北邮国际学院互联网应用cousework.docx

北邮国际学院互联网应用cousework.docx

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北邮国际学院互联网应用cousework

Pop3

Thepop3client-sideprogramisintendtofulfilthefollowingthreemaintasks:

1.Resolvethepop3serverdomainnameandconvertitintoIPaddresstoestablishaTCPconnectionbetweentheclientandtheserver.

2.GuidetheuserlogintheE-mail.

3.ProvidecommonfunctionsofE-mailfortheuser,includinggetthenumberandlistoftheE-mails,displaythecontentofmails,deletethemails,searchtextinmailsanddisplaythemailsbysubject.

Specificallyspeaking,thelog-inprocess'srequirements:

Afterestablishingtheconnectionwiththeserversuccessfully,requireusernameandpasswordfromtheuserandcheckwhethertheyarevalid.

Thefivecommonfunctions'requirementsare:

1.GetthenumberandlistoftheE-mails

Whenuserentersthecorrespondingcommand,theprogramcandisplaythenumberorthelistoftheE-mailsorderlyonscreen.

2.Displaythecontentofmails

Allowuserstochoosethemailtheywanttocheckbyprovidingtwochoices---downloadandprintitonscreen.

3.Deletethemails

Allowuserstochoosethemailtheywanttodeleteanddeleteitfromthemailbox.

4.searchtextinmails

Whenuserentersthetextstheywanttosearch,theprogramwilldisplaythefilenamesofthefilescontainit.

5.Displaythemailsbysubject

DisplaytheE-mailbysubject,meaningfileswiththesamesubjectswillbegroupedtogether.

Therefore,Idecomposethewholeprogramintothreepartsbywritingtwootherfunctionsapartfrommain（）--voidlogOn（）andvoidlogged（）.Thefirsttaskisimplementedinmain（）bycallingthefunctionintgetIP（）;thesecondtaskisimplementedinthefunctionvoidlogged（）;thelastoneisimplementedinthefunctionvoidlogOn（）.SincetherearetoomanyfunctionsneedtobeachievedinthelogOn（）,fiveotherfunctionsarecalledinit,theyare:

intprintMail（）;intchkEnd（int）;intmakeChoice（char*）;voidsrch（）;voidsortSub（）.

Thus,thewholeprogramisdecomposedinto10modules（10functions）asshowninthebelowchart:

intmain（）:

themainfunctioniswhereaprogramstartsexecution;itcallsthreefunctionsinit:

intgetIP（）,voidlogOn（）andvoidlogged（）.

intgetIP（char[]）:

itisusedtoconvertthereceivedpop3serverdomainnametoIPaddress.Whencalledinmain（）function,anargumentinchar[]typewillbepassedtoitandthenconvertedtoIPaddressindotteddecimalnotation.

voidlogOn（）:

itiscalledinfunctionmain（）andusedforguidingtheuserlogontoE-mail.Thefunctionintmygetch（）iscalledinittogeteachenteredcharacterimplicitly.

voidlogged（）:

itiscalledinfunctionmain（）toprovide7commonfunctionsofE-mailstotheuser.

intmygetch（）:

itiscalledinfunctionvoidlogOn（）tomaketheenteredcharacterfromtheuserinvisible.

intprintMail（）:

itiscalledinfunctionvoidlogged（）toprintanddownloadtheE-mail.FunctionintchkEnd（int）iscalledbyittochecktheendofthemessage.

intchkEnd（int）:

itisusedtocheckwetherthereceivedmessagefromtheserverhasreachedtotheend.WhencalledinthefunctionintprintMail（）,thelengthofthereceivedininttypeispassedtoit.Itwillthenreturn0or1toindicatewhetheritistheendofthemail.

intmakeChoice（char*a）:

itisusedtocheckwhichcommanddoestheuserinput.Whencalledinthefunctionlogged（）,theuser'scommandinchar*typeispassedtoit.Then,itreturnthecorrespondingintegerininttype.

voidsrch（）:

itiscalledbythefunctionlogged（）toaccomplishthe"searchbytext"task.

voidsortSub（）:

itiscalledbythefunctionlogged（）toaccomplishthe"displaybysubject"task.

Overallflowchart

Designofdatastructure

Intheprogram,thereareelevenglobalvaribles:

FILE_MODE0644

----Definethemodeofopeningafile.

PORT110

----PortnumberfortheTCPconnection.

char*IP

----holdtheserver'sIPaddress.

msg[250]

----holdthereceived

comd[2][200]={"USER","PASS"},

command[5][200]={"STAT\n","LIST\n","RETR","DELE""QUIT\n"},

mail[250];

intrecvMsgSize,sock,qt=0,dl=0;

intmain（）:

First,Iuseawhileloop,inwhichtheIPresolveandlogontasksareimplemented.Aglobalvaribleipininttypeisusedtocontroltheloop.Itissetto0atthebeginning.WhenthefunctionintgetIP（）successfullyconvertthereceivedpop3serverdomainnameintotheIPaddress,itwillreturn1tothevaribleip,theipwillbesetto1sothatthewhileloopcanbeended.Then,iftheexpressionstrstr（msg,"+OK"）!

=NULListrue,thefunctionvoidlogOn（）andvoidlogged（）willbecalledconsequentlytofinishtheothertwotasks,ifitisfalse,thesocketwillbeclosedandtheprogramwillbeended.

intprintMail（）;

Itiscalledinfunctionvoidlogged（）toprintanddownloadtheE-mail.Astheflowchartshows,theprogramfirstprovidetwochoicesfortheuser----1and2.Iftheuserenter1,afilenameisrequiredfromtheuserinordertocreateafileholdingthemail.Ifthechoiceis2,themailwillbeprintedoutonthescreen.Toreceivethemailproperly,awhileloopisusedwhichiscontrolledbythevariableiininttype.Itissettozeroatthebeginning.Then250charactersarereceivedintheglobalvariablecharmail[250]eachtime,ifthelengthofmailislessthan250,thefunctionintchkEnd（）iscalledtocheckwetheritreachestheendofthemail.Ifitistheend,thefunctionwillreturn1,whichisgiventoitoendthewhileloop.

intmakeChoice（char*a）;

Itisusedtocheckwhichcommanddoestheuserinput.Whencalledinthefunctionlogged（）,theuser'scommandinchar*typeispassedtoit.Then,itreturnthecorrespondingintegerininttype.Astheflowchartshows,whentheuser'scommandis"stat","ls","find"or"sort",thevariableintchoicewillbesetto0,1,5and6orderly.Whenthecommandis"get"or"dele",theprogramwillrequiretheusertoenterthenumberofthemailtheywanttogetordelete,thensetchoiceto2and3correspondingly.Iftheenteredcommandis"quit",theglobalvariableqtissetto1andthechoiceissetto4.Ifthecommandisnotmatchtoallthecommandmentionedabove,thechoiceissetto7.Atlast,returnchoice.

voidlogOn（）

Itiscalledinfunctionmain（）andusedforguidingtheuserlogontotheE-mail.Thefunctionintmygetch（）iscalledinittogeteachcharacterimplicitly.

Astheflowchartshows,awhileloopisusedtoallowtheuserentertheusernameandpasswordrepeatedly.Itfirstrequireausernamefromtheuser.Thengenerateandsendthepop3commandout.Ifthestrstr（msg,"+OK"）!

=NULL,thenrequiretheuserenterthepassword.Tomakethepasswordenteredimplicitly,thefunctionintmygetch（）iscalledinaforloop.Ifthereceivedcharacteris'\n',theforloopisendedifnotprint'*'.Then,sendthepasswordinpop3style,ifthestrstr（msg,"+OK"）!

=NULL,printoutthereceivedmessageandstepoutthewhileloop.

voidlogged（）:

Itiscalledinfunctionmain（）toprovide7commonfunctionsoftheE-mailtotheuser.Awhileloopisusedinittoallowtheuserrepeatingchoosethecommand.Theglobalvariableqtininttypeisusedtocontrolthewhileloop.Itissetto0atthebeginning.Intheloop,theprogramfirstprovidesomeinformationsabouthowtochoosedifferentcommandstorealizedifferentfunctions.Then,itcallsthefunctionmakeChoice（）bypassingthestringgotfromuser'stoit,thereturnvalueofthefunctionisgiventoainttypevariablen.Accordingtothevalueofn,correspondingpop3commandissentoutandcorrespondingfunctionsarecalled.Thewhileloopwillcontinuetorununlesstheenteredcommandfromtheuseris"quit".BecausewhenthestringpassedinthefunctionintmakeChoice（）is"quit",theglobalvariableqtwillbesetto1sothatthewhileloopcanbeended.

sortSub（）

itiscalledbythefunctionlogged（）toaccomplishthe"displaybysubject"task.Thisfunctioniswrittenontheconditionthatthefilenameareallnumberssothataforloopcanbeadoptedtoopeneachofthemtosorttheirsubjects.Anarrayofstrings--chars[7][100]isdefinedtoholdthesubjectofeachfileinordertosortthesubjectsinthesecondforloop.AvariablefsinFILE*typeisdefinedtosetupafilesteam.Inthefirstforloop,Ididin'tsetaconditiontocontroltheloopsothatitcancontinuerunninguntilafailureofopenningthefileaccurs.Eachtimeintheloop,Iusethefunctionsnprintftoconvertthevariablenininttypetoastringstoredinvariablejandopenthefilenamed"m".IfthefsisNULL,breaktostepoutofthelooptodothesecondforloop.Ifnot,enterawhileloop,inwhichIusefgetstoreadalineinthefileeachtime.Ifthefirstcharacterinthelineis'S',gettheremainingpartafterthestring''Subject"byusingthestrtokfunctionandcopyittos[i].Thenclosethefilesteamandbreakthewhileloop.Inthesecondforloop,Iusebubblesortmethodtosortthesubjectsandprintthemout.Tocomparethesubjects,thefunctionstrcmpisused.

voidsrch（）

Thisfunctioniswrittenontheconditionthatthefilenameareallnumbers.First,theprogrampromptamessagetoasktheuserenterthetexttheywantsearchandsavethetextintothevariablecontentinchar[]type.Then,aforloopisadoptedtoopeneachfiletofindthetext.Intheloop,Ifirstusefunctionsnprintf（j,2,"%ld",i）toconvertthevariableiinunsignedlongtypetojinchar[]type.Thenopenthefilenamedj,ifthefilecannotopen,print"Done!

"andbreaktheloop,ifnot,readthefileintothevariablebufinchar[].Usethefunctionstrstrtofindthetextinthebuf.Iftheexpression--strstr（buf,content）==NULListrue,print"jisnone"wherejisthefilena