Add Retry-After hint

[gautam1168]

Fixes issue 1878

[steve-chavez]

Great work @gautam1168!

I've just tried your change by doing

sudo systemctl stop postgresql

curl -I localhost:3000/projects

HTTP/1.1 503 Service Unavailable

Date: Tue, 17 Aug 2021 16:54:18 GMT
Server: postgrest/8.0.0 (b3899e7)
Retry-After: 16
Content-Type: application/json; charset=utf-8

Retry-After is now showing!

Ideally we'd be able to add a test, but our io-tests(in Python) need some work to support restarting/starting the postgres instance(#1766).

So this should be good. Don't forget to add an entry to the CHANGELOG!

[steve-chavez]

Just noted something that perhaps should be handled in another PR: the connection worker delay is not being respected.

On v7, it used to be that all requests would get rejected with 503 while the connection worker is running. But on v8.0, the connection recovery is done whenever a new request comes in:

curl -I localhost:3000/projects
HTTP/1.1 503 Service Unavailable
Date: Tue, 17 Aug 2021 17:15:12 GMT
Server: postgrest/8.0.0 (b3899e7)
Retry-After: 32
Content-Type: application/json; charset=utf-8

sudo systemctl start postgresql

## just a second after

curl -I localhost:3000/projects
HTTP/1.1 200 OK
Date: Tue, 17 Aug 2021 17:15:46 GMT
Server: postgrest/8.0.0 (b3899e7)
Content-Range: 0-58/*
Content-Location: /projects
Content-Type: application/json; charset=utf-8

## postgrest is already recovered

## The connection worker will report the reconnection later(after 32 sec):
## 17/Aug/2021:12:16:05 -0500: Connection successful
## 17/Aug/2021:12:16:05 -0500: Config re-loaded
## 17/Aug/2021:12:16:06 -0500: Schema cache loade

This is probably a side effect of doing #1559.

[gautam1168]

@steve-chavez I have added an entry to CHANGELOG.md in the unreleased fixes section. Should it be in the Added section?

Regarding connection worker delay not being respected. I am assuming you will be opening another issue to handle that and maybe I will give that a try too. But next want to try to add the limit=0 feature request from another issue.

[gautam1168]

I figured since its not a bug it should be in the Added section and moved it.

I will figure out how to rebase against the upstream repository and resolve this conflict.

[gautam1168]

@steve-chavez I have resolved the conflict and squashed my changes to a single commit. I have also added a better commit message and included the issue number that is fixed in the description.

[monacoremo]

Great work!

[steve-chavez]

LGTM! Merging 🚀