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# //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 [//nix/nint](../../nix/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
```
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