TypeError: Bytes or str expected, not Buffer during client.start authentication (v2.26.21, Browser/Next.js)

[artem-lazarev]

Hi gramJS team,

I'm encountering a TypeError: Bytes or str expected, not Buffer when attempting to log in using the client.start method in a browser environment.

Version Info:

• gramJS (telegram package): 2.26.21
• Session: StringSession

Environment:

• Runtime: Browser (within a Next.js application)
• Bundler: Next.js internal (Webpack/Turbopack)
• (Optional: Node.js version used for building: [Your Node.js Version, e.g., v18.18.0])

Problem Description:

After successfully connecting (client.connect()) and requesting a phone code (client.sendCode()), the subsequent call to client.start() fails with the Bytes or str expected, not Buffer error. This occurs specifically during the phase where gramJS likely handles the password/2FA step internally (signInWithPassword appears in the stack trace).

Steps to Reproduce (Conceptual):

1. Initialize TelegramClient with apiId, apiHash, and an empty StringSession in a browser environment.
2. Call await client.connect();
3. Call await client.sendCode({ apiId, apiHash }, phoneNumber);
4. Prompt the user for the received phone code and optionally their 2FA password.
5. Call await client.start({ phoneNumber: ..., phoneCode: async () => code, password: async () => password, onError: ... });

Relevant Code Snippet:

This is how client.start is being called within my Zustand store:

// Helper function to provide auth parameters
const createAuthParamCallback = <T extends string>(param: T): () => Promise<T> => {
  return async () => {
    return param;
  };
};

// Inside an async function handling login:
async function loginWithCodePassword({ phoneCode, password = '' }) {
  // ... retrieve client, apiId, apiHash, phoneNumber from state ...

  console.log('[TG Store] Attempting to login with code/password...');
  // Set loading state, etc.

  try {
    console.log('[TG Store] Calling client.start...');
    await client.start({
      phoneNumber: phoneNumber, // String from state
      password: createAuthParamCallback(password), // Always a string (defaulted to '')
      phoneCode: createAuthParamCallback(phoneCode), // String from user input
      onError: (err: Error) => {
        console.error('[TG Store] client.start onError callback triggered:', err);
        // Propagate or handle error
        throw err;
      },
    });
    // ... handle success ...
  } catch (error: any) {
    // ... handle failure ...
     console.error('[TG Store] Login failed during client.start:', error); // <-- This logs the error
  }
}

Error Log & Stack Trace:

[TG Store] Calling client.start...
[TG Store] client.start onError callback triggered: Error: Bytes or str expected, not Buffer
    at serializeBytes (generationHelpers.js:247:19)
    at argToBytes (api.js:106:20)
    at VirtualClass.getBytes (api.js:415:42)
    at argToBytes (api.js:113:22)
    at VirtualClass.getBytes (api.js:415:42)
    at new RequestState (RequestState.js:13:29)
    at Object.invoke (users.js:48:19)
    at async Object.signInWithPassword (auth.js:319:31)
    at async _authFlow (auth.js:363:11)
    at async Object.start (auth.js:52:5)
    at async loginWithCodePassword (telegramStore.ts:220:7) // <-- My code calling client.start
    at async handleCodePasswordSubmit (page.tsx:57:5)     // <-- UI handler calling loginWithCodePassword

(The same error/stack trace is caught by the outer try/catch block)

Expected Behavior:

client.start() should resolve successfully, completing the login process and allowing the session to be saved.

Actual Behavior:

client.start() throws the TypeError: Bytes or str expected, not Buffer, preventing login. The error originates deep within the gramJS library's internal serialization or authentication logic.

[H2xDev]

@artem-lazarev
I suppose you have installed v2.26.22, not v2.26.21. Try install exactly v2.26.21. I got this bug on v2.26.22, but on 21 it works fine.