Add custom token support to exposePort for stable preview URLs

.changeset/custom-port-tokens.md

@@ -0,0 +1,24 @@
+---
+'@cloudflare/sandbox': minor
+---
+
+Add support for custom tokens in `exposePort()` to enable stable preview URLs across deployments.
+
+You can now pass a custom token when exposing ports to maintain consistent preview URLs between container restarts and deployments. This is useful for sharing URLs with users or maintaining stable references in production environments.
+
+```typescript
+// With custom token - URL stays the same across restarts
+const { url } = await sandbox.exposePort(8080, {
+  hostname: 'example.com',
+  token: 'my-stable-token' // 1-63 chars: a-z, 0-9, -, _
+});
+// url: https://8080-sandbox-id-my-stable-token.example.com
+
+// Without token - generates random 16-char token (existing behavior)
+const { url } = await sandbox.exposePort(8080, {
+  hostname: 'example.com'
+});
+// url: https://8080-sandbox-id-abc123random4567.example.com
+```
+
+Custom tokens must be 1-63 characters and contain only lowercase letters, numbers, hyphens, and underscores to ensure URL and DNS compatibility.

packages/sandbox/src/clients/port-client.ts

@@ -15,6 +15,12 @@ export type { PortExposeResult, PortCloseResult, PortListResult };
 export interface ExposePortRequest {
   port: number;
   name?: string;
+  /**
+   * Custom token for the preview URL (optional)
+   * If not provided, a random 16-character token will be generated
+   * Must be 1-63 characters, containing only lowercase letters, numbers, hyphens, and underscores
+   */
+  token?: string;
 }
 
 /**
@@ -33,14 +39,16 @@ export class PortClient extends BaseHttpClient {
    * @param port - Port number to expose
    * @param sessionId - The session ID for this operation
    * @param name - Optional name for the port
+   * @param token - Optional custom token for the preview URL
    */
   async exposePort(
     port: number,
     sessionId: string,
-    name?: string
+    name?: string,
+    token?: string
   ): Promise<PortExposeResult> {
     try {
-      const data = { port, sessionId, name };
+      const data = { port, sessionId, name, token };
 
       const response = await this.post<PortExposeResult>(
         '/api/expose-port',

packages/sandbox/src/request-handler.ts

@@ -116,9 +116,9 @@ export async function proxyToSandbox<
 
 function extractSandboxRoute(url: URL): RouteInfo | null {
   // Parse subdomain pattern: port-sandboxId-token.domain (tokens mandatory)
-  // Token is always exactly 16 chars (generated by generatePortToken)
+  // Token can be any length (1-63 chars) containing only [a-z0-9_-]
   const subdomainMatch = url.hostname.match(
-    /^(\d{4,5})-([^.-][^.]*?[^.-]|[^.-])-([a-z0-9_-]{16})\.(.+)$/
+    /^(\d{4,5})-([^.-][^.]*?[^.-]|[^.-])-([a-z0-9_-]+)\.(.+)$/
   );
 
   if (!subdomainMatch) {
@@ -142,8 +142,8 @@ function extractSandboxRoute(url: URL): RouteInfo | null {
     return null;
   }
 
-  // DNS subdomain length limit is 63 characters
-  if (sandboxId.length > 63) {
+  // DNS subdomain length limit is 63 characters (applies to each component)
+  if (sandboxId.length > 63 || token.length > 63) {
     return null;
   }
 

packages/sandbox/src/sandbox.ts

@@ -2089,7 +2089,34 @@ export class Sandbox<Env = unknown> extends Container<Env> implements ISandbox {
     return this.client.files.exists(path, session);
   }
 
-  async exposePort(port: number, options: { name?: string; hostname: string }) {
+  /**
+   * Expose a port and get a preview URL for accessing services running in the sandbox
+   *
+   * @param port - Port number to expose (1024-65535)
+   * @param options - Configuration options
+   * @param options.hostname - Your Worker's domain name (required for preview URL construction)
+   * @param options.name - Optional friendly name for the port
+   * @param options.token - Optional custom token for the preview URL (1-63 characters: lowercase letters, numbers, hyphens, underscores)
+   *                       If not provided, a random 16-character token will be generated automatically
+   * @returns Preview URL information including the full URL, port number, and optional name
+   *
+   * @example
+   * // With auto-generated token
+   * const { url } = await sandbox.exposePort(8080, { hostname: 'example.com' });
+   * // url: https://8080-sandbox-id-abc123random4567.example.com
+   *
+   * @example
+   * // With custom token for stable URLs across deployments
+   * const { url } = await sandbox.exposePort(8080, {
+   *   hostname: 'example.com',
+   *   token: 'my-stable-token'
+   * });
+   * // url: https://8080-sandbox-id-my-stable-token.example.com
+   */
+  async exposePort(
+    port: number,
+    options: { name?: string; hostname: string; token?: string }
+  ) {
     // Check if hostname is workers.dev domain (doesn't support wildcard subdomains)
     if (options.hostname.endsWith('.workers.dev')) {
       const errorResponse: ErrorResponse = {
@@ -2103,7 +2130,12 @@ export class Sandbox<Env = unknown> extends Container<Env> implements ISandbox {
     }
 
     const sessionId = await this.ensureDefaultSession();
-    await this.client.ports.exposePort(port, sessionId, options?.name);
+    await this.client.ports.exposePort(
+      port,
+      sessionId,
+      options?.name,
+      options?.token
+    );
 
     // We need the sandbox name to construct preview URLs
     if (!this.sandboxName) {
@@ -2112,8 +2144,17 @@ export class Sandbox<Env = unknown> extends Container<Env> implements ISandbox {
       );
     }
 
-    // Generate and store token for this port (storage is protected by input gates)
-    const token = this.generatePortToken();
+    // Use custom token or generate a random one
+    let token: string;
+    if (options.token) {
+      // Validate custom token
+      this.validateCustomToken(options.token);
+      token = options.token;
+    } else {
+      token = this.generatePortToken();
+    }
+
+    // Store token for this port (storage is protected by input gates)
     const tokens =
       (await this.ctx.storage.get<Record<string, string>>('portTokens')) || {};
     tokens[port.toString()] = token;
@@ -2228,6 +2269,27 @@ export class Sandbox<Env = unknown> extends Container<Env> implements ISandbox {
     return storedToken === token;
   }
 
+  private validateCustomToken(token: string): void {
+    // Token must be at least 1 character
+    if (token.length === 0) {
+      throw new SecurityError(`Custom token cannot be empty.`);
+    }
+
+    // Token should have reasonable length for URL compatibility (max 63 chars for DNS subdomain)
+    if (token.length > 63) {
+      throw new SecurityError(
+        `Custom token too long. Maximum 63 characters allowed (DNS subdomain limit). Received: ${token.length} characters.`
+      );
+    }
+
+    // Token must only contain lowercase alphanumeric, hyphens, and underscores (URL-safe)
+    if (!/^[a-z0-9_-]+$/.test(token)) {
+      throw new SecurityError(
+        `Custom token must contain only lowercase letters (a-z), numbers (0-9), hyphens (-), and underscores (_). Invalid token provided.`
+      );
+    }
+  }
+
   private generatePortToken(): string {
     // Generate cryptographically secure 16-character token using Web Crypto API
     // Available in Cloudflare Workers runtime

packages/sandbox/tests/port-client.test.ts

@@ -56,6 +56,39 @@ describe('PortClient', () => {
       expect(result.url.startsWith('https://')).toBe(true);
     });
 
+    it('should expose ports with custom tokens', async () => {
+      const customToken = 'my-custom-token';
+      const mockResponse: PortExposeResult = {
+        success: true,
+        port: 8080,
+        url: 'https://8080-sandbox-my-custom-token.example.com',
+        timestamp: '2023-01-01T00:00:00Z'
+      };
+
+      mockFetch.mockResolvedValue(
+        new Response(JSON.stringify(mockResponse), { status: 200 })
+      );
+
+      const result = await client.exposePort(
+        8080,
+        'session-custom',
+        'api',
+        customToken
+      );
+
+      expect(result.success).toBe(true);
+      expect(result.port).toBe(8080);
+      expect(result.url).toContain(customToken);
+
+      // Verify the token was sent in the request
+      expect(mockFetch).toHaveBeenCalledWith(
+        expect.any(String),
+        expect.objectContaining({
+          body: expect.stringContaining(customToken)
+        })
+      );
+    });
+
     it('should expose API services on different ports', async () => {
       const mockResponse: PortExposeResult = {
         success: true,

packages/sandbox/tests/sandbox.test.ts

@@ -887,4 +887,104 @@ describe('Sandbox - Automatic Session Management', () => {
       ).resolves.toBeUndefined();
     });
   });
+
+  describe('custom token validation', () => {
+    beforeEach(() => {
+      // Mock the exposePort client call
+      vi.spyOn(sandbox.client.ports, 'exposePort').mockResolvedValue({
+        success: true,
+        port: 8080,
+        url: 'http://localhost:8080',
+        timestamp: new Date().toISOString()
+      });
+
+      // Mock storage for tokens
+      vi.mocked(mockCtx.storage!.get).mockResolvedValue({});
+      vi.mocked(mockCtx.storage!.put).mockResolvedValue(undefined);
+    });
+
+    it('should accept valid custom tokens of various lengths', async () => {
+      const shortToken = 'short';
+      const result1 = await sandbox.exposePort(8080, {
+        hostname: 'example.com',
+        token: shortToken
+      });
+
+      expect(result1.port).toBe(8080);
+      expect(result1.url).toContain(shortToken);
+
+      const longToken = 'my-very-long-custom-token-12345';
+      const result2 = await sandbox.exposePort(8081, {
+        hostname: 'example.com',
+        token: longToken
+      });
+
+      expect(result2.port).toBe(8081);
+      expect(result2.url).toContain(longToken);
+    });
+
+    it('should reject empty tokens', async () => {
+      await expect(
+        sandbox.exposePort(8080, {
+          hostname: 'example.com',
+          token: ''
+        })
+      ).rejects.toThrow('Custom token cannot be empty');
+    });
+
+    it('should reject tokens exceeding DNS subdomain limit', async () => {
+      const tooLongToken = 'a'.repeat(64); // 64 chars, exceeds 63 limit
+      await expect(
+        sandbox.exposePort(8080, {
+          hostname: 'example.com',
+          token: tooLongToken
+        })
+      ).rejects.toThrow('Custom token too long. Maximum 63 characters allowed');
+    });
+
+    it('should reject tokens with invalid characters', async () => {
+      await expect(
+        sandbox.exposePort(8080, {
+          hostname: 'example.com',
+          token: 'ABCD1234efgh5678' // uppercase not allowed
+        })
+      ).rejects.toThrow('Custom token must contain only lowercase letters');
+    });
+
+    it('should reject tokens with special characters', async () => {
+      await expect(
+        sandbox.exposePort(8080, {
+          hostname: 'example.com',
+          token: 'abcd!@#$%^&*1234'
+        })
+      ).rejects.toThrow('Custom token must contain only lowercase letters');
+    });
+
+    it('should allow tokens with hyphens and underscores', async () => {
+      const validToken = 'abc-123_def-456';
+      const result = await sandbox.exposePort(8080, {
+        hostname: 'example.com',
+        token: validToken
+      });
+
+      expect(result.port).toBe(8080);
+      expect(result.url).toContain(validToken);
+    });
+
+    it('should generate random token when not provided', async () => {
+      const result = await sandbox.exposePort(8080, {
+        hostname: 'example.com'
+      });
+
+      expect(result.port).toBe(8080);
+
+      // Verify a token was stored
+      expect(mockCtx.storage!.put).toHaveBeenCalledWith(
+        'portTokens',
+        expect.objectContaining({
+          '8080': expect.stringMatching(/^[a-z0-9_-]{16}$/)
+        })
+      );
+    });
+  });
 });

packages/shared/src/request-types.ts

@@ -101,6 +101,12 @@ export interface FileExistsRequest {
 export interface ExposePortRequest {
   port: number;
   name?: string;
+  /**
+   * Custom token for the preview URL (optional)
+   * If not provided, a random 16-character token will be generated
+   * Must be 1-63 characters, containing only lowercase letters, numbers, hyphens, and underscores
+   */
+  token?: string;
 }
 
 /**