feat(web/bubblegum): nix CGI programming framework
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>
This commit is contained in:
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221
web/bubblegum/default.nix
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221
web/bubblegum/default.nix
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{ depot, lib, pkgs, ... }:
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let
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inherit (depot.nix.yants)
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defun
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restrict
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struct
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string
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int
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attrs
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enum
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;
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inherit (depot.nix)
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runExecline
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getBins
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;
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headers = attrs string;
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statusCodes = {
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# 1xx
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"Continue" = 100;
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"Switching Protocols" = 101;
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"Processing" = 102;
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"Early Hints" = 103;
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# 2xx
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"OK" = 200;
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"Created" = 201;
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"Accepted" = 202;
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"Non-Authoritative Information" = 203;
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"No Content" = 204;
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"Reset Content" = 205;
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"Partial Content" = 206;
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"Multi Status" = 207;
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"Already Reported" = 208;
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"IM Used" = 226;
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# 3xx
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"Multiple Choices" = 300;
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"Moved Permanently" = 301;
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"Found" = 302;
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"See Other" = 303;
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"Not Modified" = 304;
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"Use Proxy" = 305;
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"Switch Proxy" = 306;
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"Temporary Redirect" = 307;
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"Permanent Redirect" = 308;
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# 4xx
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"Bad Request" = 400;
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"Unauthorized" = 401;
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"Payment Required" = 402;
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"Forbidden" = 403;
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"Not Found" = 404;
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"Method Not Allowed" = 405;
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"Not Acceptable" = 406;
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"Proxy Authentication Required" = 407;
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"Request Timeout" = 408;
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"Conflict" = 409;
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"Gone" = 410;
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"Length Required" = 411;
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"Precondition Failed" = 412;
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"Payload Too Large" = 413;
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"URI Too Long" = 414;
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"Unsupported Media Type" = 415;
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"Range Not Satisfiable" = 416;
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"Expectation Failed" = 417;
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"I'm a teapot" = 418;
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"Misdirected Request" = 421;
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"Unprocessable Entity" = 422;
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"Locked" = 423;
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"Failed Dependency" = 424;
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"Too Early" = 425;
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"Upgrade Required" = 426;
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"Precondition Required" = 428;
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"Too Many Requests" = 429;
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"Request Header Fields Too Large" = 431;
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"Unavailable For Legal Reasons" = 451;
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# 5xx
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"Internal Server Error" = 500;
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"Not Implemented" = 501;
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"Bad Gateway" = 502;
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"Service Unavailable" = 503;
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"Gateway Timeout" = 504;
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"HTTP Version Not Supported" = 505;
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"Variant Also Negotiates" = 506;
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"Insufficient Storage" = 507;
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"Loop Detected" = 508;
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"Not Extended" = 510;
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"Network Authentication Required" = 511;
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};
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status = enum "bubblegum.status"
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(builtins.attrNames statusCodes);
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/* Generate a CGI response. Takes three arguments:
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1. Status of the response as a string which is
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the descriptive name in the protocol, e. g.
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`"OK"`, `"Not Found"` etc.
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2. Attribute set describing extra headers to
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send, keys and values should both be strings.
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3. Response content as a string.
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See the [README](./README.md) for an example.
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Type: Status -> Headers -> Body -> string
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*/
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respond = defun [ status headers string string ]
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(s: hs: body:
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let
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code = status.match s statusCodes;
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renderedHeaders = lib.concatStrings
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(lib.mapAttrsToList (n: v: "${n}: ${v}\r\n") hs);
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in
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lib.concatStrings [
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"Status: ${toString code} ${s}\r\n"
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renderedHeaders
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"\r\n"
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body
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]);
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/* Returns the value of the `SCRIPT_NAME` environment
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variable used by CGI.
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*/
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scriptName = builtins.getEnv "SCRIPT_NAME";
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/* Returns the value of the `PATH_INFO` environment
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variable used by CGI. All cases that could be
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considered as the CGI script's root (i. e.
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`PATH_INFO` is empty or `/`) is mapped to `"/"`
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for convenience.
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*/
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pathInfo =
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let
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p = builtins.getEnv "PATH_INFO";
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in
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if builtins.stringLength p == 0
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then "/"
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else p;
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/* Helper function which converts a path from the
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root of the CGI script (i. e. something which
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could be the content of `PATH_INFO`) to an
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absolute path from the web root by also
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utilizing `scriptName`.
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Type: string -> string
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*/
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absolutePath = defun [ string string ]
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(path:
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if builtins.substring 0 1 path == "/"
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then "${scriptName}${path}"
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else "${scriptName}/${path}");
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bins = getBins pkgs.coreutils [ "env" "tee" "cat" "printf" "chmod" ]
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// getBins depot.users.sterni.nint [ "nint" ];
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/* Type: args -> either path derivation string -> derivation
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*/
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writeCGI =
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{ # if given sets the `PATH` to search for `nix-instantiate`
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# Useful when using for example thttpd which unsets `PATH`
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# in the CGI environment.
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binPath ? ""
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# name of the resulting derivation. Defaults to `baseNameOf`
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# the input path or name of the input derivation.
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# Must be given if the input is a string.
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, name ? null
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}:
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input: let
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drvName =
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if name != null
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then name
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else if builtins.isPath input
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then baseNameOf input
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else if lib.isDerivation input
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then input.name
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else builtins.throw "Need name";
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script =
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if builtins.isPath input || lib.isDerivation input
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then input
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else if builtins.isString input
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then pkgs.writeText "${drvName}-source" input
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else builtins.throw "Unsupported input: ${lib.generators.toPretty {} input}";
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shebang = lib.concatStringsSep " " ([
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"#!${bins.env}"
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# use the slightly cursed /usr/bin/env -S which allows us
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# to pass any number of arguments to our interpreter
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# instead of maximum one using plain shebang which considers
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# everything after the first space as the second argument.
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"-S"
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] ++ lib.optionals (builtins.stringLength binPath > 0) [
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"PATH=${binPath}"
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] ++ [
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"${bins.nint}"
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# always pass depot so scripts can use this library
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"--arg depot '(import ${depot.depotPath} {})'"
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]);
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in runExecline.local drvName {} [
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"importas" "out" "out"
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"pipeline" [
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"foreground" [
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"if" [ bins.printf "%s\n" shebang ]
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]
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"if" [ bins.cat script ]
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]
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"if" [ bins.tee "$out" ]
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"if" [ bins.chmod "+x" "$out" ]
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"exit" "0"
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];
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in {
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inherit
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respond
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pathInfo
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scriptName
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absolutePath
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writeCGI
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;
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}
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