c - udp套接字到底接收什么？

Question

  #include <sys/socket.h>
  #include <netinet/in.h>
  #include <netinet/udp.h>

  udp_socket = socket(AF_INET, SOCK_DGRAM, 0);

当我使用 UDP 套接字时，我是只接收有效负载还是也接收 UDP header ？

Answer 1

您可以或不能访问的内容取决于套接字的创建方式。

以下是与您的问题相关的文档中的评论:

The recv() function shall receive a message from a connection-mode or connectionless-mode socket. It is normally used with connected sockets because it does not permit the application to retrieve the source address of received data.

(强调我的)

read more here ...

编辑:如果您想要访问 header 信息，请阅读此链接和以下链接。

...You cannot create a raw socket with IPPROTO_UDP and manipulate the UDP header; likewise with TCP. To manipulate the IP header as well as either the TCP or UDP header (or any other protocol encapsulated in IP), you must use the IP_HDRINCL socket option with a raw socket. ...

阅读more on the topic ...