add a structured cache::Age header

Author: yoshuawuyts

src/cache/age.rs

@@ -0,0 +1,117 @@
+use crate::headers::{HeaderName, HeaderValue, Headers, ToHeaderValues, AGE};
+use crate::Status;
+
+use std::fmt::Debug;
+use std::option;
+use std::time::Duration;
+
+/// HTTP `Age` header
+///
+/// # Specifications
+///
+/// - [RFC 7234  Hypertext Transfer Protocol (HTTP/1.1): Caching](https://tools.ietf.org/html/rfc7234#section-5.1)
+///
+/// # Examples
+///
+/// ```
+/// # fn main() -> http_types::Result<()> {
+/// #
+/// use http_types::Response;
+/// use http_types::cache::Age;
+/// use std::time::Duration;
+///
+/// let age = Age::new(Duration::from_secs(12));
+///
+/// let mut res = Response::new(200);
+/// age.apply(&mut res);
+///
+/// let age = Age::from_headers(res)?.unwrap();
+/// assert_eq!(age, Age::new(Duration::from_secs(12)));
+/// #
+/// # Ok(()) }
+/// ```
+#[derive(Debug, Ord, PartialOrd, Eq, PartialEq)]
+pub struct Age {
+    dur: Duration,
+}
+
+impl Age {
+    /// Create a new instance of `Age`.
+    pub fn new(dur: Duration) -> Self {
+        Self { dur }
+    }
+
+    /// Create an instance of `Age` from a `Headers` instance.
+    ///
+    /// # Implementation note
+    ///
+    /// A header value of `"null"` is treated the same as if no header was sent.
+    pub fn from_headers(headers: impl AsRef<Headers>) -> crate::Result<Option<Self>> {
+        let headers = match headers.as_ref().get(AGE) {
+            Some(headers) => headers,
+            None => return Ok(None),
+        };
+
+        // If we successfully parsed the header then there's always at least one
+        // entry. We want the last entry.
+        let header = headers.iter().last().unwrap();
+
+        let num: u64 = header.as_str().parse().status(400)?;
+        let dur = Duration::from_secs_f64(num as f64);
+
+        Ok(Some(Self { dur }))
+    }
+
+    /// Insert a `HeaderName` + `HeaderValue` pair into a `Headers` instance.
+    pub fn apply(&self, mut headers: impl AsMut<Headers>) {
+        headers.as_mut().insert(AGE, self.value());
+    }
+
+    /// Get the `HeaderName`.
+    pub fn name(&self) -> HeaderName {
+        AGE
+    }
+
+    /// Get the `HeaderValue`.
+    pub fn value(&self) -> HeaderValue {
+        let output = self.dur.as_secs().to_string();
+
+        // SAFETY: the internal string is validated to be ASCII.
+        unsafe { HeaderValue::from_bytes_unchecked(output.into()) }
+    }
+}
+
+impl ToHeaderValues for Age {
+    type Iter = option::IntoIter<HeaderValue>;
+    fn to_header_values(&self) -> crate::Result<Self::Iter> {
+        // A HeaderValue will always convert into itself.
+        Ok(self.value().to_header_values().unwrap())
+    }
+}
+
+#[cfg(test)]
+mod test {
+    use super::*;
+    use crate::headers::Headers;
+
+    #[test]
+    fn smoke() -> crate::Result<()> {
+        let age = Age::new(Duration::from_secs(12));
+
+        let mut headers = Headers::new();
+        age.apply(&mut headers);
+
+        let age = Age::from_headers(headers)?.unwrap();
+        assert_eq!(age, Age::new(Duration::from_secs(12)));
+        Ok(())
+    }
+
+    #[test]
+    fn bad_request_on_parse_error() -> crate::Result<()> {
+        let mut headers = Headers::new();
+        headers.insert(AGE, "<nori ate the tag. yum.>");
+        let err = Age::from_headers(headers).unwrap_err();
+        assert_eq!(err.status(), 400);
+        Ok(())
+    }
+}

src/cache/mod.rs

@@ -10,6 +10,8 @@
 //! - [MDN: HTTP Conditional Requests](https://developer.mozilla.org/en-US/docs/Web/HTTP/Conditional_requests)
 
 mod cache_control;
+mod age;
 
 pub use cache_control::CacheControl;
 pub use cache_control::CacheDirective;
+pub use age::Age;