优雅 panic
1.预期宕机和非预期宕机
go
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) } } }
go
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