Cross-workspace migration: attachments broken after import

[ameenhere]

First of all, huge thanks for building slackdump. Super useful!

I've run into an issue with a cross-workspace migration and wanted to check if anyone has solved this before I go down a rabbit hole building something custom.

Setup

1. Export a private channel (including all attachments) from Workspace A using slackdump
2. Import the resulting zip into Workspace B using Slack's native import wizard

What's happening

The export looks great, all JSON files and attachments are present in the zip. However, after importing into the destination workspace, only the messages come through. Every attachment ends up as a broken ~56KB file with the correct extension but unusable contents.

Root cause (as I understand it)

The Slack import wizard resolves attachments by following the file URLs embedded in the JSON files. Those URLs still point back to the original workspace, which the import wizard has no access to. So they likely resolve to 401/404 responses that get saved as the dummy files.

The actual files are in the zip locally. The problem is there's no mechanism to tell the import wizard to resolve those URLs from the zip contents instead of fetching them remotely.

What I'm considering

Re-hosting all the attachment files somewhere publicly accessible (S3, OneDrive, etc.) and doing a find/replace on the URLs in the JSON files before re-zipping. It would work in theory, but feels tedious and fragile at scale.

Has anyone tackled this? Is there a cleaner approach I'm missing?

[rusq]

Hey @ameenhere , you are correct, Slack tries to fetch those files from a URL specified in the File object. Have a look at this comment: #399 (comment) . I haven't tested it myself, so please report if it works for you?

The same script is in the contrib directory

[ameenhere]

Thanks for the reply! I'll try it out and report back.