How do I configure multiple HTML binary files for PDF generation in self-hosted Gotenberg?

Below is a detailed explanation of the error and how to resolve it:

What the Error Means

The error message:

The item has no binary field ‘[object Object]’ [item 0]

indicates that the node is trying to access a binary property using a value that isn’t recognized as a valid field name. In n8n, binary data is stored on each item under a specific property name (for example, “data”). Here, instead of passing your expected string (the name of the binary field), an object is being passed (which when converted becomes “[object Object]”).

Likely Causes

• Multiple Files in One Item: You mentioned you are trying to send both an index.html (main content) and a footer.html (footer) in one execution. In n8n, each file must be stored on its own binary property. If you combine them on the same property or use an incorrect reference, the receiving node (in your case, the gotenberg node) won’t recognize it.
• Incorrect Expression Usage: If you use an expression or variable that returns an object instead of a string (the actual binary field name), the node will not be able to find the field.
• Field Name Mismatch: The parameter where you specify the input binary field name might not match the field created by a previous node (for example, a “Convert to File” or “Read/Write Files from Disk” node).

How to Fix It

1. Store Each File in a Separate Binary Field:
   Ensure that when you process your files, the main PDF content (index.html) and the footer (footer.html) are stored in uniquely named binary properties. For example, use:

   • index for the main content
   • footer for the footer

2. Reference the Correct Binary Property Name:
   In the node (Gotenberg) that sends the files to create the PDF, double-check that you’re referencing the correct binary field names. For instance:

   • For the main content, if you named it index, the parameter should exactly be "index".
   • For the footer, if you named it footer, it should be referenced as "footer".

   Example Expression:
   If you’re using an expression to supply the field name, it should directly return the string rather than an object. For example:

   JSCopied
   // Correct: returns a string value 'index'
   {{ 'index' }}

   Instead of something that might accidentally return an object.

3. Check Upstream Node Output:
   Open the output of the node where you’re creating or processing the binary data and confirm that the binary field names are exactly what you expect. The field names should be visible under the item’s “binary” object. For example:

   JSONCopied
   {
     "json": { ... },
     "binary": {
       "index": { ... },
       "footer": { ... }
     }
   }

   Adjust your references in the gotenberg node so that they match these names.

4. Review Gotenberg Node Configuration:
   Ensure that each input parameter (for the HTML and footer files) has the proper field name inserted. Often the error arises from a typo or misconfiguration within these parameters.

Summary

The error is due to the node expecting a binary field but receiving an object (or an incorrect field name). To fix it:

• Make sure each file (index.html and footer.html) is assigned to its own binary property with a clear, string name.
• Verify that the node parameters point exactly to these field names.
• Check that any expressions you use return a valid string and not an object.

Following these steps should resolve the error and allow your workflow to process multiple files correctly with your self-hosted Gotenberg instance.