phantomjsscreenshot.go

package phantomjsscreenshot

import (
	"bufio"
	"bytes"
	"encoding/base64"
	"fmt"
	"github.com/google/uuid"
	"github.com/pkg/errors"
	"os"
	"os/exec"
)

var dir = "/tmp/"

// EncodingField tells the browser what we've encoded and how to decode it
const EncodingField = "data:image/jpeg;base64,"

// getUUID returns a UUID string to be used for naming
func getUUID() string {
	uid, _ := uuid.NewRandom()
	return uid.String()
}

// Hello enables the calling agent to determine whether the webshot service
// has been setup correctly. If it returns false then we can configure the
// agent to not call screenshots every time. It may help to reduce the setup
// overhead for folks wishing to run this service for themselves.
func Hello() bool {

	// run the most basic command we can, e.g. just the cmd in the
	// OS. Any error should be that the cmd isn't available to call
	command := "phantomjs"

	// execute the command and if there's an error return false
	cmd := exec.Command(command)
	err := cmd.Run()
	if err != nil {
		return false
	}

	// we're all good, return true...
	return true
}

// GrabScreenshot returns a link to a screenshot for retrieval on localhost
// and and errors encountered along the way with the calling application
// returns fileloc, command output, error. The link will not always resolve
// given a protocol, e.g. http:// but more testing is needed to demonstrate
// this on multiple systems. If width and height are set to -1 then no resize
// happens on the way out of this function.
func GrabScreenshot(link string, width int, height int) (string, error) {

	//get new filename
	filename := dir + getUUID() + ".jpg"

	//ideal command on server...
	//phantomjs /usr/js/httpreserve.js http://www.bbc.co.uk bbc.jpg

	command := "phantomjs"
	script := "/usr/js/httpreserve.js"
	hyperlink := link

	args := []string{script, hyperlink, filename}
	cmd := exec.Command(command, args...)

	var out bytes.Buffer
	cmd.Stdout = &out

	err := cmd.Run()
	if err != nil {
		return "", errors.Wrap(err, "phantomjs command run")
	}

	//convert to thumbnail...
	//convert site_thumbnail.jpg -resize 500x450 site_thumbnail.jpg
	if width > 0 && height > 0 {
		command = "convert"
		resize := "-resize"
		dimensions := fmt.Sprintf("%dx%d",width,height)
		args = []string{filename, resize, dimensions, filename}
		cmd = exec.Command(command, args...)
		err = cmd.Run()
		if err != nil {
			message := fmt.Sprintf("ImageMagick command run, params: %s %s %s", command, resize, dimensions)
			return "", errors.Wrap(err, message)
		}
	}

	// output base64 string...
	b64, err := b64png(filename)

	err = os.Remove(filename)
	if err != nil {
		return b64, errors.Wrap(err, "error removing file, b64 may not be nil")
	}

	return b64, nil
}

func b64png(filename string) (string, error) {

	f, err := os.Open(filename)
	if err != nil {
		return "", err
	}
	defer f.Close()

	// create a new buffer base on file size
	fi, _ := f.Stat()

	size := fi.Size()
	buf := make([]byte, size)

	// read file content into buffer
	fReader := bufio.NewReader(f)
	fReader.Read(buf)

	// convert the buffer bytes to base64 string - use buf.Bytes() for new image
	b64 := base64.StdEncoding.EncodeToString(buf)

	// add data encoding information for html
	b64 = EncodingField + b64

	// Embed into an html without PNG file
	return b64, nil
}