?ìí??·ó|ó?ò??-?úè?1ú?÷′ó?￠2?é??aê?á÷DDá??eà′?￡àyè?QQ?￠2?μ?url.cn￡?D?àéμ?sinaurl.cnμè?￡
?ò???úQQ?￠2?é?·￠2?í??·μ?ê±oò￡??￠2??á×??ˉ?D±eí??·￡?2￠????×a??￡?àyè?￡ohttp://url.cn/2hytQx
?aê2?′òa?a?ù×?μ?￡??-òò?ò??óD?a?ù??μ?￡o
?￠2??T??×?êy?a140×?ò?ì?￡????′è?1??ò??Dèòa·￠ò?D?á??óé?è￥￡?μ?ê??a??á??ó·?3￡μ?3¤￡?ò??áóú???üòa??ó??ò???úèYμ?ò?°??a·ù￡??a???¨ê?2??ü±??êDíμ?￡??ùò??ìí??·ó|????éúá??￡
?ìí??·?éò??ú?ò??????à??éò?oüo?μ????a·???URL??DD1üàí?￡óDò?2?·?í??·?éò??áo-??±?á|￡?1???μèD??￠￡??a?ù?ò???éò?í¨1yó??§μ??ù±¨￡?íêè?1üàí?a??á??ó??2?3????ú?ò??μ?ó|ó??D￡?ó|?aí??ùμ?URLí¨1y?ó?ü??·¨??oó￡?μ?μ?μ?μ??·ê?ò??ùμ??￡
?ò???éò???ò??μáDμ?í??·??DDá÷á?￡?μ??÷μèí3??￡?íú?ò3?′ó?àêyó??§μ?1?×￠μ?￡??a?ùóDà?óú?ò????????μ?oóD?1¤×÷?üo?μ?×÷3???2??￡
??êμò?é?èyμ?′?ê???è?1?μ?￡?òò?a?ú?ò?ó??à′μ?2?·??????D?áó|ó?μ?￡??ùò??íá??aá?ò???￡??????èà′?′?′?ìí??·ó3é???·¨μ?àí??￡¨í?é??òμ?μ?×êá?￡?￡o
??3¤í??·md5éú3é32??????′?￡?·??a4??￡?????8??×??ú￡?
???a?????-?·′|àí￡?è?8??×??ú￡??????′3é16????′?ó?0x3fffffff(30??1)ó?2ù×÷￡??′3?1y30??μ?o???′|àí￡?
?a30??·?3é6??￡???5??μ?êy×?×÷?a×???±íμ??÷òyè?μ?ì??¨×?·?￡?òà′???DD??μ?6??×?·?′?￡?
×üμ?md5′??éò???μ?4??6??′?￡?è?à???μ?è?òaò????í?é×÷?a?a??3¤urlμ??ìurlμ??·￡?
oü?òμ￥μ?àí??￡??ò??2￠2?ò??¨?μμ?μ?μ?URLê??¨ò?μ?￡?μ?ê??ò???ü1?è?3?4×éURL￡??a?ù??o?2??á3???ì?′óμ????′?￡
????à′?′?′3ìDò2?·?￡o
′ú??è???:
public static string [] ShortUrl( string url)
{
//?éò?×??¨ò?éú3éMD5?ó?ü×?·?′??°μ??ìo?KEY
string key = ?±Leejor?± ;
//òaê1ó?éú3éURLμ?×?·?
string [] chars = new string []{
?±a?± , ?±b?± , ?±c?± , ?±d?± , ?±e?± , ?±f?± , ?±g?± , ?±h?± ,
?±i?± , ?±j?± , ?±k?± , ?±l?± , ?±m?± , ?±n?± , ?±o?± , ?±p?± ,
?±q?± , ?±r?± , ?±s?± , ?±t?± , ?±u?± , ?±v?± , ?±w?± , ?±x?± ,
?±y?± , ?±z?± , ?±0?? , ?±1?? , ?±2?? , ?±3?? , ?±4?? , ?±5?? ,
?±6?? , ?±7?? , ?±8?? , ?±9?? , ?±A?± , ?±B?± , ?±C?± , ?±D?± ,
?±E?± , ?±F?± , ?±G?± , ?±H?± , ?±I?± , ?±J?± , ?±K?± , ?±L?± ,
?±M?± , ?±N?± , ?±O?± , ?±P?± , ?±Q?± , ?±R?± , ?±S?± , ?±T?± ,
?±U?± , ?±V?± , ?±W?± , ?±X?± , ?±Y?± , ?±Z?±
};
//??′?è?í??·??DDMD5?ó?ü
string hex = System.Web.Security.FormsAuthentication.HashPasswordForStoringInConfigFile(key + url, ?±md5?? );
string [] resUrl = new string [4];
for ( int i = 0; i < 4; i++)
{
//°??ó?ü×?·?°′??8??ò?×é16????ó?0x3FFFFFFF??DD??ó?????
int hexint = 0x3FFFFFFF & Convert.ToInt32( ?±0x?± + hex.Substring(i * 8, 8), 16);
string outChars = string .Empty;
for ( int j = 0; j < 6; j++)
{
//°?μ?μ?μ??μó?0x0000003D??DD??ó?????￡?è?μ?×?·?êy×échars?÷òy
int index = 0x0000003D & hexint;
//°?è?μ?μ?×?·??à?ó
outChars += chars[index];
//??′??-?·°′??óòò?5??
hexint = hexint >> 5;
}
//°?×?·?′?′?è???ó|?÷òyμ?ê?3?êy×é
resUrl[i] = outChars;
}
return resUrl;
}
???ú?éò??±?óê1ó???·?·¨￡??éò?μèμ???????×é?μ￡o
′ú??è???:
ShortUrl(http://www.jb51.net)[0]; //μ?μ??μfAVfui
ShortUrl(http://www.jb51.net)[1]; //μ?μ??μ3ayQry
ShortUrl(http://www.jb51.net)[2]; //μ?μ??μUZzyUr
ShortUrl(http://www.jb51.net)[3]; //μ?μ??μ36rQZn
?ú′?·??a??URLμ?êy?Y·???￡??ò??è?í???TTServer￡?óDμ??óó??éò???óDìy?μ1y￡?????ê??a??êy?Y?aμ??ééü￡o
Tokyo Cabinet ê?è?±?è? Mikio Hirabayashi￡¨??á???D?￡?¤?￥ú?`￥? ?a·￠μ?ò???DBMêy?Y?a(×￠￡o′ó???|?|μ?DBMêy?Y?aqdbm?íê????a·￠μ?)￡???êy?Y?a?áD′·?3￡?ì?￡insert:0.4sec/1000000 recordes(2500000qps)￡?D′è?100íòêy?Y??Dèòa0.4???￡search:0.33sec/1000000 recordes (3000000 qps)￡??áè?100íòêy?Y??Dèòa0.33???￡
?éò??′μ???óú×?μ?ààDíμ?êy?YKey/Valueμ?2é?ˉ￡??a??êy?Y?a?éò??μê??ò???°??1yD§?ê·?3￡??μ?￡????ò??è?′?μ?D??é￡?ó?à′??short url/long urlμ??????ùo?2?1y?￡
???μí3ê1ó?6???ì??×?·?à′±íê?è?o?3¤?èμ?í??·?￡ óDD§μ?×?·?′ú??ê?ASCII ??A’μ?’Z’oí’0??μ?’5??￡????D????×?·?°üo?2 ^ 5￡¨32￡?×′ì??￡ 6?ì??×?·??éó?óú????32 ^ 6￡¨1073741824￡?μ?í??·
ê×?è￡???Dèòaò???êy?Y?a±íà′′?′￠oí?ì?÷??ó3é?μ?í??·?￡
′ú??è???:
CREATE TABLE mappedURL (μ?CREATE TABLE mappedURL￡¨
shortCode char (6) not null ,
lognURL text not null ,
PRIMARY KEY shortCodeInd (shortCode),
);
??′?￡???Dèòa?¨ò?ò?????·¨??3¤μ?URLó3é?μ??ìμ?URL?￡ ??·¨é???ò??-?ééü1yá??￡
μúèy￡???Dèòa′′?¨ò???í?ò3￡?′óêy?Y?aμ??ìí??·μ?ó3é??òμ??-ê?μ?URL,2￠???¨?ò???￡
?a?a?a?a?a?a?a?a?a?a?a?a?a?a?a?a?a?a?a
MD5 ò??-±????aá?￡?òò′?2???3y1￥?÷???±?ì?àí? MD5 μ? url êμ????òa??μ?μ??é?üD??￡è?1?2??????a???é??￡?md5 collision μ??é?üD?ó|??ê??°??μíμ?￡?1à?????òóDéú???ê???′2?μ??￡
áíía??2??÷°×?°?àí?μ?URL??′???3?à′μ??ü?μ±?D???ê?ò??ùμ??±μ?êμ?êó?í??áê?ê2?′?￡?í???àí?μ? URL ??ó|2?í?μ??ü?μ￡?ò?°?ò22??á?ì3éì?′óμ?à?·?°é￡???óD 6 ??μ?×???êy×?×éo????éò?èY?é??ê?òú??±??ˉ?￡
?ò?yê?óDmd5 collisionμ?μ￡D?2??ê?a???êìaμ??￡?àí?μ?URLòa??ó|?àí?μ??ü?μê?òò?a??ò???URLμ??·??Dèòa?¨ò?μ???ó|μ?êy?Y?a?Dμ?ò?ì?±íêy?Y￡?μ??±?óó?URLà′2é?ˉ?á±è???y￡?òò?a￡o
??òa′?′￠μ?URLoí?à1?μ?????êy?Yá?·?3￡′ó?￡
???òóDD?URL?áoü3¤￡??ùò?òaó?text×????￡
??è?1?1t?￡3??¨ò?μ??ü?μó?varcharà′′?′￠￡??ù?ù?Y?a???ü?μè￥2é?ˉ?í?á·?3￡·?±??ì?Y?￡
?í??gità???μ?object hash￡? ???°?ù±?é?2?ó?????3?í?°é?￡
bit.lyμèurl shorter·t??ê????′êμ??μ?￡?
Dè2?Dèòa′óhash?ü?μ·′?ò2é?òurl￡? è?1?óD?a?ùμ?òa?ó￡? url???¨Dèòa′?ò???μ?·?￡? ?a?ù?í?éò??ú3?í?μ?ê±oò??DD?ùé￠áD
MD5ê?128??hash??￡¨4????êy￡???????êy4??×??ú￡??￡òò′?￡?ò???urlμ?MD5??￡?óD2μ?128′?·?￡¨?′2e128￡????é?ü?￡??òa?ò3?à′μ?á???urlμ?MD5???àμèμ??é?üD?￡?ê?2e128·???ò?￡??′r=2e-128
?ùè?url?-MD5oó2?è?êy?Y?a￡?μúò???url2?è?μ?2??á·￠éú???′￡?μú?t??MD52?è?ê±￡??ü?úμúò?ì????′μ????êê?r?￡μúèyì?url2?è?ê±￡????′???ê ê?2?ár￡?ò?′?ààí?￡?μúnì?2?è?ê±·￠éú???′μ????êê?(n-1)?ár?￡n??MD5??￡????DóDá??????′μ????êê??aD????ê?óoí?￡￡¨1￡?2￡?3￡??-+(n- 1))?ár = (1/2)?án?á(n-1)?ár
??óún??MD5??μ??ˉo?￡?′??ú???′μ????êê?￡¨1/2)*(n/2e64)e2
òò′?￡???óDn′óμ??éò?ó?2e64±è?a￡?2?Dèòa?????üμ?3?í??êìa?￡??2μ?64′?·??1ê?oü′óμ??￡
?ùò?￡???òa2?ê???òa1￥?÷￡?ò?°?ó|ó?ê?2?ì??áóDcollisionμ?
C# URL?ìμ??·?1????·¨?°?ìí??·?-àí?a??
本文地址: http://www.paobuke.com/develop/c-develop/pbk23108.html
