halo-dev/halo · error · ServerWebInputException

Invalid type of parameter 'file'.

Error message

Invalid type of parameter 'file'.

What it means

Thrown as a ServerWebInputException (HTTP 400) in AttachmentUcEndpoint's PostAttachmentRequest builder when multipartData.getFirst("file") is not an instance of FilePart — the 'file' part is missing entirely or is a FormFieldPart (text) rather than a file upload.

Source

Thrown at application/src/main/java/run/halo/app/core/endpoint/uc/AttachmentUcEndpoint.java:371

         * @param multipartData is multipart data from request.
         * @return post attachment request data.
         */
        public static PostAttachmentRequest from(MultiValueMap<String, Part> multipartData) {
            var part = multipartData.getFirst("postName");
            String postName = null;
            if (part instanceof FormFieldPart formFieldPart) {
                postName = formFieldPart.value();
            }

            part = multipartData.getFirst("singlePageName");
            String singlePageName = null;
            if (part instanceof FormFieldPart formFieldPart) {
                singlePageName = formFieldPart.value();
            }

            part = multipartData.getFirst("file");
            if (!(part instanceof FilePart file)) {
                throw new ServerWebInputException("Invalid type of parameter 'file'.");
            }

            return new PostAttachmentRequest(file, postName, singlePageName);
        }
    }
}

View on GitHub (pinned to d2f5165f9c)

Solutions

1. Attach the binary under a 'file' multipart field with a filename so WebFlux parses it as a FilePart.
2. Verify the multipart request includes both the file part and any postName/singlePageName text fields with correct names.
3. Confirm Content-Type is multipart/form-data with a valid boundary.

Example fix

// before: curl -F postName=p -F file=@/no/such  (or file omitted)
// after:  curl -F postName=p -F file=@/path/to/attachment.png

// ensure the 'file' field is an actual file upload before submit
if (!(formData.get("file") instanceof File)) {
    showUserError("Attach a file under the 'file' field");
    return;
}

When it happens

Trigger: POST to the user-center post-attachment upload endpoint where the 'file' multipart part is absent or sent as a plain text field. The instanceof FilePart check fails and the guard throws.

Common situations: Client used the wrong field name; file sent as a string path instead of an attachment; form library did not set a filename/Content-Type; integration test posted only postName/singlePageName fields.

Related errors

• Invalid part of file
• Invalid part of policyName
• Required url is missing.
• Required url is missing.
• Policy name must not be blank

AI-assisted analysis of halo-dev/halo@d2f5165f9c (2026-08-14). Data as JSON: /api/errors/7d89f77da03d840f. Report an issue: GitHub.