From 93a746aaaa092ffc3e7eb37e1df30bfd3a28435f Mon Sep 17 00:00:00 2001 From: sterni Date: Sun, 21 Feb 2021 12:57:40 +0100 Subject: 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 --- web/bubblegum/README.md | 68 +++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 68 insertions(+) create mode 100644 web/bubblegum/README.md (limited to 'web/bubblegum/README.md') diff --git a/web/bubblegum/README.md b/web/bubblegum/README.md new file mode 100644 index 0000000000..0e09c1c65e --- /dev/null +++ b/web/bubblegum/README.md @@ -0,0 +1,68 @@ +# //web/bubblegum + +`bubblegum` is a CGI programming library for the Nix expression language. +It provides a few helpers to make writing CGI scripts which are executable +using [//users/sterni/nint](../../users/sterni/nint/README.md) convenient. + +An example nix.cgi script looks like this (don't worry about the shebang +too much, you can use `web.bubblegum.writeCGI` to set this up without +thinking twice): + +```nix +#!/usr/bin/env nint --arg depot '(import /path/to/depot {})' +{ depot, ... }: + +let + inherit (depot.web.bubblegum) + respond + ; +in + +respond "OK" { + "Content-type" = "text/html"; + # further headers… +} '' + + + + + hello world + + + hello world! + + +'' +``` + +As you can see, the core component of `bubblegum` is the `respond` +function which takes three arguments: + +* The response status as the textual representation which is also + returned to the client in the HTTP protocol, e. g. `"OK"`, + `"Not Found"`, `"Bad Request"`, … + +* An attribute set mapping header names to header values to be sent. + +* The response body as a string. + +Additionally it exposes a few helpers for working with the CGI +environment like `pathInfo` which is a wrapper around +`builtins.getEnv "PATH_INFO"`. The documentation for all exposed +helpers is inlined in [default.nix](./default.nix) (you should be +able to use `nixdoc` to render it). + +For deployment purposes it is recommended to use `writeCGI` which +takes a nix CGI script in the form of a derivation, path or string +and builds an executable nix CGI script which has the correct shebang +set and is automatically passed a version of depot from the nix store, +so the script has access to the `bubblegum` library. + +For example nix CGI scripts and a working deployment using `thttpd` +see the [examples directory](./examples). You can also start a local +server running the examples like this: + +``` +$ nix-build -A web.bubblegum.examples && ./result +# navigate to http://localhost:9000 +``` -- cgit 1.4.1