tvl-depot/web/bubblegum/examples/blog.nix

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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
{ depot, ... }:
let
inherit (depot)
lib
;
inherit (depot.users.sterni.nix)
url
fun
string
;
inherit (depot.web.bubblegum)
pathInfo
scriptName
respond
absolutePath
;
# substituted using substituteAll in default.nix
blogdir = "@blogdir@";
# blogdir = toString ./posts; # for local testing
parseDate = post:
let
matched = builtins.match "/?([0-9]+)-([0-9]+)-([0-9]+)-.+" post;
in
if matched == null
then [ 0 0 0 ]
else builtins.map builtins.fromJSON matched;
parseTitle = post:
let
matched = builtins.match "/?[0-9]+-[0-9]+-[0-9]+-(.+).html" post;
in
if matched == null
then "no title"
else builtins.head matched;
dateAtLeast = a: b:
builtins.all fun.id
(lib.zipListsWith (partA: partB: partA >= partB) a b);
byPostDate = a: b:
dateAtLeast (parseDate a) (parseDate b);
posts = builtins.sort byPostDate
(builtins.attrNames
(lib.filterAttrs (_: v: v == "regular")
(builtins.readDir blogdir)));
generic = { title, inner, ... }: ''
<!doctype html>
<html>
<head>
<meta charset="utf-8">
<title>${title}</title>
<style>a:link, a:visited { color: blue; }</style>
</head>
<body>
${inner}
</body>
</html>
'';
index = posts: ''
<main>
<h1>blog posts</h1>
<ul>
'' + lib.concatMapStrings (post: ''
<li>
<a href="${absolutePath (url.encode {} post)}">${parseTitle post}</a>
</li>
'') posts + ''
</ul>
</main>
'';
formatDate =
let
# Assume we never deal with years < 1000
formatDigit = d: string.fit {
char = "0"; width = 2;
} (toString d);
in lib.concatMapStringsSep "-" formatDigit;
post = title: post: ''
<main>
<h1>${title}</h1>
<div id="content">
${builtins.readFile (blogdir + "/" + post)}
</div>
</main>
<footer>
<p>Posted on ${formatDate (parseDate post)}</p>
<nav><a href="${scriptName}">index</a></nav>
</footer>
'';
validatePathInfo = pathInfo:
let
chars = string.toChars pathInfo;
in builtins.length chars > 1
&& !(builtins.elem "/" (builtins.tail chars));
response =
if pathInfo == "/"
then {
title = "blog";
status = "OK";
inner = index posts;
}
else if !(validatePathInfo pathInfo)
then {
title = "Bad Request";
status = "Bad Request";
inner = "No slashes in post names 😡";
}
# CGI should already url.decode for us
else if builtins.pathExists (blogdir + "/" + pathInfo)
then rec {
title = parseTitle pathInfo;
status = "OK";
inner = post title pathInfo;
} else {
title = "Not Found";
status = "Not Found";
inner = "<h1>404 not found</h1>";
};
in
respond response.status {
"Content-type" = "text/html";
} (generic response)