Provides a uniform server-side API for CGI, FastCGI, SCGI, and HTTP web applications. Offers both lower- and higher- level api options among other common (optional) things like websocket and event source serving support, session management, and job scheduling.

import arsd.cgi;

// Instead of writing your own main(), you should write a function
// that takes a Cgi param, and use mixin GenericMain
// for maximum compatibility with different web servers.
void hello(Cgi cgi) {

	if("name" in cgi.get)
		cgi.write("Hello, " ~ cgi.get["name"]);
		cgi.write("Hello, world!");

mixin GenericMain!hello;


import arsd.cgi;

class MyApi : WebObject {
	string hello(string name = null) {
		if(name is null)
			return "Hello, world!";
			return "Hello, " ~ name;
mixin DispatcherMain!(
Please note that using the higher-level api will add a dependency on arsd.dom and arsd.jsvar to your application. If you use dmd -i or ldc2 -i to build, it will just work, but with dub, you will have do dub add arsd-official:jsvar and dub add arsd-official:dom yourself.

Test on console (works in any interface mode):

$ ./cgi_hello GET / name=whatever

If using http version (default on dub builds, or on custom builds when passing -version=embedded_httpd to dmd):

$ ./cgi_hello --port 8080
# now you can go to http://localhost:8080/?name=whatever

Please note: the default port for http is 8085 and for scgi is 4000. I recommend you set your own by the command line argument in a startup script instead of relying on any hard coded defaults. It is possible though to code your own with RequestServer, however.

Public Imports

public import std.string;
Undocumented in source.
public import std.stdio;
Undocumented in source.
public import std.conv;
Undocumented in source.



alias KeepExistingPresenter = typeof(null)

Placeholder for use with dispatchSubsection's NewPresenter argument to indicate you want to keep the parent's presenter.


class BasicDataServerSession(Data)

An implementation of Session that works on real cgi connections utilizing the BasicDataServer.

class BufferedInputRange

This is NOT ACTUALLY an input range! It is too different. Historical mistake kinda.

class Cgi

The main interface with the web request

class CgiTester

A helper test class for request handler unittests.

class CollectionOf(Obj)

Base class for REST collections.

class ConnectionClosedException

thrown when a connection is closed remotely while we waiting on data from it

class EventSourceServerImplementation
class ListeningConnectionManager

To use this thing:

class MockSession(Data)

A mock object that works like the real session, but doesn't actually interact with any actual database or http connection. Simply stores the data in its instance members.

class ResourceNotFoundException

You can throw this from an api handler to indicate a 404 response. This is done by the presentExceptionAsHtml function in the presenter.

class RestObject(CRTP)

The base of all REST objects, to be used with serveRestObject and serveRestCollectionOf.

class WebObject

The base class for the dispatcher function and object support.

class WebPresenter(CRTP)

A web presenter is responsible for rendering things to HTML to be usable in a web browser.

class WebSocket



enum AddTrailingSlash
enum RemoveTrailingSlash

UDA used to indicate to the dispatcher that a trailing slash should always be added to or removed from the url. It will do it as a redirect header as-needed.


void cgiMainImpl(string[] args)

This is the function GenericMain calls. View its source for some simple boilerplate you can copy/paste and modify, or you can call it yourself from your main.

string[][string] decodeVariables(string data, string separator, string[]* namesInOrder, string[]* valuesInOrder)

breaks down a url encoded string

string[string] decodeVariablesSingle(string data)

breaks down a url encoded string, but only returns the last value of any array

string defaultListeningHost()

Default host for listening. for scgi, null (aka all interfaces) for all others. If you want the server directly accessible from other computers on the network, normally use null. If not, is a bit better. Settable with default handlers with --listening-host command line argument.

ushort defaultListeningPort()

Returns the default listening port for the current cgi configuration. 8085 for embedded httpd, 4000 for scgi, irrelevant for others.

auto dispatchSubsection(string urlPrefix)

Allows for a subsection of your dispatched urls to be passed through other a pre-request filter, optionally pick up an new presenter class, and then be dispatched to their own handlers.

auto dispatchTo(string urlPrefix)

Dispatches the URL (and anything under it) to another dispatcher function. The function should look something like this:

Cgi dummyCgi(Cgi.RequestMethod method, string url, ubyte[] data, void delegate(const(ubyte)[]) outputSink)

use this for testing or other isolated things when you want it to be no-ops

string encodeVariables(string[string] data)

url encodes the whole string

string encodeVariables(string[][string] data)

url encodes a whole string

bool gzipRecommendedForContentType(string contentType)

Returns true if I recommend gzipping content of this type. You might want to call it from your Presenter classes before calling cgi.write.

auto handleWith(string urlPrefix)

Dispatches the URL to a specific function.

string makeDataUrl(string mimeType, void[] data)

Makes a data:// uri that can be used as links in most newer browsers (IE8+).

string rawurlencode(char[] data)

Encodes all but the explicitly unreserved characters per rfc 3986 Alphanumeric and -_.~ are the only ones left unencoded name is borrowed from php

auto serveApi(string urlPrefix)

Serves a class' methods, as a kind of low-state RPC over the web. To be used with dispatcher.

auto serveRedirect(string urlPrefix, string redirectTo, int code)

Redirects one url to another

auto serveRestObject(string urlPrefix)

Serves a REST object, similar to a Ruby on Rails resource.

auto serveStaticData(string urlPrefix, immutable(void)[] data, string contentType)

Serves static data. To be used with dispatcher.

auto serveStaticData(string urlPrefix, immutable(ubyte)[] data, string contentType, string filenameToSuggestAsDownload)

See serveStaticFile if you want to serve a file off disk.

auto serveStaticFile(string urlPrefix, string filename, string contentType)

Serves a static file. To be used with dispatcher.

auto serveStaticFileDirectory(string urlPrefix, string directory, bool recursive)

This serves a directory full of static files, figuring out the content-types from file extensions. It does not let you to descend into subdirectories (or ascend out of it, of course)

bool trySimulatedRequest(string[] args)

Tries to simulate a request from the command line. Returns true if it does, false if it didn't find the args.


interface BasicDataServer

Direct interface to the basic data add-on server. You can typically use Cgi.getSessionObject as a more convenient interface.

interface EventIoServer

You can customize your server by subclassing the appropriate server. Then, register your subclass at compile time with the registerEventIoServer template, or implement your own main function and call it yourself.

interface EventSourceServer
interface ScheduledJobServer
interface Session(Data)

A convenience object for talking to the BasicDataServer from a higher level. See: Cgi.getSessionObject.

interface SessionObject

Base for storing sessions in an array. Exists primarily for internal purposes and you should generally not use this.

Mixin templates

mixintemplate CustomCgiMain(CustomCgi, alias fun, long maxContentLength = defaultMaxContentLength)

If you want to use a subclass of Cgi with generic main, use this mixin.

mixintemplate DispatcherMain(Presenter, DispatcherArgs...)

Boilerplate mixin for a main function that uses the dispatcher function.

mixintemplate ForwardCgiConstructors()

If you are doing a custom cgi class, mixing this in can take care of the required constructors for you

mixintemplate GenericMain(alias fun, long maxContentLength = defaultMaxContentLength)

Use this instead of writing your own main

Static variables

size_t fiberStackSize;

The stack size when a fiber is created. You can set this from your main or from a shared static constructor to optimize your memory use if you know you don't need this much space. Be careful though, some functions use more stack space than you realize and a recursive function (including ones like in dom.d) can easily grow fast!


struct CreatedResource(T)

This is meant to be returned by a function that takes a form POST submission. You want to set the url of the new resource it created, which is set as the http Location header for a "201 Created" result, and you can also set a separate destination for browser users, which it sets via a "Refresh" header.

struct DefaultFormat

UDA: default format to respond for this method

struct DispatcherData(Presenter)

Used exclusively with dispatchTo

struct DisplayName

UDA: The name displayed to the user in auto-generated HTML.

struct MultipleResponses(T...)

Can return one of the given types, decided at runtime. The syntax is to declare all the possible types in the return value, then you can return typeof(return)(...value...) to construct it.

struct Redirection

You can return this from WebObject subclasses for redirections.

struct RequestServer

A server control and configuration struct, as a potential alternative to calling GenericMain or cgiMainImpl. See the source of cgiMainImpl to an example of how you can use it.

struct ScheduledJobHelper

See schedule to make one of these. You then call one of the methods here to set it up:

struct Uri

Represents a url that can be broken down or built up through properties

struct UrlName

UDA: The name used in the URL or web parameter.

struct ifCalledFromWeb(alias func)

This can be attached to any constructor or function called from the cgi system.


template AutomaticForm(alias customizer)

Implies POST path for the thing itself, then GET will get the automatic form.

template dispatcher(definitions...)

A URL dispatcher.

template passFilterOrIssueError(alias filter, int errorCode)

For use with dispatchSubsection. Calls your filter with the request and if your filter returns false, this issues the given errorCode and stops processing.

template schedule(alias fn, T...)

First step to schedule a job on the scheduled job server.

Detailed Description

Build Configurations

cgi.d tries to be flexible to meet your needs. It is possible to configure it both at runtime (by writing your own main function and constructing a RequestServer object) or at compile time using the version switch to the compiler or a dub subConfiguration.

If you are using dub, use:

subConfiguration "arsd-official:cgi" "VALUE_HERE"

or to dub.json:

"subConfigurations": {"arsd-official:cgi": "VALUE_HERE"}

to change versions. The possible options for VALUE_HERE are:

  • embedded_httpd for the embedded httpd version (built-in web server). This is the default for dub builds. You can run the program then connect directly to it from your browser.
  • cgi for traditional cgi binaries. These are run by an outside web server as-needed to handle requests.
  • fastcgi for FastCGI builds. FastCGI is managed from an outside helper, there's one built into Microsoft IIS, Apache httpd, and Lighttpd, and a generic program you can use with nginx called spawn-fcgi. If you don't already know how to use it, I suggest you use one of the other modes.
  • scgi for SCGI builds. SCGI is a simplified form of FastCGI, where you run the server as an application service which is proxied by your outside webserver.
  • stdio_http for speaking raw http over stdin and stdout. This is made for systemd services. See RequestServer.serveSingleHttpConnectionOnStdio for more information.

With dmd, use:

Interfaces(mutually exclusive)
-version=plain_cgiThe default building the module alone without dub - a traditional, plain CGI executable will be generated.
-version=embedded_httpdA HTTP server will be embedded in the generated executable. This is default when building with dub.
-version=fastcgiA FastCGI executable will be generated.
-version=scgiA SCGI (SimpleCGI) executable will be generated.
-version=embedded_httpd_hybridA HTTP server that uses a combination of processes, threads, and fibers to better handle large numbers of idle connections. Recommended if you are going to serve websockets in a non-local application.
-version=embedded_httpd_threadsThe embedded HTTP server will use a single process with a thread pool. (use instead of plain embedded_httpd if you want this specific implementation)
-version=embedded_httpd_processesThe embedded HTTP server will use a prefork style process pool. (use instead of plain embedded_httpd if you want this specific implementation)
-version=embedded_httpd_processes_accept_after_forkIt will call accept() in each child process, after forking. This is currently the only option, though I am experimenting with other ideas. You probably should NOT specify this right now.
-version=stdio_httpThe embedded HTTP server will be spoken over stdin and stdout.
Tweaks(can be used together with others)
-version=cgi_with_websocketThe CGI class has websocket server support. (This is on by default now.)
-version=with_opensslnot currently used
-version=cgi_embedded_sessionsThe session server will be embedded in the cgi.d server process
-version=cgi_session_server_processThe session will be provided in a separate process, provided by cgi.d.

For example,

For CGI, dmd yourfile.d cgi.d then put the executable in your cgi-bin directory.

For FastCGI: dmd yourfile.d cgi.d -version=fastcgi and run it. spawn-fcgi helps on nginx. You can put the file in the directory for Apache. On IIS, run it with a port on the command line (this causes it to call FCGX_OpenSocket, which can work on nginx too).

For SCGI: dmd yourfile.d cgi.d -version=scgi and run the executable, providing a port number on the command line.

For an embedded HTTP server, run dmd yourfile.d cgi.d -version=embedded_httpd and run the generated program. It listens on port 8085 by default. You can change this on the command line with the --port option when running your program.

Simulating requests

If you are using one of the GenericMain or DispatcherMain mixins, or main with your own call to RequestServer.trySimulatedRequest, you can simulate requests from your command-ine shell. Call the program like this:

./yourprogram GET / name=adr

And it will print the result to stdout instead of running a server, regardless of build more..

CGI Setup tips

On Apache, you may do SetHandler cgi-script in your .htaccess file to set a particular file to be run through the cgi program. Note that all "subdirectories" of it also run the program; if you configure /foo to be a cgi script, then going to /foo/bar will call your cgi handler function with cgi.pathInfo == "/bar".

Overview Of Basic Concepts

cgi.d offers both lower-level handler apis as well as higher-level auto-dispatcher apis. For a lower-level handler function, you'll probably want to review the following functions:

Input: Cgi.get,, Cgi.request, Cgi.files, Cgi.cookies, Cgi.pathInfo, Cgi.requestMethod, and HTTP headers (Cgi.headers, Cgi.userAgent, Cgi.referrer, Cgi.accept, Cgi.authorization, Cgi.lastEventId)

Output: Cgi.write, Cgi.header, Cgi.setResponseStatus, Cgi.setResponseContentType, Cgi.gzipResponse

Cookies: Cgi.setCookie, Cgi.clearCookie, Cgi.cookie, Cgi.cookies

Caching: Cgi.setResponseExpires, Cgi.updateResponseExpires, Cgi.setCache

Redirections: Cgi.setResponseLocation

Other Information: Cgi.remoteAddress, Cgi.https, Cgi.port, Cgi.scriptName, Cgi.requestUri, Cgi.getCurrentCompleteUri, Cgi.onRequestBodyDataReceived

Websockets: Websocket, websocketRequested, acceptWebsocket. For websockets, use the embedded_httpd_hybrid build mode for best results, because it is optimized for handling large numbers of idle connections compared to the other build modes.

Overriding behavior for special cases streaming input data: see the virtual functions Cgi.handleIncomingDataChunk, Cgi.prepareForIncomingDataChunks, Cgi.cleanUpPostDataState

A basic program using the lower-level api might look like:

1 import arsd.cgi;
3 // you write a request handler which always takes a Cgi object
4 void handler(Cgi cgi) {
5 	/+
6 		when the user goes to your site, suppose you are being hosted at
8 		If the user goes to
9 		then the url will be parsed out into the following pieces:
11 			cgi.pathInfo == "/test". This is everything after yourapp's name. (If you are doing an embedded http server, your app's name is blank, so pathInfo will be the whole path of the url.)
13 			cgi.scriptName == "yourapp". With an embedded http server, this will be blank.
15 == ""
17 			cgi.https == false
19 			cgi.queryString == "name=value" (there's also, which will be "?name=value", including the ?)
21 			The query string is further parsed into the `get` and `getArray` members, so:
23 			cgi.get == ["name": "value"], meaning you can do `cgi.get["name"] == "value"`
25 			And
27 			cgi.getArray == ["name": ["value"]].
29 			Why is there both `get` and `getArray`? The standard allows names to be repeated. This can be very useful,
30 			it is how http forms naturally pass multiple items like a set of checkboxes. So `getArray` is the complete data
31 			if you need it. But since so often you only care about one value, the `get` member provides more convenient access.
33 		We can use these members to process the request and build link urls. Other info from the request are in other members, we'll look at them later.
34 	+/
35 	switch(cgi.pathInfo) {
36 		// the home page will be a small html form that can set a cookie.
37 		case "/":
38 			cgi.write(`<!DOCTYPE html>
39 			<html>
40 			<body>
41 				<form method="POST" action="set-cookie">
42 					<label>Your name: <input type="text" name="name" /></label>
43 					<input type="submit" value="Submit" />
44 				</form>
45 			</body>
46 			</html>
47 			`, true); // the , true tells it that this is the one, complete response i want to send, allowing some optimizations.
48 		break;
49 		// POSTing to this will set a cookie with our submitted name
50 		case "/set-cookie":
51 			// HTTP has a number of request methods (also called "verbs") to tell
52 			// what you should do with the given resource.
53 			// The most common are GET and POST, the ones used in html forms.
54 			// You can check which one was used with the `cgi.requestMethod` property.
55 			if(cgi.requestMethod == Cgi.RequestMethod.POST) {
57 				// headers like redirections need to be set before we call `write`
58 				cgi.setResponseLocation("read-cookie");
60 				// just like how url params go into cgi.get/getArray, form data submitted in a POST
61 				// body go to Please note that a POST request can also have get
62 				// params in addition to post params.
63 				//
64 				// There's also a convenience function `cgi.request("name")` which checks post first,
65 				// then get if it isn't found there, and then returns a default value if it is in neither.
66 				if("name" in {
67 					// we can set cookies with a method too
68 					// again, cookies need to be set before calling `cgi.write`, since they
69 					// are a kind of header.
70 					cgi.setCookie("name" ,["name"]);
71 				}
73 				// the user will probably never see this, since the response location
74 				// is an automatic redirect, but it is still best to say something anyway
75 				cgi.write("Redirecting you to see the cookie...", true);
76 			} else {
77 				// you can write out response codes and headers
78 				// as well as response bodies
79 				//
80 				// But always check the cgi docs before using the generic
81 				// `header` method - if there is a specific method for your
82 				// header, use it before resorting to the generic one to avoid
83 				// a header value from being sent twice.
84 				cgi.setResponseLocation("405 Method Not Allowed");
85 				// there is no special accept member, so you can use the generic header function
86 				cgi.header("Accept: POST");
87 				// but content type does have a method, so prefer to use it:
88 				cgi.setResponseContentType("text/plain");
90 				// all the headers are buffered, and will be sent upon the first body
91 				// write. you can actually modify some of them before sending if need be.
92 				cgi.write("You must use the POST http verb on this resource.", true);
93 			}
94 		break;
95 		// and GETting this will read the cookie back out
96 		case "/read-cookie":
97 			// I did NOT pass `,true` here because this is writing a partial response.
98 			// It is possible to stream data to the user in chunks by writing partial
99 			// responses the calling `cgi.flush();` to send the partial response immediately.
100 			// normally, you'd only send partial chunks if you have to - it is better to build
101 			// a response as a whole and send it as a whole whenever possible - but here I want
102 			// to demo that you can.
103 			cgi.write("Hello, ");
104 			if("name" in cgi.cookies) {
105 				import arsd.dom; // dom.d provides a lot of helpers for html
106 				// since the cookie is set, we need to write it out properly to
107 				// avoid cross-site scripting attacks.
108 				//
109 				// Getting this stuff right automatically is a benefit of using the higher
110 				// level apis, but this demo is to show the fundamental building blocks, so
111 				// we're responsible to take care of it.
112 				cgi.write(htmlEntitiesEncode(cgi.cookies["name"]));
113 			} else {
114 				cgi.write("friend");
115 			}
117 			// note that I never called cgi.setResponseContentType, since the default is text/html.
118 			// it doesn't hurt to do it explicitly though, just remember to do it before any cgi.write
119 			// calls.
120 		break;
121 		default:
122 			// no path matched
123 			cgi.setResponseStatus("404 Not Found");
124 			cgi.write("Resource not found.", true);
125 	}
126 }
128 // and this adds the boilerplate to set up a server according to the
129 // compile version configuration and call your handler as requests come in
130 mixin GenericMain!handler; // the `handler` here is the name of your function

Even if you plan to always use the higher-level apis, I still recommend you at least familiarize yourself with the lower level functions, since they provide the lightest weight, most flexible options to get down to business if you ever need them.

In the lower-level api, the Cgi object represents your HTTP transaction. It has functions to describe the request and for you to send your response. It leaves the details of how you o it up to you. The general guideline though is to avoid depending any variables outside your handler function, since there's no guarantee they will survive to another handler. You can use global vars as a lazy initialized cache, but you should always be ready in case it is empty. (One exception: if you use -version=embedded_httpd_threads -version=cgi_no_fork, then you can rely on it more, but you should still really write things assuming your function won't have anything survive beyond its return for max scalability and compatibility.)

A basic program using the higher-level apis might look like:

import arsd.cgi;

struct LoginData {
	string currentUser;

class AppClass : WebObject {
	string foo() {}

mixin DispatcherMain!(
	"/assets/.serveStaticFileDirectory("assets/", true), // serve the files in the assets subdirectory

Guide for PHP users

(Please note: I wrote this section in 2008. A lot of PHP hosts still ran 4.x back then, so it was common to avoid using classes - introduced in php 5 - to maintain compatibility! If you're coming from php more recently, this may not be relevant anymore, but still might help you.)

If you are coming from old-style PHP, here's a quick guide to help you get started:

	$foo = $_POST["foo"];
	$bar = $_GET["bar"];
	$baz = $_COOKIE["baz"];

	$user_ip = $_SERVER["REMOTE_ADDR"];
	$host = $_SERVER["HTTP_HOST"];
	$path = $_SERVER["PATH_INFO"];

	setcookie("baz", "some value");

	echo "hello!";
import arsd.cgi;
void app(Cgi cgi) {
	string foo =["foo"];
	string bar = cgi.get["bar"];
	string baz = cgi.cookies["baz"];

	string user_ip = cgi.remoteAddress;
	string host =;
	string path = cgi.pathInfo;

	cgi.setCookie("baz", "some value");


mixin GenericMain!app

Array elements

In PHP, you can give a form element a name like "something[]", and then $_POST["something"] gives an array. In D, you can use whatever name you want, and access an array of values with the cgi.getArray["name"] and cgi.postArray["name"] members.


PHP has a lot of stuff in its standard library. cgi.d doesn't include most of these, but the rest of my arsd repository has much of it. For example, to access a MySQL database, download database.d and mysql.d from my github repo, and try this code (assuming, of course, your database is set up):

import arsd.cgi;
import arsd.mysql;

void app(Cgi cgi) {
	auto database = new MySql("localhost", "username", "password", "database_name");
	foreach(row; mysql.query("SELECT count(id) FROM people"))
		cgi.write(row[0] ~ " people in database");

mixin GenericMain!app;

Similar modules are available for PostgreSQL, Microsoft SQL Server, and SQLite databases, implementing the same basic interface.


This micro-example uses the dispatcher api to act as a simple http file server, serving files found in the current directory and its children.

import arsd.cgi;

mixin DispatcherMain!(
	"/".serveStaticFileDirectory(null, true)

Same as the previous example, but written out long-form without the use of DispatcherMain nor GenericMain.

import arsd.cgi;

void requestHandler(Cgi cgi) {
		"/".serveStaticFileDirectory(null, true)

// mixin GenericMain!requestHandler would add this function:
void main(string[] args) {
	// this is all the content of [cgiMainImpl] which you can also call

	// cgi.d embeds a few add on functions like real time event forwarders
	// and session servers it can run in other processes. this spawns them, if needed.

	// cgi.d allows you to easily simulate http requests from the command line,
	// without actually starting a server. this function will do that.
	if(trySimulatedRequest!(requestHandler, Cgi)(args))

	RequestServer server;
	// you can change the default port here if you like
	// server.listeningPort = 9000;

	// then call this to let the command line args override your default

	// here is where you could print out the listeningPort to the user if you wanted

	// and serve the request(s) according to the compile configuration

	// or you could explicitly choose a serve mode like this:
	// server.serveEmbeddedHttp!requestHandler();

cgi.d has built-in testing helpers too. These will provide mock requests and mock sessions that otherwise run through the rest of the internal mechanisms to call your functions without actually spinning up a server.

import arsd.cgi;

void requestHandler(Cgi cgi) {


// D doesn't let me embed a unittest inside an example unittest
// so this is a function, but you can do it however in your real program
/* unittest */ void runTests() {
	auto tester = new CgiTester(&requestHandler);

	auto response = tester.GET("/");
	assert(response.code == 200);

See Also

You may also want to see arsd.dom, arsd.webtemplate, and maybe some functions from my old arsd.html for more code for making web applications. dom and webtemplate are used by the higher-level api here in cgi.d.

For working with json, try arsd.jsvar.

arsd.database, arsd.mysql, arsd.postgres, arsd.mssql, and arsd.sqlite can help in accessing databases.

If you are looking to access a web application via HTTP, try arsd.http2.