
+  ]
+
+let ordered_collection enc
+      ({ id; total_items; contents }: _ Types.ordered_collection) =
+  ap_obj "OrderedCollection" [
+    "id" @? id <: E.string;
+    "totalItems" @ total_items <: E.int;
+    match contents with
+    | `First page -> "first" @ page <: ordered_collection_page enc
+    | `Items (true, items) -> "orderedItems" @ items <: E.list enc
+    | `Items (false, items) -> "items" @ items <: E.list enc
+  ]
+
+(** * Events *)
+
+let create enc ({ id; actor; published; to_; cc; direct_message; obj; raw=_ }:
+                  _ Types.create) =
+  ap_obj "Create" [
+    "id" @ id <: E.string;
+    "actor" @ actor <: E.string;
+    "published" @? published <: ptime;
+    "to" @ to_ <: E.(list string);
+    "cc" @ cc <: E.(list string);
+    "directMessage"  @ direct_message <: E.bool;
+    "object" @ obj <: enc;
+  ]
+
+let announce enc ({ id; actor; published; to_; cc; obj; raw=_ } : _ Types.announce) =
+  ap_obj "Announce" [
+    "id" @ id <: E.string;
+    "actor" @ actor <: E.string;
+    "published" @? published <: ptime;
+    "to" @ to_ <: E.(list string);
+    "cc" @ cc <: E.(list string);
+    "object" @ obj <: enc;
+  ]
+
+let accept enc ({ id; actor; published; obj; raw=_ } : _ Types.accept) =
+  ap_obj "Accept" [
+    "id" @ id <: E.string;
+    "actor" @ actor <: E.string;
+    "published" @? published <: ptime;
+    "object" @ obj <: enc;
+  ]
+
+let undo enc ({ id; actor; published; obj; raw=_ } : _ Types.undo) =
+  ap_obj "Undo" [
+    "id" @ id <: E.string;
+    "actor" @ actor <: E.string;
+    "published" @? published <: ptime;
+    "object" @ obj <: enc;
+  ]
+
+let delete enc ({ id; actor; published; obj; raw=_ } : _ Types.delete) =
+  ap_obj "Delete" [
+    "id" @ id <: E.string;
+    "actor" @ actor <: E.string;
+    "published" @? published <: ptime;
+    "object" @ obj <: enc;
+  ]
+
+(** * Objects *)
+
+let public_key (key: Types.public_key) =
+  obj [
+    "id" @ key.id <: E.string;
+    "owner" @ key.owner <: E.string;
+    "publicKeyPem" @ key.pem <: E.string;
+  ]
+
+let icon (url: string) =
+  obj [
+    "type" @ "Image" <: E.string;
+    "url" @ url <: E.string;
+  ]
+
+let person ({ id; name; url; inbox; outbox;
+              preferred_username; summary;
+              manually_approves_followers;
+              discoverable; followers; following;
+              public_key=key; icon=i; raw=_ }: Types.person) =
+  ap_obj "Person" [
+
+    "id" @ id <: E.string;
+
+    "name" @? name <: E.string;
+    "url" @? url <: E.string;
+
+    "preferredUsername" @? preferred_username <: E.string;
+
+    "inbox" @ inbox <: E.string;
+    "outbox" @ outbox <: E.string;
+
+    "summary" @? summary <: E.string;
+
+    "publicKey" @ key <: public_key;
+
+    "manuallyApprovesFollowers" @ manually_approves_followers <: E.bool;
+
+    "discoverable" @ discoverable <: E.bool;
+
+    "followers" @? followers <: E.string;
+    "following" @? following <: E.string;
+
+    "icon" @? i <: icon;
+  ]
+
+let state = function
+    `Pending -> E.string "pending"
+  | `Cancelled -> E.string "cancelled"
+
+
+let follow ({ id; actor; cc; object_; to_; state=st; raw=_ }: Types.follow) =
+  ap_obj "Follow" [
+    "id" @ id <: E.string;
+    "actor" @ actor <: E.string;
+    "to" @ to_ <: E.list E.string;
+    "cc" @ cc <: E.list E.string;
+    "object" @ object_ <: E.string;
+    "state" @? st <: state;
+  ]
+
+let tag ({ ty; href; name }: Types.tag) =
+  ap_obj (match ty with `Mention -> "Mention" | `Hashtag -> "Hashtag") [
+    "href" @ href <: E.string;
+    "name" @ name <: E.string;
+  ]
+
+let attachment ({media_type; name; url; type_}: Types.attachment) =
+  obj [
+    "type" @? type_ <: E.string;
+    "mediaType" @? media_type <: E.string;
+    "name" @? name <: E.string;
+    "url" @ url <: E.string;
+  ]
+
+let note ({ id; actor; to_; in_reply_to; cc; content; sensitive; source; summary;
+            attachment=att;
+            published; tags; raw=_ }: Types.note) =
+  let att = match att with [] -> None | _ -> Some att in
+  ap_obj "Note" [
+    "id" @ id <: E.string;
+    "actor" @ actor <: E.string;
+    "attachment" @? att <: E.list attachment;
+    "to" @ to_ <: E.list E.string;
+    "inReplyTo" @? in_reply_to <: E.string;
+    "cc" @ cc <: E.list E.string;
+    "content" @ content <: E.string;
+    "sensitive" @ sensitive <: E.bool;
+    "source" @? source <: E.string;
+    "summary" @? summary <: E.string;
+    "published" @? published <: ptime;
+    "tags" @ tags <: E.list (or_raw tag);
+  ]
+
+let block ({ id; obj; published; actor; raw=_ }: Types.block) =
+  ap_obj "Block" [
+    "id" @ id <: E.string;
+    "object" @ obj <: E.string;
+    "actor" @ actor <: E.string;
+    "published" @? published <: ptime;
+  ]
+
+let like ({ id; actor; published; obj; raw=_ }: Types.like) =
+  ap_obj "Like" [
+    "id" @ id <: E.string;
+    "actor" @ actor <: E.string;
+    "object" @ obj <: E.string;
+    "published" @? published <: ptime;
+  ]
+
+
+let core_obj : Types.core_obj E.encoder = function
+  | `Follow f -> follow f
+  | `Block b -> block b
+  | `Note n -> note n
+  | `Person p -> person p
+  | `Like l -> like l
+  | `Link r -> E.string r
+
+let event enc : _ Types.event E.encoder = function
+  | `Announce a -> announce enc a
+  | `Undo u -> undo enc u
+  | `Delete d -> delete enc d
+  | `Create c -> create enc c
+  | `Accept a -> accept enc a
+
+let object_ : Types.obj E.encoder = function
+  | #Types.core_obj as c -> core_obj c
+  | #Types.core_event as e -> event core_obj e
+
+module Webfinger = struct
+
+  let ty = function
+    | `ActivityJson -> E.string Constants.ContentType.activity_json
+    | `Html -> E.string Constants.ContentType.html
+    | `ActivityJsonLd -> E.string Constants.ContentType.ld_json_activity_streams
+    | `Json -> E.string Constants.ContentType.plain_json
+
+  let link = function
+    | Types.Webfinger.Self (t, href) -> obj [
+      "href" @ href <: E.string;
+      "rel" @ Constants.Webfinger.self_rel <: E.string;
+      "type" @ t <: ty;
+    ]
+    | ProfilePage (t, href) ->
+      obj [
+        "href" @ href <: E.string;
+        "rel" @ Constants.Webfinger.profile_page <: E.string;
+        "type" @ t <: ty;
+      ]
+    | OStatusSubscribe template -> obj [
+      "rel" @ Constants.Webfinger.ostatus_rel <: E.string;
+      "template" @ template <: E.string;
+    ]
+
+  let query_result ({subject;aliases;links}: Types.Webfinger.query_result) =
+    obj [
+      "subject" @ subject <: E.string;
+      "aliases" @ aliases <: E.(list string);
+      "links" @ links <: E.list link;
+    ]
+
+end
+
+module Nodeinfo = struct
+
+  let software (s: Types.Nodeinfo.software) =
+    obj [
+      "name" @ s.name <: E.string;
+      "version" @ s.version <: E.string;
+    ]
+
+  let usage_users ({ total; active_month; active_half_year }: Types.Nodeinfo.usage_users) =
+    obj [
+      "total" @ total <: E.int;
+      "activeMonth" @ active_month <: E.int;
+      "activeHalfyear" @ active_half_year <: E.int;
+    ]
+
+  let usage ({ local_posts; users } : Types.Nodeinfo.usage) =
+    obj [
+      "users" @ users <: usage_users;
+      "localPosts" @ local_posts <: E.int
+    ]
+
+  let t ({ software=software'; protocols; inbound_services; outbound_services; usage=usage';
+           open_registrations; metadata; raw=_ } : Types.Nodeinfo.t) =
+    obj [
+      "version" @ "2.0" <: E.string;
+      "software" @ software' <: software;
+      "protocols" @ protocols <: E.list E.string;
+      "services" @ obj [
+        "inbound" @ inbound_services <: E.list E.string;
+        "outbound" @ outbound_services <: E.list E.string;
+      ] <: Fun.id;
+      "usage" @ usage' <: usage;
+      "openRegistrations" @ open_registrations <: E.bool;
+      "metadata" @? metadata <: Fun.id;
+    ]
+
+end
+
+
+(* module Build (S: sig
+ *     type user
+ * 
+ *     val owner: user -> Uri.t
+ * 
+ *   end) = struct
+ * 
+ * end *)
diff --git a/lib/activitypub/readme.md b/lib/activitypub/readme.md
new file mode 100644
index 0000000..7282026
--- /dev/null
+++ b/lib/activitypub/readme.md
@@ -0,0 +1,5 @@
+# Activitypub Encoding
+
+This module defines functions to parse to and from activitypub JSONs from other servers.
+
+Taken from [Ocamlot](https://github.com/gopiandcode/ocamlot).
diff --git a/lib/activitypub/types.ml b/lib/activitypub/types.ml
new file mode 100644
index 0000000..e4a56e9
--- /dev/null
+++ b/lib/activitypub/types.ml
@@ -0,0 +1,245 @@
+type yojson = Yojson.Safe.t
+let pp_yojson fmt vl = Yojson.Safe.pretty_print fmt vl
+let equal_yojson l r = Yojson.Safe.equal l r
+
+(** * Collections *)
+type 'a ordered_collection_page = {
+  id: string;
+  prev: string option;
+  next: string option;
+  is_ordered: bool;
+  items: 'a list;
+  part_of: string option;
+  total_items: int option;
+} [@@deriving show, eq]
+
+
+type 'a ordered_collection = {
+  id: string option;
+  total_items: int;
+  contents: [
+    | `Items of (bool * 'a list)
+    | `First of 'a ordered_collection_page
+  ]
+} [@@deriving show, eq]
+
+(** * Events *)
+type 'a create = {
+  id: string;
+  actor: string;
+  published: Ptime.t option;
+  to_: string list;
+  cc: string list;
+  direct_message: bool;
+  obj: 'a;
+  raw: yojson;
+} [@@deriving show, eq]
+
+
+type 'a announce = {
+  id: string;
+  actor: string;
+  published: Ptime.t option;
+  to_: string list;
+  cc: string list;
+  obj: 'a;
+  raw: yojson;
+} [@@deriving show, eq]
+
+
+type 'a accept = {
+  id: string;
+  actor: string;
+  published: Ptime.t option;
+  obj: 'a;
+  raw: yojson;
+} [@@deriving show, eq]
+
+type 'a undo = {
+  id: string;
+  actor: string;
+  published: Ptime.t option;
+  obj: 'a;
+  raw: yojson;
+} [@@deriving show, eq]
+
+type 'a delete = {
+  id: string;
+  actor: string;
+  published: Ptime.t option;
+  obj: 'a;
+  raw: yojson;
+}
+[@@deriving show, eq]
+
+type 'a event = [
+    `Create of 'a create
+  | `Announce of 'a announce
+  | `Accept of 'a accept
+  | `Undo of 'a undo
+  | `Delete of 'a delete
+] [@@deriving show, eq]
+
+
+(** * Objects *)
+type public_key = {
+  id: string;
+  owner: string;
+  pem: string;
+} [@@deriving show, eq]
+
+type person = {
+  id: string;
+  name: string option;
+  url: string option;
+
+  preferred_username: string option;
+
+  inbox: string;
+  outbox: string;
+
+  summary: string option;
+
+  public_key: public_key;
+
+  manually_approves_followers: bool;
+
+  discoverable: bool;
+  followers: string option;
+  following: string option;
+  icon: string option;
+  raw: yojson;
+}  [@@deriving show, eq]
+
+type follow = {
+  id: string;
+  actor: string;
+  cc: string list;
+  to_: string list;
+  object_: string;
+  state: [`Pending | `Cancelled ] option;
+  raw: yojson;
+} [@@deriving show, eq]
+
+type tag = {
+  ty: [`Mention | `Hashtag ];
+  href: string;
+  name: string;
+} [@@deriving show, eq]
+
+type attachment = {
+  media_type: string option;
+  name: string option;
+  type_: string option;
+  url: string;
+} [@@deriving show, eq]
+
+type note = {
+  id: string;
+  actor: string;
+  attachment: attachment list;
+  to_: string list;
+  in_reply_to: string option;
+  cc: string list;
+  content: string;
+  sensitive: bool;
+  source: string option;
+  summary: string option;
+  published: Ptime.t option;
+  tags: [ `Raw of yojson | `Value of tag ] list;
+  raw: yojson;
+} [@@deriving show, eq]
+
+type block = {
+  id: string;
+  obj: string;
+  published: Ptime.t option;
+  actor: string;
+  raw: yojson;
+} [@@deriving show, eq]
+
+type like = {
+  id: string;
+  actor: string;
+  published: Ptime.t option;
+  obj: string;
+  raw: yojson;
+}
+[@@deriving show, eq]
+
+
+type core_obj = [
+    `Person of person
+  | `Follow of follow
+  | `Note of note
+  | `Block of block
+  | `Like of like
+  | `Link of string
+] [@@deriving show, eq]
+
+type core_event = core_obj event
+[@@deriving show, eq]
+
+type obj = [ core_obj | core_event ]
+[@@deriving show, eq]
+
+module Webfinger = struct
+
+  type ty = [ `Html | `Json | `ActivityJson | `ActivityJsonLd ]
+  [@@deriving show, eq]
+
+  type link =
+    | Self of ty * string
+    | ProfilePage of ty * string
+    | OStatusSubscribe of string
+  [@@deriving show, eq]
+
+  type query_result = {
+    subject: string;
+    aliases: string list;
+    links: link list;
+  }
+  [@@deriving show, eq]
+
+  let self_link query =
+    query.links
+    |> List.find_map (function
+        | Self ((`ActivityJson | `ActivityJsonLd | `Json), url) -> Some (Uri.of_string url)
+        | _ -> None)
+
+end
+
+module Nodeinfo = struct
+
+  type software = {
+    name: string;
+    version: string;
+  }
+  [@@deriving show, eq]
+
+  type usage_users = {
+    total: int;
+    active_month: int;
+    active_half_year: int;
+  }
+  [@@deriving show, eq]
+
+  type usage = {
+    local_posts: int;
+    users: usage_users;
+  }
+  [@@deriving show, eq]
+
+  type t = {
+    software: software;
+    protocols: string list;
+    inbound_services: string list;
+    outbound_services: string list;
+    usage: usage;
+    open_registrations: bool;
+    metadata: yojson option;
+    raw: yojson;
+  }
+  [@@deriving show, eq]
+
+end
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