Avoid panics (#392)

- Use `Result` as much as possible
- Display errors instead of panicking

TODO (maybe in another PR? this one is already quite big):
- Find a way to merge Ructe/ErrorPage types, so that we can have routes returning `Result<X, ErrorPage>` instead of panicking when we have an `Error`
- Display more details about the error, to make it easier to debug

(sorry, this isn't going to be fun to review, the diff is huge, but it is always the same changes)

plume-common/src/activity_pub/inbox.rs

@@ -1,4 +1,4 @@
-use activitypub::{activity::Create, Object};
+use activitypub::{activity::Create, Error as ApError, Object};
 
 use activity_pub::Id;
 
@@ -13,31 +13,30 @@ pub enum InboxError {
 }
 
 pub trait FromActivity<T: Object, C>: Sized {
-    fn from_activity(conn: &C, obj: T, actor: Id) -> Self;
+    type Error: From<ApError>;
 
-    fn try_from_activity(conn: &C, act: Create) -> bool {
-        if let Ok(obj) = act.create_props.object_object() {
-            Self::from_activity(
-                conn,
-                obj,
-                act.create_props
-                    .actor_link::<Id>()
-                    .expect("FromActivity::try_from_activity: id not found error"),
-            );
-            true
-        } else {
-            false
-        }
+    fn from_activity(conn: &C, obj: T, actor: Id) -> Result<Self, Self::Error>;
+
+    fn try_from_activity(conn: &C, act: Create) -> Result<Self, Self::Error> {
+        Self::from_activity(
+            conn,
+            act.create_props.object_object()?,
+            act.create_props.actor_link::<Id>()?,
+        )
     }
 }
 
 pub trait Notify<C> {
-    fn notify(&self, conn: &C);
+    type Error;
+
+    fn notify(&self, conn: &C) -> Result<(), Self::Error>;
 }
 
 pub trait Deletable<C, A> {
-    fn delete(&self, conn: &C) -> A;
-    fn delete_id(id: &str, actor_id: &str, conn: &C);
+    type Error;
+
+    fn delete(&self, conn: &C) -> Result<A, Self::Error>;
+    fn delete_id(id: &str, actor_id: &str, conn: &C) -> Result<A, Self::Error>;
 }
 
 pub trait WithInbox {