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airkiss server 实现过程遇到的问题

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airkiss server使用udp broadcast实现，包括两部分

  1. udp client广播airkiss编码数据
  2. udp server接收device广播的random数据

socket type

常用的三种类型

  1. SOCK_STREAM流式的套接字可以提供可靠的、面向连接的通讯流
  2. SOCK_DGRAM数据报套接字定义了一种无连接的服务，数据通过相互独立的报文进行传输，是无序的，并且不保证可靠，无差错
  3. SOCK_RAW原始套接字主要用于一些协议的开发，可以进行比较底层的操作

关系如下

其中SOCK_STREAM (TCP)、SOCK_DGRAM (UDP)工作在传输层，SOCK_RAW工作在网络层。SOCK_RAW可以处理ICMP、IGMP等网络报文、特殊的IPv4报文、可以通过IP_HDRINCL套接字选项由用户构造IP头。

setsocket 指定 interface

socket发送数据默认根据路由表来发送，如果要指定interface可以使用setsocket选项SO_BINDTODEVICE来实现

struct ifreq ifr;
memset(&ifr, 0, sizeof(ifr));
snprintf(ifr.ifr_name, sizeof(ifr.ifr_name), "wlan0");
if ((rc = setsockopt(sock, SOL_SOCKET, SO_BINDTODEVICE, (void *)&ifr, sizeof(ifr))) < 0) {
    perror("Server-setsockopt() error for SO_BINDTODEVICE");
    printf("%s\n", strerror(errno));
    close(sock);
    exit(-1);
}

需要注意测试时，server与client要选定相同的interface，否则不再一个子网中，导致测试失败

参考文章：setsockopt 的 SO_BINDTODEVICE 套接口选项

  1. 对于TCP 套接口、UDP 套接口、RAW 套接口，可以通过SO_BINDTODEVICE 套接口选项将套接口绑定到指定的网络接口上。绑定之后，套接口的所有数据包收发都只经过指定的网络接口
  2. 对于PACKET 类型的套接口，不能通过SO_BINDTODEVICE绑定到指定的网络接口上，而要通过bind(2)来与特定的网络接口绑定，所用的套接口地址结构为struct sockaddr_ll，此套接口地址结构是链路层的地址结构，独立于具体的网络设备。比如，该地址结构既可以用于表示PPP 设备，也能用于表示ethernet 设备

broadcast

广播地址255.255.255.255，在头文件netinet/in.h中定义为INADDR_BROADCAST

/* Address to accept any incoming messages. */
#define INADDR_ANY      ((unsigned long int) 0x00000000)

/* Address to send to all hosts. */
#define INADDR_BROADCAST    ((unsigned long int) 0xffffffff)
  • INADDR_ANYA表示地址为0.0.0.0，表示不确定地址、任意地址或所有地址。也就是表示本机的所有IP，因为有些机子不止一块网卡，多网卡的情况下，这个就表示所有网卡IP地址的意思
  • INADDR_BROADCAST表示广播地址255.255.255.255，仅用于本地连接，如果不指定interface，根据路由表确定

设置广播属性

/* Set socket to allow broadcast */
broadcastPermission = 1;
if (setsockopt(sock, SOL_SOCKET, SO_BROADCAST, (void *) &broadcastPermission,
               sizeof(broadcastPermission)) < 0) {
    printf("setsockopt() SO_BROADCAST failed\n");
}

udp broadcast

/* Create socket for sending/receiving datagrams */
if ((sock = socket(PF_INET, SOCK_DGRAM, IPPROTO_UDP)) < 0) {
    printf("socket() failed\n");
}
/* Set socket to allow broadcast */
broadcastPermission = 1;
if (setsockopt(sock, SOL_SOCKET, SO_BROADCAST, (void *) &broadcastPermission,
            sizeof(broadcastPermission)) < 0) {
    printf("setsockopt() SO_BROADCAST failed\n");
}
struct sockaddr_in broadcastAddr;
char *buffer = NULL;

buffer = malloc(length);
memset(buffer, 'a', length);

/* Construct local address structure */
memset(&broadcastAddr, 0, sizeof(broadcastAddr));           /* Zero out structure */
broadcastAddr.sin_family = AF_INET;                         /* Internet address family */
broadcastAddr.sin_addr.s_addr = INADDR_BROADCAST;           /* Broadcast IP address */
broadcastAddr.sin_port = htons(BROADCAST_PORT);             /* Broadcast port */

sendto(s_akHandler.sock_fd, buffer, length, 0, (struct sockaddr *)&broadcastAddr, sizeof(broadcastAddr));

bind

  1. TCP通信时，server必须bind自己本机地址和端口。client不需要blind
  2. UDP通信时与TCP一样

bind不是server专属，一般情况下client是不用调用bind的，一切都交给内核搞定！

server需要bind的原因

因为服务器是时时在监听有没有客户端的连接，如果服务器不绑定 IP 和端口的话，客户端上线的时候怎么连到服务器呢，所以服务器要绑定 IP 和端口，而客户端就不需要了，客户端上线是主动向服务器发出请求的，因为服务器已经绑定了 IP 和端口，所以客户端上线的就向这个 IP 和端口发出请求，这时因为客户开始发数据了（发上线请求）, 系统就给客户端分配一个随机端口，这个端口和客户端的 IP 会随着上线请求一起发给服务器，服务收到上线请求后就可以从中获起发此请求的客户的 IP 和端口，接下来服务器就可以利用获起的 IP 和端口给客户端回应消息了

server需要bind：port和ip addr

  • port包括公共端口和私有端口
  • ip addr目的是限制了服务端进程创建的 socket 只接受那些目的地为此 IP 地址的客户链接，一般server使用servaddr.sin_addr.s_addr = htonl(INADDR_ANY)，表示不指定client ip，来者不拒

数据收发时限

struct timeva timeout;
timeout.tv_sec=5;
timeout.tv_usec=0;

// 接受时限
setsockopt(serversocket, SQL_SOCKET,SO_RCVTIMEO, (char*)&timeout,sizeof(timeout));

// 发送时限
setsockopt(serversocket, SQL_SOCKET,SO_SNDTIMEO, (char*)&timeout,sizeof(timeout));

Example

udp server

#include <stdio.h>      // Default System Calls
#include <stdlib.h>     // Needed for OS X
#include <string.h>     // Needed for Strlen
#include <sys/socket.h> // Needed for socket creating and binding
#include <netinet/in.h> // Needed to use struct sockaddr_in
#include <time.h>       // To control the timeout mechanism

#define EXPR_SIZE   1024
#define BUFLEN      512
#define TRUE        1
#define SERVERLEN   1024

int main(int argc, char **argv){

    struct sockaddr_in myaddr;  // address of the server
    struct sockaddr_in claddr;  // address of the client
    char buf[BUFLEN];
    int fd;
    long recvlen;
    socklen_t clientlen;



    if((fd = socket(AF_INET, SOCK_DGRAM, 0)) < 0){
        perror("cannot create socket");
        return 0;
    }

    memset((char *)&myaddr, 0, sizeof(myaddr));
    myaddr.sin_family = AF_INET;
    myaddr.sin_addr.s_addr = htonl(INADDR_ANY);
    myaddr.sin_port = htons(0);

    if(bind(fd, (struct sockaddr *)&myaddr, sizeof(myaddr)) < 0){
        perror("cannot bind");
        return 0;
    }
    clientlen = sizeof(claddr);

    while (TRUE) {
        recvlen = recvfrom(fd, buf, BUFLEN, 0, (struct sockaddr *)&claddr, &clientlen);
        if (recvlen < 0) {
            perror("cannot recvfrom()");
            return 0;
        }
        printf("Received %ld bytes\n",recvlen);
        buf[recvlen] = 0;
        printf("Received message: \"%s\"\n",buf);

    }

    return 0;
}

udp client

使用bind版本

#include <stdio.h>      // Default System Calls
#include <stdlib.h>     // Needed for OS X
#include <string.h>     // Needed for Strlen
#include <sys/socket.h> // Needed for socket creating and binding
#include <netinet/in.h> // Needed to use struct sockaddr_in
#include <time.h>       // To control the timeout mechanism

#define EXPR_SIZE   1024
#define BUFLEN      512
#define TRUE        1
#define FALSE       0
#define SERVERLEN   1024

int main(int argc, char **argv){

    long portNum;           // Since it's possible to input a value bigger
                            // than 65535 we'll be using long to
                            // avoid overflows
    char expr[EXPR_SIZE];
    char server[SERVERLEN];
    int fd;                 // file descriptor for the connected socket
    int buf[512];
    struct hostent *h;           // information of the host
    unsigned int addrLen;        // address length after getting the port number
    struct sockaddr_in myaddr;   // address of the client
    struct sockaddr_in servaddr; // server's address
    unsigned int exprLen;
    socklen_t slen = sizeof(servaddr);

    printf("Enter server name or IP address:");
    scanf("%s",server);
    printf("Enter port:");
    scanf("%ld",&portNum);
    if ((portNum < 0) || (portNum > 65535)) {
        printf("Invalid port number. Terminating.");
        return 0;
    }
    printf("Enter expression:");
    scanf("%s",expr);

    if((fd = socket(AF_INET, SOCK_DGRAM, 0)) < 0){
        perror("cannot create socket");
        return 0;
    }

    memset((char *)&myaddr, 0, sizeof(myaddr));
    myaddr.sin_family = AF_INET;
    myaddr.sin_addr.s_addr = htonl(INADDR_ANY);
    myaddr.sin_port = htons(0);

    if(bind(fd, (struct sockaddr *)&myaddr, sizeof(myaddr)) < 0){
        perror("cannot bind");
        return 0;
    }

    /*
     // Discovering the port number the OS allocated
     addrLen = sizeof(myaddr);
     if(getsockname(fd, (struct sockaddr *)&myaddr, &addrLen) < 0){
     perror("cannot getsockname");
     return 0;
     }
     printf("local port number = %d\n", ntohs(myaddr.sin_port));
     */

    memset((char*)&servaddr, 0, sizeof(servaddr));
    servaddr.sin_family = AF_INET;
    servaddr.sin_port = htonl(portNum);

    exprLen = sizeof(expr);


    while(TRUE){
        printf("Sending message to %s port %ld\n",server, portNum);
        if (sendto(fd, expr, strlen(expr), 0, (struct sockaddr *)&servaddr, slen) < 0) {
            perror("cannot sendto()");
        }
        printf("Success\n");

    }


    return 0;
}

不使用bind版本

#include<sys/types.h>
#include<sys/socket.h>
#include<unistd.h>
#include<netinet/in.h>
#include<arpa/inet.h>
#include<stdio.h>
#include<stdlib.h>
#include<errno.h>
#include<netdb.h>
#include<stdarg.h>
#include<string.h>

#define SERVER_PORT 8000
#define BUFFER_SIZE 1024
#define FILE_NAME_MAX_SIZE 512

int main()
{
    /* 服务端地址 */
    struct sockaddr_in server_addr;
    bzero(&server_addr, sizeof(server_addr));
    server_addr.sin_family = AF_INET;
    //server_addr.sin_addr.s_addr = htonl(INADDR_BROADCAST);
    server_addr.sin_addr.s_addr = inet_addr("127.0.0.1");
    server_addr.sin_port = htons(SERVER_PORT);

    /* 创建 socket */
    int client_socket_fd = socket(AF_INET, SOCK_DGRAM, 0);
    if (client_socket_fd < 0) {
        perror("Create Socket Failed:");
        exit(1);
    }

    /* 输入文件名到缓冲区 */
    char file_name[FILE_NAME_MAX_SIZE + 1];
    bzero(file_name, FILE_NAME_MAX_SIZE + 1);
    printf("Please Input File Name On Server:\t");
    scanf("%s", file_name);

    char buffer[BUFFER_SIZE];
    bzero(buffer, BUFFER_SIZE);
    strncpy(buffer, file_name, strlen(file_name) > BUFFER_SIZE ? BUFFER_SIZE : strlen(file_name));

    /* 发送文件名 */
    if (sendto(client_socket_fd, buffer, BUFFER_SIZE, 0, (struct sockaddr *)&server_addr, sizeof(server_addr)) < 0) {
        perror("Send File Name Failed:");
        exit(1);
    }

    close(client_socket_fd);
    return 0;
}

Ref

  1. how to bind raw socket to specific interface
  2. 广播及确定网络配置
  3. UDP-Broadcast on all interfaces
  4. socket 下的广播与多播实现
  5. Linux 网络编程之 UDP Socket 程序示例
  6. socket 通信关于 bind 那点事
  7. 简单分析一下 socket 中的 bind
  8. 为什么 TCP 服务端需要调用 bind 函数而客户端通常不需要呢？