Simple Go Web App

The web_static.go web application in Listing 2 shows the static web page in Listing 3. The web app uses the net/http library to define a default handler (line 9), that calls the static page (line 10). The app then listens and serves up data on port 8081 (line 14).

To compile and test web_static.go, enter:

$ go build web_static.go
$ ./web_static
Default Web Page

When you use a web browser to call the Rasp Pi address at port 8081 (Figure 2), you should see the message This is a static test page from the Go application every time the page is called.

Figure 2: Go web app with a static page.

GPIO Web App

The final step is to pull everything together so that a web page can pass parameters to a Go app that shells out to the gpio  command-line utility. To begin, you create new web page (go_buttons.html) with two buttons (Listing 4). HTML anchor tags pass the /on and /off parameters to the web app.

A CACHE-CONTROL meta tag set to NO-STORE ensures that the web page always refreshes. If you don't include this meta tag, the web page might only update once.

The Go GPIO web app go_buttons.go (Listing 5) now includes two additional http.HandleFunc handler functions: one for the /on parameter (line 30) and one for the /off parameter (line 37). These handler functions pass the required pin state to a function called gpio.

The newly created gpio function acts very much like the earlier writepin7.go code (Listing 1), in that it shells out twice to the gpio command-line utility: the first time to write a value and the second time to read the value back. Web page requests, GPIO pin results, and errors are shown in the terminal.

The syntax to compile and run the go_buttons.go code with some sample web requests is:

$ go build go_buttons.go
$ ./go_buttons
Default Web Page
Web Page sent : ON
GPIO Pin 4 value : 1
Default Web Page
Web Page sent : OFF
GPIO Pin 4 value : 0

Figure 3 shows the web output and the test setup.

Figure 3: Go Rasp Pi GPIO web app and setup.

Summary

Go offers a robust platform for web applications. From the basic web page example in this article, I created more advanced Rasp Pi projects, such as the rover shown in Figure 4 that required writing to multiple GPIO pins.

Figure 4: Raspberry Pi rover.

For a polished application, I would rather use a native Go library for GPIO calls, but for prototyping and troubleshooting, I found the gpio command-line utility was very useful.

The next step for my Rasp Pi projects will be to add JavaScript and Ajax to show dynamic values.