Simplify socket path code

[newhoggy]

Instead of reading CARDANO_NODE_SOCKET_PATH in every command, do it once in main and then use it as a default value in --socket-path option if available.

Also read CARDANO_NODE_NETWORK_ID and use that if neither --testnet-magic nor --mainnet supplied.

[dcoutts]

I'll go out on a limb and claim that it is never necessary to use unsafePerformIO in application code. And most uses do bite you in the end (often when refactoring later).

We should just do it properly.

[newhoggy]

I understand that most uses case bite you in the end, but the one use case we're you using it to initialise a constant that never changes isn't one of them and I never use it for any other reason.

[dcoutts]

Our attitude should be to simply not use it (in application code), rather than looking for justification as to why it might not be so bad in this or that case.

It's not "Haskell". It has no semantics.

[newhoggy]

The code no longer uses unsafePerformIO.

[Jimbo4350]

Nice 👍. Just one comment for you to consider.

[Jimbo4350]

Why not leverage Alternative (<|>)?:

pSocketPath :: EnvCli -> Parser SocketPath
pSocketPath envCli =
  let opts = mconcat
              [ Opt.long "socket-path"
              , Opt.metavar "SOCKET_PATH"
              , Opt.help $ mconcat
                [ "Path to the node socket.  This overrides the CARDANO_NODE_SOCKET_PATH "
                , "environment variable"
                ]
              , Opt.completer (Opt.bashCompleter "file")
              ]
  in fmap SocketPath (Opt.strOption opts) <|>
     -- Default to the socket path specified by the environment variable if it is available.
     pure (maybe (error "No socket path specified via cli nor env var") SocketPath $ envCliSocketPath envCli)

And then we can error immediately rather than the networking code throw some obscure error.

[newhoggy]

We already use Alternative via asum. If CARDANO_NODE_SOCKET_PATH is not supplied, the code as it currently is will error immediately because --socket-path is the only Alternative in this case. The CLI parsing will fail because --socket-path is not supplied and it is the only alternative. You only get the fallback alternative if CARDANO_NODE_SOCKET_PATH is supplied, in which case the socket path provided by the environment variable is the default and --socket-path will override.

[newhoggy]

I updated the CLI help message to be clearer.