Getting Amazonka S3 to work with localstack

I'm writing this in case someone else is getting strange errors when trying to use amazonka-s3 with localstack. It took me rather too long finding the answer and neither the errors I got from Amazonka nor from localstack were very helpful.

The code I started with for setting up the connection looked like this

main = do
  awsEnv <- AWS.overrideService localEndpoint <$> AWS.newEnv AWS.discover
  -- do S3 stuff
  where
    localEndpoint = AWS.setEndpoint False "localhost" 4566

A few years ago, when I last wrote some Haskell to talk to S3 this was enough¹, but now I got some strange errors.

It turns out there are different ways to address buckets and the default, which is used by AWS itself, isn't used by localstack. The documentation of S3AddressingStyle has more details.

So to get it to work I had to change the S3 addressing style as well and ended up with this code instead

main = do
  awsEnv <- AWS.overrideService (s3AddrStyle . localEndpoint) <$> AWS.newEnv AWS.discover
  -- do S3 stuff
  where
    localEndpoint = AWS.setEndpoint False "localhost" 4566
    s3AddrStyle svc = svc {AWS.s3AddressingStyle = AWS.S3AddressingStylePath}