Retain deleted messages and channels temporarily, to preserve events for replay.

Previously, when a channel (message) was deleted, `hi` would send events to all _connected_ clients to inform them of the deletion, then delete all memory of the channel (message). Any disconnected client, on reconnecting, would not receive the deletion event, and would de-synch with the service. The creation events were also immediately retconned out of the event stream, as well.

With this change, `hi` keeps a record of deleted channels (messages). When replaying events, these records are used to replay the deletion event. After 7 days, the retained data is deleted, both to keep storage under control and to conform to users' expectations that deleted means gone.

To match users' likely intuitions about what deletion does, deleting a channel (message) _does_ immediately delete some of its associated data. Channels' names are blanked, and messages' bodies are also blanked. When the event stream is replayed, the original channel.created (message.sent) event is "tombstoned", with an additional `deleted_at` field to inform clients. The included client does not use this field, at least yet.

The migration is, once again, screamingingly complicated due to sqlite's limited ALTER TABLE … ALTER COLUMN support.

This change also contains capabilities that would allow the API to return 410 Gone for deleted channels or messages, instead of 404. I did experiment with this, but it's tricky to do pervasively, especially since most app-level interfaces return an `Option<Channel>` or `Option<Message>`. Redesigning these to return either `Ok(Channel)` (`Ok(Message)`) or `Err(Error::NotFound)` or `Err(Error::Deleted)` is more work than I wanted to take on for this change, and the utility of 410 Gone responses is not obvious to me. We have other, more pressing API design warts to address.

5 files changed, 41 insertions, 19 deletions

diff --git a/src/test/fixtures/channel.rs b/src/test/fixtures/channel.rs
index b678717..a1dda61 100644
--- a/src/test/fixtures/channel.rs
+++ b/src/test/fixtures/channel.rs
@@ -1,10 +1,17 @@
+use std::future;
+
 use faker_rand::{
     en_us::{addresses::CityName, names::FullName},
     faker_impl_from_templates,
 };
 use rand;
 
-use crate::{app::App, channel::Channel, clock::RequestedAt};
+use crate::{
+    app::App,
+    channel::{self, Channel},
+    clock::RequestedAt,
+    event::Event,
+};
 
 pub async fn create(app: &App, created_at: &RequestedAt) -> Channel {
     let name = propose();
@@ -22,3 +29,17 @@ struct Name(String);
 faker_impl_from_templates! {
     Name; "{} {}", CityName, FullName;
 }
+
+pub fn events(event: Event) -> future::Ready<Option<channel::Event>> {
+    future::ready(match event {
+        Event::Channel(channel) => Some(channel),
+        _ => None,
+    })
+}
+
+pub fn created(event: channel::Event) -> future::Ready<Option<channel::event::Created>> {
+    future::ready(match event {
+        channel::Event::Created(event) => Some(event),
+        channel::Event::Deleted(_) => None,
+    })
+}
diff --git a/src/test/fixtures/event.rs b/src/test/fixtures/event.rs
index 7fe2bf3..fa4fbc0 100644
--- a/src/test/fixtures/event.rs
+++ b/src/test/fixtures/event.rs
@@ -1,11 +1,8 @@
-use crate::{
-    event::Event,
-    message::{Event::Sent, Message},
-};
+use crate::message::{Event, Message};
 
 pub fn message_sent(event: &Event, message: &Message) -> bool {
     matches!(
         &event,
-        Event::Message(Sent(event)) if message == &event.into()
+        Event::Sent(event) if message == &event.into()
     )
 }
diff --git a/src/test/fixtures/filter.rs b/src/test/fixtures/filter.rs
deleted file mode 100644
index 84d27b0..0000000
--- a/src/test/fixtures/filter.rs
+++ /dev/null
@@ -1,11 +0,0 @@
-use futures::future;
-
-use crate::{channel::Event::Created, event::Event, message::Event::Sent};
-
-pub fn messages() -> impl FnMut(&Event) -> future::Ready<bool> {
-    |event| future::ready(matches!(event, Event::Message(Sent(_))))
-}
-
-pub fn created() -> impl FnMut(&Event) -> future::Ready<bool> {
-    |event| future::ready(matches!(event, Event::Channel(Created(_))))
-}
diff --git a/src/test/fixtures/message.rs b/src/test/fixtures/message.rs
index 381b10b..eb00e7c 100644
--- a/src/test/fixtures/message.rs
+++ b/src/test/fixtures/message.rs
@@ -1,6 +1,15 @@
+use std::future;
+
 use faker_rand::lorem::Paragraphs;
 
-use crate::{app::App, channel::Channel, clock::RequestedAt, login::Login, message::Message};
+use crate::{
+    app::App,
+    channel::Channel,
+    clock::RequestedAt,
+    event::Event,
+    login::Login,
+    message::{self, Message},
+};
 
 pub async fn send(app: &App, channel: &Channel, login: &Login, sent_at: &RequestedAt) -> Message {
     let body = propose();
@@ -14,3 +23,10 @@ pub async fn send(app: &App, channel: &Channel, login: &Login, sent_at: &Request
 pub fn propose() -> String {
     rand::random::<Paragraphs>().to_string()
 }
+
+pub fn events(event: Event) -> future::Ready<Option<message::Event>> {
+    future::ready(match event {
+        Event::Message(event) => Some(event),
+        _ => None,
+    })
+}
diff --git a/src/test/fixtures/mod.rs b/src/test/fixtures/mod.rs
index 41f7e13..9658831 100644
--- a/src/test/fixtures/mod.rs
+++ b/src/test/fixtures/mod.rs
@@ -4,7 +4,6 @@ use crate::{app::App, clock::RequestedAt, db};
 
 pub mod channel;
 pub mod event;
-pub mod filter;
 pub mod future;
 pub mod identity;
 pub mod login;