MSG_ OOB MSG_ PEEK

This article introduces you to an example to illustrate MSG_OOB MSG_PEEK MSG_DONTWAIT, It mainly includes an example to illustrate MSG_OOB MSG_PEEK MSG_DONTWAIT Using examples 、 Application skills 、 Summary of basic knowledge points and precautions , It has certain reference value , If you need a friend, please refer to it .

This kind of data is transmitted through the signal SIGURG To inform , So we need to use signal / sigaction To register a signal processing function , stay signal First, you need to fcntl(clientfd,F_SETOWN,getpid()) , Since this signal is generated by the socket , The owner of the socket is the operating system , Only set the owner of the socket to the current process ,SIGURG Will be passed to this process , Otherwise, you will not receive SIGURG The signal , Only ordinary data can be accepted .

        MSG_PEEK : Peek for data in the buffer , recv(clientfd,buf,BUFSIZ,MSG_PEEK) , Data is not removed from the buffer .

        MSG_DONTWAIT : Don't block

        MSG_OOB : Just by tcp The head of the urgent Mode transmitted , And only one byte will be read as oob data . for example :send(sockfd,"1234",strlen("1234"),MSG_OOB); Only the last byte :4 Will be treated as oob data , Other data "123" Will be read as normal data .

receive oob data ：

  1 #include <stdio.h>
  2 #include <string.h>
  3 #include <stdlib.h>
  4
  5 #include <sys/types.h>          /* See NOTES */
  6 #include <sys/socket.h>
  7
  8 #include <netinet/in.h>
  9 #include <netinet/tcp.h>
 10 #include <netdb.h>
 11
 12 #include <fcntl.h>
 13 #include <unistd.h>
 14
 15 #include <errno.h>
 16 #include <signal.h>
 17
 18 #define PORT 10000
 19
 20 static void urg_handler(int sig);
 21 int clientfd = 0;
 22
 23 int main(int argc, char ** argv)
 24 {
 25     int listenfd = socket(AF_INET, SOCK_STREAM, 0);
 26
 27     struct sockaddr_in serv_addr, client_addr;
 28     memset(&serv_addr,0,sizeof(serv_addr));
 29     memset(&client_addr,0,sizeof(client_addr));
 30     serv_addr.sin_family = AF_INET;
 31     serv_addr.sin_port = htons(PORT);
 32     serv_addr.sin_addr.s_addr = INADDR_ANY;
 33     if(bind(listenfd, (struct sockaddr *)&serv_addr,sizeof(serv_addr)) < 0){
 34         perror("bind");
 35         return  0;
 36     }
 37
 38     if(listen(listenfd, 10) < 0) {
 39         perror("listen");
 40         return 0;
 41     }
 42
 43     socklen_t client_socklen = sizeof(client_addr);
 44     clientfd = accept(listenfd, (struct sockaddr *)&client_addr, &client_socklen);
 45
 46     // Be careful ,  If the socket owner is not set ,  This process will not receive SIGURG  The signal .
 47     fcntl(clientfd, F_SETOWN, getpid());
 48     // Register signal functions 
 49     signal(SIGURG, urg_handler);
 50
 51     int n = 0;
 52     char buf[BUFSIZ];
 53
 65
 66
 67     // Accept common data .
 68     while((n = recv(clientfd, buf, BUFSIZ, 0)) != 0){
 69         if( -1 == n){
 70             perror("recv error");
 71             printf("error no : %d\n" ,errno);
 72             continue;
 73         }
 74         buf[n] = 0;
 75         printf("normal buf:%s\n", buf);
 76     }
 77     close(clientfd);
 78     close(listenfd);
 79     return 0;
 80 }
 81
 82 static void urg_handler(int sig)
 83 {
 84     char buf[30];
 85
 86     //  Accept OOB data ,  Only the last byte can be accepted ,  Other bytes are accepted as normal data 
 87     int n = recv(clientfd ,buf, 30, MSG_OOB);
 88     printf("\noob len : %d, " , n);
 89     buf[n] = 0;
 90     printf("oob data:%s\n\n" , buf);
 91 }
                              

send out oob data ：

test result ：

[email protected]:~/a_test/a02_MSG_OOB$ ./oob_send 127.0.0.1 10000
data1: data1
oobdata1: oobdata1
data2: data2
oob_data2: oob_data2

Above ： A total of 4 Time data ： Normal transmission data1,oob send out oobdata1, Normal transmission data2,oob send out oob_data2

[email protected]:~/a_test/a02_MSG_OOB$ ./oob_recv
normal buf:data1

oob len : 1, oob data:1

normal buf:oobdata
normal buf:data2

oob len : 1, oob data:2

normal buf:oob_data

Above ： Normal reception data1 and data2 The data of ; but oob Data sent , branch 2 Partial reception ： Part of it is oob The last time you receive and send data 1 Bytes of data , Above ：oob data：1 and 2, The rest of the data , Are received normally .