[Fixed] Next.js error TypeError: Cannot read properties of undefined (reading 'headers') – Rest

The Problem:

Next.js 13 application uses a REST API route to interact with OpenAI’s API for content generation. Upon sending a POST request to the API route for creating chapters in a course, the user encounters a ‘TypeError: Cannot read properties of undefined (reading ‘headers’)’ error. The involved files include ‘gpt.ts’, ‘route.ts’, a schema file for Prisma, and the folder structure. The Insomnia REST response is empty, and the expected outcome was a JSON response with generated course content.

The Solutions:

Solution 1: Verify OpenAI API Credentials

The issue you’re encountering is most likely due to an error in your OpenAI API credentials. Here’s what you can do to resolve it:

1. Check Your API Key:

   • Ensure that you’re using a valid OpenAI API key. You can create one by signing up for an account on the OpenAI website.

2. Check Your API Usage:

   • Make sure that you’re not exceeding your API usage limits. You can check your usage in the OpenAI dashboard.

3. Check Your API Endpoint:

   • Verify that you’re sending the request to the correct OpenAI API endpoint. The correct endpoint for chat completions is "https://generativelanguage.googleapis.com/v1beta2/models/chat:complete".

4. Check Your Request Headers:

   • Ensure that you’re including the necessary headers in your request. The following headers are required:
     • "Content-Type: application/json"
     • "Authorization: Bearer [your API key]"

5. Check Your Request Payload:

   • Make sure that the request payload is properly formatted. The payload should be a JSON object with the following properties:
     • "context": A string containing the conversation history
     • "messages": An array of objects, each representing a user or assistant message
     • "model": The name of the OpenAI model to use (e.g., "text-bison-001")

After verifying these aspects, try sending the request again. If you’re still having issues, you can reach out to OpenAI’s support team for further assistance.

Solution 2: Check for errors in the catch block

To resolve the issue, check for errors in the catch block and return a response accordingly. This will help in identifying and handling any potential errors that may occur during the API call.

Here’s an updated version of the catch block in your route.ts file:

catch (error) {
  if (error instanceof ZodError) {
    return new NextResponse("Invalid Body", { status: 400 });
  } else {
    console.error(error);
    return new NextResponse("Internal server error", { status: 500 });
  }
}

Now, when an error occurs that is not related to Zod validation, it will be logged and a 500 status code will be returned to the client. This will prevent the "read properties of undefined" error and provide a more meaningful error message.

Remember to add necessary error handling and logging mechanisms to your application to help debug and troubleshoot any potential issues in the future.

Solution 3: Check for Headers

Ensure that the `headers `object is present in the request. Add the following line to the beginning of your `POST` route handler in `route.ts`:

const { headers } = req;

Make sure that headers is present before proceeding with the rest of the code. This will help resolve the error by ensuring that the headers object is available when accessing its properties.

Video Explanation: