335d22d376
There's no need to put the error variables in a larger scope, nor define them earlier than necessary. If anything, it makes the code harder to follow, such as figuring out when nil errors are returned.
About chromedp 
Package chromedp is a faster, simpler way to drive browsers in Go using the Chrome Debugging Protocol (for Chrome, Edge, Safari, etc) without external dependencies (ie, Selenium, PhantomJS, etc).
NOTE: chromedp's API is currently unstable, and may change at a moments notice. There are likely extremely bad bugs lurking in this code. CAVEAT USER.
Installation
Install in the usual way:
go get -u github.com/knq/chromedp
Usage
Below is a simple Google search performed using chromedp (taken from examples/simple):
This example shows logic for a simple search for a known website, clicking on the right link, and then taking a screenshot of a specific element on the loaded page and saving that to a local file on disk.
// examples/simple/main.go
package main
import (
"context"
"fmt"
"io/ioutil"
"log"
"time"
cdp "github.com/knq/chromedp"
cdptypes "github.com/knq/chromedp/cdp"
)
func main() {
var err error
// create context
ctxt, cancel := context.WithCancel(context.Background())
defer cancel()
// create chrome instance
c, err := cdp.New(ctxt, cdp.WithLog(log.Printf))
if err != nil {
log.Fatal(err)
}
// run task list
var site, res string
err = c.Run(ctxt, googleSearch("site:brank.as", "Home", &site, &res))
if err != nil {
log.Fatal(err)
}
// shutdown chrome
err = c.Shutdown(ctxt)
if err != nil {
log.Fatal(err)
}
// wait for chrome to finish
err = c.Wait()
if err != nil {
log.Fatal(err)
}
log.Printf("saved screenshot from search result listing `%s` (%s)", res, site)
}
func googleSearch(q, text string, site, res *string) cdp.Tasks {
var buf []byte
sel := fmt.Sprintf(`//a[text()[contains(., '%s')]]`, text)
return cdp.Tasks{
cdp.Navigate(`https://www.google.com`),
cdp.WaitVisible(`#hplogo`, cdp.ByID),
cdp.SendKeys(`#lst-ib`, q+"\n", cdp.ByID),
cdp.WaitVisible(`#res`, cdp.ByID),
cdp.Text(sel, res),
cdp.Click(sel),
cdp.WaitVisible(`a[href="/brankas-for-business"]`, cdp.ByQuery),
cdp.WaitNotVisible(`.preloader-content`, cdp.ByQuery),
cdp.Location(site),
cdp.ScrollIntoView(`.banner-section.third-section`, cdp.ByQuery),
cdp.Sleep(2 * time.Second), // wait for animation to finish
cdp.Screenshot(`.banner-section.third-section`, &buf, cdp.ByQuery),
cdp.ActionFunc(func(context.Context, cdptypes.Handler) error {
return ioutil.WriteFile("screenshot.png", buf, 0644)
}),
}
}
Please see the examples directory for some more examples, and please refer to the GoDoc API listing for a summary of the API and Actions.
Links + Resources
TODO
- Move timeouts to context (defaults)
- Implement more query selector options (allow over riding context timeouts)
- Contextual actions for "dry run" (or via an accumulator?)
- Network loader / manager
- Profiler