windows_service_template

This is a quick and easy template to create a Windows service in C. I had trouble finding a good basic implementation online, and I needed to write a service, so I went ahead and wrote this one.

Compiling

I wrote this in Microsoft Visual Studio 2008. I have no idea if it will compile on a newer version of Visual Studio - I don't have any of them.

To build it, I simply run...

$ build.bat

Which builds both Debug and Release builds, based on the .vcproj file. You can also load up the .vcproj file in Visual Studio and compile it there.

Structure

There are two main pieces to this project that are tied together by main.c:

The first is service_cli.c - it's a module for programmatically installing, uninstalling, or updating permissions on a Windows service. See service_cli.h for documentation on each function, and main.c for a usage example.

The second is service.c - it implements a simple Windows service.

There is also a small logging framework that logs messages to the system EventLog - it can be found in log.c.

Using the CLI

The CLI is mostly self documenting - see service_cli.h.

The most complex part is probably the permissions. Setting permissions on a service is fairly intricate, but using the service_cli API is pretty easy.

Effectively, if you call set_permission("name", WinBuiltinUsersSid), it will grant built-in users the ability to start and stop that service. That's not generally a great idea - it's essentially RCE - but it's something I wanted to be able to do.

Writing a service

Basically, there are three parts to writing a service...

• First, fill out do_service_startup_stuff() with any startup bits you need. If anything is particularly slow, you'll want to call service_report_status() to let the Service Manager know that stuff is happening!

• Second, fill out do_service_run_stuff() with code that implements the service. Right now, it simply waits for stop_event to fire - that event should always stop the service immediately, unless you change do_service_shutdown_stuff().

• Finally, fill out do_service_shutdown_stuff() with any cleanup you need. When it gets called, it's the service's responsibility to stop everything and exit. Right now set an event that is consumed by do_service_run_stuff(), which is a common way to do it.

Other than that, the world is your oyster!

Logging

I created some simple log functions: SERVICE_INFO(), SERVICE_WARNING(), and SERVICE_ERROR(). They take printf-style varargs, and send the output to the Windows eventlog.

SERVICE_ERROR() additionally includes the result of GetLastError().