Golang Selenium package - connect to selenium server and headless chrome

I'm using the Go selenium package https://godoc.org/github.com/tebeka/selenium

And I'm running headless chrome + selenium-server inside a docker container on localhost:4444

The server seems to be fine since I can access the web console via http://localhost:4444/wd/hub/static/resource/hub.html

But I'm trying to get the "Hello world" example to work with the existing docker container.

This is the example from the GoDocs page for the selenium driver:

// Run some code on play.golang.org and display the result
package main

import (
	"fmt"
	"time"

	"github.com/tebeka/selenium"
)

var code = `
package main
import "fmt"

func main() {
	fmt.Println("Hello WebDriver!\n")
}
`

// Errors are ignored for brevity.

func main() {
	// Connect to the selenium server
	caps := selenium.Capabilities{"browserName": "firefox"}
	wd, err := selenium.NewRemote(caps, "http://127.0.0.1:4444")
	if err != nil {
		fmt.Println(err)
	}
	defer wd.Quit()

	// Get simple playground interface
	wd.Get("http://play.golang.org/?simple=1")
	
	// Enter code in textarea
	elem, _ := wd.FindElement(selenium.ByCSSSelector, "#code")
	elem.Clear()
	elem.SendKeys(code)

	// Click the run button
	btn, _ := wd.FindElement(selenium.ByCSSSelector, "#run")
	btn.Click()

	// Get the result
	div, _ := wd.FindElement(selenium.ByCSSSelector, "#output")

	output := ""
	// Wait for run to finish
	for {
		output, _ = div.Text()
		if output != "Waiting for remote server..." {
			break
		}
		time.Sleep(time.Millisecond * 100)
	}

	fmt.Printf("Got: %s\n", output)
}

I tried changing the "browserName" to "chrome" but I get this error:

panic: got content type "text/html", expected "application/json"

goroutine 1 [running]:
main.main()
	/home/user01/Code/golang_src/golang_exercises/33_selenium/selenium.go:28 +0x457
exit status 2

I can't find anything in the GoDoc selenium documentation regarding the chrome browser and how to connect to it via the selenium-server.

I would appreciate any hints as to what might be going wrong here.

Update:

It seems that removing the URL address and leaving it empty has fixed the connection problems:

wd, err := selenium.NewRemote(caps, "")

That said, I'm still having issues with the example. Mainly it seems like it connects to the Go Playground website, gets the right elements, but when it comes to sending the input elem.SendKeys(code) it doesn't send it properly and the text box is empty. Resulting in bad output from the Playground:

Got: can't load package: package main: 
tmp/sandbox573608783/main.go:1:1: expected 'package', found 'EOF'

Program exited.

try run it in headless mode:

caps := selenium.Capabilities{"browserName": "chrome"}

chromeCaps := chrome.Capabilities{
	Path:  "",
	Args: []string{
		"--headless", // <<<
		"--no-sandbox",
		"--user-agent=Mozilla/5.0 (Macintosh; Intel Mac OS X 10_13_2) AppleWebKit/604.4.7 (KHTML, like Gecko) Version/11.0.2 Safari/604.4.7",
	},
}
caps.AddChrome(chromeCaps)

wd, err := selenium.NewRemote(caps, fmt.Sprintf("http://127.0.0.1:%d", port))

I also use selenium in Docker, it can run by this:

wd, err := selenium.NewRemote(caps, "http://127.0.0.1:4444/wd/hub")

After some debugging I found out that the issue was due to the fact that my Docker container did not have the X server inside it.

When the selenium package tried to send input it would generate this error message:

unknown error: unknown error: an X display is required for keycode conversions, consider using Xvfb
  (Session info: headless chrome=60.0.3095.5)
  (Driver info: chromedriver=2.29.461571 (8a88bbe0775e2a23afda0ceaf2ef7ee74e822cc5),platform=Linux 4.4.0-77-generic x86_64) (WARNING: The server did not provide any stacktrace information)
Command duration or timeout: 40 milliseconds
Build info: version: '3.3.1', revision: '5234b32', time: '2017-03-10 09:04:52 -0800'
System info: host: 'e3bf5382c62d', ip: '171.14.0.3', os.name: 'Linux', os.arch: 'amd64', os.version: '4.4.0-77-generic', java.version: '1.8.0_121'
Driver info: org.openqa.selenium.chrome.ChromeDriver
Capabilities [{applicationCacheEnabled=false, rotatable=false, mobileEmulationEnabled=false, networkConnectionEnabled=false, chrome={chromedriverVersion=2.29.461571 (8a88bbe0775e2a23afda0ceaf2ef7ee74e822cc5), userDataDir=/tmp/.org.chromium.Chromium.mFhqlU}, takesHeapSnapshot=true, pageLoadStrategy=normal, databaseEnabled=false, handlesAlerts=true, hasTouchScreen=false, version=60.0.3095.5, platform=LINUX, browserConnectionEnabled=false, nativeEvents=true, acceptSslCerts=true, locationContextEnabled=true, webStorageEnabled=true, browserName=chrome, takesScreenshot=true, javascriptEnabled=true, cssSelectorsEnabled=true, unexpectedAlertBehaviour=}]
Session ID: 681f9de5f91baeaaa3100cf297767a2d

I have not yet installed the X server inside the Docker container but I'm confident that it will fix the error that occurs when sending input to the headless chrome instance via selenium.