Change Accept Mime negotiation

Previously we just checked whether one of the available mime types
equaled one of the accepted mime types. This commit extends Mime with
subset functionality, describing exactly a mime being accepted by an
accept header.

Author: halvko

src/content/accept.rs

@@ -129,8 +129,8 @@ impl Accept {
 
         // Try and find the first encoding that matches.
         for accept in &self.entries {
-            if available.contains(accept) {
-                return Ok(accept.media_type.clone().into());
+            if let Some(accept) = available.iter().find(|m| m.subset_eq(accept.media_type())) {
+                return Ok(accept.clone().into());
             }
         }
 

src/mime/mod.rs

@@ -103,6 +103,45 @@ impl Mime {
             .position(|(k, _)| k == &name)
             .map(|pos| self.params.remove(pos).1)
     }
+
+    /// Check if this mime is a subtype of another mime.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// // All mime types are subsets of */*
+    /// use http_types::mime::Mime;
+    /// use std::str::FromStr;
+    ///
+    /// assert!(Mime::from_str("text/css").unwrap().subset_eq(&Mime::from_str("*/*").unwrap()));
+    ///
+    /// // A mime type is subset of itself
+    /// assert!(Mime::from_str("text/css").unwrap().subset_eq(&Mime::from_str("text/css").unwrap()));
+    ///
+    /// // A mime type which is otherwise a subset with extra parameters is a subset of a mime type without those parameters
+    /// assert!(Mime::from_str("text/css;encoding=utf-8").unwrap().subset_eq(&Mime::from_str("text/css").unwrap()));
+    ///
+    /// // A mime type more general than another mime type is not a subset
+    /// assert!(!Mime::from_str("*/css;encoding=utf-8").unwrap().subset_eq(&Mime::from_str("text/css").unwrap()));
+    /// ```
+    pub fn subset_eq(&self, other: &Mime) -> bool {
+        if other.basetype() != "*" && self.basetype() != other.basetype() {
+            return false;
+        }
+        if other.subtype() != "*" && self.subtype() != other.subtype() {
+            return false;
+        }
+        for (name, value) in other.params.iter() {
+            if !self
+                .param(name.as_str())
+                .map(|v| v == value)
+                .unwrap_or(false)
+            {
+                return false;
+            }
+        }
+        true
+    }
 }
 
 impl Display for Mime {