Hello World

Note: mod_swift only provides a very low level raw API. If you want something more convenient, checkout ApacheExpress.

But lets do a simple mods_helloworld module for demonstration purposes.

Setup Module

Setup a new directory and initialize it as an Apache Swift module:

$ mkdir mods_helloworld && cd mods_helloworld
$ swift apache init
The Swift Apache build environment looks sound.

  module:    mods_helloworld
  config:    debug
  product:   /Users/helge/tmp/tests/mods_helloworld/.build/mods_helloworld.so
  apxs:      /usr/local/bin/apxs
  mod_swift: /usr/local/opt/mod_swift

This creates a Swift Package Manager module and places an example Apache entry point into it:

$ tree
├── Package.swift
└── Sources
    └── mods_helloworld
        └── mods_helloworld.swift

2 directory, 2 files

The Package.swift just loads the Apache wrapper module we provide:

import PackageDescription

let package = Package(
    name: "mods_helloworld",

    dependencies: [
      .package(url: "https://github.com/modswift/Apache.git", from: "0.5.0")

    targets: [
      .target(name: "mods_helloworld", dependencies: [ "Apache" ])

The mods_helloworld.swift source file contains a demo Apache module. The file can be named anything (but main.swift, which would produce a tool instead of a library ;-)

import CApache
import Apache

var module = CApache.module(name: "mods_helloworld")

func mods_helloworldHandler(p: UnsafeMutablePointer<request_rec>?) -> Int32 {
  // example content handler, modify to your liking
  var req = ApacheRequest(raw: p!)

  req.contentType = "text/html; charset=ascii"
  req.puts("<html><head><title>Hello mod_swift</title>\(semanticUI)</head>")
  req.puts("<body><div class='ui main container' style='margin-top: 1em;'>")
  req.puts("<h3>Welcome to mods_helloworld</h3>")
  defer { req.puts("</div></body></html>") }

  req.puts("<h4>Links of Interest</h4>")
  req.puts("  <li><a href='http://mod-swift.org/'>mod-swift.org</a></li>")
  req.puts("  <li><a href='http://apacheexpress.io/'>ApacheExpress</a></li>")
  req.puts("  <li><a href='https://httpd.apache.org/'>Apache</a></li>")

  return OK

fileprivate func register_hooks(pool: OpaquePointer?) {
  // hookup the handlers you want
  ap_hook_handler(mods_helloworldHandler, nil, nil, APR_HOOK_MIDDLE)

public func ApacheMain(cmd: UnsafeMutablePointer<cmd_parms>) {
  module.register_hooks = register_hooks

  let rc = apz_register_swift_module(cmd, &module)
  assert(rc == APR_SUCCESS, "Could not add Swift module!")

Explanation of the Source

Module Structure

At the top this prepares the Apache module structure. The structure identifies our module within Apache. It contains the name, links to our callbacks, and optionally configuration data (yes, you can also add your own configuration directives to the Apache config).

var module = CApache.module(name: "mods_helloworld")

Which is registered at the bottom, in the ApacheMain function:


ApacheMain is the primary entry point which is called by mod_swift when it executes the LoadSwiftModule directive in the Apache configuration. The @_cdecl isn't actually required in this case, but can be necessary in more complex setups. It tells Apache where to find the entry function (Apache being written in C, needs to have a C name, which often, but not always can be derived - the cdecl makes it explicit).

public func ApacheMain(cmd: UnsafeMutablePointer<cmd_parms>) {
  module.register_hooks = register_hooks

  let rc = apz_register_swift_module(cmd, &module)

Within the ApacheMain function, we attach the register_hooks callback to the module. And after that, register our Swift module as a regular Apache module. When Apache starts up, it runs its configuration process (actually twice, checkout the module devguide for more info). A part of that is registering the module hooks, in our example:


fileprivate func register_hooks(pool: OpaquePointer?) {
  // hookup the handlers you want
  ap_hook_handler(mods_helloworldHandler, nil, nil, APR_HOOK_MIDDLE)

There are hooks which allow you to add callbacks to pretty much any part of Apache (configuration, process handling, path translation, authorization, etc.). In our simple case we just register a so called 'handler'. Handlers are pretty similar to what one may know as Middleware from other frameworks. And just like Middleware, they can decline to handle a request (return DECLINED), or process it (return OK or an error code). Lets look at our handler:


Again, you can use any name. This is just a generated one. Also, you can have as many handlers as you want!

func mods_helloworldHandler(p: UnsafeMutablePointer<request_rec>?) -> Int32 {
  var req = ApacheRequest(raw: p!)
  req.contentType = "text/html; charset=ascii"
  req.puts("<h3>Welcome to mods_helloworld</h3>")
  return OK

The argument this function receives is the raw Apache C structure representing the current HTTP request. First thing we do is wrap it in a ApacheRequest Swift object, to make the API nicer (you can still call all Apache C API on the raw pointer!).

Next we assign a content-type to the response (Apache uses a single object to represent both, Request and Response) and write out some content using req.puts.

Then we return OK to tell Apache that our handler processed the request and no other content handler needs to run.

Build Module

Now that we looked at the source, lets build the module: swift apache build first invokes swift build and subsequently converts the build results into an Apache module shared library (mods_helloworld.so).

$ swift apache build
Fetching https://github.com/modswift/Apache.git
Fetching https://github.com/modswift/CApache.git
Completed resolution in 3.65s
Cloning https://github.com/modswift/CApache.git
Resolving https://github.com/modswift/CApache.git at 2.0.1
Cloning https://github.com/modswift/Apache.git
Resolving https://github.com/modswift/Apache.git at 0.5.0
[2/2] Compiling Swift Module 'mods_helloworld' (1 sources)

$ ls -hl .build/mods_helloworld.so
-rwxr-xr-x  1 helge  staff   173K 12 Mai 15:29 .build/mods_helloworld.so

Run Module

The swift apache serve command will generate an Apache configuration and start Apache with it. You can then access your module in the browser using either

$ swift apache serve
Note: DocRoot /usr/local/var/www/htdocs
Starting Apache on port 8042/8442:
GET /helloworld/ 200 715 - 0ms

Note of interest: 0ms, the duration of the request. Yes, it is that fast ;-)

In case you wonder, the generated Apache configuration can be found in .build/debug/apache.conf.