Provide the frontend translations via the /po.js path (#1126)

## Problem

- Reimplement the translation support for the web frontend

## Solution

- Route the `/po.js` path to the code which redirects to the requested
translations or returns an empty JS file if the requested language is
not found.

rust/agama-server/Cargo.toml

@@ -39,7 +39,7 @@ utoipa = { version = "4.2.0", features = ["axum_extras"] }
 config = "0.14.0"
 rand = "0.8.5"
 jsonwebtoken = "9.2.0"
-axum-extra = { version = "0.9.2", features = ["typed-header"] }
+axum-extra = { version = "0.9.2", features = ["cookie", "typed-header"] }
 chrono = { version = "0.4.34", default-features = false, features = [
   "now",
   "std",

rust/agama-server/src/web/http.rs

@@ -5,11 +5,13 @@ use super::{
     state::ServiceState,
 };
 use axum::{
+    body::Body,
     extract::State,
-    http::{header::SET_COOKIE, HeaderMap},
+    http::{header, HeaderMap, HeaderValue, StatusCode},
     response::IntoResponse,
     Json,
 };
+use axum_extra::extract::cookie::CookieJar;
 use pam::Client;
 use serde::{Deserialize, Serialize};
 use utoipa::ToSchema;
@@ -62,7 +64,7 @@ pub async fn login(
     let mut headers = HeaderMap::new();
     let cookie = format!("agamaToken={}; HttpOnly", &token);
     headers.insert(
-        SET_COOKIE,
+        header::SET_COOKIE,
         cookie.parse().expect("could not build a valid cookie"),
     );
 
@@ -76,7 +78,7 @@ pub async fn logout(_claims: TokenClaims) -> Result<impl IntoResponse, AuthError
     let mut headers = HeaderMap::new();
     let cookie = "agamaToken=deleted; HttpOnly; Expires=Thu, 01 Jan 1970 00:00:00 GMT".to_string();
     headers.insert(
-        SET_COOKIE,
+        header::SET_COOKIE,
         cookie.parse().expect("could not build a valid cookie"),
     );
     Ok(headers)
@@ -90,3 +92,61 @@ pub async fn logout(_claims: TokenClaims) -> Result<impl IntoResponse, AuthError
 pub async fn session(_claims: TokenClaims) -> Result<(), AuthError> {
     Ok(())
 }
+
+// builds a response tuple for translation redirection
+fn redirect_to_file(file: &str) -> (StatusCode, HeaderMap, Body) {
+    tracing::info!("Redirecting to translation file {}", file);
+
+    let mut response_headers = HeaderMap::new();
+    // translation found, redirect to the real file
+    response_headers.insert(
+        header::LOCATION,
+        // if the file exists then the name is a valid value and unwrapping is safe
+        HeaderValue::from_str(file).unwrap(),
+    );
+
+    (
+        StatusCode::TEMPORARY_REDIRECT,
+        response_headers,
+        Body::empty(),
+    )
+}
+
+// handle the /po.js request
+// the requested language (locale) is sent in the "agamaLang" HTTP cookie
+// this reimplements the Cockpit translation support
+pub async fn po(State(state): State<ServiceState>, jar: CookieJar) -> impl IntoResponse {
+    if let Some(cookie) = jar.get("agamaLang") {
+        tracing::info!("Language cookie: {}", cookie.value());
+        // try parsing the cookie
+        if let Some((lang, region)) = cookie.value().split_once('-') {
+            // first try language + country
+            let target_file = format!("po.{}_{}.js", lang, region.to_uppercase());
+            if state.public_dir.join(&target_file).exists() {
+                return redirect_to_file(&target_file);
+            } else {
+                // then try the language only
+                let target_file = format!("po.{}.js", lang);
+                if state.public_dir.join(&target_file).exists() {
+                    return redirect_to_file(&target_file);
+                };
+            }
+        } else {
+            // use the cookie as is
+            let target_file = format!("po.{}.js", cookie.value());
+            if state.public_dir.join(&target_file).exists() {
+                return redirect_to_file(&target_file);
+            }
+        }
+    }
+
+    tracing::info!("Translation not found");
+    // fallback, return empty javascript translations if the language is not supported
+    let mut response_headers = HeaderMap::new();
+    response_headers.insert(
+        header::CONTENT_TYPE,
+        HeaderValue::from_static("text/javascript"),
+    );
+
+    (StatusCode::OK, response_headers, Body::empty())
+}

rust/agama-server/src/web/service.rs

@@ -74,6 +74,7 @@ impl MainServiceBuilder {
         let state = ServiceState {
             config: self.config,
             events: self.events,
+            public_dir: self.public_dir.clone(),
         };
 
         let api_router = self
@@ -84,9 +85,12 @@ impl MainServiceBuilder {
             .route("/ping", get(super::http::ping))
             .route("/auth", post(login).get(session).delete(logout));
 
+        tracing::info!("Serving static files from {}", self.public_dir.display());
         let serve = ServeDir::new(self.public_dir);
+
         Router::new()
             .nest_service("/", serve)
+            .route("/po.js", get(super::http::po))
             .nest("/api", api_router)
             .layer(TraceLayer::new_for_http())
             .layer(CompressionLayer::new().br(true))

rust/agama-server/src/web/state.rs

@@ -1,6 +1,7 @@
 //! Implements the web service state.
 
 use super::{config::ServiceConfig, EventsSender};
+use std::path::PathBuf;
 
 /// Web service state.
 ///
@@ -9,4 +10,5 @@ use super::{config::ServiceConfig, EventsSender};
 pub struct ServiceState {
     pub config: ServiceConfig,
     pub events: EventsSender,
+    pub public_dir: PathBuf,
 }