** server.c – 展示一個stream socket server
#define PORT "3490" // 提供給使用者連線的 port
#define BACKLOG 10 // 有多少個特定的連線佇列(pending connections queue)
void sigchld_handler(int s)
while(waitpid(-1, NULL, WNOHANG) > 0);
void *get_in_addr(struct sockaddr *sa)
if (sa->sa_family == AF_INET) {
return &(((struct sockaddr_in*)sa)->sin_addr);
return &(((struct sockaddr_in6*)sa)->sin6_addr);
int sockfd, new_fd; // 在 sock_fd 進行 listen,new_fd 是新的連線
struct addrinfo hints, *servinfo, *p;
struct sockaddr_storage their_addr; // 連線者的位址資訊
char s[INET6_ADDRSTRLEN];
memset(&hints, 0, sizeof hints);
hints.ai_family = AF_UNSPEC;
hints.ai_socktype = SOCK_STREAM;
hints.ai_flags = AI_PASSIVE; // 使用我的 IP
if ((rv = getaddrinfo(NULL, PORT, &hints, &servinfo)) != 0) {
fprintf(stderr, "getaddrinfo: %s\n", gai_strerror(rv));
// 以迴圈找出全部的結果,並綁定(bind)到第一個能用的結果
for(p = servinfo; p != NULL; p = p->ai_next) {
if ((sockfd = socket(p->ai_family, p->ai_socktype,
p->ai_protocol)) == -1) {
perror("server: socket");
if (setsockopt(sockfd, SOL_SOCKET, SO_REUSEADDR, &yes,
if (bind(sockfd, p->ai_addr, p->ai_addrlen) == -1) {
fprintf(stderr, "server: failed to bind\n");
freeaddrinfo(servinfo); // 全部都用這個 structure
if (listen(sockfd, BACKLOG) == -1) {
sa.sa_handler = sigchld_handler; // 收拾全部死掉的 processes
sigemptyset(&sa.sa_mask);
sa.sa_flags = SA_RESTART;
if (sigaction(SIGCHLD, &sa, NULL) == -1) {
printf("server: waiting for connections...\n");
while(1) { // 主要的 accept() 迴圈
sin_size = sizeof their_addr;
new_fd = accept(sockfd, (struct sockaddr *)&their_addr, &sin_size);
inet_ntop(their_addr.ss_family,
get_in_addr((struct sockaddr *)&their_addr),
printf("server: got connection from %s\n", s);
if (!fork()) { // 這個是 child process
close(sockfd); // child 不需要 listener
if (send(new_fd, "Hello, world!", 13, 0) == -1)
close(new_fd); // parent 不需要這個