fix: preserve preview path when proxying tunnel requests (#3)

Author: skulidropek

src/__tests__/config.test.ts

@@ -53,4 +53,21 @@ describe("resolveConfig", () => {
     expect(config.deviceSecret).toBe("secret123");
     expect(config.port).toBe(4010);
   });
+
+  it("reads previewPath from legacy spawndock.config.json", () => {
+    const dir = mkdtempSync(join(tmpdir(), "spawndock-config-"));
+    writeFileSync(
+      join(dir, "spawndock.config.json"),
+      JSON.stringify({
+        controlPlaneUrl: "http://localhost:8787",
+        projectSlug: "my-app",
+        deviceSecret: "secret123",
+        localPort: 4010,
+        previewPath: "/preview/my-app",
+      }),
+    );
+
+    const config = resolveConfig([], dir);
+    expect(config.previewPath).toBe("/preview/my-app");
+  });
 });

src/__tests__/tunnel.test.ts

@@ -0,0 +1,18 @@
+import { describe, expect, it } from "vitest";
+
+import { buildWsUrl } from "../tunnel.js";
+
+describe("buildWsUrl", () => {
+  it("includes protocol version and token query params", () => {
+    const url = buildWsUrl({
+      controlPlane: "https://api.example.com",
+      projectSlug: "demo",
+      deviceSecret: "secret123",
+      port: 3000,
+    });
+
+    expect(url).toBe(
+      "wss://api.example.com/tunnel/connect?protocolVersion=1&token=secret123",
+    );
+  });
+});

src/config.ts

@@ -6,6 +6,7 @@ export interface TunnelConfig {
   projectSlug: string;
   deviceSecret: string;
   port: number;
+  previewPath?: string;
 }
 
 const PRIMARY_CONFIG_FILE = "spawndock.dev-tunnel.json";
@@ -46,8 +47,10 @@ function normalizeConfig(data: unknown): Partial<TunnelConfig> {
       : typeof record.localPort === "number"
         ? record.localPort
         : undefined;
+  const previewPath =
+    typeof record.previewPath === "string" ? record.previewPath : undefined;
 
-  return { controlPlane, projectSlug, deviceSecret, port };
+  return { controlPlane, projectSlug, deviceSecret, port, previewPath };
 }
 
 function readConfigFile(dir: string): Partial<TunnelConfig> {
@@ -134,10 +137,11 @@ export function resolveConfig(
   const projectSlug = args.projectSlug ?? env.projectSlug ?? file.projectSlug;
   const deviceSecret = args.deviceSecret ?? env.deviceSecret ?? file.deviceSecret;
   const port = args.port ?? env.port ?? file.port ?? 3000;
+  const previewPath = file.previewPath;
 
   if (!controlPlane) throw new Error("Missing --control-plane or SPAWNDOCK_CONTROL_PLANE");
   if (!projectSlug) throw new Error("Missing --project-slug or SPAWNDOCK_PROJECT_SLUG");
   if (!deviceSecret) throw new Error("Missing --device-secret or SPAWNDOCK_DEVICE_SECRET");
 
-  return { controlPlane, projectSlug, deviceSecret, port };
+  return { controlPlane, projectSlug, deviceSecret, port, previewPath };
 }

src/tunnel.ts

@@ -10,6 +10,22 @@ export function createTunnel(config: TunnelConfig): void {
   connect(wsUrl, config, localOrigin);
 }
 
+function resolveForwardedPath(previewPath: string | undefined, path: string): string {
+  if (!previewPath || previewPath.length === 0) {
+    return path;
+  }
+
+  const normalizedPreviewPath = previewPath.replace(/\/$/, "");
+  const [pathname, query = ""] = path.split("?");
+
+  const forwardedPath =
+    pathname === "/"
+      ? `${normalizedPreviewPath}/`
+      : `${normalizedPreviewPath}${pathname}`;
+
+  return query.length > 0 ? `${forwardedPath}?${query}` : forwardedPath;
+}
+
 export function buildWsUrl(config: TunnelConfig): string {
   if (!URL.canParse(config.controlPlane)) {
     throw new Error(`Invalid control plane URL: ${config.controlPlane}`);
@@ -64,7 +80,13 @@ function connect(wsUrl: string, config: TunnelConfig, localOrigin: string): void
 
     if (msg.type === "http-request") {
       try {
-        const response = await proxyRequest(msg.request, localOrigin);
+        const response = await proxyRequest(
+          {
+            ...msg.request,
+            path: resolveForwardedPath(config.previewPath, msg.request.path),
+          },
+          localOrigin,
+        );
         ws.send(serialize({ type: "http-response", response }));
       } catch (err: any) {
         ws.send(serialize({