Canonicalize login and channel names.

Canonicalization does two things:

* It prevents duplicate names that differ only by case or only by normalization/encoding sequence; and
* It makes certain name-based comparisons "case-insensitive" (generalizing via Unicode's case-folding rules).

This change is complicated, as it means that every name now needs to be stored in two forms. Unfortunately, this is _very likely_ a breaking schema change. The migrations in this commit perform a best-effort attempt to canonicalize existing channel or login names, but it's likely any existing channels or logins with non-ASCII characters will not be canonicalize correctly. Since clients look at all channel names and all login names on boot, and since the code in this commit verifies canonicalization when reading from the database, this will effectively make the server un-usuable until any incorrectly-canonicalized values are either manually canonicalized, or removed

It might be possible to do better with [the `icu` sqlite3 extension][icu], but (a) I'm not convinced of that and (b) this commit is already huge; adding database extension support would make it far larger.

[icu]: https://sqlite.org/src/dir/ext/icu

For some references on why it's worth storing usernames this way, see <https://www.b-list.org/weblog/2018/nov/26/case/> and the refernced talk, as well as <https://www.b-list.org/weblog/2018/feb/11/usernames/>. Bennett's treatment of this issue is, to my eye, much more readable than the referenced Unicode technical reports, and I'm inclined to trust his opinion given that he maintains a widely-used, internet-facing user registration library for Django.

1 files changed, 46 insertions, 3 deletions

diff --git a/src/channel/app.rs b/src/channel/app.rs
index ea60943..b8ceeb0 100644
--- a/src/channel/app.rs
+++ b/src/channel/app.rs
@@ -2,12 +2,16 @@ use chrono::TimeDelta;
 use itertools::Itertools;
 use sqlx::sqlite::SqlitePool;
 
-use super::{repo::Provider as _, Channel, History, Id, Name};
+use super::{
+    repo::{LoadError, Provider as _},
+    Channel, History, Id,
+};
 use crate::{
     clock::DateTime,
     db::{Duplicate as _, NotFound as _},
     event::{repo::Provider as _, Broadcaster, Event, Sequence},
     message::repo::Provider as _,
+    name::{self, Name},
 };
 
 pub struct Channels<'a> {
@@ -38,7 +42,7 @@ impl<'a> Channels<'a> {
 
     // This function is careless with respect to time, and gets you the channel as
     // it exists in the specific moment when you call it.
-    pub async fn get(&self, channel: &Id) -> Result<Option<Channel>, sqlx::Error> {
+    pub async fn get(&self, channel: &Id) -> Result<Option<Channel>, Error> {
         let mut tx = self.db.begin().await?;
         let channel = tx.channels().by_id(channel).await.optional()?;
         tx.commit().await?;
@@ -88,7 +92,7 @@ impl<'a> Channels<'a> {
         Ok(())
     }
 
-    pub async fn expire(&self, relative_to: &DateTime) -> Result<(), sqlx::Error> {
+    pub async fn expire(&self, relative_to: &DateTime) -> Result<(), ExpireError> {
         // Somewhat arbitrarily, expire after 90 days.
         let expire_at = relative_to.to_owned() - TimeDelta::days(90);
 
@@ -137,6 +141,17 @@ pub enum CreateError {
     DuplicateName(Name),
     #[error(transparent)]
     Database(#[from] sqlx::Error),
+    #[error(transparent)]
+    Name(#[from] name::Error),
+}
+
+impl From<LoadError> for CreateError {
+    fn from(error: LoadError) -> Self {
+        match error {
+            LoadError::Database(error) => error.into(),
+            LoadError::Name(error) => error.into(),
+        }
+    }
 }
 
 #[derive(Debug, thiserror::Error)]
@@ -147,4 +162,32 @@ pub enum Error {
     Deleted(Id),
     #[error(transparent)]
     Database(#[from] sqlx::Error),
+    #[error(transparent)]
+    Name(#[from] name::Error),
+}
+
+impl From<LoadError> for Error {
+    fn from(error: LoadError) -> Self {
+        match error {
+            LoadError::Database(error) => error.into(),
+            LoadError::Name(error) => error.into(),
+        }
+    }
+}
+
+#[derive(Debug, thiserror::Error)]
+pub enum ExpireError {
+    #[error(transparent)]
+    Database(#[from] sqlx::Error),
+    #[error(transparent)]
+    Name(#[from] name::Error),
+}
+
+impl From<LoadError> for ExpireError {
+    fn from(error: LoadError) -> Self {
+        match error {
+            LoadError::Database(error) => error.into(),
+            LoadError::Name(error) => error.into(),
+        }
+    }
 }