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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/examples/blog.nix | |
| 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/examples/blog.nix')
| -rw-r--r-- | web/bubblegum/examples/blog.nix | 134 |
1 files changed, 134 insertions, 0 deletions
diff --git a/web/bubblegum/examples/blog.nix b/web/bubblegum/examples/blog.nix new file mode 100644 index 000000000000..f79ab0627e88 --- /dev/null +++ b/web/bubblegum/examples/blog.nix @@ -0,0 +1,134 @@ +{ 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) |