Restrict login names.

There's no good reason to use an empty string as your login name, or to use one so long as to annoy others. Names beginning or ending with whitespace, or containing runs of whitespace, are also a technical problem, so they're also prohibited.

This change does not implement [UTS #39], as I haven't yet fully understood how to do so.

[UTS #39]: https://www.unicode.org/reports/tr39/

1 files changed, 23 insertions, 0 deletions

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)
+}