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| author | sterni <sternenseemann@systemli.org> | 2021-02-21T11·57+0100 |
|---|---|---|
| committer | sterni <sternenseemann@systemli.org> | 2021-04-01T18·50+0000 |
| commit | 93a746aaaa092ffc3e7eb37e1df30bfd3a28435f (patch) | |
| tree | 4197f3d5c7b5e2c4cdcb4be3dd1a17ed3ecc2ad7 /web/bubblegum/README.md | |
| parent | 68f3ac64c4a2ae50dcb125f067692536f647e370 (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/README.md')
| -rw-r--r-- | web/bubblegum/README.md | 68 |
1 files changed, 68 insertions, 0 deletions
diff --git a/web/bubblegum/README.md b/web/bubblegum/README.md new file mode 100644 index 000000000000..0e09c1c65ed6 --- /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… +} '' + <!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](./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 +``` |