ActionMessageFormatActionMessageFormatAMF3(中文版FixedBywhatwhatwecallhumannatureisactuallyhumanhabitAdobeSystemsInc.AMF3SpecificationCategory:ActionScriptSerialization類別：AS序列化ActionMessageFormat--AMFCopyrightCopyright(c)AdobeSystemsInc.(2002-2006).AllRightsAbstractActionMessageFormat(AMF)isacompactbinaryformatthatisusedtoserializeActionScriptobjectgraphs.OnceserializedanAMFencodedobjectgraphmaybeusedtopersistandretrievethepublicstateofanapplicationacrosssessionsorallowtwoendpointstocommunicatethroughtheexchangeofstronglytypedAMF(ActionMessageFormat動作信息格式)是用來序列化AS(ActionScript動作腳本)實例對象(objectgraphs的壓縮的二進制格式。序列化的AMF編碼的實例對象可用來持久化，并且在不同的會話中獲得應用的公共狀態(tài)，或者允許在兩個端點(比如客戶端和服務器端--譯者注)通過強類型數據交換進行通信。AMFwasintroducedinFlashPlayer6in2001andremainedunchangedwiththeintroductionofActionScript2.0inFlashPlayer7andwiththereleaseofFlashPlayer8.ThisversionofAMFisreferredtoasAMF0(See[AMF0]).InFlashPlayer9,ActionScript3.0wasintroducedalongwithanewActionScriptVirtualMachine(AVM+)-thenewdatatypesandlanguagefeaturesmadepossiblebytheseimprovementspromptedAMFtobeupdated. GiventheopportunitytoreleaseanewversionofAMF,severaloptimizationswerealsomadetotheencodingformattoremoveredundantinformationfromserializeddata.ThisspecificationdefinesthisupdatedversionofAMF,namelyAMF3.AF引進于01年的FasPaer6A.0的asPaer7和asPaer8中沒有改變的保留了。這個版本的AF參考于A(查閱[A])。在FasPaer9中，A.0同新的AS虛擬機(AV一起被引進—新的數據類型和語言特性的改進致使AF升級成為可能，給了一個發(fā)布新的AF版本的機會，新版本的AF在序列化數據的時候做了一些優(yōu)化，使得編碼格式去除了一些冗余信息。升級后的AF版本便是A3。TableofContents目錄(略PurposeActionMessageFormat(AMF)isacompactbinaryformatthatisusedtoserializeActionScriptobjectgraphs.OnceserializedanAMFencodedobjectgraphmaybeusedtopersistandretrievethepublicstateofanapplicationacrosssessionsorallowtwoendpointstocommunicatethroughtheexchangeofstronglytypeddata.(譯者注：之前有翻譯ThefirstversionofAMF,referredtoasAMF0,supportssendingcomplexobjectsbyreferencewhichhelpstoavoidsendingredundantinstancesinanobjectgraph.第一個版本的AMF，即AMF0Italsoallowsendpointstorestoreobjectrelationshipsandsupportcircularreferenceswhileavoidingproblemssuchasinfiniterecursionduringserialization.他也允許端點存儲對象關系，并且支持在避免問題--如在序列化時無窮的遞歸--的情況下的循環(huán)AnewversionofAMF,referredtoasAMF3tocoincidewiththereleaseofActionScript3.0,improvesonAMF0bysendingobjecttraitsandstringsbyreferenceinadditiontoobjectinstances.新版本的AMF，即AMF3，與AS3.0版本保持一致，在通過引用發(fā)送除對象實例外的對象特性和字符串做了改進。AMF3alsosupportssomenewdatatypesintroducedinActionScriptNotationalConventions標記轉換AugmentedBNF參數化的TypedefinitionsinthisspecificationuseAugmentedBackus-NaurForm(ABNF)syntax在這個規(guī)格中類型定義使用參數化的巴克斯范式(ABNF)語法[RFC2234]BNFisaformalmeta-syntaxusedtoexpresscontext-freeGrammars.BNFisoneofthemostcommonlyusedmeta-syntacticnotationsforspecifyingthesyntaxofprogramminglanguages,commandsets,PDUs,andsimilarthings.However,pureBNFisratherlimited,sothetwovariationsEBNFandABNFhavebecomemorepopular.)ThereadershouldbefamiliarwiththisnotationbeforereadingthisThroughoutthisdocumentbytesareassumedtobeoctets,or8-這個文檔的字節(jié)是8Anunsignedbyte(8-bits,anAnunsigned16-bitintegerinbigendian(network)byteorderAnunsigned32-bitintegerinbigendian(network)byteorder8byteIEEE-754doubleprecisionfloatingpointvalueinnetworkbyteorder(signbitinlowmemory).Amegabyteor1048576MorecomplicateddatatyperulesrequirespecialtreatmentwhichisoutlinedVariableLengthUnsigned29-bitInteger可變長度的無符號29AMF3makesuseofaspecialcompactformatforwritingintegerstoreducethenumberofbytesrequiredforencoding.AMF3Aswithanormal32-bitinteger,upto4bytesarerequiredtoholdthevaluehoweverthehighbitofthefirst3bytesareusedasflagstodeterminewhetherthenextbyteispartoftheinteger.對于一個正常的32-bit的整數，需要4個字節(jié)來存儲，然而前3個字節(jié)的最高位是用于標識下一個字節(jié)是不是整數的一部分Withupto3bitsofthe32bitsbeingusedasflags,only29significantbitsremainforencodinganinteger.Thismeansthelargestunsignedintegervaluethatcanberepresentedis229–1在32-bit中多達3個bit是用來標志的，所以對編碼的一個整數僅僅有29個bit大的無符號的整數值是229-1InABNFsyntax,thevariablelengthunsigned29-bitintegertypeisdescribedas在ABNF語法中,可變長度的無符號的29位的整型數據類型描述如下StringsandUTF-AMF0andAMF3use(non-modified)UTF-8toencodestrings.UTF-8istheabbreviationfor8-bitUnicodeTransformationFormat.UTF-8stringsaretypicallyprecededwithabyte-lengthheaderfollowedbyasequenceofvariablelength(1to4octets)encodedUnicodecode-points.AMF0和AMF3使用UTF-8來編碼字符串（沒有變化的）。UTF-8是8-bit的UnicodeTransformationFormat（統(tǒng)一的傳輸格式）的縮寫。UTF-8字符串是典型的字節(jié)長度為頭，緊跟著編碼Unicode編碼點的可變長度（1到4個字節(jié)）的字節(jié)序列。AMF3usesaslightlymodifiedbyte-lengthheader;adetaileddescriptionisprovidedbelowandreferredtothroughoutthedocument.AMF3InABNFsyntax,[RFC3629]describesUTF-8as在ABNF句法，[RFC3629]描述UTF-8ForAMF3astringcanbeencodedasastringliteralorastring對于AMF3Avariablelengthunsigned29-bitintegerisusedfortheheaderandthefirstbitisflagthatspecifieswhichtypeofstringisencoded.可變長度的無符號的29-bit的整數用于頭，并且第一個bitIftheflagis0,astringliteralisencodedandtheremainingbitsareusedtoencodethebyte-lengthoftheUTF-8encodedString.標識為0時，字符串是字面上編碼的，余下的位數是用來編碼UTF-8Iftheflagis1,thenastringreferenceisencodedandtheremainingbitsareusedtoencodeanindextotheimplicitstringreferencetable.標識為1（譯者注：標識位的意義前后定義的不一樣NotethatthisencodingimposessometheoreticallimitsontheuseofThenumberofuniqueStringsthatcanbesentbyreferenceislimitedto228-1,andthebyte-lengthofeachUTF-8encodedStringislimitedto228-1bytes(approx256MB).一個被引用發(fā)送的字符串的最大長度是：228-1，每一個UTF-8編碼的字符串長度是228-1字節(jié)（大概256MB）。Summaryofimprovements改進的摘要ThefollowingisatableoftheimprovementsandchangesinAMF以下是AMF3ObjecttraitscannowbesentbyreferenceStringscannowbesentbyreferenceint/uinttypeflash.utils.ByteArraytypesupport,canalsobesentbyreference對flash.utils.ByteArray類型的支持，也可以通過引用發(fā)送flash.utils.IExternalizablesupport對flash.utils.IExternalizableVariablelengthencodingschemeforintegerstoreducedatasize旨在壓縮數據大小的可變長度的整數的編碼策略ReferencesaresentusingvariablelengthintegerStringUTF-8lengthusesvariablelengthintegerUTF-8的字符串長度使用可變長度的整數Arraycountusesvariablelengthinteger數組的長度使用可變長度的整數AsingleArraytypemarkercoversbothstrictandECMA一個單獨的Array數組數據類型覆蓋了嚴格的和ECMA兩個數組DatesnolongersendtimezoneinformationDatescannowbesentbyXMLDocumentUTF-8lengthusesvariablelengthintegerXMLDocument的UTF-8的長度使用可變長度整數XMLDocumentcannowbesentbyreferenceXMLDocument可以通過引用發(fā)送XMLtypesupport,canalsobesentbyreferenceXML也可以通過應用發(fā)送XMLUTF-8lengthusesvariablelengthintegerByteArraytypelengthusesvariablelengthintegerBooleantrueandfalsearenowsentasonebytetypemarkersBoolean類型使用一個字節(jié)標識。UnsupportedtypemarkerhasbeenReservedRecordSetandMoviecliptypemarkershavebeen保留了RecordSet和MovieclipReferenceInAMF3,Strings,ComplexObjects(whichinAMF3aredefinedasanonymousObjects,typedObjects,Arrays,Dates,XMLDocument,XML,andByteArrays)andanObjectType'sTraitscannowbesentbyreference.xml文檔，xml,字節(jié)數組）Thismeansthatinsteadofsendingredundantinformation,thesecomponentsofAMFcansimplyrefertoanearlieroccurrenceofacomponent.這意味著不發(fā)送冗余信息，這些AMFThisreferenceisanintegerformingazero-basedindexthatisencodedinthecomponentinformation,typicallyinthefirstnumberthatappearsaftertherelevanttypemarker(seethetypedefinitionsforObject,Array,Date,XMLDocument,XMLandByteArraybelowforexactdetails).這個引用從0開始索引的整數，被編碼在組件信息中，典型地出現在相關的類型標識（詳細情況查閱下面Object,Array,Date,XMLDocument,XMLandByteArray類型定義）之后第一個數字。Theseindexesformavirtual"table"ofreferencesthatadeserializerandserializermustmaintainwhenreadingandwritingAMF3formatteddata.Notethat3separatereferencetablesareusedforStrings,ComplexObjectsandObjectTraitsrespectively.Thereare13typesinAMF3.Atypemarkerisonebyteinlengthanddescribesthetypeofencodeddatathatfollows.有13個AMF3Thesetofpossibletypemarkersarelistedbelow(valuesarerepresentedinhexadecimal所有可能的類型標識羅列如下（值是用16進制表示的Typemarkersmaybefollowedbytheactualencodedtypedata,orifthemarkerrepresentsasinglepossiblevalue(suchasnull)thennofurtherinformationneedstobeencoded.AMF3makesuseofthreereferencetablesforstrings,objectsandtraits(thecharacteristicsofobjectsthatdefineastrongtypesuchastheclassnameandpublicmembernames).AMF3使用三個引用表，分別用于字符串，對象和特性（一個強類型的對象特征有如類的名字和公共成員名字）ThesetablesareconsideredimplicitastheyarenotencodedasauniqueentityintheEachtypethatcanbesentbyreferencemayinsteadbeencodedusinganindextotheappropriatereferencetable.StringscanbesentbyreferenceusinganindextothestringObject,Array,XML,XMLDocument,ByteArray,DateandinstancesofuserdefinedClassescanbesentbyreferenceusinganindextotheobjecttable.XML，XMLDocument，ByteArray，Date和用法定義的類實例可以使用對象表的索引來進行引用發(fā)送。ObjectsandinstancesofuserdefinedClasseshavetraitinformationwhichcanalsobesentbyreferenceusinganindextothetraitstable.undefinedType未定義類型Theundefinedtypeisrepresentedbytheundefinedtypemarker.Nofurtherinformationisencodedforthisvalue.NotethatendpointsotherthantheAVMmaynothavetheconceptofundefinedandmaychoosetorepresentundefinedasnull.nullThenulltypeisrepresentedbythenulltypemarker.NofurtherinformationisencodedforthisfalseThefalsetypeisrepresentedbythefalsetypemarkerandisusedtoencodeaBooleanvalueoffalse.False類型用false類型標識來表示，并且用false的Boolean值來編碼。NotethatinActionScript3.0theconceptofaprimitiveandObjectformofBooleandoesnotexist.Nofurtherinformationisencodedforthisvalue.注意：在AS3.0中，基本的Object形式的Boolean概念不復存在。trueThetruetypeisrepresentedbythetruetypemarkerandisusedtoencodeaBooleanvalueoftrue.NotethatinActionScript3.0theconceptofaprimitiveandObjectformofBooleandoesnotexist.Nofurtherinformationisencodedforthisvalue.（譯者：和false類似integerInAMF3integersareserializedusingavariablelengthunsigned29-bit在AMF3中，整數是使用可變長度的無符號的29-bitTheActionScript3.0integertypes-asigned'int'typeandanunsigned'uint'type-arealsorepresentedusing29-bitsinAVM+.AS3.0intuint標識無符號的，在AVM+中也使用29-bitIfthevalueofanunsignedinteger(uint)isgreaterorequalto229orifthevalueofasignedinteger(int)isgreaterthanorequalto228thenitwillberepresentedbyAVM+asadoubleandthusserializedinusingtheAMF3doubletype.如果uint整數大于或等于229,int整數大于等于228，在AVM+AMF3doubleTheAMF3doubletypeisencodedinthesamemannerastheAMF0Numbertype.AMF3的雙精度浮點型和AMF0的的雙精度浮點型的編碼是一樣的。ThistypeisusedtoencodeanActionScriptNumberoranActionScriptintofvaluegreaterthanequalto228oranActionScriptuintofvaluegreaterthanorequaltoTheencodedvalueisalwaysan8byteIEEE-754doubleprecisionfloatingpointvalueinnetworkbyteorder(signbitinlowmemory).編碼的值在網絡序列中總是一個8個字節(jié)的IEEE-754的雙精度浮點值（符號位在低位內存StringActionScriptStringvaluesarerepresentedusingasinglestringtypeinAMF3-theconceptofstringandlongstringtypesfromAMF0isnotused.StringscanbesentasareferencetoapreviouslyoccurringStringbyusinganindextotheimplicitstringreferencetable.StringsareencodingusingUTF-8-howevertheheadermayeitherdescribeastringliteralorastring（譯者：以上都是之前翻譯了的TheemptyStringisneversentbyXMLDocumentActionScript3.0introducedanewXMLtype(see3.13)howeverthelegacyXMLDocumenttyperetainedinthelanguageas雖然遺產類XMLDocument被保留了下了，AS3.0還是引進了XMLSimilartoAMF0,thestructureofanXMLDocumentneedstobeflattenedintoastringrepresentationforserialization.和AMF0類似，XMLDocumentAswithotherstringsinAMF,thecontentisencodedinUTF-XMLDocumentscanbesentasareferencetoapreviouslyoccurringXMLDocumentinstancebyusinganindextotheimplicitobjectreferencetable.對于當前產生的XMLDocument實例，可以使用隱含的對象引用表的一個索引來進行引用發(fā)送。NotethatthisencodingimposessometheoreticallimitsontheuseofXMLDocument.Thebyte-lengthofeachUTF-8encodedXMLDocumentinstanceislimitedto228-1bytes(approx256MB).（譯者：以上都是之前翻譯了的DateInAMF3anActionScriptDateisserializedsimplyasthenumberofmillisecondselapsedsincetheepochofmidnight,1stJan1970intheUTCtimezone.在AMF3中，AS日期簡單地序列化為一個從公元1970年1月1日零點，使用UTCLocaltimezoneinformationisnotDatescanbesentasareferencetoapreviouslyoccurringDateinstancebyusinganindextotheimplicitobjectreferencetable.ArrayActionScriptArraysaredescribedbasedonthenatureoftheirindices,i.e.theirtypeandhowtheyarepositionedintheArray.AS的數組是基于他的自然索引來描述的，例如：他們的類型和他們在數組中的位置Thefollowingtableoutlinesthetermsandtheirmeaning:containsonlyordinal(numeric)ordinalindicesstartat0anddonotcontaingapsbetweensuccessiveindices(thatis,everyindexisdefinedfrom0forthelengthofthearray)索引從0開始，不包含連續(xù)索引中的間隙（來說都是從0開始定義的containsatleastonegapbetweentwo在兩個索引中至少包含一個間隙containsatleastonenon-ordinal(string)index(sometimesreferredtoasanECMA至少包含一個非順序（字符串）索引（一些時候是ECMA數組 AMFconsidersArraysintwoparts,thedenseportionandtheassociativeportion.AMF把數組分為兩個部分，密集部分和關聯(lián)部分。Thebinaryrepresentationoftheassociativeportionconsistsofname/valuepairs(potentiallynone)terminatedbyanemptystring.對于關聯(lián)部分的二進制表示由以空字符串結束的名/值對（可能沒有）組成。Thebinaryrepresentationofthedenseportionisthesizeofthedenseportion(potentiallyzero)followedbyanorderedlistofvalues(potentiallynone).密集部分的二進制表示是跟著順序的列表值（可能沒有）的密集部分的大?。赡苁橇悖㏕heorderthesearewritteninAMFisfirstthesizeofthedenseportion,anemptystringterminatedlistofname/valuepairs,followedbysizevalues.在AMFObjectAsingleAMF3typehandlesActionScriptObjectsandcustomuserclasses.Theterm'traits'isusedtodescribethedefiningcharacteristicsofaclass.Inadditionto'anonymous'objectsand'typed'objects,ActionScript3.0introducestwofurthertraitstodescribehowobjectsareserialized,namely'dynamic'and'externalizable'.Thefollowingtableoutlinesthetermsandtheirmeanings:aninstanceofaninstanceoftheactualActionScriptObjecttypeoraninstanceofaClasswithoutaregisteredalias(thatwillbetreatedlikeanObjectondeserialization)真實的AS對象實例或沒有別名注冊的類對象實例（反序列化時，他會像對象一樣ActionMessageActionMessageFormatAMF3(中文版FixedBywhatwhatwecallhumannatureisactuallyhumanhabitaninstanceofaClasswitharegistered有別名注冊的類對象實例aninstanceofaClassdefinitionwiththedynamictraitpublicvariablememberscanbeaddedandremovedfrominstancesdynamicallyatExternalizaaninstanceofaClassthatimplementsflash.utils.IExternalizableandcompletelycontrolstheserializationofitsmembers(nopropertynamesareincludedinthetrait實現了flash.utils.IExternalizable接口的類實例并且完全控制他的成員的序列化（他們的特性信息中沒有屬性名Inadditiontothesecharacteristics,anobject'straitsinformationmayalsoincludeasetofpublicvariableandpublicread-writeablepropertynamesdefinedonaClass(i.e.publicmembersthatarenot除了這些特性，對象特性信息也可能包括一組在類中定義公共變量和公共可讀寫的屬性名（如：公共成員但不是函數）。Theorderofthemembernamesisimportantasthemembervaluesthatfollowthetraitsinformationwillbeintheexactsameorder.ThesemembersareconsideredsealedmembersastheyareexplicitlydefinedbytheIfthetypeisdynamic,afurthersectionmaybeincludedafterthesealedmembersthatlistsdynamicmembersasname/valuepairs.如果類型是動態(tài)的，在封裝好的成員之后的部分會列出動態(tài)成員的名/OnecontinuestoreadindynamicmembersuntilanamethatistheemptystringisObjectscanbesentasareferencetoapreviouslyoccurringObjectbyusinganindextotheimplicitobjectreferencetable.Furthermore,traitinformationcanalsobesentasareferencetoapreviouslyoccurringsetoftraitsbyusinganindextotheimplicittraitsreferencetable.;Thefirst(low)bitisa低位第一位（bit）;(representingwhetheran;follows表示是否跟著個實例對象withvalue0toimply;thisisnotaninstancebut;Theremaining1to;significantbitsareusedtoencode;objectreferenceindex(an余下的1到28個有效的位是用來編碼一個對象引用的索引（一個整數;Thefirst(low)bitisaflag;valueThesecondbitisa;(representingwhethera;referencefollows)withvalue0;implythatthisobjectstraits;beingsentbyThe;1to27significantbitsareused;encodeatraitreferenceindex;余下的27位表示引用值（一個整數;Thefirst(low)bitisaflag;value1.Thesecondbitisaflag;value1.Thethirdbitisaflag;valueTheremaining1to;significantbitsarenot;(thetraitsmembercountwould;be余下的26位無意義（特性成員的數量必須是;Thefirst(low)bitisaflag;value1.Thesecondbitisaflag;value1.Thethirdbitisaflag;valueThefourthbitisa;specifyingwhetherthetype;Avalueof0implies;dynamic,avalueof1implies0表示不是動態(tài)的，1;Dynamictypesmayhaveasetof;valuepairsfordynamicmembers;thesealedmemberTheremaining1to25significantbits;usedtoencodethenumberof;traitsmembernamesthatfollow;theclassname(an;Note:usetheemptystring;anonymousUTF-8-vrvalue-;Anotherdynamicmember;untilthestring-typeis;emptyobject-markerobject-marker(U29O-ref|(U29O-traits-extclass-name*(U8))|U29O-traits-ref|(U29O-traitsclass-name*(UTF-8-vr)))NotethatforU29O-traits-ext,aftertheclass-namefollowsanindeterminablenumberofbytes注意對于U29O-traits-ext，類名之后跟著的*(U8)Thisrepresentsthecompletelycustomserializationof"externalizable"TheclientandserverhaveanagreementastohowtoreadinthisXMLActionScript3.0introducesanewXMLtypethatsupportsE4Xsyntax.AS3.0引進了一個新的XML類型，支持E4X句法。ForserializationpurposestheXMLtypeneedstobeflattenedintoastringXMLAswithotherstringsinAMF,thecontentisencodedusingUTF-XMLinstancescanbesentasareferencetoapreviouslyoccurringXMLinstancebyusinganindextotheimplicitobjectreferencetable.NotethatthisencodingimposessometheoreticallimitsontheuseofXML.Thebyte-lengthofeachUTF-8encodedXMLinstanceislimitedto228-1bytes(approx256MB).ByteArrayActionScript3.0introducesanewtypetoholdanArrayofbytes,namelyByteArray.AS3.0引進了新的類型表示字節(jié)數組，即ByteArray。AMF3serializesthistypeusingavariablelengthencoding29-bitintegerforthebyte-lengthprefixfollowedbytherawbytesoftheByteArray.ByteArrayinstancescanbesentasareferencetoapreviouslyoccurringByteArrayinstancebyusinganindextotheimplicitobjectreferencetable.ActionMessageFormatActionMessageFormatAMF3(中文版FixedBywhatwhatwecallhumannatureisactuallyhumanhabitNotethatthisencodingimposessometheoreticallimitsontheuseofByteArray.Themaximumbyte-lengthofeachByteArrayinstanceislimitedto228-1bytes(approx256MB).NetConnectionandAMFInadditiontoserializingActionScripttypes,AMFcanbeusedintheasynchronousinvocationsofremoteservices.Asimplemessagingstructureisusedtosendabatchofrequeststoaremote一個簡單的消息結構是使用對遠程端點發(fā)送一批請求。TheformatofthismessagingstructureisAMF0(See[AMF0].這個消息結構的格式AMF0參考[AMF0])AcontextheadervalueormessagebodycanswitchtoAMF3encodingusingthespecialavmplus-object-markertype.使用一個特殊的avmplus-object-marker的類型可使一個上下文頭值或消息體切換到AMF3編SimilartoAMF0,AMF3objectreferencetables,objecttraitreferencetablesandstringreferencetablesmustbereseteachtimeanewcontextheaderormessageisprocessed.和AMF0類似，AMF3對象引用表，對象特性引用表和字符串引用表必須在每次新的上下文頭或消息處理完時復位一次。NetConnectioninActionScriptThequalifiedclassnameforNetConnectioninActionScript3.0is.NetConnection.NetConnection在AS3.0中的合適的類名是.NetConnection。Thisclasscontinuestousearespondertohandleresultandstatusresponsesfromaremoteendpoint,however,astronglytypedResponderclassisnowrequired.Thefullyqualifiedclassnameis類，類的全名是fas.e.espnerForeventsotherthannormalresultandstatusresponsesNetConnectiondispatcheseventsforwhichthedevelopercanaddlisteners.TheseeventsareoutlinedDispatchedwhenanexceptionisthrownasynchronously-i.e.fromnativeasynchronouscode.Dispatchedwhenaninput