gopl-zh.github.com/vendor/gopl.io/ch5/title2/title.go

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// Copyright © 2016 Alan A. A. Donovan & Brian W. Kernighan.
// License: https://creativecommons.org/licenses/by-nc-sa/4.0/
// See page 145.
// Title2 prints the title of an HTML document specified by a URL.
// It uses defer to simplify closing the response body stream.
package main
import (
"fmt"
"net/http"
"os"
"strings"
"golang.org/x/net/html"
)
// Copied from gopl.io/ch5/outline2.
func forEachNode(n *html.Node, pre, post func(n *html.Node)) {
if pre != nil {
pre(n)
}
for c := n.FirstChild; c != nil; c = c.NextSibling {
forEachNode(c, pre, post)
}
if post != nil {
post(n)
}
}
//!+
func title(url string) error {
resp, err := http.Get(url)
if err != nil {
return err
}
defer resp.Body.Close()
ct := resp.Header.Get("Content-Type")
if ct != "text/html" && !strings.HasPrefix(ct, "text/html;") {
return fmt.Errorf("%s has type %s, not text/html", url, ct)
}
doc, err := html.Parse(resp.Body)
if err != nil {
return fmt.Errorf("parsing %s as HTML: %v", url, err)
}
// ...print doc's title element...
//!-
visitNode := func(n *html.Node) {
if n.Type == html.ElementNode && n.Data == "title" &&
n.FirstChild != nil {
fmt.Println(n.FirstChild.Data)
}
}
forEachNode(doc, visitNode, nil)
//!+
return nil
}
//!-
func main() {
for _, arg := range os.Args[1:] {
if err := title(arg); err != nil {
fmt.Fprintf(os.Stderr, "title: %v\n", err)
}
}
}