Add socket activation support - #1516
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Socket activation is generally nice to have / considered good practice, but this will especially be useful later because it makes parallel local (i.e. via `cabal`, not just inside a Nix build) integration testing easier. We try socket activation by default, falling back to binding a port ourselves. `--socket-activation-only` and `--no-socket-activation` force either side; `--ip`/`--port` imply the latter, since asking for an address to listen on is a request to bind it ourselves. (Use `--base-uri` if you only meant to change the advertised URI.) A key implementation detail: `setNonBlockIfNeeded` must be called on the inherited fd so that GHC's IO manager (epoll) can handle `accept`/`recv` correctly in the threaded runtime. Without this, the server starts but connections hang — discovered and fixed via the NixOS VM integration test.
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Socket activation is generally nice to have / considered good practice, but this will especially be useful later because it makes parallel local (i.e. via
cabal, not just inside a Nix build) integration testing easier.We try socket activation by default, falling back to binding a port ourselves.
--socket-activation-onlyand--no-socket-activationforce either side;--ip/--portimply the latter, since asking for an address to listen on is a request to bind it ourselves. (Use--base-uriif you only meant to change the advertised URI.)A key implementation detail:
setNonBlockIfNeededmust be called on the inherited fd so that GHC's IO manager (epoll) can handleaccept/recvcorrectly in the threaded runtime. Without this, the server starts but connections hang — discovered and fixed via the NixOS VM integration test.