Add Content-MD5 header

Author: sunsided

src/common/content_md5.rs

@@ -0,0 +1,55 @@
+use std::convert::TryInto;
+use {Header, HeaderValue};
+
+/// `Content-MD5` header, defined in
+/// [RFC1864](https://datatracker.ietf.org/doc/html/rfc1864)
+///
+/// ## ABNF
+///
+/// ```text
+/// Content-Length = 1*DIGIT
+/// ```
+///
+/// ## Example values
+///
+/// * `Q2hlY2sgSW50ZWdyaXR5IQ==`
+///
+/// # Example
+///
+/// ```
+/// # extern crate headers;
+/// use headers::ContentMd5;
+///
+/// let md5 = ContentMd5([0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 0, 1, 2, 3, 4, 5]);
+/// ```
+#[derive(Clone, Copy, Debug, PartialEq)]
+pub struct ContentMd5(pub [u8; 16]);
+
+static CONTENT_MD5: ::http::header::HeaderName =
+    ::http::header::HeaderName::from_static("content-md5");
+
+impl Header for ContentMd5 {
+    fn name() -> &'static ::http::header::HeaderName {
+        &CONTENT_MD5
+    }
+
+    fn decode<'i, I: Iterator<Item = &'i HeaderValue>>(values: &mut I) -> Result<Self, ::Error> {
+        let value = values.next().ok_or_else(::Error::invalid)?;
+
+        // Ensure base64 encoded length fits the expected MD5 digest length.
+        if value.len() < 22 || value.len() > 24 {
+            return Err(::Error::invalid());
+        }
+
+        let value = value.to_str().map_err(|_| ::Error::invalid())?;
+        let vec = base64::decode(value).map_err(|_| ::Error::invalid())?;
+        Ok(Self(vec.try_into().map_err(|_| ::Error::invalid())?))
+    }
+
+    fn encode<E: Extend<::HeaderValue>>(&self, values: &mut E) {
+        let encoded = base64::encode(self.0);
+        if let Ok(value) = HeaderValue::from_str(&encoded) {
+            values.extend(std::iter::once(value));
+        }
+    }
+}

src/common/mod.rs

@@ -29,6 +29,7 @@ pub use self::content_encoding::ContentEncoding;
 //pub use self::content_language::ContentLanguage;
 pub use self::content_length::ContentLength;
 pub use self::content_location::ContentLocation;
+pub use self::content_md5::ContentMd5;
 pub use self::content_range::ContentRange;
 pub use self::content_type::ContentType;
 pub use self::cookie::Cookie;
@@ -149,6 +150,7 @@ mod content_encoding;
 //mod content_language;
 mod content_length;
 mod content_location;
+mod content_md5;
 mod content_range;
 mod content_type;
 mod cookie;