Document subscription endpoints, fix typos

Also adds a quick error case on the subscription endpoints
to avoid 500s

docs/api/pleroma_api.md

@@ -52,7 +52,7 @@ Request parameters can be passed via [query strings](https://en.wikipedia.org/wi
     * `confirm`
     * `captcha_solution`: optional, contains provider-specific captcha solution,
     * `captcha_token`: optional, contains provider-specific captcha token
-    * `token`: invite token required when the registerations aren't public.
+    * `token`: invite token required when the registrations aren't public.
 * Response: JSON. Returns a user object on success, otherwise returns `{"error": "error_msg"}`
 * Example response:
 ```
@@ -114,5 +114,53 @@ See [Admin-API](Admin-API.md)
 * Method `POST`
 * Authentication: required
 * Params:
-    * `id`: notifications's id
+    * `id`: notification's id
 * Response: JSON. Returns `{"status": "success"}` if the reading was successful, otherwise returns `{"error": "error_msg"}`
+
+## `/api/v1/pleroma/accounts/:id/subscribe`
+### Subscribe to receive notifications for all statuses posted by a user
+* Method `POST`
+* Authentication: required
+* Params:
+    * `id`: account id to subscribe to
+* Response: JSON, returns a mastodon relationship object on success, otherwise returns `{"error": "error_msg"}`
+* Example response:
+```json
+{
+  id: "abcdefg",
+  following: true,
+  followed_by: false,
+  blocking: false,
+  muting: false,
+  muting_notifications: false,
+  subscribing: true,
+  requested: false,
+  domain_blocking: false,
+  showing_reblogs: true,
+  endorsed: false
+}
+```
+
+## `/api/v1/pleroma/accounts/:id/unsubscribe`
+### Unsubscribe to stop receiving notifications from user statuses
+* Method `POST`
+* Authentication: required
+* Params:
+    * `id`: account id to unsubscribe from
+* Response: JSON, returns a mastodon relationship object on success, otherwise returns `{"error": "error_msg"}`
+* Example response:
+```json
+{
+  id: "abcdefg",
+  following: true,
+  followed_by: false,
+  blocking: false,
+  muting: false,
+  muting_notifications: false,
+  subscribing: false,
+  requested: false,
+  domain_blocking: false,
+  showing_reblogs: true,
+  endorsed: false
+}
+```

lib/pleroma/web/mastodon_api/mastodon_api_controller.ex

@@ -864,22 +864,30 @@ def unblock_domain(%{assigns: %{user: blocker}} = conn, %{"domain" => domain}) d
   end
 
   def subscribe(%{assigns: %{user: user}} = conn, %{"id" => id}) do
-    with %User{} = subscription_target <- User.get_by_id(id) do
-      {:ok, subscription_target} = User.subscribe(user, subscription_target)
-
+    with %User{} = subscription_target <- User.get_by_id(id),
+         {:ok, subscription_target} = User.subscribe(user, subscription_target) do
       conn
       |> put_view(AccountView)
       |> render("relationship.json", %{user: user, target: subscription_target})
+    else
+      {:error, message} ->
+        conn
+        |> put_resp_content_type("application/json")
+        |> send_resp(403, Jason.encode!(%{"error" => message}))
     end
   end
 
   def unsubscribe(%{assigns: %{user: user}} = conn, %{"id" => id}) do
-    with %User{} = subscription_target <- User.get_by_id(id) do
-      {:ok, subscription_target} = User.unsubscribe(user, subscription_target)
-
+    with %User{} = subscription_target <- User.get_by_id(id),
+         {:ok, subscription_target} = User.unsubscribe(user, subscription_target) do
       conn
       |> put_view(AccountView)
       |> render("relationship.json", %{user: user, target: subscription_target})
+    else
+      {:error, message} ->
+        conn
+        |> put_resp_content_type("application/json")
+        |> send_resp(403, Jason.encode!(%{"error" => message}))
     end
   end