From a7906311cada4e1d4fc2fe0a20284499a2de4598 Mon Sep 17 00:00:00 2001
From: Brandon Thomas <echelon@gmail.com>
Date: Sun, 15 Mar 2026 21:24:04 -0400
Subject: [PATCH] add "extension"

---
 .../lib/url_utils/src/extension/extension.rs  | 146 ++++++++++++++++++
 crates/lib/url_utils/src/extension/mod.rs     |   1 +
 2 files changed, 147 insertions(+)
 create mode 100644 crates/lib/url_utils/src/extension/extension.rs

diff --git a/crates/lib/url_utils/src/extension/extension.rs b/crates/lib/url_utils/src/extension/extension.rs
new file mode 100644
index 0000000000..a92df6d43c
--- /dev/null
+++ b/crates/lib/url_utils/src/extension/extension.rs
@@ -0,0 +1,146 @@
+use std::borrow::Cow;
+use std::fmt;
+
+/// A file extension that can be either a compile-time constant or a runtime-parsed value.
+///
+/// ```
+/// use url_utils::extension::extension::Extension;
+///
+/// // Static constants (no allocation)
+/// const PNG: Extension = Extension::from_static("png", ".png");
+/// assert_eq!(PNG.without_period(), "png");
+/// assert_eq!(PNG.with_period(), ".png");
+///
+/// // Runtime parsing (allocates only if needed)
+/// let ext = Extension::new("mp4");
+/// assert_eq!(ext.without_period(), "mp4");
+/// assert_eq!(ext.with_period(), ".mp4");
+/// ```
+#[derive(Clone, Eq, Hash)]
+pub struct Extension {
+  /// The extension without the leading period, e.g. "png", "mp4".
+  value: Cow<'static, str>,
+
+  /// The extension with the leading period, e.g. ".png", ".mp4".
+  dotted: Cow<'static, str>,
+}
+
+impl Extension {
+  /// Creates an `Extension` from static strings at compile time.
+  /// Pass both the bare extension and the dotted form.
+  ///
+  /// ```
+  /// use url_utils::extension::extension::Extension;
+  /// const MP4: Extension = Extension::from_static("mp4", ".mp4");
+  /// ```
+  pub const fn from_static(ext: &'static str, dotted: &'static str) -> Self {
+    Self {
+      value: Cow::Borrowed(ext),
+      dotted: Cow::Borrowed(dotted),
+    }
+  }
+
+  /// Creates an `Extension` from a `&str` at runtime.
+  /// The input must NOT include a leading period.
+  pub fn new(ext: &str) -> Self {
+    let dotted = format!(".{}", ext);
+    Self {
+      value: Cow::Owned(ext.to_string()),
+      dotted: Cow::Owned(dotted),
+    }
+  }
+
+  /// Returns the extension without the leading period, e.g. `"png"`.
+  pub fn without_period(&self) -> &str {
+    &self.value
+  }
+
+  /// Returns the extension with the leading period, e.g. `".png"`.
+  pub fn with_period(&self) -> &str {
+    &self.dotted
+  }
+}
+
+impl PartialEq for Extension {
+  fn eq(&self, other: &Self) -> bool {
+    self.value == other.value
+  }
+}
+
+impl fmt::Debug for Extension {
+  fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+    write!(f, "Extension(\"{}\")", self.value)
+  }
+}
+
+impl fmt::Display for Extension {
+  fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+    write!(f, "{}", self.value)
+  }
+}
+
+#[cfg(test)]
+mod tests {
+  use super::*;
+
+  const PNG: Extension = Extension::from_static("png", ".png");
+  const MP4: Extension = Extension::from_static("mp4", ".mp4");
+  const MP3: Extension = Extension::from_static("mp3", ".mp3");
+
+  #[test]
+  fn static_without_period() {
+    assert_eq!(PNG.without_period(), "png");
+    assert_eq!(MP4.without_period(), "mp4");
+    assert_eq!(MP3.without_period(), "mp3");
+  }
+
+  #[test]
+  fn static_with_period() {
+    assert_eq!(PNG.with_period(), ".png");
+    assert_eq!(MP4.with_period(), ".mp4");
+    assert_eq!(MP3.with_period(), ".mp3");
+  }
+
+  #[test]
+  fn runtime_without_period() {
+    let ext = Extension::new("webm");
+    assert_eq!(ext.without_period(), "webm");
+  }
+
+  #[test]
+  fn runtime_with_period() {
+    let ext = Extension::new("webm");
+    assert_eq!(ext.with_period(), ".webm");
+  }
+
+  #[test]
+  fn unknown_extension() {
+    let ext = Extension::new("foobar");
+    assert_eq!(ext.without_period(), "foobar");
+    assert_eq!(ext.with_period(), ".foobar");
+  }
+
+  #[test]
+  fn equality() {
+    let a = Extension::new("png");
+    assert_eq!(a, PNG);
+  }
+
+  #[test]
+  fn clone() {
+    let a = Extension::new("wav");
+    let b = a.clone();
+    assert_eq!(a, b);
+  }
+
+  #[test]
+  fn display() {
+    assert_eq!(format!("{}", PNG), "png");
+    assert_eq!(format!("{}", Extension::new("xyz")), "xyz");
+  }
+
+  #[test]
+  fn debug() {
+    assert_eq!(format!("{:?}", PNG), "Extension(\"png\")");
+  }
+}
diff --git a/crates/lib/url_utils/src/extension/mod.rs b/crates/lib/url_utils/src/extension/mod.rs
index e847b17dfd..fd91386742 100644
--- a/crates/lib/url_utils/src/extension/mod.rs
+++ b/crates/lib/url_utils/src/extension/mod.rs
@@ -1,2 +1,3 @@
 pub mod download_extension;
+pub mod extension;
 pub mod extract_download_extension_from_url;
\ No newline at end of file