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authorsterni <sternenseemann@systemli.org>2021-02-21T11·57+0100
committersterni <sternenseemann@systemli.org>2021-04-01T18·50+0000
commit93a746aaaa092ffc3e7eb37e1df30bfd3a28435f (patch)
tree4197f3d5c7b5e2c4cdcb4be3dd1a17ed3ecc2ad7 /web/bubblegum/examples/hello.nix
parent68f3ac64c4a2ae50dcb125f067692536f647e370 (diff)
feat(web/bubblegum): nix CGI programming framework r/2394
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>
Diffstat (limited to 'web/bubblegum/examples/hello.nix')
-rw-r--r--web/bubblegum/examples/hello.nix80
1 files changed, 80 insertions, 0 deletions
diff --git a/web/bubblegum/examples/hello.nix b/web/bubblegum/examples/hello.nix
new file mode 100644
index 000000000000..881426bd1212
--- /dev/null
+++ b/web/bubblegum/examples/hello.nix
@@ -0,0 +1,80 @@
+{ depot, ... }:
+
+let
+  inherit (depot)
+    lib
+    ;
+
+  inherit (depot.web.bubblegum)
+    pathInfo
+    respond
+    absolutePath
+    ;
+
+  routes = {
+    "/" = {
+      status = "OK";
+      title = "index";
+      content = ''
+        Hello World!
+      '';
+    };
+    "/clock" = {
+      status = "OK";
+      title = "clock";
+      content = ''
+        It is ${toString builtins.currentTime}s since 1970-01-01 00:00 UTC.
+      '';
+    };
+    "/coffee" = {
+      status = "I'm a teapot";
+      title = "coffee";
+      content = ''
+        No coffee, I'm afraid
+      '';
+    };
+  };
+
+  notFound = {
+    status = "Not Found";
+    title = "404";
+    content = ''
+      This page doesn't exist.
+    '';
+  };
+
+  navigation =
+    lib.concatStrings (lib.mapAttrsToList
+      (p: v: "<li><a href=\"${absolutePath p}\">${v.title}</a></li>")
+      routes);
+
+  template = { title, content, ... }: ''
+    <!doctype html>
+    <html lang="en">
+    <head>
+      <meta charset="utf-8">
+      <title>${title}</title>
+      <style>a:link, a:visited { color: blue; }</style>
+    </head>
+    <body>
+      <hgroup>
+      <h1><code>//web/bubblegum</code></h1>
+      <h2>example app</h2>
+      </hgroup>
+      <header>
+        <nav>
+          <ul>${navigation}</ul>
+        </nav>
+      </header>
+      <main>
+        <p>${content}</p>
+      </main>
+    </body>
+  '';
+
+  response = routes."${pathInfo}" or notFound;
+
+in
+  respond response.status {
+    "Content-type" = "text/html";
+  } (template response)