瞭解網絡傳輸協議的人都知道，採用TCP實現文件傳輸很簡單。相對於TCP，由於UDP是面向無連接、不可靠的傳輸協議，所以我們需要考慮丟包和後發先至（包的順序）的問題，所以我們想要實現UDP傳輸文件，則需要解決這兩個問題。方法就是給數據包編號，按照包的順序接收並存儲，接收端接收到數據包後發送確認信息給發送端，發送端接收確認數據以後再繼續發送下一個包，如果接收端收到的數據包的編號不是期望的編號，則要求發送端重新發送。
下面展示的是基於linux下C語言實現的一個示例程序，該程序定義一個包的結構體，其中包含數據和包頭，包頭裏包含有包的編號和數據大小，經過測試後，該程序可以成功傳輸一個視頻文件。
具體實現代碼如下：
server端代碼如下：
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/*************************************************************************
>
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 /*
包頭 */typedef
struct{
int
id; int
buf_size; }PackInfo;
/*
接收包 */struct
SendPack {
PackInfo
head; char
buf[BUFFER_SIZE]; }
data; int
main() {
/*
發送id */ int
send_id = 0; /*
接收id */ int
receive_id = 0; /*
創建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); /*
創建socket */ int
server_socket_fd = socket(AF_INET, SOCK_DGRAM, 0); if(server_socket_fd
== -1) {
perror("Create
Socket Failed:");
exit(1);
}
/*
綁定套接口 */ if(-1
== (bind(server_socket_fd,(struct
sockaddr*)&server_addr,sizeof(server_addr))))
{
perror("Server
Bind Failed:");
exit(1);
}
/*
數據傳輸 */ while(1)
{
/*
定義一個地址，用於捕獲客戶端地址 */ struct
sockaddr_in client_addr; socklen_t
client_addr_length = sizeof(client_addr);
/*
接收數據 */ 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);
}
/*
從buffer中拷貝出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); /*
打開文件 */ FILE
*fp = fopen(file_name,
"r");
if(NULL
== fp) {
printf("File:%s
Not Found.\n",
file_name); }
else {
int
len = 0; /*
每讀取一段數據，便將其發給客戶端 */ 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; /*
發送id放進包頭,用於標記順序 */ data.head.buf_size
= len; /*
記錄數據長度 */ if(sendto(server_socket_fd,
(char*)&data,
sizeof(data),
0, (struct
sockaddr*)&client_addr, client_addr_length) < 0) {
perror("Send
File Failed:");
break;
}
/*
接收確認消息 */ 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和發送的id不相同,重新發送 */ if(sendto(server_socket_fd,
(char*)&data,
sizeof(data),
0, (struct
sockaddr*)&client_addr, client_addr_length) < 0) {
perror("Send
File Failed:");
break;
}
/*
接收確認消息 */ recvfrom(server_socket_fd,
(char*)&pack_info,
sizeof(pack_info),
0, (struct
sockaddr*)&client_addr, &client_addr_length); receive_id
= pack_info.id; }
}
/*
關閉文件 */ fclose(fp);
printf("File:%s
Transfer Successful!\n",
file_name); }
}
close(server_socket_fd);
return
0; }
|
client端代碼如下：
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/*************************************************************************
>
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 /*
包頭 */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; /*
服務端地址 */ 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);
/*
創建socket */ int
client_socket_fd = socket(AF_INET, SOCK_DGRAM, 0); if(client_socket_fd
< 0) {
perror("Create
Socket Failed:");
exit(1);
}
/*
輸入文件名到緩衝區 */ 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));
/*
發送文件名 */ if(sendto(client_socket_fd,
buffer, BUFFER_SIZE,0,(struct
sockaddr*)&server_addr,server_addr_length) < 0) {
perror("Send
File Name Failed:");
exit(1);
}
/*
打開文件，準備寫入 */ FILE
*fp = fopen(file_name,
"w");
if(NULL
== fp) {
printf("File:\t%s
Can Not Open To Write\n",
file_name); exit(1);
}
/*
從服務器接收數據，並寫入文件 */ 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;
/*
發送數據包確認信息 */ 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!");
}
/*
寫入文件 */ 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) /*
如果是重發的包 */ {
pack_info.id
= data.head.id; pack_info.buf_size
= data.head.buf_size; /*
重發數據包確認信息 */ 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; } |
感興趣的朋友可以動手測試一下該程序，相信會對大家的Linux下C語言網絡編程帶來一定的幫助。