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, 33 insertions, 4 deletions

diff --git a/src/token/app.rs b/src/token/app.rs
index d4dd1a0..c19d6a0 100644
--- a/src/token/app.rs
+++ b/src/token/app.rs
@@ -7,12 +7,14 @@ use futures::{
 use sqlx::sqlite::SqlitePool;
 
 use super::{
-    repo::auth::Provider as _, repo::Provider as _, Broadcaster, Event as TokenEvent, Id, Secret,
+    repo::{self, auth::Provider as _, Provider as _},
+    Broadcaster, Event as TokenEvent, Id, Secret,
 };
 use crate::{
     clock::DateTime,
     db::NotFound as _,
-    login::{Login, Name, Password},
+    login::{Login, Password},
+    name::{self, Name},
 };
 
 pub struct Tokens<'a> {
@@ -65,14 +67,16 @@ impl<'a> Tokens<'a> {
         used_at: &DateTime,
     ) -> Result<(Id, Login), ValidateError> {
         let mut tx = self.db.begin().await?;
-        let login = tx
+        let (token, login) = tx
             .tokens()
             .validate(secret, used_at)
             .await
             .not_found(|| ValidateError::InvalidToken)?;
         tx.commit().await?;
 
-        Ok(login)
+        let login = login.as_snapshot().ok_or(ValidateError::LoginDeleted)?;
+
+        Ok((token, login))
     }
 
     pub async fn limit_stream<E>(
@@ -162,15 +166,40 @@ pub enum LoginError {
     #[error(transparent)]
     Database(#[from] sqlx::Error),
     #[error(transparent)]
+    Name(#[from] name::Error),
+    #[error(transparent)]
     PasswordHash(#[from] password_hash::Error),
 }
 
+impl From<repo::auth::LoadError> for LoginError {
+    fn from(error: repo::auth::LoadError) -> Self {
+        use repo::auth::LoadError;
+        match error {
+            LoadError::Database(error) => error.into(),
+            LoadError::Name(error) => error.into(),
+        }
+    }
+}
+
 #[derive(Debug, thiserror::Error)]
 pub enum ValidateError {
     #[error("invalid token")]
     InvalidToken,
+    #[error("login deleted")]
+    LoginDeleted,
     #[error(transparent)]
     Database(#[from] sqlx::Error),
+    #[error(transparent)]
+    Name(#[from] name::Error),
+}
+
+impl From<repo::LoadError> for ValidateError {
+    fn from(error: repo::LoadError) -> Self {
+        match error {
+            repo::LoadError::Database(error) => error.into(),
+            repo::LoadError::Name(error) => error.into(),
+        }
+    }
 }
 
 #[derive(Debug)]