Go DNS故障与TCP传输正常与UDP

Question

我已经尝试了我能想到的所有方法，但还是碰壁。我想知道是否有人能给我指出正确的方向或可能发现问题?

我正在尝试编写自己的DNS服务器，原因有几个，主要是学习经验。

有几点需要注意:

• 我使用Go
使用">
• ; gopacket"用于DNS数据包反/序列化
• 使用UDP协议时，服务器按预期工作

所以在得到UDP工作的响应后，我决定是时候实现TCP了。下面是侦听TCP传入连接的代码片段。

// Listen TCP
c, err := t.Accept()
if err != nil {
log.Println(err)
}
go func(c net.Conn) {
tbuff := make([]byte, 4096)
_, err = c.Read(tbuff)
if err != nil {
fmt.Println(err)
}
clientAddr := addrt
packet := gopacket.NewPacket(tbuff, layers.LayerTypeDNS, gopacket.Default)
dnsPacket := packet.Layer(layers.LayerTypeDNS)
tcp, _ := dnsPacket.(*layers.DNS)
if !limiter(clientAddr.String()) {
c.Close()
}
tbuff = DNSHandle(tcp)
c.Write(tbuff)
c.Close()
}(c)

当我在TCP上发出dig命令时，服务器接受连接并将接收到的字节数据传递给dnhandle函数(与UDP处理程序相同)。数据似乎与使用UDP时非常不同。

数据包反序列化后的UDP请求:

&{{[91 174 1 32 0 1 0 0 0 0 0 1 11 116 101 115 116 101 120 97 109 112 108 101 3 99 111 109 0 0 1 0 1 0 0 41 16 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 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数据包反序列化后的TCP请求:

<nil>

但是如果我把tbuff改成[2:]:

packet := gopacket.NewPacket(tbuff[2:], layers.LayerTypeDNS, gopacket.Default)

它传递请求，但格式不正确(我想你会期望的):

&{{[114 11 1 32 0 1 0 0 0 0 0 1 11 116 101 115 116 101 120 97 109 112 108 101 3 99 111 109 0 0 1 0 1 0 0 41 16 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 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0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0] []} 29195 false Query false false true false 2 No Error 1 0 0 1 [{[116 101 115 116 101 120 97 109 112 108 101 46 99 111 109] A IN}] [] [] [{[] OPT Unknown 0 0 [] <nil> [] [] [] [] {[] [] 0 0 0 0 0} {0 0 0 []} {0 []} [] {0 0 []} []}] [46 116 101 115 116 101 120 97 109 112 108 101 46 99 111 109]}

我知道这可能是一个很长的机会，但任何帮助将是非常欢迎的。

编辑:

感谢@Steffen Ullrich， @selbie。我已经设法让我的代码工作了。它不是很漂亮，需要更多的工作，但这里是一个POC片段:

// Listen TCP
c, err := t.Accept()
if err != nil {
log.Println(err)
}
go func(c net.Conn) {
tbuff := make([]byte, 4096)
msize := make([]byte, 2)
size, err := c.Read(tbuff)
if err != nil {
fmt.Println(err)
}
DNSMsgLength := binary.BigEndian.Uint16(tbuff[:2])
if int(DNSMsgLength) == size-2 {
fmt.Println("Size correct")
}
clientAddr := addrt
packet := gopacket.NewPacket(tbuff[2:], layers.LayerTypeDNS, gopacket.Default)
dnsPacket := packet.Layer(layers.LayerTypeDNS)
tcp, _ := dnsPacket.(*layers.DNS)
if !limiter(clientAddr.String()) {
c.Close()
}
tbuff = DNSHandle(tcp)
binary.BigEndian.PutUint16(msize, uint16(len(tbuff)))
tbuff = append(msize, tbuff...)
c.Write(tbuff)
c.Close()
}(c)

Answer 1

但是如果我将tbuff改为[2:]:

来自RFC 1035节4.2.2:

4.2.2。TCP使用

通过TCP连接发送的消息使用服务器端口53(十进制)。的消息前缀为两个字节长度的字段这传递了一个信息长度，不包括两个字节长度字段。这个长度字段允许在开始之前组装完整消息的低级处理解析它

因此，如果将TCP上的DNS与UDP上的DNS处理得一样，你就错了——在TCP中，DNS消息的前缀是包含消息长度的2个字节。

这是必需的，因为TCP是字节流，而不是像UDP这样的数据报协议。这意味着不能简单地假设c.Read(...)将返回一条完整的DNS消息。可能还没有收到完整的消息，但也可能收到了多个DNS消息。检查长度前缀