feat: add a custom header with infohash to the download endpoints

Endpoint where you can download a torrent file have now a custom header
containing the torrent infohash:

The name of the header is: "x-torrust-torrent-infohash"

It is added becuase in the frontend we need the infohash in a cypress
test and this way we do not need to parse the downloaded torrent which
is faster and simpler.

src/web/api/v1/contexts/torrent/handlers.rs

@@ -94,7 +94,7 @@ pub async fn download_torrent_handler(
         return ServiceError::InternalServerError.into_response();
     };
 
-    torrent_file_response(bytes, &format!("{}.torrent", torrent.info.name))
+    torrent_file_response(bytes, &format!("{}.torrent", torrent.info.name), &torrent.info_hash())
 }
 
 /// It returns a list of torrents matching the search criteria.
@@ -244,7 +244,7 @@ pub async fn create_random_torrent_handler(State(_app_data): State<Arc<AppData>>
         return ServiceError::InternalServerError.into_response();
     };
 
-    torrent_file_response(bytes, &format!("{}.torrent", torrent.info.name))
+    torrent_file_response(bytes, &format!("{}.torrent", torrent.info.name), &torrent.info_hash())
 }
 
 /// Extracts the [`TorrentRequest`] from the multipart form payload.

src/web/api/v1/contexts/torrent/responses.rs

@@ -1,6 +1,6 @@
 use axum::response::{IntoResponse, Response};
 use axum::Json;
-use hyper::{header, StatusCode};
+use hyper::{header, HeaderMap, StatusCode};
 use serde::{Deserialize, Serialize};
 
 use crate::models::torrent::TorrentId;
@@ -23,15 +23,33 @@ pub fn new_torrent_response(torrent_id: TorrentId, info_hash: &str) -> Json<OkRe
     })
 }
 
+/// Builds the binary response for a torrent file.
+///
+/// # Panics
+///
+/// Panics if the filename is not a valid header value for the `content-disposition`
+/// header.
 #[must_use]
-pub fn torrent_file_response(bytes: Vec<u8>, filename: &str) -> Response {
-    (
-        StatusCode::OK,
-        [
-            (header::CONTENT_TYPE, "application/x-bittorrent"),
-            (header::CONTENT_DISPOSITION, &format!("attachment; filename={filename}")),
-        ],
-        bytes,
-    )
-        .into_response()
+pub fn torrent_file_response(bytes: Vec<u8>, filename: &str, info_hash: &str) -> Response {
+    let mut headers = HeaderMap::new();
+    headers.insert(
+        header::CONTENT_TYPE,
+        "application/x-bittorrent"
+            .parse()
+            .expect("HTTP content type header should be valid"),
+    );
+    headers.insert(
+        header::CONTENT_DISPOSITION,
+        format!("attachment; filename={filename}")
+            .parse()
+            .expect("Torrent filename should be a valid header value for the content disposition header"),
+    );
+    headers.insert(
+        "x-torrust-torrent-infohash",
+        info_hash
+            .parse()
+            .expect("Torrent infohash should be a valid header value for the content disposition header"),
+    );
+
+    (StatusCode::OK, headers, bytes).into_response()
 }