notification: add Go CDK pubsub support

[jba]

Add the gocdk_pub_sub package, which supports the Go Cloud Development
Kit pubsub API.

Link in all current providers.

Update the notification scaffold.

[chrislusf]

Nice! There are some build errors:

'''
121.52s$ go get ./weed/...
package gocloud.dev/pubsub/awssnssqs: unrecognized import path "gocloud.dev/pubsub/awssnssqs" (parse https://gocloud.dev/pubsub/awssnssqs?go-get=1: no go-import meta tags ())
package gocloud.dev/pubsub/azuresb: unrecognized import path "gocloud.dev/pubsub/azuresb" (parse https://gocloud.dev/pubsub/azuresb?go-get=1: no go-import meta tags ())
package gocloud.dev/pubsub/natspubsub: unrecognized import path "gocloud.dev/pubsub/natspubsub" (parse https://gocloud.dev/pubsub/natspubsub?go-get=1: no go-import meta tags ())
The command "go get ./weed/..." failed and exited with 1 during .
Your build has been stopped.
'''

[chrislusf]

FYI: the build log

https://travis-ci.org/chrislusf/seaweedfs/builds/508889375

[chrislusf]

Can this gocloud.dev/pubsub be moved/cloned to github?

Seems this is not new: googleapis/google-cloud-go#820 happened more than one year ago.

[jba]

I'm working on this; it is a problem with go-import redirects for the gocloud.dev import paths.

[jba]

Tests are passing now.

[chrislusf]

Thanks a lot!

Is there any way to avoid this in the future? These go import redirects seem fragile.

[jba]

Is there any way to avoid this in the future? These go import redirects seem fragile.

We're automating our process so this won't happen again.

More generally, the Go ecosystem will soon have proxies, which will pretty much end availability issues. Run go help goproxy in Go 1.12.

[chrislusf]

@jba SeaweedFS use the notification to replicate files across systems. The current PR implemented SendMessage(). We need another one to ReceiveMessage(), similar to https://github.com/chrislusf/seaweedfs/blob/master/weed/replication/sub/notification_google_pub_sub.go#L94

Could you please also help here? Thanks!

[jba]

Sure, I'll try to get to it this week.