是服务器端套接字并不定位具体的客户端套接字而是处文档格式.docx

是服务器端套接字并不定位具体的客户端套接字而是处文档格式.docx

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serveracceptstheconnection,adialogcanbeginwithbetweentheclientandtheserver. 

Oncetheclientisdonewithwhateveritneedstodoitcanclosetheconnectionwiththeserver.Connectionsareexpensiveinthesensethatserversallowfiniteconnectionstooccur. 

Duringthetimeclienthasanactiveconnectionitcansendthedatatotheserverand/orreceivethedata.

Thecomplexitybeginshere.Wheneitherside（clientorserver）sendsdatatheothersideissupposedtoreadthedata.Buthowwilltheothersideknowwhendatahasarrived.Therearetwooptions-eithertheapplicationneedstopollforthedataatregularintervalsorthereneedstobesomesortofmechanismthatwouldenableapplicationtogetnotificationsandapplicationcanreadthedataatthattime.Well,afterallWindowsisaneventdrivensystemandthenotificationsystemseemsanobviousandbestchoiceanditinfactis. 

AsIsaidthetwoapplicationsthatneedtocommunicatewitheachother 

needtomakeaconnectionfirst.Inorderforthetwoapplicationtomakeconnectionsthetwoapplicationsneedtoidentifyeachother（oreachother'

scomputer）.Computersonnetworkhaveauniqueidentifiercalled 

I.P.addresswhichisrepresentedindot-notationlike10.20.120.127etc.Letsseehowallthisworksin.NET.

System.Net.SocketsNamespace

Beforewegoanyfurther,downloadthesourcecodeattachedwiththisarticle.Extractthezipfiletoafoldersayc:

\Tempyouwillseefollowingtwofolders:

∙Server

∙Client

IntheServerfoldertherewillbeoneEXE.AndintheclienttherewillbethesourcecodeinC#thatisourclient.TherewillbeonefilecalledSocketClient.sln 

whichthesolutionfile.IfyoudoubleclickthatyourVS.NETwillbelaunchedandyouwillseethe 

projectSocketClientProjinthesolution.UnderthisprojectyouwillhaveSocketClientForm.csfile. 

Nowbuildthecode（bypressingCtrl-Shift-B）andrunthecodeyouwillseethefollowingdialogbox:

AsyoucanseethedialogboxhasafieldforHostIPaddress（whichistheIPaddressofthemachineonwhichyouwillruntheServerApplication（locatedunderServerfolder））.AlsothereisafieldwhereyoucanspecifyportnumberatwhichtheServerislistening.TheserverappIhaveprovidedherelistensatport8221.SoIhavespecifiedporttobe8221.

Afterspecifyingtheseparametersweneedtoconnecttotheserver.SopressingConnectwillconnecttotheserverandtoclosetheconnectionpressClose.TosendsomedatatotheservertypesomedatainthefieldnearthebuttonnameTxandifyoupressRxtheapplicationwillblockunlessthereissomedatatoread.

Withthisinfoletsnowtrytocheckthecodebehindthis:

Socketprogrammingin.NETismadepossiblebySocketclasspresentinsidetheSystem.Net.Socketsnamespace. 

Socketclass 

hasseveralmethodandpropertiesandaconstructor.

Thefirststepistocreateanobjectofthisclass.

Sincethereisonlyoneconstructorwehavenochoicebuttouseit.

Hereishowtocreatethesocket:

m_socListener=newSocket（AddressFamily.InterNetwork,SocketType.Stream,ProtocolType.IP）;

ThefirstparameteristheaddressfamilywhichwewilluseinterNetwork-otheroptionsincludeBanyanNetBiosetc. 

AddressFamilyisanenumdefinedinSocketsnamespace.

Nextweneedtospecifysockettype:

andwewouldusereliabletwowayconnection-basedsockets（stream）insteadofun-reliableConnectionlesssockets（datagrams）.SoweobviouslyspecifystreamasthesockettypeandfinallyweareusingTCP/IPsowewouldspecifyprotocoltypeasTcp.

OncewehavecreatedaSocketweneedtomakeaconnectiontotheserversinceweareusingconnection-basedcommunication.

Toconnecttotheremotecomputer 

weneedtoknowtheIPAddressandportatwhichtoconnect. 

In.NETthereisaclassunderSystem.NetnamespacecalledIPEndPointwhichrepresentsanetworkcomputer 

asanIPaddressandaportnumber.

TheIPEndPointhastwo 

constructors-onethattakesaIPAddressandPortnumber 

andonethattakeslongandportnumber.SincewehavecomputerIPaddresswewouldusetheformer

publicIPEndPoint（System.Net.IPAddressaddress,intport）;

AsyoucanseethefirstparametertakesaIPAddressobject.IfyouexaminetheIPAddressclassyouwillseethatithasastaticmethodcalledParsethatreturnsIPAddressgivenastring（ofdotnotation）andsecondparameterwillbetheportnumber.OncewehaveendpointreadywecanuseConnectmethodofSocketclasstoconnecttotheendpoint 

（remoteservercomputer）.

Hereisthecode:

System.Net.IPAddressipAdd=System.Net.IPAddress.Parse（"

10.10.101.200"

）;

System.Net.IPEndPointremoteEP=newIPEndPoint（iAdd,8221）;

m_socClient.Connect（remoteEP）;

ThesethreelinesofcodewillmakeaconnectiontotheremotehostrunningoncomputerwithIP10.10.101.200andlisteningatport8221.IftheServerisrunningandstarted（listening）,theconnectionwillsucceed.IfhowevertheserverisnotrunninganexceptioncalledSocketExceptionwillbethrown.Ifyoucatchthe 

exceptionandchecktheMessagepropertyoftheexceptioninthiscaseyouseefollowingtext:

"

Noconnectioncouldbemadebecausethetargetmachineactivelyrefusedit."

Similarlyifyoualreadyhavemadeaconnectionandtheserversomehowdies,youwillgetfollowingexceptionifyoutrytosenddata.

Anexistingconnectionwasforciblyclosedbytheremotehost"

Assumingthattheconnectionismade,youcansenddatatoothersideusingtheSendmethodoftheSocketclass.

Sendmethodhasseveraloverloads.Allofthemtakeabytearray.Forexampleifyouwanttosend"

HelloThere"

tohostyoucanusefollowingcall:

try

{

StringszData="

;

byte[]byData=System.Text.Encoding.ASCII.GetBytes（szData）;

m_socClient.Send（byData）;

}

catch（SocketExceptionse）

MessageBox.Show（se.Message）;

NotethattheSendmethodisblocking.Whatitmeansthecallwillblocktillthedatahasbeensentoranexceptionhasbeenthrown.Thereisannon-blockingversionofthesendwhichwewilldiscussinthenextpartofthisarticle.

SimilartoSendthereisaReceivemethodontheSocketclass.Youcanreceivedatausingfollowingcall:

byte[]buffer=newbyte[1024];

intiRx=m_socClient.Receive（buffer）;

TheReceivemethodagainisblocking.Itmeansthatifthereisnodataavailablethecallwillblockuntilsomedataarrivesoran 

exception 

isthrown.

Non-blockingversionofReceivemethodismoreusefulthanthenon-blockingversionofSendbecauseifweoptforblockReceive,weareeffectivelydoingpolling.Thereisnoeventsaboutdataarrival.Thismodeldoesnotworkwellforseriousapplications.Butallthatisthesubjectofournextpartofthisarticle.Fornowwewillsettlewiththeblockingversion.

InordertousethesourcecodeandapplicationhereyouwouldneedtoruntheServerfirst:

HereisthewayServerlookslike:

WhenyoulaunchtheServer,clickStarttostartlistening.TheServerlistensatport8221.Somakesureyouspecifytheportnumber8221intheportfieldofourclientapplication.AndintheIPAddressfieldofClientAppentertheIPAddressofthemachineonwhichtheServerisrunning.IfyousendsomedatatoserverfromtheclientbypressingTxbutton,youwillseethatdatainthegrayedouteditbox.

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ThecontentprovidedinthisarticleisnotwarrantedorguaranteedbyDeveloperShed,Inc.Thecontentprovidedisintendedforentertainmentand/oreducationalpurposesinordertointroducetothereaderkeyideas,concepts,and/orproductreviews.Assuchitisincumbentuponthereadertoemployreal-worldtacticsforsecurityandimplementationofbestpractices.Wearenotliableforanynegativeconsequencesthatmayresultfromimplementinganyinformationcoveredinourarticlesortutorials.Ifthisisahardwarereview,itisnotrecommendedtoopenand/ormodifyyourhardware.

Althoughyoucanarguethatonecanovercometheseshortcomingsbymultithreadingmeaningthatonecanspawnanewthreadandletthatthreaddothepollingandnotifiesthemainthreadofthedata.Wellthisconceptwillworkwell.ButevenifyoucreateanewthreaditwouldrequireyourmainthreadtosharetheCPUtimewiththisnewthread.Windowsoperatingsystem（WindowsNT/2000/XP）providewhatiscalledCompletionPortIOmodelfordoingoverlapped（asynchronous）IO.

ThedetailsofIOCompletionportarebeyondthescopeofthecurrentdiscussion,buttomakeitsimpleyoucanthinkofIOCompletionPortsasthemostefficientmechanismfordoingasynchronousIOinWindowsthatisprovidedbytheOperatingsystem.CompletionPortmodelcanbeappliedtoanykindofIOincludingthefileread/writ