From 4cb65ecbac8da344467f15ae51868d187d55fcdd Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?=E7=8B=AC=E5=AD=A4=E4=BC=B6=E4=BF=9C?= <1184662350@qq.com>
Date: Mon, 12 Dec 2022 01:12:00 +0800
Subject: [PATCH] =?UTF-8?q?day7=E5=87=BD=E6=95=B0=20Panic=E6=9C=BA?=
 =?UTF-8?q?=E5=88=B6=20recover=E6=9C=BA=E5=88=B6=20=E7=BB=83=E4=B9=A05.19?=
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---
 src/study/day7Function/Panic.go               | 31 ++++++++++++++
 .../day7Function/Practice/Practice5.19.go     | 27 ++++++++++++
 src/study/day7Function/Recover.go             | 42 +++++++++++++++++++
 3 files changed, 100 insertions(+)
 create mode 100644 src/study/day7Function/Panic.go
 create mode 100644 src/study/day7Function/Practice/Practice5.19.go
 create mode 100644 src/study/day7Function/Recover.go

diff --git a/src/study/day7Function/Panic.go b/src/study/day7Function/Panic.go
new file mode 100644
index 0000000..45808b1
--- /dev/null
+++ b/src/study/day7Function/Panic.go
@@ -0,0 +1,31 @@
+package main
+
+import (
+	"fmt"
+	"os"
+	"runtime"
+)
+
+func main() {
+
+	// 当发生 panic时,会立即执行该GorouTime的defer函数,
+	// 然后程序崩溃, 并输出日志信息
+	// 日志信息包括panic的文字描述, 函数名, 报错行号, 堆栈信息
+
+	// 勤奋的程序员认为任何崩溃都表明代码中存在漏洞，
+	// 所以对于大部分漏洞，我们应该使用Go提供的错误机制，
+	// 而不是panic，尽量避免程序的崩溃。
+
+	defer printStack()
+	f(3)
+}
+func printStack() {
+	var buf [4096]byte
+	n := runtime.Stack(buf[:], false)
+	os.Stdout.Write(buf[:n])
+}
+func f(x int) {
+	fmt.Printf("f(%d)\n", x+0/x) // panics if x == 0
+	defer fmt.Printf("defer %d\n", x)
+	f(x - 1)
+}
diff --git a/src/study/day7Function/Practice/Practice5.19.go b/src/study/day7Function/Practice/Practice5.19.go
new file mode 100644
index 0000000..76aea75
--- /dev/null
+++ b/src/study/day7Function/Practice/Practice5.19.go
@@ -0,0 +1,27 @@
+package main
+
+import (
+	"fmt"
+	"log"
+)
+
+func main() {
+	ret := practice()
+	fmt.Println(ret)
+}
+
+func practice() (result int) {
+	defer func() {
+		if r := recover(); r != nil {
+			log.Println("Recovered in f", r)
+			// 断言, 参考第七章7.10节的内容
+			// see: https://zhuanlan.zhihu.com/p/149015320
+			// 具体作用为检查接口中是否包含int类型的值, 并返回该值
+			// panic接受一个类型为any的参数
+			// 该参数的any类型实际为一个空接口
+			// 参考Go安装目录 /src/builtin/builtin.go:95 :252
+			result = r.(int) // 断言 int
+		}
+	}()
+	panic(34)
+}
diff --git a/src/study/day7Function/Recover.go b/src/study/day7Function/Recover.go
new file mode 100644
index 0000000..7f9791a
--- /dev/null
+++ b/src/study/day7Function/Recover.go
@@ -0,0 +1,42 @@
+package main
+
+import (
+	"Study/src/study/day7Function/HtmlTools"
+	"fmt"
+	"golang.org/x/net/html"
+)
+
+func main() {
+	// 定义该defer语句的函数发生了panic异常，recover会使程序从panic中恢复，
+	t, _ := soleTitle(HtmlTools.GetHtml())
+	fmt.Println(t)
+}
+
+// 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 nonempty title.
+	HtmlTools.ForEachNode(doc, func(n *html.Node) {
+		if n.Type == html.ElementNode && n.Data == "title" &&
+			n.FirstChild != nil {
+			if title != "" {
+				panic(bailout{}) // multiple titleelements
+			}
+			title = n.FirstChild.Data
+		}
+	}, nil)
+	if title == "" {
+		return "", fmt.Errorf("no title element")
+	}
+	return title, nil
+}