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-rw-r--r--web/bubblegum/default.nix251
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diff --git a/web/bubblegum/default.nix b/web/bubblegum/default.nix
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+{ depot, lib, pkgs, ... }:
+
+let
+
+  inherit (depot.nix)
+    runExecline
+    getBins
+    utils
+    sparseTree
+    nint
+    ;
+
+  minimalDepot = sparseTree depot.path.origSrc [
+    # general depot things
+    "default.nix"
+    "nix/readTree"
+    # nixpkgs for lib and packages
+    "third_party/nixpkgs"
+    "third_party/overlays"
+    # bubblegum and its dependencies
+    "web/bubblegum"
+    "nix/runExecline"
+    "nix/utils"
+    "nix/sparseTree"
+    # tvix docs for svg demo
+    "tvix/docs"
+    # for blog.nix
+    "users/sterni/nix"
+  ];
+
+  statusCodes = {
+    # 1xx
+    "Continue" = 100;
+    "Switching Protocols" = 101;
+    "Processing" = 102;
+    "Early Hints" = 103;
+    # 2xx
+    "OK" = 200;
+    "Created" = 201;
+    "Accepted" = 202;
+    "Non-Authoritative Information" = 203;
+    "No Content" = 204;
+    "Reset Content" = 205;
+    "Partial Content" = 206;
+    "Multi Status" = 207;
+    "Already Reported" = 208;
+    "IM Used" = 226;
+    # 3xx
+    "Multiple Choices" = 300;
+    "Moved Permanently" = 301;
+    "Found" = 302;
+    "See Other" = 303;
+    "Not Modified" = 304;
+    "Use Proxy" = 305;
+    "Switch Proxy" = 306;
+    "Temporary Redirect" = 307;
+    "Permanent Redirect" = 308;
+    # 4xx
+    "Bad Request" = 400;
+    "Unauthorized" = 401;
+    "Payment Required" = 402;
+    "Forbidden" = 403;
+    "Not Found" = 404;
+    "Method Not Allowed" = 405;
+    "Not Acceptable" = 406;
+    "Proxy Authentication Required" = 407;
+    "Request Timeout" = 408;
+    "Conflict" = 409;
+    "Gone" = 410;
+    "Length Required" = 411;
+    "Precondition Failed" = 412;
+    "Payload Too Large" = 413;
+    "URI Too Long" = 414;
+    "Unsupported Media Type" = 415;
+    "Range Not Satisfiable" = 416;
+    "Expectation Failed" = 417;
+    "I'm a teapot" = 418;
+    "Misdirected Request" = 421;
+    "Unprocessable Entity" = 422;
+    "Locked" = 423;
+    "Failed Dependency" = 424;
+    "Too Early" = 425;
+    "Upgrade Required" = 426;
+    "Precondition Required" = 428;
+    "Too Many Requests" = 429;
+    "Request Header Fields Too Large" = 431;
+    "Unavailable For Legal Reasons" = 451;
+    # 5xx
+    "Internal Server Error" = 500;
+    "Not Implemented" = 501;
+    "Bad Gateway" = 502;
+    "Service Unavailable" = 503;
+    "Gateway Timeout" = 504;
+    "HTTP Version Not Supported" = 505;
+    "Variant Also Negotiates" = 506;
+    "Insufficient Storage" = 507;
+    "Loop Detected" = 508;
+    "Not Extended" = 510;
+    "Network Authentication Required" = 511;
+  };
+
+  /* Generate a CGI response. Takes three arguments:
+
+     1. Status of the response as a string which is
+        the descriptive name in the protocol, e. g.
+        `"OK"`, `"Not Found"` etc.
+     2. Attribute set describing extra headers to
+        send, keys and values should both be strings.
+     3. Response content as a string.
+
+     See the [README](./README.md) for an example.
+
+    Type: either int string -> attrs string -> string -> string
+  */
+  respond =
+    # response status as an integer (status code) or its
+    # textual representation in the HTTP protocol.
+    # See `statusCodes` for a list of valid options.
+    statusArg:
+    # headers as an attribute set of strings
+    headers:
+    # response body as a string
+    bodyArg:
+    let
+      status =
+        if builtins.isInt statusArg
+        then {
+          code = statusArg;
+          line = lib.findFirst
+            (line: statusCodes."${line}" == statusArg)
+            null
+            (builtins.attrNames statusCodes);
+        } else if builtins.isString statusArg then {
+          code = statusCodes."${statusArg}" or null;
+          line = statusArg;
+        } else {
+          code = null; line = null;
+        };
+      renderedHeaders = lib.concatStrings
+        (lib.mapAttrsToList (n: v: "${n}: ${toString v}\r\n") headers);
+      internalError = msg: respond 500 {
+        Content-type = "text/plain";
+      } "bubblegum error: ${msg}";
+      body = builtins.tryEval bodyArg;
+    in
+      if status.code == null || status.line == null
+      then internalError "Invalid status ${lib.generators.toPretty {} statusArg}."
+      else if !body.success
+      then internalError "Unknown evaluation error in user code"
+      else lib.concatStrings [
+        "Status: ${toString status.code} ${status.line}\r\n"
+        renderedHeaders
+        "\r\n"
+        body.value
+      ];
+
+  /* Returns the value of the `SCRIPT_NAME` environment
+     variable used by CGI.
+  */
+  scriptName = builtins.getEnv "SCRIPT_NAME";
+
+  /* Returns the value of the `PATH_INFO` environment
+     variable used by CGI. All cases that could be
+     considered as the CGI script's root (i. e.
+     `PATH_INFO` is empty or `/`) is mapped to `"/"`
+     for convenience.
+  */
+  pathInfo =
+    let
+      p = builtins.getEnv "PATH_INFO";
+    in
+      if builtins.stringLength p == 0
+      then "/"
+      else p;
+
+  /* Helper function which converts a path from the
+     root of the CGI script (i. e. something which
+     could be the content of `PATH_INFO`) to an
+     absolute path from the web root by also
+     utilizing `scriptName`.
+
+     Type: string -> string
+  */
+  absolutePath = path:
+    if builtins.substring 0 1 path == "/"
+    then "${scriptName}${path}"
+    else "${scriptName}/${path}";
+
+  bins = getBins pkgs.coreutils [ "env" "tee" "cat" "printf" "chmod" ]
+      // getBins nint [ "nint" ];
+
+  /* Type: args -> either path derivation string -> derivation
+  */
+  writeCGI =
+    { # if given sets the `PATH` to search for `nix-instantiate`
+      # Useful when using for example thttpd which unsets `PATH`
+      # in the CGI environment.
+      binPath ? ""
+      # name of the resulting derivation. Defaults to `baseNameOf`
+      # the input path or name of the input derivation.
+      # Must be given if the input is a string.
+    , name ? null
+    , ...
+    }@args:
+    input: let
+      drvName =
+        if builtins.isString input || args ? name
+        then args.name
+        else utils.storePathName input;
+      script =
+        if builtins.isPath input || lib.isDerivation input
+        then input
+        else if builtins.isString input
+        then pkgs.writeText "${drvName}-source" input
+        else builtins.throw "Unsupported input: ${lib.generators.toPretty {} input}";
+      shebang = lib.concatStringsSep " " ([
+        "#!${bins.env}"
+        # use the slightly cursed /usr/bin/env -S which allows us
+        # to pass any number of arguments to our interpreter
+        # instead of maximum one using plain shebang which considers
+        # everything after the first space as the second argument.
+        "-S"
+      ] ++ lib.optionals (builtins.stringLength binPath > 0) [
+        "PATH=${binPath}"
+      ] ++ [
+        "${bins.nint}"
+        # always pass depot so scripts can use this library
+        "--arg depot '(import ${minimalDepot} {})'"
+      ]);
+    in runExecline.local drvName {} [
+      "importas" "out" "out"
+      "pipeline" [
+        "foreground" [
+          "if" [ bins.printf "%s\n" shebang ]
+        ]
+        "if" [ bins.cat script ]
+      ]
+      "if" [ bins.tee "$out" ]
+      "if" [ bins.chmod "+x" "$out" ]
+      "exit" "0"
+    ];
+
+in {
+  inherit
+    respond
+    pathInfo
+    scriptName
+    absolutePath
+    writeCGI
+    ;
+}