Implement a CDN saver

[arschles]

This would complement the CDN getter. The getter just gets a redirect location for a module; the setter should upload/update:

• The versions list
• The go.mod file
• The version metadata
• The source zip

It should also enter a redirect location (that the getter can fetch) into the CDN metadata store.

Make sure to put the entire operation (enter into CDN metadata store + upload) in a critical section. Ideas:

• Lock/lease the directory on the CDN
  • Azure blob storage gives you versioned blobs and also lock semantics for blobs (see here)
  • Google Cloud Storage gives you generational versioning and preconditions (see here and here)
  • Quick research on S3 indicates that blobs (buckets?) have versions. Need more to research whether the API includes preconditions for generations

[arschles]

the storage saver interface exists and it's implemented in all our storage drivers. closing