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I was wandering through Google Images behind a state diagram for server and client model and I ended up finding this here:
I aroused curiosity regarding the image above due to the fact that the use of the function is cited bind() on the client’s side. This seemed a little strange, because I learned that the function bind() should only be used by the server and not by the client.
However, I come here with the following doubts:
- What a role the function
bind()plays in a client code? - Why in the diagram says that the use of the function
bind()is optional? As the function
bind()could be applied in the code below?client. c
#include <stdio.h> #include <stdlib.h> #include <string.h> #include <netdb.h> #include <unistd.h> #include <arpa/inet.h> #include <sys/types.h> #include <sys/socket.h> #include <netinet/in.h> #define SRV_ADDR "127.0.0.1" #define SRV_PORT "9009" int make_socket(void){ int ecode, sockfd; struct addrinfo *results=NULL, hints; memset(&hints, 0, sizeof(struct addrinfo)); hints.ai_family=AF_INET; hints.ai_socktype=SOCK_STREAM; hints.ai_protocol=IPPROTO_TCP; if((ecode=getaddrinfo(SRV_ADDR, SRV_PORT, &hints, &results))!=0){ sockfd=-1; }else{ struct addrinfo *it=NULL; for(it=results; it!=NULL; it=it->ai_next){ if((sockfd=socket(it->ai_family, it->ai_socktype, it->ai_protocol))==-1){ continue; } if(connect(sockfd, it->ai_addr, it->ai_addrlen)==0){ break; } close(sockfd); } freeaddrinfo(results); if(it==NULL){ sockfd=-1; } } return sockfd; } short get_msg(char *msg, size_t n){ int rv; if(fgets(msg, n, stdin)!=NULL){ size_t len=strlen(msg); msg[len-1]='\0'; //elimina o \n rv=0; }else{ rv=-1; } return rv; } int main(void){ int sockfd=make_socket(); if(sockfd!=-1){ short rv; char msg[101]; printf("\n"); do{ do{ printf("Você >"); if((rv=get_msg(msg, 101))!=0){ printf("\n* Falha na leitura!"); printf("\n |.__Escreva a mensagem novamente.\n\n"); } send(sockfd, msg, 101, 0); }while(rv!=0); if(strcmp(msg, "!exit")!=0){ recv(sockfd, msg, 101, 0); printf("Estranho: %s\n", msg); } }while(strcmp(msg, "!exit")!=0); close(sockfd); } return 0; }