networking socket使用方法

Basicsocetprogramming

JensBandener∗(StudentElektro-andInformationstechnology)

May6,2010

Introduction

Thisshortskriptexplainsthebasicimplementationstepsforsocketbasednet-workcommunication.

Socketsareendpointsofbidirectionalinter-processornetworkcommunicationsusinganIPbasednetworkeitherforstreambasedorfordatagrambasedtrans-fers.Thesocketconnectioncanbeusedtotransferdataofanytypebetweenthetwoendpoints.Thesocketinterfaceisprovidedbytheoperatingsystem,whichmanagesthesocketsandtheconnection-information.

AttheEndofthisskriptyoufindaworkingexampleserver/clientapplicationshowingtheneccessarystepsforcommunicationbetweentheserverandtheclient.

∗Jens.Bandener@rub.de

with sequenzing andpacket transferContents

Introduction

2Socketcategories

2.1Communicationmodell........................3Socketprogramming

3.1Creatingsockets.......3.2Connectionestablishment..3.3Bindthesocket........3.4Server-side-listenandaccept3.5Sendingandreceivingdata.

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4Simpleserver-clientapplication

4.1clientside...............................4.2serverside...............................

2Socketcategories

TCPsocketsarestructuresdevelopedasusableinterfacesforimplementingnetworkconnectiontoapplications.Socketsareanindustrialstandardandimplementedinmanyprogramminglanguages.

Generally,aSocketisanfiledescriptorandcanbedevidedintotwomaincategories:(1)streamand(2)datagrammsockets.

Figure1:socketcategories

Thefirstcategory,stream,isusede.g.inTCPconnections.Streambasedsockedsprovidesequenzingandanerrorcorrection.Sequenzingmeans,thatthesocetconnectionguarantees,thateachsegmentofthefileisachievedinthesameorderitwassent.

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processDatagrammbasedsockets,e.g.usedinUDPprotocols,arepackedorientedtransfers.Thisisaconnectionlesstransferinwhichthefileisdividedinpacketsbeforetransfering.Incontrasttothestreamtransfers,thedatagrammbasedtransfershavenoerrorcorrectionorsequenzing.

2.1Communicationmodell

Figure2:socetcommunication

Figure2showsthemainideainthesocketarchitecture.Insteadofprogram-mingthelowlevelnetworkcommunication,youcancreateasocket-connectionbetweentwoprocessesmanagedbytheoperatingsystem.Afterconnectingtwosocketsyoucanuseallstandartfunctionstoe.g.forwardfilesetc.tothesocet.Thesocketmanagestheremainingcommunicationprocess.Thisproceedingisverysimilartotheinterprocess-communicationintheunixsystem.

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3.1

Socketprogramming

Creatingsockets

Socketscanbecreatedusingthesocket()command.Therequiredlibrariesforsocketprogrammingaresys/types.handthesys/socket.hlibrary.

Whencreatinganewsocketyouhavetospecifythefamily,thetypeandthedesiredprotocolforthesocket.

Listing1:creatinganewsocket

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intsocket(intfamily,inttype,intprotocoll)

Thefirstparameterintfamiliyspecifiestheprotocolfamily.ThemostcommonprotocolistheAF_INETfortheTCP/IPcommunicationortheAF_UNIXforthelocalinterprocesscommunicationwithintheunix-system.Anextractofthepossiblefamiliesislistedintable1.

Thesecondparameterspecifiesthesockettype.Typicallyyouchoosebetweenstream-sockets(SOCK_STREAM)anddatagramm-sockets(SOCK_DGRAM).Thereareafewmoretypesforspecialuseswhicharenotannotatedatthispoint.

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adress

AF_UNIX,AF_LOCAL

AF_INETAF_IPX

protocol

PF_UNIX,PF_LOCAL

PF_INETPF_IPX

meaning

localcommunication

IPv4internetcommunication(TCP/IP)

IPX-Novell-protocol

Table1:protocolfamilies,firstparameter

Thethirdandlastparameterallowsyoutochoosetheusedprotocol.Typicallythisparameterissetto0whichmeansthatthedefaultprotocolforthespecifiedsocked-typeisused.

3.2Connectionestablishment

Toconnecttwoprocesseswithalreadyimplementedsocketsyoucanusetheconnect()commandtoestablishtheconnection.

Listing2:connectingasocket

123

intconnect(

intsockfd,

structsockaddr∗addresssocklen_taddress_length);

Youneedtospecifythethreeparametersintheconnect()commandtoestablishtheconnection.Asintheexampleprogrammattheendofthisscript,theclienttypicallyconnectstoaserverapplicationn.Sotheconnect()commandwillbefoundintheclientapplication.

Thefistparametergivesthesocket,whichisusedfortheconnectiontotheserver.Thesecondparameterspecifiesthetheaddresstothedestinationsocket.Thisstructisspecifiedinthenetinet/in.hheaderfile.

Listing3:extractnetinet/in.h

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#include#includestructsockaddr_in{

unsignedshortintsin_family;unsignedshortintsin_port;structin_addrsin_addr;

}

structin_addr{

in_addr_ts_addr;

}...

Tomatchtherequiredtypesintheconnectcall,youneedtocastthesecondparametertostructsockaddr.

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Listing4:connectingasocket

123

structsockaddr_inaddr;

intconnect(socket,(structsockaddr∗)&addr,

sizeof(addr));

Alternativetothecasttothesockaddryoucouldstraightusethestructsockaddr.Theadvantageofthesockaddr_inistheoptiontogivetheaddressandtheportseparatelyinsteadofgivingtheprotocolspecificaddress.

3.3Bindthesocket

Afterconnectingthesocketyouneedto“bind”thesockettoaspecifiedport.Thecallforthebind()functionissimilartotheconnect()function.

Listing5:bindfunction

123

intbind(

intsockfd,

structsockaddr∗addresssocklen_taddress_length);

Incaseofasuccessfulbindthebind()functionreturns0,otherwiseitreturns−1forafailure.

3.4Server-side-listenandaccept

Ontheoppositeside,heretheserverapplication,theserver-socketneedstolistenonthespecifiedportandpossiblyaccepttheincomingconnectionfromtheclientapplications.Typicallyitispossibletohandlemorethenoneincomingconnection.Forthiscasethesocketusesawaitingstacktohandletheincomingconnections.

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intlisten(intsocket,intstack);

Incomingconnectionscanbehandledbytheaccept()command.

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intaccept(

intsocket,

structsockaddr∗address,socklen_t∗address_length);

3.5Sendingandreceivingdata

Tosendorreceivedatayoucanusethecommonstandardfunctions.Whithwrite()youcansenddatatoasocketaswellalsread()receivesdatafromasocket.

Listing6:send/receive

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#include

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2345

ssize_twrite(intsocket,constvoid∗data,

size_tdata_length);

ssize_tread(intsocket,void∗data,

size_tdata_length);Aftertransmissioniscompleted,theclose()commandclosestheconnection.

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#include

intclose(intsocket);

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4.1

Simpleserver-clientapplication

clientside

Thefollowinglistinggivesanexampleforaclientapplicationusingasocketfornetworkcommunication.Theapplicationconnectstoaserverandreceivesamessagefromtheserverside.Thereceivedmessagestringisprintedintheshellbeforetheconnectionisclosedontheclientside.

Listing7:client.c

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#include#include#include#include#include#include#include#include

#defineBUF1024

intmain(intargc,char∗∗argv){

intcreate_socket;

char∗buffer=malloc(BUF);structsockaddr_inaddress;intsize;

if(argc<2){

printf(\"input␣parameter␣incorrect\");exit(EXIT_FAILURE);

}

printf(\"creating␣socket...\");

if((create_socket=socket(AF_INET,

SOCK_STREAM,0))>0)

printf(\"Socket␣created!\\n\");address.sin_family=AF_INET;

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address.sin_port=htons(15000);

inet_aton(argv[1],&address.sin_addr);

if(connect(create_socket,

(structsockaddr∗)&address,sizeof(address))==0)

printf(\"connection␣established␣to␣%s...\",

inet_ntoa(address.sin_addr));

size=recv(create_socket,buffer,

BUF−1,0);

if(size>0)

buffer[size]=’\\0’;

printf(\"\\n␣received:␣%s␣\\n\",buffer);

close(create_socket);returnEXIT_SUCCESS;

}

4.2serverside

Ontheserversideasocketiscreatedandlisteningtoaspecifiedport.Whenaclientconnectstotheserverapplicationamessagestringissendtotheclient.

Listing8:server.c

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#include#include#include#include#include#include#include#include

#defineBUF1024

intmain(void){

intcreate_socket,new_socket;socklen_taddrlen;

char∗buffer=malloc(BUF);ssize_tsize;

structsockaddr_inaddress;constinty=1;

printf(\"creating␣server␣socket...\");if((create_socket=

socket(AF_INET,SOCK_STREAM,0))>0)printf(\"socked␣created!\\n\");

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setsockopt(create_socket,SOL_SOCKET,

SO_REUSEADDR,&y,sizeof(int));address.sin_family=AF_INET;

address.sin_addr.s_addr=INADDR_ANY;address.sin_port=htons(15000);

if(bind(create_socket,

(structsockaddr∗)&address,sizeof(address))!=0){

printf(\"ERROR...␣specified␣port␣in␣use␣\\n\");

}

listen(create_socket,5);

addrlen=sizeof(structsockaddr_in);

while(1){

new_socket=accept(create_socket,

(structsockaddr∗)&address,&addrlen);if(new_socket>0){

printf(\"client␣connected...\\n\");

}

send(new_socket,\"−−>␣server␣message\",

strlen(\"−−>␣server␣message\"),0);

printf(\"message␣send␣to␣client...\\n\");close(new_socket);

}

close(create_socket);return0;

}

Tocompiletheapplicationsyoucanrunthegcccompilerwithoutanyspecialparameters.

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gcc−oserverserver.cgcc−oclientclient.c

Theeasiestwaytotesttheserverclientcommunicationistoopenaownterminalfortheserverandfortheclientseparately.

Theserverapplicationmustbestartedfirst,sothattheporttowichtheclienttriestoconnectislistened.Inthefirstterminalruntheserverapplicationasfollowing:

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./server

creatingserversocket...sockedcreated!

Startingtheclientapplicationrequiresaremoteipaddresstoconnectto.Inthiscasetheserverandtheclientapplicationarerunningonthesamemachinesothatyoucanuse127.0.0.1asremoteip.Insteadofthisipyoucanuseanyotheriprepresentingmachinetheserverapplicationisrunningon.

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./client127.0.0.1

creatingsocket...Socketcreated!

connectionestablishedto127.0.0.1...received:−−>servermessage

Whentheserversendsthemessagetotheclientsideastatusmessageispromtedontheserversideaswell.

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clientconnected...

messagesendtoclient...

Thisexamplecanbeextendedtotransferanyothertypeofdatabetweenthetwosides.

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References

[WolfJ09]JürgenWolfLinux-Unix-Programmierung.

3.aktualisierteunderweiterteAuflageGalileo,2009,pp407-518ISBN-10:3836213664

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