83 lines
1.7 KiB
Go
83 lines
1.7 KiB
Go
// Copyright © 2016 Alan A. A. Donovan & Brian W. Kernighan.
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// License: https://creativecommons.org/licenses/by-nc-sa/4.0/
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// See page 144.
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// Title1 prints the title of an HTML document specified by a URL.
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package main
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/*
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//!+output
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$ go build gopl.io/ch5/title1
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$ ./title1 http://gopl.io
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The Go Programming Language
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$ ./title1 https://golang.org/doc/effective_go.html
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Effective Go - The Go Programming Language
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$ ./title1 https://golang.org/doc/gopher/frontpage.png
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title: https://golang.org/doc/gopher/frontpage.png
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has type image/png, not text/html
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//!-output
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*/
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import (
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"fmt"
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"net/http"
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"os"
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"strings"
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"golang.org/x/net/html"
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)
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// Copied from gopl.io/ch5/outline2.
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func forEachNode(n *html.Node, pre, post func(n *html.Node)) {
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if pre != nil {
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pre(n)
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}
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for c := n.FirstChild; c != nil; c = c.NextSibling {
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forEachNode(c, pre, post)
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}
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if post != nil {
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post(n)
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}
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}
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//!+
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func title(url string) error {
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resp, err := http.Get(url)
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if err != nil {
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return err
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}
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// Check Content-Type is HTML (e.g., "text/html; charset=utf-8").
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ct := resp.Header.Get("Content-Type")
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if ct != "text/html" && !strings.HasPrefix(ct, "text/html;") {
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resp.Body.Close()
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return fmt.Errorf("%s has type %s, not text/html", url, ct)
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}
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doc, err := html.Parse(resp.Body)
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resp.Body.Close()
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if err != nil {
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return fmt.Errorf("parsing %s as HTML: %v", url, err)
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}
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visitNode := func(n *html.Node) {
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if n.Type == html.ElementNode && n.Data == "title" &&
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n.FirstChild != nil {
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fmt.Println(n.FirstChild.Data)
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}
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}
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forEachNode(doc, visitNode, nil)
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return nil
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}
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//!-
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func main() {
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for _, arg := range os.Args[1:] {
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if err := title(arg); err != nil {
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fmt.Fprintf(os.Stderr, "title: %v\n", err)
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}
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}
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}
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