BasePath support

[rrooding]

I'm trying to use the Next.js basePath option (vercel/next.js#4998) with serverless-next.js but I'm having some problems.

Please let me know if I'm missing something but as far as I can see this is not supported yet.

I am happy to contribute a PR but would like to discuss the implementation first. My suggestion is to read the basePath setting from the next.config.js file during deployment and, when configured, use that for the following:

• Change uploadAssetsToS3 to upload to <basePath>/ subdirectory in the bucket
• Change the Cloudfront origins to <basePath>/_next/static/*, <basePath>/static/*, etc..

Anything else?

[danielcondemarin]

@rrooding A couple of thoughts from me on the approach:

• Rather than reading from the next.config.js file its easier to read from .next/routes-manifest.json which contains the basePath property.

• I'm not sure you actually need to a new directory in the s3 bucket. As long as the CloudFront cache behaviour maps <basePath>/_next/static/* -> s3 _next/static/* should be OK I think. Only saying because it may be simpler to implement to start with at least.

FYI - I've raised an RFC for multi-zones like support here that is sort of related.

Feel free to start a PR and I'll help out with approach and testing.

[rrooding]

I was on holiday, but just got to fixing the last failure, if you could have a look at it again 👍

[rrooding]

PR is merged