Change redirection to caching local copy and then serving download

i.e. this allows clients to request partial downloads with range headers

config/default.json5

@@ -11,4 +11,5 @@
     view: {
         cache: false,
     },
+    assets_base_dir: 'downloads',
 }

src/controllers/GiteaRepoLatestReleaseController.ts

@@ -4,6 +4,11 @@ import * as https from "https";
 import config from "config";
 import {log} from "swaf/Logger";
 import {NotFoundHttpError} from "swaf/HttpError";
+import * as fs from "fs";
+import {promisify} from "util";
+import path from "path";
+
+export const ASSETS_BASE_DIR = config.get<string>('assets_base_dir');
 
 export default class GiteaRepoLatestReleaseController extends Controller {
     public routes(): void {
@@ -15,7 +20,7 @@ export default class GiteaRepoLatestReleaseController extends Controller {
         const {owner, name, file} = req.params;
         if (!owner || !name) return next();
 
-        https.get(`${config.get('gitea_instance_url')}/api/v1/repos/${owner}/${name}/releases`, {
+        const httpRequest = https.get(`${config.get('gitea_instance_url')}/api/v1/repos/${owner}/${name}/releases`, {
             headers: {
                 'Accept': 'application/json',
             },
@@ -24,7 +29,7 @@ export default class GiteaRepoLatestReleaseController extends Controller {
             r.on('data', c => {
                 data += c;
             });
-            r.on('end', () => {
+            r.on('end', async () => {
                 try {
                     const releases = JSON.parse(data);
 
@@ -32,8 +37,19 @@ export default class GiteaRepoLatestReleaseController extends Controller {
                         for (const release of releases) {
                             for (const asset of release.assets) {
                                 if (asset.name === file) {
-                                    log.debug('Redirect to', asset.browser_download_url);
-                                    return res.redirect(302, asset.browser_download_url);
+                                    log.debug('Download', asset.browser_download_url);
+                                    return await this.download(req, res, next, {
+                                        repo: {
+                                            owner: owner,
+                                            name: name,
+                                        },
+                                        asset: {
+                                            id: asset.id,
+                                            name: asset.name,
+                                            url: asset.browser_download_url,
+                                            size: asset.size,
+                                        },
+                                    });
                                 }
                             }
                         }
@@ -50,8 +66,58 @@ export default class GiteaRepoLatestReleaseController extends Controller {
                     return next(e);
                 }
             });
-        }).on('error', err => {
+        });
+        httpRequest.on('error', err => {
             log.error(err);
         });
+        httpRequest.end();
+    }
+
+    protected async download(
+        req: Request,
+        res: Response,
+        next: NextFunction,
+        downloadProperties: DownloadProperties,
+    ): Promise<void> {
+        // Make base dir
+        if (!await promisify(fs.exists)(ASSETS_BASE_DIR)) {
+            await promisify(fs.mkdir)(ASSETS_BASE_DIR);
+        }
+
+        const assetPath = path.resolve(ASSETS_BASE_DIR, '' + downloadProperties.asset.id);
+
+        // Download asset if it doesn't exist
+        if (!await promisify(fs.exists)(assetPath)) {
+            const file = fs.createWriteStream(assetPath);
+            await new Promise((resolve, reject) => {
+                const httpRequest = https.get(downloadProperties.asset.url, res => {
+                    res.on('end', () => {
+                        resolve();
+                    });
+                    res.pipe(file);
+                });
+                httpRequest.on('error', () => {
+                    reject();
+                });
+                httpRequest.end();
+            });
+            file.close();
+        }
+
+        // Respond
+        return res.download(assetPath, downloadProperties.asset.name);
     }
 }
+
+export type DownloadProperties = {
+    repo: {
+        owner: string;
+        name: string;
+    };
+    asset: {
+        id: string,
+        name: string;
+        url: string;
+        size: number;
+    };
+};