Typed ETags

src/cache/mod.rs

@@ -7,7 +7,6 @@
 //! # Further Reading
 //!
 //! - [MDN: HTTP Caching](https://developer.mozilla.org/en-US/docs/Web/HTTP/Caching)
-//! - [MDN: HTTP Conditional Requests](https://developer.mozilla.org/en-US/docs/Web/HTTP/Conditional_requests)
 
 mod cache_control;
 

src/conditional/etag.rs

@@ -0,0 +1,183 @@
+use crate::headers::{HeaderName, HeaderValue, Headers, ToHeaderValues, ETAG};
+use crate::{Error, StatusCode};
+
+use std::fmt::Debug;
+use std::option;
+
+/// HTTP Entity Tags.
+///
+/// ETags provide an ID for a particular resource, enabling clients and servers
+/// to reason about caches and make conditional requests.
+///
+/// # Specifications
+///
+/// - [RFC 7232 HTTP/1.1: Conditional Requests](https://tools.ietf.org/html/rfc7232#section-2.3)
+///
+/// # Examples
+///
+/// ```
+/// # fn main() -> http_types::Result<()> {
+/// #
+/// use http_types::Response;
+/// use http_types::conditional::ETag;
+///
+/// let etag = ETag::new("0xcafebeef".to_string());
+///
+/// let mut res = Response::new(200);
+/// etag.apply(&mut res);
+///
+/// let etag = ETag::from_headers(res)?.unwrap();
+/// assert_eq!(etag, ETag::Strong(String::from("0xcafebeef")));
+/// #
+/// # Ok(()) }
+/// ```
+#[derive(Debug, Clone, Eq, PartialEq)]
+pub enum ETag {
+    /// An ETag using strong validation.
+    Strong(String),
+    /// An ETag using weak validation.
+    Weak(String),
+}
+
+impl ETag {
+    /// Create a new ETag that uses strong validation.
+    pub fn new(s: String) -> Self {
+        debug_assert!(!s.contains('\\'), "ETags ought to avoid backslash chars");
+        Self::Strong(s)
+    }
+
+    /// Create a new ETag that uses weak validation.
+    pub fn new_weak(s: String) -> Self {
+        debug_assert!(!s.contains('\\'), "ETags ought to avoid backslash chars");
+        Self::Weak(s)
+    }
+
+    /// Create a new instance from headers.
+    ///
+    /// Only a single ETag per resource is assumed to exist. If multiple ETag
+    /// headers are found the last one is used.
+    pub fn from_headers(headers: impl AsRef<Headers>) -> crate::Result<Option<Self>> {
+        let headers = match headers.as_ref().get(ETAG) {
+            Some(headers) => headers,
+            None => return Ok(None),
+        };
+
+        // If a header is returned we can assume at least one exists.
+        let s = headers.iter().last().unwrap().as_str();
+
+        let mut weak = false;
+        let s = match s.strip_prefix("W/") {
+            Some(s) => {
+                weak = true;
+                s
+            }
+            None => s,
+        };
+
+        let s = match s.strip_prefix('"').and_then(|s| s.strip_suffix('"')) {
+            Some(s) => s.to_owned(),
+            None => {
+                return Err(Error::from_str(
+                    StatusCode::BadRequest,
+                    "Invalid ETag header",
+                ))
+            }
+        };
+
+        let etag = if weak { Self::Weak(s) } else { Self::Strong(s) };
+        Ok(Some(etag))
+    }
+
+    /// Sets the `ETag` header.
+    pub fn apply(&self, mut headers: impl AsMut<Headers>) {
+        headers.as_mut().insert(ETAG, self.value());
+    }
+
+    /// Get the `HeaderName`.
+    pub fn name(&self) -> HeaderName {
+        ETAG
+    }
+
+    /// Get the `HeaderValue`.
+    pub fn value(&self) -> HeaderValue {
+        let s = match self {
+            Self::Strong(s) => format!(r#""{}""#, s),
+            Self::Weak(s) => format!(r#"W/"{}""#, s),
+        };
+        // SAFETY: the internal string is validated to be ASCII.
+        unsafe { HeaderValue::from_bytes_unchecked(s.into()) }
+    }
+
+    /// Returns `true` if the ETag is a `Strong` value.
+    pub fn is_strong(&self) -> bool {
+        matches!(self, Self::Strong(_))
+    }
+
+    /// Returns `true` if the ETag is a `Weak` value.
+    pub fn is_weak(&self) -> bool {
+        matches!(self, Self::Weak(_))
+    }
+}
+
+impl ToHeaderValues for ETag {
+    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 etag = ETag::new("0xcafebeef".to_string());
+
+        let mut headers = Headers::new();
+        etag.apply(&mut headers);
+
+        let etag = ETag::from_headers(headers)?.unwrap();
+        assert_eq!(etag, ETag::Strong(String::from("0xcafebeef")));
+        Ok(())
+    }
+
+    #[test]
+    fn smoke_weak() -> crate::Result<()> {
+        let etag = ETag::new_weak("0xcafebeef".to_string());
+
+        let mut headers = Headers::new();
+        etag.apply(&mut headers);
+
+        let etag = ETag::from_headers(headers)?.unwrap();
+        assert_eq!(etag, ETag::Weak(String::from("0xcafebeef")));
+        Ok(())
+    }
+
+    #[test]
+    fn bad_request_on_parse_error() -> crate::Result<()> {
+        let mut headers = Headers::new();
+        headers.insert(ETAG, "<nori ate the tag. yum.>");
+        let err = ETag::from_headers(headers).unwrap_err();
+        assert_eq!(err.status(), 400);
+        Ok(())
+    }
+
+    #[test]
+    fn validate_quotes() -> crate::Result<()> {
+        assert_entry_err(r#""hello"#, "Invalid ETag header");
+        assert_entry_err(r#"hello""#, "Invalid ETag header");
+        assert_entry_err(r#"/O"valid content""#, "Invalid ETag header");
+        assert_entry_err(r#"/Wvalid content""#, "Invalid ETag header");
+        Ok(())
+    }
+
+    fn assert_entry_err(s: &str, msg: &str) {
+        let mut headers = Headers::new();
+        headers.insert(ETAG, s);
+        let err = ETag::from_headers(headers).unwrap_err();
+        assert_eq!(format!("{}", err), msg);
+    }
+}

src/conditional/mod.rs

@@ -0,0 +1,13 @@
+//! HTTP conditional headers.
+//!
+//! Web page performance can be significantly improved by caching resources.
+//! This submodule includes headers and types to communicate how and when to
+//! cache resources.
+//!
+//! # Further Reading
+//!
+//! - [MDN: HTTP Conditional Requests](https://developer.mozilla.org/en-US/docs/Web/HTTP/Conditional_requests)
+
+mod etag;
+
+pub use etag::ETag;

src/lib.rs

@@ -118,6 +118,7 @@ pub mod url {
 mod utils;
 
 pub mod cache;
+pub mod conditional;
 pub mod headers;
 pub mod mime;