文章出处 @ http://blog.csdn.net/gatieme
TCP编程流程说明
（1）SERVER 服务器端编程流程
TCP服务器端编程流程如下：
① 创建套接字socket； ② 绑定套接字bind； ③ 设置套接字为监听模式，进入被动接受连接状态listen； ④ 接受请求，建立连接accpet； ⑤ 读写数据read/write； ⑥ 终止连接close。
（2） CLIENT客户端编程流程
TCP客户端编程流程如下：
① 创建套接字socket； ② 与远程服务器建立连接connect； ③ 读写数据read/write； ④ 终止连接close。
异常机制
3） TCP服务器三种异常情况
TCP服务器有三种异常情况，分别为服务器主机崩溃、服务器主机崩溃后重启、服务器主机关机。
服务器主机崩溃
在服务器主机崩溃的情况下，已有的TCP网络连接上发不出任何东西。 此时客户端发出数据后，会一直阻塞在套接字的读取响应。但是由于服务器主机已崩溃，TCP客户端会持续重传数据分节，试图从服务器接收一个ACK[一般重传12次（源自Berkeley的实现）]后，客户TCP最终选择放弃，返回给应用经常一个ETIMEDOUT错误；或者是因为中间路由器判定服务器主机不可达，则返回一个目的地不可达的ICMP消息响应，其错误代码为EHOSTUNREACH或ENETUNREACH。 简单来说，客户端会一直阻塞与read调用，然后一直重传，直到最后超时，客户最终会发现服务器主机已崩溃或主机不可达，然后返回一个状态码，但是这个过程可能是很长就的，解决的方法就是自己写一个read函数然后设置超时，或者加一个SO_KEEPALIVE选项，也可以通过设置套接字选项可以更改TCP持续重传等待的超时时间。
服务器主机崩溃后重启
在服务器主机崩溃后重启的情况下，如果客户在主机崩溃重启前不主动发送数据，那么客户是不会知道服务器已崩溃。
在服务器重启后，客户向服务器发送一个数据分节；由于服务器重启后丢失了以前的连接信息（尽管在服务端口上有进程监听，但连接套接字所在的端口无进程等待），因此导致服务器主机的TCP响应RST；而客户由于之前未收到服务器的响应数据，页阻塞于read调用，当客户端收到这个RST之后便返回错误ECONNRESET。
如果客户对服务器的崩溃情况很关心，即使客户不主动发送数据也这样，这需要进行相关设置（如设置套接口选项SO_KEEPALIVE或某些客户/服务器心跳函数）。
服务器主机关机 这里一般指的是正常关机，因为Unix系统关机时，会发送SIGTERM和SIGKILL信号，SIGTREM可能忽略，但是SIGKILL信号不能忽略，于是服务器将由SIGKILL终止， 当服务器主机关机的情况下，由于init进程给所有运行的进程发信号SIGTERM，这时服务器程序可以捕获该信号，并在信号处理程序中正常关闭网络连接。如果服务器程序忽略了SIGTERM信号，则init进程会等待一段固定的时间（通常是5s~20s），然后给所有还在运行的程序发信号SIGKILL。服务器将由信号SIGKILL终止，其终止时，所有打开的描述字被关闭，这导致向客户发送FIN分节，客户收到FIN分节后，能推断出服务器将终止服务。
简单的TCP套接字应用程序
我们下面将实现一个迭代类型的简单TCP服务器与客户端，实现客户端从服务器上传/下载文件（我们的程序中主要是上传）。
TCP服务器
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <errno.h>
#include <netinet/in.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <sys/wait.h>
#include <arpa/inet.h>
#include <unistd.h>
#include <signal.h>
#define TCP_SERVER_PORT 6666 /* 服务器的端口 */
#define BUFFER_SIZE 4096
#define IP_SIZE 20
#define MAX_FILENAME_SIZE 256
#define LISTEN_QUEUE 20
void
TcpServerPullFile(
int connfd,
struct sockaddr_in clientAddr,
char *fileServerRoot)
{
char buffer[BUFFER_SIZE];
char filename[MAX_FILENAME_SIZE];
char fileServerPath[MAX_FILENAME_SIZE];
FILE *stream;
int count;
int dataLength;
int writeLength;
int flag =
0;
bzero(buffer, BUFFER_SIZE);
count = recv(connfd, buffer, BUFFER_SIZE,
0);
if(count <
0)
{
perror(
"获取文件名失败...\n");
exit(
1);
}
else
{
strncpy(filename, buffer,
strlen(buffer) > MAX_FILENAME_SIZE ? MAX_FILENAME_SIZE :
strlen(buffer));
strcpy(fileServerPath, fileServerRoot);
strcat(fileServerPath, filename);
printf(
"\n获取客户端发送过来的文件名成功...\n");
printf(
"文件名[%s]\n", filename);
printf(
"文件存储路径[%s]\n\n", fileServerPath);
}
if((stream = fopen(fileServerPath,
"w")) == NULL)
{
perror(
"file open error...\n");
exit(
1);
}
else
{
bzero(buffer,BUFFER_SIZE);
}
printf(
"正在接收来自%s的文件....\n",inet_ntoa(clientAddr.sin_addr));
dataLength =
0;
while((dataLength = recv(connfd, buffer, BUFFER_SIZE,
0)) >
0)
{
flag++;
if(flag ==
1)
{
printf(
"正在接收来自%s的文件....\n", inet_ntoa(clientAddr.sin_addr));
}
if(dataLength <
0)
{
printf(
"接收错误i\n");
exit(
1);
}
writeLength = fwrite(buffer,
sizeof(
char), dataLength, stream);
if(writeLength != dataLength)
{
printf(
"file write failed\n");
exit(
1);
}
bzero(buffer,BUFFER_SIZE);
}
if(flag >
0)
{
printf(
"%s的文件传送完毕\n", inet_ntoa(clientAddr.sin_addr));
}
if(flag==
0)
{
printf(
"%s的文件传输失败\n", inet_ntoa(clientAddr.sin_addr));
}
fclose(stream);
}
void TcpServerPushFile(
int connfd,
struct sockaddr_in clientAddr,
char *filePath)
{
char buff[BUFFER_SIZE];
char filename[MAX_FILENAME_SIZE];
int count;
FILE *stream;
bzero(buff, BUFFER_SIZE);
strcpy(filename,
strrchr(filePath,
'/') +
1);
strncpy(buff, filename,
strlen(filename) > MAX_FILENAME_SIZE ? MAX_FILENAME_SIZE :
strlen(filename));
count = send(connfd, buff, BUFFER_SIZE,
0);
printf(
"服务器待发送的文件名[%s]..\n", filename);
if(count <
0)
{
perror(
"Send file information");
exit(
1);
}
if((stream = fopen(filePath,
"rb")) == NULL)
{
printf(
"File :%s not found!\n",filePath);
}
printf(
"服务器打开文件成功...\n");
printf(
"正在向客户端发送文件...\n");
bzero(buff, BUFFER_SIZE);
int fileBlockLength =
0;
while((fileBlockLength = fread(buff,
sizeof(
char), BUFFER_SIZE, stream)) >
0)
{
printf(
"读取了:%d个数据...\n",fileBlockLength);
if(send(connfd, buff, fileBlockLength,
0) <
0)
{
perror(
"Send file error...\n");
perror(
"向客户端发送文件失败...\n");
exit(
1);
}
bzero(buff,BUFFER_SIZE);
}
fclose(stream);
printf(
"服务器发送文件成功\n");
}
extern int errno;
int main(
int argc,
char *argv[])
{
struct sockaddr_in serverAddr;
int socketFd;
bzero(&serverAddr,
sizeof(serverAddr));
serverAddr.sin_family = AF_INET;
serverAddr.sin_addr.s_addr = htons(INADDR_ANY);
serverAddr.sin_port = htons(TCP_SERVER_PORT);
socketFd = socket(AF_INET, SOCK_STREAM,
0);
if(socketFd <
0)
{
perror(
"socket create error\n");
exit(-
1);
}
else
{
printf(
"socket create success...\n");
printf(
"创建套接字成功[errno = %d]...\n", errno);
}
if(bind(socketFd, (
struct sockaddr*)&serverAddr,
sizeof(serverAddr)) >
0)
{
perror(
"bind error\n");
exit(
1);
}
else
{
printf(
"server bind port %d success...\n", TCP_SERVER_PORT);
printf(
"服务器绑定端口%d成功...\n", TCP_SERVER_PORT);
}
if(listen(socketFd, LISTEN_QUEUE))
{
printf(
"Server listen error[errno = %d]...\n", errno);
exit(-
1);
}
else
{
printf(
"Server listen success...\n");
printf(
"服务器开始监听...\n");
}
struct sockaddr_in clientAddr;
socklen_t length =
sizeof(clientAddr);
int connFd;
while(
1 )
{
connFd = accept(socketFd, (
struct sockaddr*)&clientAddr, &length);
if(connFd == -
1)
{
printf(
"accept error[%d]...\n", errno);
continue;
}
else
{
printf(
"获取到从客户端%s的连接...\n", inet_ntoa(clientAddr.sin_addr));
TcpServerPullFile(connFd, clientAddr,
"./sdata/");
close(connFd);
}
}
}
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TCP客户端
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <netinet/in.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <sys/wait.h>
#include <arpa/inet.h>
#include <unistd.h>
#include <signal.h>
#define TCP_SERVER_PORT 6666
#define MAX_FILENAME_SIZE 256
#define IP_SIZE 20
#define BUFFER_SIZE 4096
void TcpClientPushFile(
int socketFd,
char *filePath)
{
FILE *stream;
char buffer[BUFFER_SIZE];
char filename[MAX_FILENAME_SIZE];
int count =
0;
bzero(buffer, BUFFER_SIZE);
strcpy(filename,
strrchr(filePath,
'/') +
1);
strncpy(buffer, filename,
strlen(filename) > MAX_FILENAME_SIZE ? MAX_FILENAME_SIZE :
strlen(filename));
count = send(socketFd, buffer, BUFFER_SIZE,
0);
printf(
"客户端待上传待文件名[%s]..\n", filename);
if(count <
0)
{
perror(
"Send file information");
exit(
1);
}
if((stream = fopen(filePath,
"r")) == NULL)
{
printf(
"Can't open the file [%s]\n", filePath);
exit(
1);
}
else
{
printf(
"客户端打开文件成功\n");
}
printf(
"正在向服务器传上传文件...\n");
count =
0;
bzero(buffer, BUFFER_SIZE);
while((count = fread(buffer,
1, BUFFER_SIZE, stream)) >
0)
{
if(send(socketFd, buffer, count,
0) <
0)
{
printf(
"send file error...\n");
break;
}
bzero(buffer, BUFFER_SIZE);
}
printf(
"向服务器发送文件成功...\n");
if(fclose(stream))
{
printf(
"file close error\n");
exit(
1);
}
else
{
printf(
"关闭文件流成功...\n");
}
close(socketFd);
}
void TcpClientPullFile(
int socketFd,
char *filePath)
{
char buff[BUFFER_SIZE];
char filename[MAX_FILENAME_SIZE];
int count, writeLength, dataLength;
FILE *stream;
bzero(buff,BUFFER_SIZE);
count = recv(socketFd, buff, BUFFER_SIZE,
0);
if(count <
0)
{
perror(
"获取文件名失败...\n");
exit(
1);
}
strncpy(filename, buff,
strlen(buff) > MAX_FILENAME_SIZE ? MAX_FILENAME_SIZE :
strlen(buff));
printf(
"Preparing download file : %s", filename);
if((stream = fopen(filename,
"wb+")) == NULL)
{
perror(
"create file %s error...\n");
perror(
"创建文件失败...\n");
exit(
1);
}
bzero(buff, BUFFER_SIZE);
dataLength =
0;
while((dataLength = recv(socketFd, buff, BUFFER_SIZE,
0)) !=
0)
{
if(dataLength <
0)
{
perror(
"download error...\n");
perror(
"下载文件失败...\n");
exit(
1);
}
writeLength = fwrite(buff,
sizeof(
char), dataLength, stream);
if(writeLength < dataLength)
{
perror(
"file write error...\n");
perror(
"写入文件失败...\n");
exit(
1);
}
bzero(buff, BUFFER_SIZE);
}
printf(
"下载来自服务器%s的文件成功\n", filename);
printf(
"Receieved file:%s finished!\n", filename);
fclose(stream);
}
int main(
int argc,
char *argv[])
{
char serverIp[IP_SIZE];
if(argc >=
2)
{
printf(
"You have given to much parameters...\n");
printf(
"Yous should give the IP address after %s\n without any other parametes...\n", (
char *)argv[
0]);
}
else if(argc ==
1)
{
strcpy(serverIp,
"127.0.0.1");
}
else
{
strcpy(serverIp, argv[
1]);
}
struct sockaddr_in serverAddr;
int socketFd;
bzero(&serverAddr,
sizeof(serverAddr));
serverAddr.sin_family = AF_INET;
serverAddr.sin_addr.s_addr = inet_addr(serverIp);
serverAddr.sin_port = htons(TCP_SERVER_PORT);
socketFd = socket(AF_INET, SOCK_STREAM,
0);
if(socketFd <
0)
{
printf(
"socket error\n");
exit(-
1);
}
if(connect(socketFd, (
struct sockaddr*)&serverAddr,
sizeof(serverAddr)) <
0)
{
printf(
"Can Not Connect To %s\n", serverIp);
exit(
1);
}
else
{
printf(
"connect to the server %s SUCCESS...\n", serverIp);
printf(
"连接服务器成功...\n");
}
TcpClientPushFile(socketFd,
"./cdata/push");
close(socketFd);
}
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由于TCP和UDP在实现流程上有很多异曲同工之处，因此我们后面的拓展优化将主要针对TCP套接字程序，我们在下一篇开始UDP的套接字编程详解，理解了TCP不同的实现思想之后稍加修改即可。。。。
运行情况
