Add cache control header for default avatars.

set_version.sh

 #!/bin/bash
-export version=0.5.1-alpha.20
+export version=0.5.1-alpha.21
 echo "pub const VERSION: &str = \"${version}\";" > src/version.rs

src/routes/users/get_default_avatar.rs

-use rocket::response::NamedFile;
+use rocket::{Request, Response};
+use rocket::response::{self, NamedFile, Responder};
 use std::path::Path;
 
 use crate::database::Ref;
 
+pub struct CachedFile(NamedFile);
+
+pub static CACHE_CONTROL: &'static str = "public, max-age=31536000, immutable";
+
+impl<'r> Responder<'r, 'static> for CachedFile {
+    fn respond_to(self, req: &'r Request<'_>) -> response::Result<'static> {
+        Response::build_from(self.0.respond_to(req)?)
+            .raw_header("Cache-control", CACHE_CONTROL)
+            .ok()
+    }
+}
+
 #[get("/<target>/default_avatar")]
-pub async fn req(target: Ref) -> Option<NamedFile> {
+pub async fn req(target: Ref) -> Option<CachedFile> {
     match target.id.chars().nth(25).unwrap() {
         '0' | '1' | '2' | '3' | '4' | '5' | '6' | '7' => {
-            NamedFile::open(Path::new("assets/user_red.png")).await.ok()
+            NamedFile::open(Path::new("assets/user_red.png")).await.ok().map(|n| CachedFile(n))
         }
         '8' | '9' | 'A' | 'C' | 'B' | 'D' | 'E' | 'F' => {
             NamedFile::open(Path::new("assets/user_green.png"))
                 .await
-                .ok()
+                .ok().map(|n| CachedFile(n))
         }
         'G' | 'H' | 'J' | 'K' | 'M' | 'N' | 'P' | 'Q' => {
             NamedFile::open(Path::new("assets/user_blue.png"))
                 .await
-                .ok()
+                .ok().map(|n| CachedFile(n))
         }
         'R' | 'S' | 'T' | 'V' | 'W' | 'X' | 'Y' | 'Z' => {
             NamedFile::open(Path::new("assets/user_yellow.png"))
                 .await
-                .ok()
+                .ok().map(|n| CachedFile(n))
         }
         _ => unreachable!(),
     }

src/version.rs

-pub const VERSION: &str = "0.5.1-alpha.20";
+pub const VERSION: &str = "0.5.1-alpha.21";