Feature: Support large sandbox content

[karlhorky]

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If the content passed to the GET define API is too large, CodeSandbox will return an HTTP 414 error (URI Too Long).

fetching the POST define API with ?json=1 (the "Define without Render" option) and then using the resulting URL for the iframe would be a workable solution:

https://codesandbox.io/docs/importing#xhr-request

This would require running asynchronous code within the transformer function, which can be achieved by returning a promise:

https://github.com/swimlane/DocSPA/blob/9155c2e07fa3105f4e7858e62e9877cfc4105706/projects/swimlane/docspa-remark-preset/src/plugins/short-codes.ts#L106

More information about async remark plugins: https://github.com/gatsbyjs/gatsby/issues/16403

[karlhorky]

I may end up implementing a PR of this myself, if I need it quick enough.