Linux网络编程之基于UDP实现可靠的文件传输示例

了解网络传输协议的人都知道，采用TCP实现文件传输很简单。相对于TCP，由于UDP是面向无连接、不可靠的传输协议，所以我们需要考虑丢包和后发先至（包的顺序）的问题，所以我们想要实现UDP传输文件，则需要解决这两个问题。方法就是给数据包编号，按照包的顺序接收并存储，接收端接收到数据包后发送确认信息给发送端，发送端接收确认数据以后再继续发送下一个包，如果接收端收到的数据包的编号不是期望的编号，则要求发送端重新发送。

下面展示的是基于linux下C语言实现的一个示例程序，该程序定义一个包的结构体，其中包含数据和包头，包头里包含有包的编号和数据大小，经过测试后，该程序可以成功传输一个视频文件。

具体实现代码如下：

server端代码如下：

/************************************************************************* 
  > File Name: server.c 
  > Author: SongLee 
 ************************************************************************/ 
#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 
 
/* 包头 */ 
typedef struct 
{ 
  int id; 
  int buf_size; 
}PackInfo; 
 
/* 接收包 */ 
struct SendPack 
{ 
  PackInfo head; 
  char buf[BUFFER_SIZE]; 
} data; 
 
 
int main() 
{ 
  /* 发送id */ 
  int send_id = 0; 
 
  /* 接收id */ 
  int receive_id = 0; 
 
  /* 创建UDP套接口 */ 
  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_ANY); 
  server_addr.sin_port = htons(SERVER_PORT); 
 
  /* 创建socket */ 
  int server_socket_fd = socket(AF_INET, SOCK_DGRAM, 0); 
  if(server_socket_fd == -1) 
  { 
    perror("Create Socket Failed:"); 
    exit(1); 
  } 
 
  /* 绑定套接口 */ 
  if(-1 == (bind(server_socket_fd,(struct sockaddr*)&server_addr,sizeof(server_addr)))) 
  { 
    perror("Server Bind Failed:"); 
    exit(1); 
  } 
 
  /* 数据传输 */ 
  while(1) 
  {   
    /* 定义一个地址，用于捕获客户端地址 */ 
    struct sockaddr_in client_addr; 
    socklen_t client_addr_length = sizeof(client_addr); 
 
    /* 接收数据 */ 
    char buffer[BUFFER_SIZE]; 
    bzero(buffer, BUFFER_SIZE); 
    if(recvfrom(server_socket_fd, buffer, BUFFER_SIZE,0,(struct sockaddr*)&client_addr, &client_addr_length) == -1) 
    { 
      perror("Receive Data Failed:"); 
      exit(1); 
    } 
 
    /* 从buffer中拷贝出file_name */ 
    char file_name[FILE_NAME_MAX_SIZE+1]; 
    bzero(file_name,FILE_NAME_MAX_SIZE+1); 
    strncpy(file_name, buffer, strlen(buffer)>FILE_NAME_MAX_SIZE?FILE_NAME_MAX_SIZE:strlen(buffer)); 
    printf("%s\n", file_name); 
 
    /* 打开文件 */ 
    FILE *fp = fopen(file_name, "r"); 
    if(NULL == fp) 
    { 
      printf("File:%s Not Found.\n", file_name); 
    } 
    else 
    { 
      int len = 0; 
      /* 每读取一段数据，便将其发给客户端 */ 
      while(1) 
      { 
        PackInfo pack_info; 
 
        if(receive_id == send_id) 
        { 
          ++send_id; 
          if((len = fread(data.buf, sizeof(char), BUFFER_SIZE, fp)) > 0) 
          { 
            data.head.id = send_id; /* 发送id放进包头,用于标记顺序 */ 
            data.head.buf_size = len; /* 记录数据长度 */ 
            if(sendto(server_socket_fd, (char*)&data, sizeof(data), 0, (struct sockaddr*)&client_addr, client_addr_length) < 0) 
            { 
              perror("Send File Failed:"); 
              break; 
            } 
            /* 接收确认消息 */ 
            recvfrom(server_socket_fd, (char*)&pack_info, sizeof(pack_info), 0, (struct sockaddr*)&client_addr, &client_addr_length); 
            receive_id = pack_info.id;  
          } 
          else 
          { 
            break; 
          } 
        } 
        else 
        { 
          /* 如果接收的id和发送的id不相同,重新发送 */ 
          if(sendto(server_socket_fd, (char*)&data, sizeof(data), 0, (struct sockaddr*)&client_addr, client_addr_length) < 0) 
          { 
            perror("Send File Failed:"); 
            break; 
          } 
          /* 接收确认消息 */ 
          recvfrom(server_socket_fd, (char*)&pack_info, sizeof(pack_info), 0, (struct sockaddr*)&client_addr, &client_addr_length); 
          receive_id = pack_info.id;  
        } 
      } 
      /* 关闭文件 */ 
      fclose(fp); 
      printf("File:%s Transfer Successful!\n", file_name); 
    } 
  } 
  close(server_socket_fd); 
  return 0; 
} 

client端代码如下：

/************************************************************************* 
  > File Name: client.c 
  > Author: SongLee 
 ************************************************************************/ 
#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 
 
/* 包头 */ 
typedef struct  
{ 
  int id; 
  int buf_size; 
}PackInfo; 
 
/* 接收包 */ 
struct RecvPack 
{ 
  PackInfo head; 
  char buf[BUFFER_SIZE]; 
} data; 
 
 
int main() 
{ 
  int id = 1; 
 
  /* 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 = inet_addr("127.0.0.1"); 
  server_addr.sin_port = htons(SERVER_PORT); 
  socklen_t server_addr_length = sizeof(server_addr); 
 
  /* 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: "); 
  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,server_addr_length) < 0) 
  { 
    perror("Send File Name Failed:"); 
    exit(1); 
  } 
 
  /* 打开文件，准备写入 */ 
  FILE *fp = fopen(file_name, "w"); 
  if(NULL == fp) 
  { 
    printf("File:\t%s Can Not Open To Write\n", file_name);  
    exit(1); 
  } 
 
  /* 从服务器接收数据，并写入文件 */ 
  int len = 0; 
  while(1) 
  { 
    PackInfo pack_info; 
 
    if((len = recvfrom(client_socket_fd, (char*)&data, sizeof(data), 0, (struct sockaddr*)&server_addr,&server_addr_length)) > 0) 
    { 
      if(data.head.id == id) 
      { 
        pack_info.id = data.head.id; 
        pack_info.buf_size = data.head.buf_size; 
        ++id; 
        /* 发送数据包确认信息 */ 
        if(sendto(client_socket_fd, (char*)&pack_info, sizeof(pack_info), 0, (struct sockaddr*)&server_addr, server_addr_length) < 0) 
        { 
          printf("Send confirm information failed!"); 
        } 
        /* 写入文件 */ 
        if(fwrite(data.buf, sizeof(char), data.head.buf_size, fp) < data.head.buf_size) 
        { 
          printf("File:\t%s Write Failed\n", file_name); 
          break; 
        } 
      } 
      else if(data.head.id < id) /* 如果是重发的包 */ 
      { 
        pack_info.id = data.head.id; 
        pack_info.buf_size = data.head.buf_size; 
        /* 重发数据包确认信息 */ 
        if(sendto(client_socket_fd, (char*)&pack_info, sizeof(pack_info), 0, (struct sockaddr*)&server_addr, server_addr_length) < 0) 
        { 
          printf("Send confirm information failed!"); 
        } 
      } 
      else 
      { 
 
      } 
    } 
    else 
    { 
      break; 
    } 
  } 
 
  printf("Receive File:\t%s From Server IP Successful!\n", file_name); 
  fclose(fp); 
  close(client_socket_fd); 
  return 0; 
}

感兴趣的朋友可以动手测试一下该程序，相信会对大家的Linux下C语言网络编程带来一定的帮助。