Add note on static file configuration

content/docs/static-files.md

@@ -54,3 +54,77 @@ Instead of showing files listing for directory, it is possible to redirect
 to a specific index file. Use the
 [*StaticFiles::index_file()*](../../actix-web/actix_web/fs/struct.StaticFiles.html#method.index_file)
 method to configure this redirect.
+
+# Configuration
+
+Generic trait `StaticFileConfig` can be used to specify various options
+for serving files:
+
+- `content_disposition_map` - function to be used for mapping file's mime to corresponding `Content-Disposition` type
+- `is_use_etag` - specifies whether `ETag` shall be calculated and included in headers.
+- `is_use_last_modifier` - specifies whether file modified timestamp should be used and added to `Last-Modified` header.
+- `is_method_allowed` - allows to control which HTTP methods are allowed to be used when accessing file.
+
+All of the above methods are optional and provided with the best defaults.
+But it is possible to customize any of them by implementing the trait onto own struct.
+
+```rust
+extern crate mime;
+extern crate actix_web;
+use actix_web::{App, HttpRequest, Result, http::Method};
+use actix_web::fs::{StaticFileConfig, NamedFile};
+use actix_web::http::header::DispositionType;
+
+use std::path::PathBuf;
+
+#[derive(Default)]
+struct MyConfig;
+
+impl StaticFileConfig for MyConfig {
+    fn content_disposition_map(typ: mime::Name) -> DispositionType {
+        DispositionType::Attachment
+    }
+}
+
+fn index(req: &HttpRequest) -> Result<NamedFile> {
+    let path: PathBuf = req.match_info().query("tail")?;
+    Ok(NamedFile::open_with_config(path, MyConfig)?)
+}
+
+fn main() {
+    App::new()
+        .resource(r"/a/{tail:.*}", |r| r.method(Method::GET).f(index))
+        .finish();
+}
+```
+
+The Configuration cal also be applied to directory service:
+
+```rust
+extern crate actix_web;
+
+use actix_web::{App};
+use actix_web::fs::{StaticFileConfig, StaticFiles};
+
+#[derive(Default)]
+struct MyConfig;
+
+impl StaticFileConfig for MyConfig {
+    fn is_use_etag() -> bool {
+        false
+    }
+
+    fn is_use_last_modifier() -> bool {
+        false
+    }
+}
+
+fn main() {
+    App::new()
+        .handler(
+            "/static",
+            StaticFiles::with_config(".", MyConfig)
+                .show_files_listing()
+        ).finish();
+}
+```