3 files changed, 34 insertions, 2 deletions
diff --git a/src/login/app.rs b/src/login/app.rs
index 2f5896f..c1bfe6e 100644
--- a/src/login/app.rs
+++ b/src/login/app.rs
@@ -3,7 +3,7 @@ use sqlx::sqlite::SqlitePool;
 use super::repo::Provider as _;
 
 #[cfg(test)]
-use super::{Login, Password};
+use super::{validate, Login, Password};
 #[cfg(test)]
 use crate::{
     clock::DateTime,
@@ -35,6 +35,10 @@ impl<'a> Logins<'a> {
         password: &Password,
         created_at: &DateTime,
     ) -> Result<Login, CreateError> {
+        if !validate::name(name) {
+            return Err(CreateError::InvalidName(name.clone()));
+        }
+
         let password_hash = password.hash()?;
 
         let mut tx = self.db.begin().await?;
@@ -57,9 +61,13 @@ impl<'a> Logins<'a> {
     }
 }
 
+#[cfg(test)]
 #[derive(Debug, thiserror::Error)]
-#[error(transparent)]
 pub enum CreateError {
+    #[error("invalid login name: {0}")]
+    InvalidName(Name),
+    #[error(transparent)]
     Database(#[from] sqlx::Error),
+    #[error(transparent)]
     PasswordHash(#[from] password_hash::Error),
 }
diff --git a/src/login/mod.rs b/src/login/mod.rs
index 279e9a6..6d10e17 100644
--- a/src/login/mod.rs
+++ b/src/login/mod.rs
@@ -6,6 +6,7 @@ pub mod password;
 pub mod repo;
 mod routes;
 mod snapshot;
+pub mod validate;
 
 pub use self::{
     event::Event, history::History, id::Id, password::Password, routes::router, snapshot::Login,
diff --git a/src/login/validate.rs b/src/login/validate.rs
new file mode 100644
index 0000000..ed3eff8
--- /dev/null
+++ b/src/login/validate.rs
@@ -0,0 +1,23 @@
+use unicode_segmentation::UnicodeSegmentation as _;
+
+use crate::name::Name;
+
+// Picked out of a hat. The power of two is not meaningful.
+const NAME_TOO_LONG: usize = 64;
+
+pub fn name(name: &Name) -> bool {
+    let display = name.display();
+
+    [
+        display.graphemes(true).count() < NAME_TOO_LONG,
+        display.chars().all(|ch| !ch.is_control()),
+        display.chars().next().is_some_and(char::is_alphanumeric),
+        display.chars().last().is_some_and(char::is_alphanumeric),
+        display
+            .chars()
+            .zip(display.chars().skip(1))
+            .all(|(a, b)| !(a.is_whitespace() && b.is_whitespace())),
+    ]
+    .into_iter()
+    .all(|value| value)
+}