mirror of
https://github.com/gopl-zh/gopl-zh.github.com.git
synced 2024-11-16 11:23:40 +00:00
100 lines
2.1 KiB
Go
100 lines
2.1 KiB
Go
// Copyright © 2016 Alan A. A. Donovan & Brian W. Kernighan.
|
|
// License: https://creativecommons.org/licenses/by-nc-sa/4.0/
|
|
|
|
// See page 153.
|
|
|
|
// Title3 prints the title of an HTML document specified by a URL.
|
|
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)
|
|
}
|
|
}
|
|
|
|
//!+
|
|
// soleTitle returns the text of the first non-empty title element
|
|
// in doc, and an error if there was not exactly one.
|
|
func soleTitle(doc *html.Node) (title string, err error) {
|
|
type bailout struct{}
|
|
|
|
defer func() {
|
|
switch p := recover(); p {
|
|
case nil:
|
|
// no panic
|
|
case bailout{}:
|
|
// "expected" panic
|
|
err = fmt.Errorf("multiple title elements")
|
|
default:
|
|
panic(p) // unexpected panic; carry on panicking
|
|
}
|
|
}()
|
|
|
|
// Bail out of recursion if we find more than one non-empty title.
|
|
forEachNode(doc, func(n *html.Node) {
|
|
if n.Type == html.ElementNode && n.Data == "title" &&
|
|
n.FirstChild != nil {
|
|
if title != "" {
|
|
panic(bailout{}) // multiple title elements
|
|
}
|
|
title = n.FirstChild.Data
|
|
}
|
|
}, nil)
|
|
if title == "" {
|
|
return "", fmt.Errorf("no title element")
|
|
}
|
|
return title, nil
|
|
}
|
|
|
|
//!-
|
|
|
|
func title(url string) error {
|
|
resp, err := http.Get(url)
|
|
if err != nil {
|
|
return err
|
|
}
|
|
|
|
// Check Content-Type is HTML (e.g., "text/html; charset=utf-8").
|
|
ct := resp.Header.Get("Content-Type")
|
|
if ct != "text/html" && !strings.HasPrefix(ct, "text/html;") {
|
|
resp.Body.Close()
|
|
return fmt.Errorf("%s has type %s, not text/html", url, ct)
|
|
}
|
|
|
|
doc, err := html.Parse(resp.Body)
|
|
resp.Body.Close()
|
|
if err != nil {
|
|
return fmt.Errorf("parsing %s as HTML: %v", url, err)
|
|
}
|
|
title, err := soleTitle(doc)
|
|
if err != nil {
|
|
return err
|
|
}
|
|
fmt.Println(title)
|
|
return nil
|
|
}
|
|
|
|
func main() {
|
|
for _, arg := range os.Args[1:] {
|
|
if err := title(arg); err != nil {
|
|
fmt.Fprintf(os.Stderr, "title: %v\n", err)
|
|
}
|
|
}
|
|
}
|