81 lines
1.4 KiB
Go
81 lines
1.4 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 133.
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// Outline prints the outline of an HTML document tree.
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package main
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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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"golang.org/x/net/html"
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)
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func main() {
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for _, url := range os.Args[1:] {
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outline(url)
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}
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}
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func outline(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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defer resp.Body.Close()
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doc, err := html.Parse(resp.Body)
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if err != nil {
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return err
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}
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//!+call
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forEachNode(doc, startElement, endElement)
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//!-call
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return nil
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}
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//!+forEachNode
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// forEachNode calls the functions pre(x) and post(x) for each node
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// x in the tree rooted at n. Both functions are optional.
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// pre is called before the children are visited (preorder) and
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// post is called after (postorder).
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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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//!-forEachNode
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//!+startend
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var depth int
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func startElement(n *html.Node) {
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if n.Type == html.ElementNode {
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fmt.Printf("%*s<%s>\n", depth*2, "", n.Data)
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depth++
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}
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}
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func endElement(n *html.Node) {
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if n.Type == html.ElementNode {
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depth--
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fmt.Printf("%*s</%s>\n", depth*2, "", n.Data)
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}
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}
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//!-startend
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