Multi Part Upload for Frappe

file_uploader.js

// Copyright (c) 2025, Revant Nandgaonkar and contributors
// License: MIT

// HTML Field has following options
// <div id="dropzoneTarget" class="fallback dropzone"> <input hidden name="file" type="file"> </div>

frappe.ui.form.on('File Uploader', {
  refresh(frm) {
    const url = '/api/method/multipart_upload.upload.multipart_file_upload';
    const chunkSize = 20 * 1024 * 1024; // 20MB

    new Dropzone('div#dropzoneTarget', {
      url,
      paramName: 'file',
      chunking: true,
      forceChunking: true,
      maxFilesize: 10 * 1024, // 10GB
      timeout: 120000, // 2 minutes,
      chunkSize, // bytes
      headers: {
        'X-Frappe-CSRF-Token': frappe.csrf_token,
      },
      params: (files, xhr, chunk) => {
        if (chunk) {
          return {
            dzchunkindex: chunk.index,
            dzchunkbyteoffset: chunk.index * chunkSize,
            dztotalchunkcount: chunk.file.upload.totalChunkCount,
            dztotalfilesize: chunk.file.size,
            // fieldname: "fieldname",
            folder: 'Attachments',
            doctype: frm.doc.doctype,
            docname: frm.doc.name,
            is_private: frm.doc.is_private,
          };
        }
      },
    });
  },
});

hooks.py

# Copyright (c) 2025, Revant Nandgaonkar and contributors
# License: MIT

# ...

app_include_css = ["https://unpkg.com/dropzone@5/dist/min/dropzone.min.css"]
app_include_js = ["https://unpkg.com/dropzone@5/dist/min/dropzone.min.js"]

upload.py

# Copyright (c) 2025, Revant Nandgaonkar and contributors
# License: MIT
# references:
# https://stackoverflow.com/a/53001103
# https://github.com/frappe/drive/blob/main/frontend/src/components/FileUploader.vue
# https://github.com/frappe/frappe/blob/develop/frappe/client.py

import os

import frappe
from frappe.utils import cint
from werkzeug.utils import secure_filename


class FileAlreadyExistsException(Exception):
    http_status_code = 400


class InternalServerException(Exception):
    http_status_code = 500


@frappe.whitelist(methods=["POST"])
def multipart_file_upload(*args, **kwargs):
    file = frappe.request.files["file"]
    filename = secure_filename(file.filename)

    is_private = frappe.form_dict.is_private or 1
    file_dir = "private/files" if is_private else "public/files"
    file_url = os.path.join(
        "/private/files" if is_private else "/files",
        filename,
    )
    save_path = os.path.join(frappe.get_site_path(file_dir), filename)
    current_chunk = int(frappe.form_dict.dzchunkindex)

    if os.path.exists(save_path) and current_chunk == 0:
        return frappe.throw(
            "File already exists",
            exc=FileAlreadyExistsException,
        )

    try:
        with open(save_path, "ab") as f:
            f.seek(int(frappe.form_dict.dzchunkbyteoffset))
            f.write(file.stream.read())
    except OSError as e:
        frappe.log_error("Could not write to file", e)

        return frappe.throw(
            ("Not sure why, but we couldn't write the file to disk"),
            exc=InternalServerException,
        )

    total_chunks = int(frappe.form_dict.dztotalchunkcount)

    if current_chunk + 1 == total_chunks:
        if os.path.getsize(save_path) != int(frappe.form_dict.dztotalfilesize):
            frappe.log_error(
                f"File {filename} was completed, "
                f"but has a size mismatch."
                f"Was {os.path.getsize(save_path)} but we"
                f" expected {frappe.form_dict.dztotalfilesize} "
            )
            # delete incomplete file
            os.remove(save_path)
            return frappe.throw("Size mismatch", exc=InternalServerException)
        else:
            frappe.log(f"File {filename} has been uploaded successfully")
    else:
        frappe.log(
            (
                f"Chunk {current_chunk + 1} of "
                f"{total_chunks} for file {filename} complete"
            )
        )

    doctype = frappe.form_dict.doctype
    docname = frappe.form_dict.docname
    fieldname = frappe.form_dict.fieldname
    folder = frappe.form_dict.folder or "Home"
    frappe_file = frappe.get_doc(
        {
            "doctype": "File",
            "attached_to_doctype": doctype,
            "attached_to_name": docname,
            "attached_to_field": fieldname,
            "folder": folder,
            "file_name": filename,
            "file_url": file_url,
            "is_private": cint(is_private),
        }
    )
    frappe_file.save(ignore_permissions=True)

    return "Chunk upload successful"