feat (backend): Add backend API to get flow info for subscriptions

backend/package.json

@@ -1,6 +1,6 @@
 {
   "name": "sub-store",
-  "version": "2.1.5",
+  "version": "2.2.0",
   "description": "Advanced Subscription Manager for QX, Loon, Surge, Stash and ShadowRocket.",
   "main": "src/main.js",
   "scripts": {

backend/src/restful/index.js

@@ -66,6 +66,7 @@ function getEnv(req, res) {
     if (isLoon) backend = 'Loon';
     if (isSurge) backend = 'Surge';
     res.json({
+        status: 200,
         backend,
     });
 }

backend/src/restful/subscriptions.js

@@ -7,6 +7,8 @@ export default function register($app) {
 
     $app.get('/download/:name', downloadSubscription);
 
+    $app.get('/api/sub/flow/:name', getFlowInfo);
+
     $app.route('/api/sub/:name')
         .get(getSubscription)
         .patch(updateSubscription)
@@ -72,6 +74,59 @@ async function downloadSubscription(req, res) {
     }
 }
 
+async function getFlowInfo(req, res) {
+    let { name } = req.params;
+    name = decodeURIComponent(name);
+    const sub = $.read(SUBS_KEY)[name];
+
+    if (!sub) {
+        res.status(404).json({
+            status: 'failed',
+            code: 'NOT_FOUND',
+        });
+    }
+    if (sub.source === 'local') {
+        res.status(500).json({
+            status: 'failed',
+            code: 'IS_LOCAL_SUB',
+        });
+    }
+    try {
+        const flowHeaders = await getFlowHeaders(sub.url);
+        if (!flowHeaders) {
+            res.status(500).json({
+                status: 'failed',
+                code: 'NO_FLOW_INFO',
+            });
+        }
+
+        // unit is KB
+        const upload = Number(flowHeaders.match(/upload=(\d+)/)[1]);
+        const download = Number(flowHeaders.match(/download=(\d+)/)[1]);
+        const total = Number(flowHeaders.match(/total=(\d+)/)[1]);
+
+        // optional expire timestamp
+        const expires = flowHeaders.match(/expire=(\d+)/);
+
+        res.status(200).json({
+            status: 'success',
+            data: {
+                expires: expires ? Number(expires[1]) : undefined,
+                total,
+                usage: {
+                    upload,
+                    download,
+                },
+            },
+        });
+    } catch (err) {
+        res.status(500).json({
+            status: 'failed',
+            code: 'NOT_AVAILABLE',
+        });
+    }
+}
+
 function createSubscription(req, res) {
     const sub = req.body;
     const allSubs = $.read(SUBS_KEY);