feat: support reverse proxy path prefix deployments (#257)

* feat: support reverse proxy path prefixes

* fix: respect BASE_URL in SAML callback fallback

* fix: make BASE_URL runtime configurable

scripts/runtime-server.ts

@@ -0,0 +1,76 @@
+import { createServer } from "node:http";
+import type { IncomingMessage, ServerResponse } from "node:http";
+
+function normalizeBasePath(basePath: string | undefined): string {
+  if (!basePath || !basePath.trim()) {
+    return "/";
+  }
+
+  let normalized = basePath.trim();
+  if (!normalized.startsWith("/")) {
+    normalized = `/${normalized}`;
+  }
+
+  normalized = normalized.replace(/\/+$/, "");
+  return normalized || "/";
+}
+
+function rewriteRequestUrl(rawUrl: string, basePath: string): string | null {
+  if (basePath === "/") {
+    return rawUrl;
+  }
+
+  const url = new URL(rawUrl, "http://localhost");
+  const pathname = url.pathname;
+
+  if (pathname === basePath || pathname === `${basePath}/`) {
+    url.pathname = "/";
+    return `${url.pathname}${url.search}`;
+  }
+
+  if (pathname.startsWith(`${basePath}/`)) {
+    url.pathname = pathname.slice(basePath.length) || "/";
+    return `${url.pathname}${url.search}`;
+  }
+
+  return null;
+}
+
+const basePath = normalizeBasePath(process.env.BASE_URL);
+const host = process.env.HOST || "0.0.0.0";
+const port = Number.parseInt(process.env.PORT || "4321", 10);
+
+process.env.ASTRO_NODE_AUTOSTART = "disabled";
+const { handler } = await import("../dist/server/entry.mjs");
+
+const server = createServer((req: IncomingMessage, res: ServerResponse) => {
+  if (!req.url) {
+    res.statusCode = 400;
+    res.end("Bad Request");
+    return;
+  }
+
+  const rewrittenUrl = rewriteRequestUrl(req.url, basePath);
+  if (rewrittenUrl === null) {
+    res.statusCode = 404;
+    res.end("Not Found");
+    return;
+  }
+
+  req.url = rewrittenUrl;
+  req.headers["x-gitea-mirror-base-rewritten"] = "1";
+
+  Promise.resolve((handler as unknown as (request: IncomingMessage, response: ServerResponse) => unknown)(req, res)).catch((error) => {
+    console.error("Unhandled runtime server error:", error);
+    if (!res.headersSent) {
+      res.statusCode = 500;
+      res.end("Internal Server Error");
+    } else {
+      res.end();
+    }
+  });
+});
+
+server.listen(port, host, () => {
+  console.log(`Runtime server listening on http://${host}:${port} (BASE_URL=${basePath})`);
+});