跨平臺(Windows+Linux)的Socket通訊程式(一)—底層封裝
【摘要】編寫Socket通訊程式是一個老話題。本文重點介紹Windows平臺和Linux平臺Socket通訊的不同,採用C++,編制了一個簡單的跨平臺的Socket通訊庫。
一、Socket通訊的基礎知識
Socket通訊是兩個計算機之間最基本的通訊方法,有TCP和UDP兩種協議。關於這兩種協議的區別,不少文章已有詳述,這裡,稍微總結一下:
1.TCP是面向連線的,是“流”式的,意即通訊兩端建立了一個“數碼流管”,該流無頭無尾,接收端保證接收順序,但不保證包的分割。
2.UDP是面向無連線的,是“包”式的,意即通訊兩端自由傳送資料包,接收端不保證接收順序,但保證包的分割與傳送端一致。
正是基於上述二者的不同,在程式設計上,它們的區別如下:對TCP連線,伺服器端過程(bind->listen->accept->send/receive)與客戶端不相同(connect->send/receive),對UDP連線,二者似乎更對等一些(伺服器端僅需要bind)。
二、socket在windows下和linux下的區別
一些文章也已涉及,這裡,也是綜合一下,並加上自己的理解。
專案 | Windows | Linux |
主要標頭檔案 | winsock.h/winsock2.h | sys/socket.h fcntl.h errno.h |
連結庫 | ws2_32.dll/lib | 連線是使用引數:-lstdc 執行時需要libstdc++.so.5,可在/usr/lib目錄中建立一個連結。 |
初始化及退出 | 初始化需要呼叫WSAStartup,退出需呼叫WSACleanup | 無 |
關閉Socket | closesocket | 與檔案操作相同close |
Socket型別 | SOCKET | 與檔案控制代碼相同int |
錯誤檢視 | WSAGetLastError | 全域性變數errno |
設定非阻塞模式 | int i=1 ioctlsocket(sockethandle,FIONBIO,&i) |
fcntl(ockethandle,F_SETFL, O_NONBLOCK) |
send/recv函式最後一個引數 | 一般設定為0 | 可以有多種組合:MSG_NOSIGNAL,MSG_DONTWAIT,MSG_WAITALL |
send的異常 | 當連線斷開,還發資料的時候,不僅send()的返回值會有反映,而且還會像系統傳送一個異常訊息,如果不作處理,程式會退 出。為此,send()函式的最後一個引數可以設定MSG_NOSIGNAL,禁止send()函式向系統傳送異常訊息。 | |
WSA巨集 | 除了可以使用標準的socket函式外,微軟自己有許多以WSA開始的函式,作為對標準socket函式的封裝(可能微軟感覺這些函式更好用一些吧) |
三、跨平臺的Socket輔助程式
以下給出原始碼。
sock_wrap.h程式碼如下,其中用到了platform.h,定義_WIN32_PLATFROM_和_LINUX_PLATFROM_兩個巨集。
#ifndef _SOCK_WRAP_H_
#define _SOCK_WRAP_H_
#include "platform.h"
#if defined(_WIN32_PLATFROM_)
#include <winsock2.h>
typedef SOCKET HSocket;
#endif
#if defined(_LINUX_PLATFORM_)
#include <netinet/in.h>
#include <sys/socket.h>
#include <sys/types.h>
typedef int HSocket;
#define SOCKET_ERROR (-1)
#define INVALID_SOCKET 0
#endif
typedef struct
{
int block;
int sendbuffersize;
int recvbuffersize;
int lingertimeout;
int recvtimeout;
int sendtimeout;
} socketoption_t;
typedef struct
{
int nbytes;
int nresult;
} transresult_t;
int InitializeSocketEnvironment();
void FreeSocketEnvironment();
void GetAddressFrom(sockaddr_in *addr, const char *ip, int port);
void GetIpAddress(char *ip, sockaddr_in *addr);
bool IsValidSocketHandle(HSocket handle);
int GetLastSocketError();
HSocket SocketOpen(int tcpudp);
void SocketClose(HSocket &handle);
int SocketBlock(HSocket hs, bool bblock);
int SocketTimeOut(HSocket hs, int recvtimeout, int sendtimeout, int lingertimeout);
int SocketBind(HSocket hs, sockaddr_in *addr);
HSocket SocketAccept(HSocket hs, sockaddr_in *addr);
int SocketListen(HSocket hs, int maxconn);
void SocketSend(HSocket hs, const char *ptr, int nbytes, transresult_t &rt);
void SocketRecv(HSocket hs, char *ptr, int nbytes, transresult_t &rt);
void SocketTryRecv(HSocket hs, char *ptr, int nbytes, int milliseconds, transresult_t &rt);
void SocketTrySend(HSocket hs, const char *ptr, int nbytes, int milliseconds, transresult_t &rt);
void SocketClearRecvBuffer(HSocket hs);
class CSockWrap
{
public:
CSockWrap(int tcpudp);
~CSockWrap();
void SetAddress(const char *ip, int port);
void SetAddress(sockaddr_in *addr);
int SetTimeOut(int recvtimeout, int sendtimeout, int lingertimeout);
int SetBufferSize(int recvbuffersize, int sendbuffersize);
int SetBlock(bool bblock);
HSocket GetHandle () { return m_hSocket;}
void Reopen(bool bForceClose);
void Close();
transresult_t Send(void *ptr, int nbytes);
transresult_t Recv(void *ptr, int nbytes );
transresult_t TrySend(void *ptr, int nbytes, int milliseconds);
transresult_t TryRecv(void *ptr, int nbytes, int milliseconds );
void ClearRecvBuffer();
protected:
HSocket m_hSocket;
sockaddr_in m_stAddr;
int m_tcpudp;
};
#endif
sock_wrap.cpp程式碼如下,其中引用了lightThread.h和spantime.h,它們的程式碼見“”。#include "platform.h"
#include <stdio.h>
#include <string.h>
#include <fcntl.h>
#include "lightthread.h"
#include "sock_wrap.h"
#include "TimeSpan.h"
#define INVALIDSOCKHANDLE INVALID_SOCKET
#if defined(_WIN32_PLATFROM_)
#include <windows.h>
#define ISSOCKHANDLE(x) (x!=INVALID_SOCKET)
#define BLOCKREADWRITE 0
#define NONBLOCKREADWRITE 0
#define SENDNOSIGNAL 0
#define ETRYAGAIN(x) (x==WSAEWOULDBLOCK||x==WSAETIMEDOUT)
#define gxsprintf sprintf_s
#endif
#if defined(_LINUX_PLATFORM_)
#include <stdlib.h>
#include <errno.h>
#include <unistd.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#define ISSOCKHANDLE(x) (x>0)
#define BLOCKREADWRITE MSG_WAITALL
#define NONBLOCKREADWRITE MSG_DONTWAIT
#define SENDNOSIGNAL MSG_NOSIGNAL
#define ETRYAGAIN(x) (x==EAGAIN||x==EWOULDBLOCK)
#define gxsprintf snprintf
#endif
void GetAddressFrom(sockaddr_in *addr, const char *ip, int port)
{
memset(addr, 0, sizeof(sockaddr_in));
addr->sin_family = AF_INET; /*地址型別為AF_INET*/
if(ip)
{
addr->sin_addr.s_addr = inet_addr(ip);
}
else
{
/*網路地址為INADDR_ANY,這個巨集表示本地的任意IP地址,因為伺服器可能有多個網絡卡,每個網絡卡也可能繫結多個IP地址,
這樣設定可以在所有的IP地址上監聽,直到與某個客戶端建立了連線時才確定下來到底用哪個IP地址*/
addr->sin_addr.s_addr = htonl(INADDR_ANY);
}
addr->sin_port = htons(port); /*埠號*/
}
void GetIpAddress(char *ip, sockaddr_in *addr)
{
unsigned char *p =(unsigned char *)( &(addr->sin_addr));
gxsprintf(ip, 17, "%u.%u.%u.%u", *p,*(p+1), *(p+2), *(p+3) );
}
int GetLastSocketError()
{
#if defined(_WIN32_PLATFROM_)
return WSAGetLastError();
#endif
#if defined(_LINUX_PLATFORM_)
return errno;
#endif
}
bool IsValidSocketHandle(HSocket handle)
{
return ISSOCKHANDLE(handle);
}
void SocketClose(HSocket &handle)
{
if(ISSOCKHANDLE(handle))
{
#if defined(_WIN32_PLATFROM_)
closesocket(handle);
#endif
#if defined(_LINUX_PLATFORM_)
close(handle);
#endif
handle = INVALIDSOCKHANDLE;
}
}
HSocket SocketOpen(int tcpudp)
{
int protocol = 0;
HSocket hs;
#if defined(_WIN32_PLATFROM_)
if(tcpudp== SOCK_STREAM) protocol=IPPROTO_TCP;
else if (tcpudp== SOCK_DGRAM) protocol = IPPROTO_UDP;
#endif
hs = socket(AF_INET, tcpudp, protocol);
return hs;
}
int SocketBind(HSocket hs, sockaddr_in *paddr)
{
return bind(hs, (struct sockaddr *)paddr, sizeof(sockaddr_in));
}
int SocketListen(HSocket hs, int maxconn)
{
return listen(hs,maxconn);
}
HSocket SocketAccept(HSocket hs, sockaddr_in *paddr)
{
#if defined(_WIN32_PLATFROM_)
int cliaddr_len = sizeof(sockaddr_in);
#endif
#if defined(_LINUX_PLATFORM_)
socklen_t cliaddr_len = sizeof(sockaddr_in);
#endif
return accept(hs, (struct sockaddr *)paddr, &cliaddr_len);
}
//
// if timeout occurs, nbytes=-1, nresult=1
// if socket error, nbyte=-1, nresult=-1
// if the other side has disconnected in either block mode or nonblock mode, nbytes=0, nresult=-1
// otherwise nbytes= the count of bytes sent , nresult=0
void SocketSend(HSocket hs, const char *ptr, int nbytes, transresult_t &rt)
{
rt.nbytes = 0;
rt.nresult = 0;
if(!ptr|| nbytes<1) return;
//Linux: flag can be MSG_DONTWAIT, MSG_WAITALL, 使用MSG_WAITALL的時候, socket 必須是處於阻塞模式下,否則WAITALL不能起作用
rt.nbytes = send(hs, ptr, nbytes, BLOCKREADWRITE|SENDNOSIGNAL);
if(rt.nbytes>0)
{
rt.nresult = (rt.nbytes == nbytes)?0:1;
}
else if(rt.nbytes==0)
{
rt.nresult=-1;
}
else
{
rt.nresult = GetLastSocketError();
rt.nresult = ETRYAGAIN(rt.nresult)? 1:-1;
}
}
// if timeout occurs, nbytes=-1, nresult=1
// if socket error, nbyte=-1, nresult=-1
// if the other side has disconnected in either block mode or nonblock mode, nbytes=0, nresult=-1
void SocketRecv(HSocket hs, char *ptr, int nbytes, transresult_t &rt)
{
rt.nbytes = 0;
rt.nresult = 0;
if(!ptr|| nbytes<1) return;
rt.nbytes = recv(hs, ptr, nbytes, BLOCKREADWRITE);
if(rt.nbytes>0)
{
return;
}
else if(rt.nbytes==0)
{
rt.nresult=-1;
}
else
{
rt.nresult = GetLastSocketError();
rt.nresult = ETRYAGAIN(rt.nresult)? 1:-1;
}
}
// nbytes= the count of bytes sent
// if timeout occurs, nresult=1
// if socket error, nresult=-1,
// if the other side has disconnected in either block mode or nonblock mode, nresult=-2
void SocketTrySend(HSocket hs, const char *ptr, int nbytes, int milliseconds, transresult_t &rt)
{
rt.nbytes = 0;
rt.nresult = 0;
if(!ptr|| nbytes<1) return;
int n;
CMyTimeSpan start;
while(1)
{
n = send(hs, ptr+rt.nbytes, nbytes, NONBLOCKREADWRITE|SENDNOSIGNAL);
if(n>0)
{
rt.nbytes += n;
nbytes -= n;
if(rt.nbytes >= nbytes) { rt.nresult = 0; break; }
}
else if( n==0)
{
rt.nresult= -2;
break;
}
else
{
n = GetLastSocketError();
if(ETRYAGAIN(n))
{
CLightThread::DiscardTimeSlice();
}
else
{
rt.nresult = -1;
break;
}
}
if(start.GetSpaninMilliseconds()>milliseconds) { rt.nresult= 1; break;}
}
}
// if timeout occurs, nbytes=-1, nresult=1
// if socket error, nbyte=-1, nresult=-1
// if the other side has disconnected in either block mode or nonblock mode, nbytes=0, nresult=-1
void SocketTryRecv(HSocket hs, char *ptr, int nbytes, int milliseconds, transresult_t &rt)
{
rt.nbytes = 0;
rt.nresult = 0;
if(!ptr|| nbytes<1) return;
if(milliseconds>2)
{
CMyTimeSpan start;
while(1)
{
rt.nbytes = recv(hs, ptr, nbytes, NONBLOCKREADWRITE);
if(rt.nbytes>0)
{
break;
}
else if(rt.nbytes==0)
{
rt.nresult = -1;
break;
}
else
{
rt.nresult = GetLastSocketError();
if( ETRYAGAIN(rt.nresult))
{
if(start.GetSpaninMilliseconds()>milliseconds) { rt.nresult= 1; break;}
CLightThread::DiscardTimeSlice();
}
else
{
rt.nresult = -1;
break;
}
}
}
}
else
{
SocketRecv(hs, ptr, nbytes, rt);
}
}
void SocketClearRecvBuffer(HSocket hs)
{
#if defined(_WIN32_PLATFROM_)
struct timeval tmOut;
tmOut.tv_sec = 0;
tmOut.tv_usec = 0;
fd_set fds;
FD_ZERO(&fds);
FD_SET(hs, &fds);
int nRet = 1;
char tmp[100];
int rt;
while(nRet>0)
{
nRet= select(FD_SETSIZE, &fds, NULL, NULL, &tmOut);
if(nRet>0)
{
nRet = recv(hs, tmp, 100,0);
}
}
#endif
#if defined(_LINUX_PLATFORM_)
char tmp[100];
while(recv(hs, tmp, 100, NONBLOCKREADWRITE)> 0);
#endif
}
int SocketBlock(HSocket hs, bool bblock)
{
unsigned long mode;
if( ISSOCKHANDLE(hs))
{
#if defined(_WIN32_PLATFROM_)
mode = bblock?0:1;
return ioctlsocket(hs,FIONBIO,&mode);
#endif
#if defined(_LINUX_PLATFORM_)
mode = fcntl(hs, F_GETFL, 0); //獲取檔案的flags值。
//設定成阻塞模式 非阻塞模式
return bblock?fcntl(hs,F_SETFL, mode&~O_NONBLOCK): fcntl(hs, F_SETFL, mode | O_NONBLOCK);
#endif
}
return -1;
}
int SocketTimeOut(HSocket hs, int recvtimeout, int sendtimeout, int lingertimeout) //in milliseconds
{
int rt=-1;
if (ISSOCKHANDLE(hs) )
{
rt=0;
#if defined(_WIN32_PLATFROM_)
if(lingertimeout>-1)
{
struct linger lin;
lin.l_onoff = lingertimeout;
lin.l_linger = lingertimeout ;
rt = setsockopt(hs,SOL_SOCKET,SO_DONTLINGER,(const char*)&lin,sizeof(linger)) == 0 ? 0:0x1;
}
if(recvtimeout>0 && rt == 0)
{
rt = rt | (setsockopt(hs,SOL_SOCKET,SO_RCVTIMEO,(char *)&recvtimeout,sizeof(int))==0?0:0x2);
}
if(sendtimeout>0 && rt == 0)
{
rt = rt | (setsockopt(hs,SOL_SOCKET, SO_SNDTIMEO, (char *)&sendtimeout,sizeof(int))==0?0:0x4);
}
#endif
#if defined(_LINUX_PLATFORM_)
struct timeval timeout;
if(lingertimeout>-1)
{
struct linger lin;
lin.l_onoff = lingertimeout>0?1:0;
lin.l_linger = lingertimeout/1000 ;
rt = setsockopt(hs,SOL_SOCKET,SO_LINGER,(const char*)&lin,sizeof(linger)) == 0 ? 0:0x1;
}
if(recvtimeout>0 && rt == 0)
{
timeout.tv_sec = recvtimeout/1000;
timeout.tv_usec = (recvtimeout % 1000)*1000;
rt = rt | (setsockopt(hs,SOL_SOCKET,SO_RCVTIMEO,&timeout,sizeof(timeout))==0?0:0x2);
}
if(sendtimeout>0 && rt == 0)
{
timeout.tv_sec = sendtimeout/1000;
timeout.tv_usec = (sendtimeout % 1000)*1000;
rt = rt | (setsockopt(hs,SOL_SOCKET, SO_SNDTIMEO, &timeout,sizeof(timeout))==0?0:0x4);
}
#endif
}
return rt;
}
int InitializeSocketEnvironment()
{
#if defined(_WIN32_PLATFROM_)
WSADATA Ws;
//Init Windows Socket
if ( WSAStartup(MAKEWORD(2,2), &Ws) != 0 )
{
return -1;
}
#endif
return 0;
}
void FreeSocketEnvironment()
{
#if defined(_WIN32_PLATFROM_)
WSACleanup();
#endif
}
//==============================================================================================================
//================================================================================================================
CSockWrap::CSockWrap(int tcpudp)
{
memset(&m_stAddr, 0, sizeof(sockaddr_in));
m_tcpudp = tcpudp;
m_hSocket = INVALIDSOCKHANDLE;
Reopen(false);
}
CSockWrap::~CSockWrap()
{
SocketClose(m_hSocket);
}
void CSockWrap::Reopen(bool bForceClose)
{
if (ISSOCKHANDLE(m_hSocket) && bForceClose) SocketClose(m_hSocket);
if (!ISSOCKHANDLE(m_hSocket) )
{
m_hSocket=SocketOpen(m_tcpudp);
}
}
void CSockWrap::SetAddress(const char *ip, int port)
{
GetAddressFrom(&m_stAddr, ip, port);
}
void CSockWrap::SetAddress(sockaddr_in *addr)
{
memcpy(&m_stAddr, addr, sizeof(sockaddr_in));
}
int CSockWrap::SetTimeOut(int recvtimeout, int sendtimeout, int lingertimeout) //in milliseconds
{
return SocketTimeOut(m_hSocket, recvtimeout, sendtimeout, lingertimeout);
}
int CSockWrap::SetBufferSize(int recvbuffersize, int sendbuffersize) //in bytes
{
int rt=-1;
if (ISSOCKHANDLE(m_hSocket) )
{
#if defined(_WIN32_PLATFROM_)
if(recvbuffersize>-1)
{
rt = setsockopt( m_hSocket, SOL_SOCKET, SO_RCVBUF, ( const char* )&recvbuffersize, sizeof( int ) );
}
if(sendbuffersize>-1)
{
rt = rt | (setsockopt(m_hSocket,SOL_SOCKET,SO_SNDBUF,(char *)&sendbuffersize,sizeof(int))==0?0:0x2);
}
#endif
}
return rt;
}
int CSockWrap::SetBlock(bool bblock)
{
return SocketBlock(m_hSocket, bblock);
}
transresult_t CSockWrap::Send(void *ptr, int nbytes)
{
transresult_t rt;
SocketSend(m_hSocket, (const char *)ptr, nbytes,rt);
return rt;
}
transresult_t CSockWrap::Recv(void *ptr, int nbytes )
{
transresult_t rt;
SocketRecv(m_hSocket, (char *)ptr, nbytes,rt);
return rt;
}
transresult_t CSockWrap::TrySend(void *ptr, int nbytes, int milliseconds)
{
transresult_t rt;
SocketTrySend(m_hSocket, (const char *)ptr, nbytes,milliseconds, rt);
return rt;
}
transresult_t CSockWrap::TryRecv(void *ptr, int nbytes, int milliseconds )
{
transresult_t rt;
SocketTryRecv(m_hSocket, (char *)ptr, nbytes,milliseconds, rt);
return rt;
}
void CSockWrap::ClearRecvBuffer()
{
SocketClearRecvBuffer(m_hSocket);
}
上面的輔助程式實際上包含了對一些常用的socket函式的封裝和一個類CSockWrap,如果需要自己組建通訊邏輯,可以直接用這些C風格的函式,CSockWrap實際上就是這樣一個應用。傳送和接收函式的返回值有點複雜,是一個結構體transresult_t,本文的意思是,如果發生接收/傳送錯誤,直接從函式的返回值大致判斷下一步的動作。
四、關於Socket通訊過程的一些討論1.關於send函式。Socket中Send函式的意思是隻要將應用程式的資料傳送到網絡卡中就算成功,將傳送端的網線拔掉與將接收端的網線拔掉,Send函式的返回可能不同,因此它的正常返回不能作為接收方是否收到的判斷條件。如果需要確保對方收到資訊,只能採用應答式,但這樣做可能會降低雙方的通訊效率。一般情況下,Send不會阻塞,除非網絡卡的傳送緩衝區已經滿了(傳送端直接掉線)。
2.關於recv函式。Recv是最常用的阻塞函式,但通常情況下,應設定其為非阻塞(windows將整個Socket連線都設為非阻塞,linux可以有兩種方式),因為,如果傳送方已經掉線,或者還需要幹別的事情,讓Recv阻塞顯然是不合適的。當然,也可以不用Recv,而用非阻塞的Select函式(本文沒有涉及Select函式),其實它們的效果是一樣的。
3.關於從send和recv函式的返回值來初步判斷網路狀態,見SocketSend等函式的註釋。
4.採用UDP通訊時,資料包的內容不宜過大,所以UDP特別適合於命令的傳輸(一次的通訊量小,但可能頻繁)。
5.SocketClearRecvBuffer函式一般用於TCP連線,當接收方發覺由”丟包“時,作為”對齊“資訊包之用。