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功能：聊天室服务器，可用telnet直接连接到服务器，发送消息则在聊天室内的所有用户都能看见。使用select实现

功能：聊天室服务器

可用telnet直接连接到服务器，发送消息则在聊天室内的所有用户都能看见。

使用select实现

#include <sys/select.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <unistd.h>
#include <stddef.h>
#include <stdlib.h>
#include <string.h>
#include <stdio.h>
#include <errno.h>
#define max(a, b) ((a) > (b) ? (a) : (b))
struct filedescriptor_node
{
    int fd;
    struct filedescriptor_node* next;
};
struct filedescriptor_set
{
    size_t len;
    struct filedescriptor_node* head;
    struct filedescriptor_node* iter;
    int max_fd;
    fd_set fds;
};
int fds_init(struct filedescriptor_set* _this)
{
    bzero(_this, sizeof(struct filedescriptor_set));
    FD_ZERO(&_this->fds);
    return 0;
}
struct filedescriptor_set*
fds_create()
{
    struct filedescriptor_set* _this;
    _this = malloc(sizeof(struct filedescriptor_set));
    if (_this == NULL)
        return NULL;
    if (fds_init(_this) == -1)
    {
        free(_this);
        return NULL;
    }
    return _this;
}
int fds_add(struct filedescriptor_set* _this, int fd)
{
    struct filedescriptor_node* p;
    p = malloc(sizeof(struct filedescriptor_node));
    if (p == NULL)
        return -1;
    p->fd = fd;
    p->next = _this->head;
    _this->head = p;        /* 在head前插入新节点 */
    ++_this->len;
    if (fd > _this->max_fd)
        _this->max_fd = fd;
    FD_SET(fd, &_this->fds);
    return 0;
}
int fds_remove(struct filedescriptor_set* _this, int fd)
{
    struct filedescriptor_node* p;
    if (_this->head->fd == fd)
    {
        p = _this->head;
        _this->head = p->next;
        free(p);
    }
    else
    {
        for (p = _this->head; p->next != NULL; p = p->next) 
            if (p->next->fd == fd)
                break;          /* 令p指向fd的前一个 */
        if (p->next == NULL)
            return -1;
    }
    --_this->len;
    if (fd == _this->max_fd)
    {
        _this->max_fd = 0;      /* _this->max_fd = _this->head->fd不正确，
                                    this->head可能为NULL */
        for (p = _this->head; p != NULL; p = p->next)
            if (p->fd > _this->max_fd)
                _this->max_fd = p->fd;
    }
    FD_CLR(fd, &_this->fds);
    return 0;
}
fd_set fds_getfdset(struct filedescriptor_set* _this)
{
    return _this->fds;
}
int fds_getmaxfd(struct filedescriptor_set* _this)
{
    return _this->max_fd;
}
void fds_iter_init(struct filedescriptor_set* _this)
{
    _this->iter = _this->head;
}
int fds_iter_next(struct filedescriptor_set* _this)
{
    if (_this->iter != NULL)
    {
        int fd = _this->iter->fd;
        _this->iter = _this->iter->next;
        return fd;
    }
    else
        return -1;
}
void fds_destroy(struct filedescriptor_set* _this)
{
    struct filedescriptor_node *p, *q;
    p = _this->head;
    q = p->next;
    while (p != NULL)
    {
        free(p);
        p = q;
        if (q != NULL)
            q = q->next;
    }
}
void fds_delete(struct filedescriptor_set* _this)
{
    fds_destroy(_this);
    free(_this);
}
int writen(int fd, char* buf, size_t len)
{
    ssize_t n;
    size_t left = len;
    while (left > 0)
    {
        if ((n = write(fd, buf, len)) <= 0)
        {
            if (errno == EINTR)
                continue;
            else
                return -1;
        }
        left -= n;
        buf += n;   
    }
    return len;     /* 无论如何也要写完，否则就是错误 */
}
int readn(int fd, char* buf, size_t len)
{
    ssize_t n;
    size_t left = len;
    while (left > 0)
    {
        if ((n = read(fd, buf, len)) < 0)
        {
            if (errno == EINTR)
                continue;
            else
                return -1;
        }
        else if (n == 0)    /* 到达EOF */
        {
            break;
        }
        left -= n;
        buf += n;
    }
    return len - left;  /* 可能提前到达EOF */
}
#define PORT 10086
#define BUF_SIZE 4096
typedef struct sockaddr SA;
int main(int argc, char* argv[])
{
    struct filedescriptor_set fds;
    int svrsock;
    struct sockaddr_in svraddr;
    svrsock = socket(AF_INET, SOCK_STREAM, 0);
    if (svrsock == -1)
    {
        perror("socket");
        exit(errno);
    }
    bzero(&svraddr, sizeof(svraddr));
    svraddr.sin_family = AF_INET;
    svraddr.sin_port = htons(PORT);
    svraddr.sin_addr.s_addr = htonl(INADDR_ANY);
    if (bind(svrsock, (SA*)&svraddr, sizeof(svraddr)) == -1)
    {
        perror("bind");
        exit(errno);
    }
    if (listen(svrsock, 64) == -1)
    {
        perror("listen");
        exit(errno);
    }
    if (fds_init(&fds) == -1)
    {
        perror("fds_init");
        exit(errno);
    }
    while (1)
    {
        int fd;
        fd_set fdset;
        char buf[BUF_SIZE];
        size_t buflen;
        fdset = fds_getfdset(&fds);
        FD_SET(svrsock, &fdset);
        if (select(max(fds_getmaxfd(&fds), svrsock) + 1, &fdset, NULL, NULL, NULL) == -1)
        {
            perror("select");
            exit(errno);
        }
        if (FD_ISSET(svrsock, &fdset))
        {
            int cltsock;
            struct sockaddr_in cltaddr;
            socklen_t cltaddrlen = sizeof(cltaddr);
            char cltaddrstr[INET_ADDRSTRLEN];
            if ((cltsock = accept(svrsock, (SA*)&cltaddr, &cltaddrlen)) == -1)
            {
                perror("accept");
                exit(errno);
            }
            if (inet_ntop(AF_INET, &cltaddr.sin_addr, cltaddrstr, INET_ADDRSTRLEN) == NULL)
            {
                perror("inet_ntop");
                exit(errno);
            }
            /* 通知新用户到达 */
            printf("incoming connection from %s:%d\n", cltaddrstr, ntohs(cltaddr.sin_port));
            snprintf(buf, BUF_SIZE, "user %s:%d joined\n", cltaddrstr, ntohs(cltaddr.sin_port));
            buflen = strlen(buf);
            for (fds_iter_init(&fds); (fd = fds_iter_next(&fds)) >= 0;)
            {
                if (writen(fd, buf, buflen) == -1)
                {
                    perror("writen");
                    exit(errno);
                }
            }
            strncpy(buf, "Welcom\n", BUF_SIZE);
            buflen = strlen(buf);
            if (writen(cltsock, buf, buflen) == -1)
            {
                perror("writen");
                exit(errno);
            }
            if (fds_add(&fds, cltsock) == -1)
            {
                perror("fds_add");
                exit(errno);
            }
        }
        for (fds_iter_init(&fds); (fd = fds_iter_next(&fds)) >= 0;)
        {
            if (FD_ISSET(fd, &fdset))
            {
                int n;
                struct filedescriptor_node* old;
                if ((n = readn(fd, buf, BUF_SIZE)) == -1)
                {
                    perror("readn");
                    exit(errno);
                }
                else if (n == 0)
                {
                    /*struct sockaddr_in cltaddr;
                    socklen_t cltaddrlen = sizeof(cltaddr);
                    char cltaddrstr[INET_ADDRSTRLEN];
                    if (getpeername(fd, (SA*)&cltaddr, &cltaddrlen) == -1)
                    {
                        perror("getpeername");
                        exit(errno);
                    }
                    if (inet_ntop(AF_INET, &cltaddr.sin_addr, cltaddrstr, INET_ADDRSTRLEN) == NULL)
                    {
                        perror("inet_ntop");
                        exit(errno);
                    }
                    printf("%s disconnected the connection\n", cltaddrstr);
                    snprintf(buf, BUF_SIZE, "user %s exited\n", cltaddrstr);
                    buflen = strlen(buf);
                    for (fds_iter_init(&fds); (fd = fds_iter_next(&fds)) >= 0;)
                    {
                        if (writen(fd, buf, buflen) == -1)
                        {
                            perror("writen");
                            exit(errno);
                        }
                    }*/
                    fds_remove(&fds, fd);
                    continue;
                }
                old = fds.iter;
                for (fds_iter_init(&fds); (fd = fds_iter_next(&fds)) >= 0;)
                {
                    if (writen(fd, buf, n) == -1)
                    {
                        perror("writen");
                        exit(errno);
                    }
                }
                fds.iter = old;
            }
        }
    }
    fds_destroy(&fds);
    return 0;
}