tvl-depot/web/bubblegum
sterni 1c0f89f4ca feat(web/bubblegum): report some errors to the user via HTTP
We can actually catch some errors that may be generated in bubblegum
applications where we can report them to the user in a way that doesn't
require curl -vv:

* Type errors in the status argument: By removing yants completely we
  not only (presumably) gain some performance, but also the ability to
  return an internal server error on an unexpected type instead of
  throwing.

* User generated evaluation errors: by using builtins.tryEval we can
  catch throws and asserts the user inserted when generating the body
  and report to the user that something went wrong. To do: also support
  for the headers.

Change-Id: I8363b9825c6c730e624eb8016a5482d63cbc1890
Reviewed-on: https://cl.tvl.fyi/c/depot/+/2849
Tested-by: BuildkiteCI
Reviewed-by: sterni <sternenseemann@systemli.org>
2021-04-05 10:54:32 +00:00
..
examples feat(web/bubblegum): report some errors to the user via HTTP 2021-04-05 10:54:32 +00:00
default.nix feat(web/bubblegum): report some errors to the user via HTTP 2021-04-05 10:54:32 +00:00
OWNERS chore(web/bubblegum): add OWNERS file 2021-04-01 22:05:31 +00:00
README.md feat(web/bubblegum): nix CGI programming framework 2021-04-01 18:50:36 +00:00

//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 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):

#!/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…
} ''
  <!doctype html>
  <html>
    <head>
      <meta charset="utf-8">
      <title>hello world</title>
    </head>
    <body>
      hello world!
    </body>
  </html>
''

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 (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. You can also start a local server running the examples like this:

$ nix-build -A web.bubblegum.examples && ./result
# navigate to http://localhost:9000