HMI file uploads

SCADA Final Aggregator has a special HTTP method to handle uploads.


The method accepts standard multipart-form data requests and processes them with Logic control macros.

File upload form

How does it work

An upload form can be either standard HTML web-form or AJAX-based. Here is an example of the standard one:

<form action="/upload" method="POST" enctype="multipart/form-data">
    Select file to upload:
    <input type="file" name="ufile">
    <input type="hidden" name="rdr" value="/ui/upload_example.html">
    <input type="hidden" name="process_macro_id" value="tests/upload_handler">
    <input type="submit" value="Upload file" name="submit">

What happens, when a file is uploaded and the method is called:

  • The form parameters are checked (“ufile” and “process_macro_id” are mandatory)

  • If there is a file to upload chosen, the macro with id, specified in “process_macro_id” is called.

  • If there is “rdr” form parameter set, the method performs redirect to the specified URI

  • Otherwise, the method returns JSON output of macro execution result:

    "args": [],
    "err": "",
    "exitcode": 0,
    "finished": true,
    "finished_in": 0.0034916,
    "item_group": "nogroup",
    "item_id": "m1",
    "item_oid": "lmacro:nogroup/m1",
    "item_type": "lmacro",
    "kwargs": {
        "content": "<binary>",
        "data": {
            "aci": {
                "id": "6d7dca71-865b-4aac-8f1d-5c4f4a979c68",
                "key_id": "masterkey"
            "content_type": "image/jpeg",
            "file_name": "wpbig.jpg",
            "form": {
                "submit": "OK"
            "sha256": "0393e47ec35f73e12d333bb719d30e3959bd140bf952c69b4139b956957a8c4c",
            "system_name": "sfa/lab-ws2"
    "out": "",
    "priority": 100,
    "status": "completed",
    "time": {
        "completed": 1607025058.628277,
        "created": 1607025058.6247854,
        "pending": 1607025058.6249535,
        "queued": 1607025058.625362,
        "running": 1607025058.6257577
    "uuid": "19a71537-cfea-4154-b1f4-dc0897216abe"


  • 400 (Bad Request) - invalid HTTP request or “ufile” or “process_macro_id” parameters are not set

  • 404 (Not Found) - the macro with the specified id is not found

  • 403 (Forbidden) - the user has no access to the requested macro

  • 500 (API Error) - all other errors

In case if the file is not specified and “rdr” param is not set, the method returns:

{ "ok": false }

Additional form parameters

  • k API key (set automatically by EVA JS Framework version 0.3.9 or above)

  • w seconds to wait until macro execution is completed

  • p: macro queue priority (default is 100, lower is better)

  • q global queue timeout, if expires, action is marked as “dead”

  • all other parameters are sent to macro as a dict data[“form”]

Processing macro

When the file upload is complete, Logic macro is being called, so the content is actually transferred for processing to the Logic Manager where the macro is located.

The macro automatically gets these parameters:

  • content content of the uploaded file (binary)

  • data upload information data:

    • aci API call info dict

    • content_type file content type, reported by client

    • file_name file name, reported by client

    • form the dict of all additional upload form parameters

    • sha256 SHA256-checksum of the uploaded file (calculated by SFA)

    • system_name system name, the file is coming from

Here’s an example of the very simple macro, which stores uploaded files in /tmp:

print(f'uploading file {data["file_name"]}')
assert data['sha256'] == sha256sum(content)
with open('/tmp/' + data['file_name'], 'wb') as fh:
    out = 'upload completed'

Security and file upload limits

  • To upload files, the user should have an access to the corresponding processing macro

  • There’s no built-in limitations for uploaded file size, but the limit can be set using SFA HTTP front-end.