这种恐慌的原因是什么？

Question

为了练习一些基本概念，我正在编写一个简单的端口扫描器。然而，当尝试实现 goroutines 时，程序会出现恐慌，并且出现分段错误：Scanning ports{Port:139 State:Open}{Port:135 State:Open}{Port:136 State:Closed}{Port:131 State:Closed}{Port:131 State:Open}{Port:134 State:Closed}{Port:134 State:Open}panic: runtime error: invalid memory address or nil pointer dereference[signal SIGSEGV: segmentation violation code=0x1 addr=0x0 pc=0x4eb26a]goroutine 20 [running]:main.scanPort(0x52033b, 0x3, 0x52203e, 0xf, 0x83)        /home/athos/Projects/go-tutorial/scanner.go:33 +0x1eacreated by main.main        /home/athos/Projects/go-tutorial/scanner.go:41 +0xf1panic: runtime error: invalid memory address or nil pointer dereference[signal SIGSEGV: segmentation violation code=0x1 addr=0x0 pc=0x4eb26a]goroutine 23 [running]:main.scanPort(0x52033b, 0x3, 0x52203e, 0xf, 0x86)        /home/athos/Projects/go-tutorial/scanner.go:33 +0x1eacreated by main.main        /home/athos/Projects/go-tutorial/scanner.go:41 +0xf1exit status 2这是我的代码：package mainimport (    "fmt"    "net"    "strconv"    "sync"    "time")var wg sync.WaitGrouptype scanResult struct {    Port  int    State string}func scanPort(protocol, hostname string, port int) {    defer wg.Done()    result := scanResult{Port: port}    socket := hostname + ":" + strconv.Itoa(port)    conn, err := net.DialTimeout(protocol, socket, 2*time.Second)    if err != nil {        result.State = "Closed"        fmt.Printf("%+v\n", result)    }    result.State = "Open"    fmt.Printf("%+v\n", result)    // Defers: FILO data structure    defer conn.Close()}func main() {    fmt.Println("Scanning ports")    for i := 130; i <= 145; i++ {        wg.Add(1)        go scanPort("tcp", "192.168.200.103", i)    }    // Wait for goroutines to complete    wg.Wait()}谁能帮我看看我做错了什么？

Answer 1

net.DialTimeout()返回连接和错误，您正确检查错误是否不是nil，但即使有错误，您只需打印并继续。

如果存在非nil错误，则不应（绝不能）使用返回的连接，因为它可能是nil无效值。如果有错误，检查/打印并返回，不要尝试使用conn.

所以简单地返回：

if err != nil {

    result.State = "Closed"

    fmt.Printf("%+v\n", result)

    return

}

此外，如果没有错误，您可以“安排”立即关闭连接，延迟。defer如果您在函数中关闭连接的最后一件事，则使用毫无意义。

所以它应该是这样的：

conn, err := net.DialTimeout(protocol, socket, 2*time.Second)

if err != nil {

    result.State = "Closed"

    fmt.Printf("%+v\n", result)

    return

}

defer conn.Close()

result.State = "Open"

fmt.Printf("%+v\n", result)