tvl-depot/web/bubblegum/examples/derivation-svg.nix

# Warning: this is *very* slow on the first request
{ depot, ... }:

let
  inherit (depot.web.bubblegum)
    respond
    ;
in
respond "OK"
{
  Content-type = "image/svg+xml";
}
  (builtins.readFile "${depot.tvix.docs.svg}/component-flow.svg")
feat(web/bubblegum): nix CGI programming framework So here is what has been keeping me up at night: At some point I realized that nix actually made a somewhat passable language for CGI programming: * That `builtins.getEnv` exists as one of the impurities of Nix is perfect as environment variables are the main way of communication from the web server to the CGI application. * We can actually read from the filesystem via builtins.readDir and builtins.readFile with bearable overhead if we avoid importing the used paths into the nix store. * Templating and routing are convenient to implement via indented strings and attribute sets respectively. Of course there are obvious limitation: * The overhead of derivations is probably much to great for them to be useful via IfD. * Even without derivations, nix evaluation is very slow to the point were a trivial application takes between 100ms and 400ms to produce a response. * We can't really cause effects other than producing a response which makes it not viable for a lot of applications. There are some ways around this: * With a custom interpreter we could have streaming and multiplexed I/O (using lazy lists emulated via attrsets) to cause such effects, but it would probably perform terribly. * We can use builtins.fetchurl to call other HTTP-based microservices, but only in very limited constraints, i. e. only GET, no headers, and only if the tarball ttl is set to 0 in the global nix.conf. * Terrible error handling capabilities because builtins.tryEval actually doesn't catch a lot of errors. To prove that it actually works, there are some demo applications, which I invite you to run and potentially break horribly: nix-build -A web.bubblegum.examples && ./result # navigate to http://localhost:9000 The setup uses thttpd and executes the nix CGI scripts using users.sterni.nint which automatically passed `depot`, so they can import the cgi library. Change-Id: I3a22a749612211627e5f8301c31ec2e7a872812c Reviewed-on: https://cl.tvl.fyi/c/depot/+/2746 Tested-by: BuildkiteCI Reviewed-by: tazjin <mail@tazj.in> 2021-02-21 12:57:40 +01:00			`# Warning: this is very slow on the first request`
			`{ depot, ... }:`

			`let`
			`inherit (depot.web.bubblegum)`
			`respond`
			`;`
			`in`
			`respond "OK"`
			`{`
			`Content-type = "image/svg+xml";`
			`}`
			`(builtins.readFile "${depot.tvix.docs.svg}/component-flow.svg")`