ISAPI Filter编程重写URL

问题描述：要在一个Web站点上实现二级域名Url的重写。例如：http://abc.company.com 重写到 http://company.com/usersite.asp?sitename=abc 其中abc二级域名不定，根据用户申请的名字来决定。服务器上有一个DNS服务。可以吧*.compay.com所有二级域名正确解析到company.com。经过重写后。浏览器中的地址是http://abc.company.com 但实际请求的地址是 http://company.com/usersite.asp?sitename=abc 让用户感觉好像在访问 http://abc.company.com

好像在Apache上用Apache的mod_rewrite，配置一下就可以轻松的解决问题了。据说微软的IIS7中也支持了这种特性，IIS7可以在 IIS 请求管道的任何地方执行一个HttpModule，下面是IIS7给的配置：

<?xml version="1.0" encoding="UTF-8"?> <configuration> <configSections> <section name="rewriter"  requirePermission="false"  type="Intelligencia.UrlRewriter.Configuration.RewriterConfigurationSectionHandler, Intelligencia.UrlRewriter" /> </configSections> <system.web> <httpModules> <add name="UrlRewriter" type="Intelligencia.UrlRewriter.RewriterHttpModule, Intelligencia.UrlRewriter" /> </httpModules> </system.web> <system.webServer> <modules runAllManagedModulesForAllRequests="true"> <add name="UrlRewriter" type="Intelligencia.UrlRewriter.RewriterHttpModule" /> </modules> <validation validateIntegratedModeConfiguration="false" /> </system.webServer> <rewriter> <rewrite url="~/products/(.+)" to="~/products.aspx?category=$1" /> </rewriter> </configuration>

遗憾的是服务器使用的是Win2003+IIS6。并且服务器上同时部署了asp程序和asp.net程序如果使用 UrlRewriter.net组件，只能在HttpModule一级重写，只能作用于所有使用 % WINDIR %\Microsoft.NET\Framework\v2.0.50727\aspnet_isapi.dll处理请求的后缀文件。如 .aspx .ascx请求。但是asp是用%WINDIR%\WINDOWS\system32\inetsrv\asp.dll来处理请求的。请求不会分检到Asp.net的HttpModule中。所以对于asp的请求，UrlRewriter.net组件的HttpModule重写不能起效。.jpg .gif .htm也不能被重写。看来只能用ISAPI Filters  http://msdn2.microsoft.com/en-us/library/ms525908.aspx 来重写了。

SAPI Filters有两个非常著名工程：
1. Helicon Techs ISAPI Rewrite:  http://www.isapirewrite.com/ 提供一个99美元(可免费试用30天)的ISAPI URL重写产品完整版，以及一个免费的轻量级版本。
2. Ionics ISAPI Rewrite:  http://cheeso.members.winisp.net/IIRF.aspx 全免费开源组件。

Helicon Techs ISAPI Rewrite的产品完整版已经解决了这个问题。可是Helicon Techs的付费手段少，在付费线购买太难用了，如果像支付宝一样好用（点击付款连再次确认都没有，直接钱就出去了 呵呵）估计会增加购买量。

看来自己动手丰衣足食的时候到了，从Ionics ISAPI Rewrite的基础上改一个可以支持二级域名重写的ISAPI Filter吧。下载Ionics Isapi Rewrite Filter(下面简写为IIRF)  http://www.codeplex.com/IIRF/Release/ProjectReleases.aspx?ReleaseId=5018 。最后一个版本是1.2.12c Beta 千万不要用1.2.12b，1.2.12b有内存泄露问题。1.2.12c修复了这个问题（加了free( myCopy )部分的代码）。

下载后主要有8 个文件。IsapiRewrite4.c TestDriver.c IirfConfig.h IirfConstants.h IirfRequestContext.h RewriteRule.h pcre-5.0/ pcre.h pcre-5.0/pcre.lib 其中的TestDriver.c是测试正则表达式的exe可以先不看。RewriteRule.h pcre-5.0/ pcre.h pcre-5.0/pcre.lib 是正则表达式解析引擎。

修改makefile中：VC="C:\Program Files\Microsoft Visual Studio 8\VC" 和PCRESOURCE=E:\Project\InUrlRewrite\SRC\pcre-5.0 部分。到.net 2.0的console下cd进入下载目录使用 nmake –f makefile编译。让工程可以正确编译。

搭建一个可以测试自己编译的ISAPI Filter的环境。建一个WebSite在ISAPI Filters添加刚刚Build好的IsapiRewrite4.dll。重启IIS。在IsapiRewrite4.ini中设置输出Log等级为5(输出详细Log)指定Log输出位置。修改%WINDIR%\system32\drivers\etc\hosts文件。在域名解析中加入127.0.0.1 abc.company.com 和 127.0.0.1 company.com这两行便于测试。在新建的WebSite中加入一个test.asp文件，test.asp中只用写Response.Write(Query("Domain")) 提供重写后的测试。

到这里所有的编程前需要的环境都部署好了。现在可以开始改 IIFR了。看完了所有的代码，发现核心的内容都在IsapiRewrite4.c中，这个文件总共有2600多行。核心的函数是DoRewrites。对外的Entry-Point Functions是GetFilterVersion HttpFilterProc TerminateFilter通过这三个方法向IIS暴露 ISAPI Filter内部的功能，IIS会调用ISAPFilter的这三个方法。在 http://msdn2.microsoft.com/en-us/library/ms525572.aspx 中有详细的介绍。

主要修改DoRewrites就基本上可以满足要求了。
1. 添加一个新的表示Pattern -> [D]。
2. 修改ApplyRules方法对Url的处理，当表示Pattern是[D]时，从GetServerVariable("HTTP_HOST", pfc)中取得http_host，拼凑到OriginalUrl前再进行正则表达式的匹配。
经过上面两部就实现了对二级域名重写的功能。 

注意：IIFR的License要求（在IsapiRewrite4.c顶部有详细的描述）很严格。可能不允许再生产，和商业使用。

修改后的工程:
1.修改RewriteRule.h 在RewriteRule结构体中加入 boolean IsMatchDomain 这个Field标识新的Pattern. 修改后的结构：

typedef struct RewriteRule { pcre * RE; char * Pattern; char * Replacement; boolean IsRedirect; int RedirectCode; boolean IsForbidden; boolean IsNotFound; boolean IsLastIfMatch; boolean IsCaseInsensitive; boolean RecordOriginalUrl; boolean IsMatchDomain; // any condition that applies struct RewriteCondition * Condition; // doubly-linked list struct RewriteRule * next; struct RewriteRule * previous; } RewriteRule, *P_RewriteRule;

2.修改IsapiRewrite4.c中的ParseRuleModifierFlags方法加入对IsMatchDomain的处理。修改后的方法：

void ParseRuleModifierFlags(char * pModifiers, RewriteRule *rule) { char MsgBuffer[512]; rule->IsRedirect= FALSE; rule->IsForbidden= FALSE; rule->IsLastIfMatch= FALSE; rule->IsNotFound= FALSE; rule->IsCaseInsensitive= FALSE; rule->RecordOriginalUrl= FALSE; rule->IsMatchDomain = FALSE; if (pModifiers==NULL) return; // no flags at all sprintf_s(MsgBuffer,512,"ParseRuleModifierFlags: %s", pModifiers); LogMsg(2, MsgBuffer); if ((pModifiers[0] != [) || (pModifiers[strlen(pModifiers)-1] != ])) { LogMsg(1, "WARNING: Badly formed RewriteRule modifier flags."); return; } else { char * p1, *p2; char * StrtokContext= NULL; p1= pModifiers+1; // skip leading [ pModifiers[strlen(pModifiers)-1]=0; // remove trailing ] p2= strtok_s(p1, ",", &StrtokContext); // split by commas while (p2 != NULL) { if (config->LogLevel >= 5 ) { sprintf_s(MsgBuffer,512,"ParseRuleModifierFlags: token %s", p2); LogMsg(5, MsgBuffer); } if (p2[0]==R) { // redirect rule->IsRedirect= TRUE; rule->RedirectCode= REDIRECT_CODE_DEFAULT; // use the default redirect code if ((p2[1]!=0) && (p2[1]===) && (p2[2]!=0)) { int n= atoi(p2+2); if ((n <= REDIRECT_CODE_MAX) && (n >= REDIRECT_CODE_MIN)) rule->RedirectCode= n; } } else if ((p2[0]==F) && (p2[1]==0)) { // forbidden (403) LogMsg(5, "rule: Forbidden"); rule->IsForbidden= TRUE; } else if ((p2[0]==N) && (p2[1]==F) && (p2[2]==0)) { // not found (404) LogMsg(5, "rule: Not found"); rule->IsNotFound= TRUE; } else if ((p2[0]==L) && (p2[1]==0)) { // Last rule to process if match LogMsg(5, "rule: Last"); rule->IsLastIfMatch= TRUE; } else if ((p2[0]==I) && (p2[1]==0)) { // case-insensitive LogMsg(5, "rule: Case Insensitive match"); rule->IsCaseInsensitive= TRUE; } else if ((p2[0]==U) && (p2[1]==0)) { // Unmangle URLs LogMsg(5, "rule: Unmangle URLs"); rule->RecordOriginalUrl= TRUE; } else if ((p2[0]==D) && (p2[1]==0)) { // Match Domain Rule URLs LogMsg(5, "rule: Match Domain URLs"); rule->IsMatchDomain = TRUE; } else { sprintf_s(MsgBuffer,512,"WARNING: unsupported RewriteRule modifier flag %s", p2); LogMsg(1, MsgBuffer); } p2= strtok_s(NULL, ",", &StrtokContext); // next token } // consistency checks if (rule->IsForbidden && rule->IsRedirect) LogMsg(1, "WARNING: Conflicting modifier flags - F,R"); if (rule->IsForbidden && rule->IsLastIfMatch) LogMsg(1, "WARNING: Redundant modifier flags - F,L"); if (rule->IsForbidden && rule->IsNotFound) LogMsg(1, "WARNING: Conflicting modifier flags - F,NF"); if (rule->IsNotFound && rule->IsLastIfMatch) LogMsg(1, "WARNING: Redundant modifier flags - NF,L"); if (rule->IsNotFound && rule->IsRedirect) LogMsg(1, "WARNING: Conflicting modifier flags - NF,R"); if (rule->IsRedirect && rule->IsLastIfMatch) LogMsg(1, "WARNING: Redundant modifier flags - R,L"); } return; }

3.修改IsapiRewrite4.c中的ApplyRules方法加入对请求中httphost部分的处理。修改后的方法：

int ApplyRules(     HTTP_FILTER_CONTEXT * pfc,     char * subject,     int depth,     /* out */ char **result,     /* out */ boolean *pRecordOriginalUrl )  { RewriteRule * current= config->rootRule; int retVal= 0; // 0 = do nothing, 1 = rewrite, 403 = forbidden, other = redirect char MsgBuffer[512]; int c=0; int RuleMatchCount, i;  int *RuleMatchVector; #if _WRITE_LOG sprintf_s(MsgBuffer,512,"ApplyRules (depth=%d)", depth); LogMsg(3, MsgBuffer); #endif if (current==NULL) { #if _WRITE_LOG   LogMsg(2, "ApplyRules: No configuration available."); #endif   return 0; } // The PCRE doc says vector length should be 3n?? why? seems like it ought to be 2n. or maybe 2n+1. // In any case we allocate 3n.  RuleMatchVector= (int *) malloc((config->MaxMatchCount*3)*sizeof(int));  // The way it works: First we evaluate the URL request, against the RewriteRule pattern.  // If there is a match, then the logic evaluates the Conditions attached to the rule.  // This may be counter-intuitive, since the Conditions appear BEFORE the rule in the file,  // but the Rule is evaluated FIRST.  // TODO: employ a MRU cache to map URLs while (current!=NULL) {   c++;   LogMsg(3, "subject");   LogMsg(3, subject);        if(current->IsMatchDomain && depth==0)   {     char *serverHost;     char *originalUrlWithDomain;     serverHost= GetServerVariable("HTTP_HOST", pfc);     originalUrlWithDomain = (char *) pfc->AllocMem(pfc, strlen(serverHost)+strlen(subject)+1, 0);     strcpy(originalUrlWithDomain,serverHost);     strcat(originalUrlWithDomain,subject);     subject = originalUrlWithDomain;   }     RuleMatchCount = pcre_exec(       current->RE, /* the compiled pattern */      NULL, /* no extra data - we didnt study the pattern */      subject, /* the subject string */      strlen(subject), /* the length of the subject */      0, /* start at offset 0 in the subject */      0, /* default options */      RuleMatchVector, /* output vector for substring position information */      config->MaxMatchCount*3); /* number of elements in the output vector */   // return code: >=0 means number of matches, <0 means error   if (RuleMatchCount < 0) {    if (RuleMatchCount== PCRE_ERROR_NOMATCH) { #if _WRITE_LOG     sprintf_s(MsgBuffer,512,"Rule %d : %d (No match)", c, RuleMatchCount );     LogMsg(3, MsgBuffer); #endif    }    else { #if _WRITE_LOG         sprintf_s(MsgBuffer,512,"Rule %d : %d (unknown error)", c, RuleMatchCount);       LogMsg(2, MsgBuffer); #endif    }   }   else if (RuleMatchCount == 0) { #if _WRITE_LOG     sprintf_s(MsgBuffer,512,"Rule %d : %d (The output vector (%d slots) was not large enough)",       c, RuleMatchCount, config->MaxMatchCount*3);    LogMsg(2, MsgBuffer); #endif   }   else {    // we have a match and we have substrings    boolean ConditionResult= FALSE;    PcreMatchResult RuleMatchResult;    PcreMatchResult CondMatchResult;  #if _WRITE_LOG    sprintf_s(MsgBuffer,512,"Rule %d : %d matches", c, RuleMatchCount);    LogMsg(2, MsgBuffer); #endif    // easier to pass these as a structure    RuleMatchResult.Subject= subject;    RuleMatchResult.SubstringIndexes= RuleMatchVector;    RuleMatchResult.MatchCount= RuleMatchCount;    // The fields in CondMatchResult may be filled by the EvaluateConditionList(), but    // we must init them because the EvaluateConditionList may never be called. The    // results reflect only the "last" Condition evaluated. This may or may not be    // the final Condition in the file; the evaluation engine wont evaluate    // Conditions unnecessarily. Check the readme for more details.    CondMatchResult.Subject= NULL;    CondMatchResult.SubstringIndexes= NULL;    CondMatchResult.MatchCount= 0;    // evaluate the condition list, if there is one.     ConditionResult=      (current->Condition==NULL) ||      EvaluateConditionList(pfc,           &RuleMatchResult,           &CondMatchResult,           current->Condition);    // Check that any associated Condition evaluates to true, before     // applying this rule.     if ( ConditionResult ) {     char *ts1;     char *newString;     // generate the replacement string     // step 1: substitute server variables, if any.     ts1= ReplaceServerVariables(pfc, current->Replacement);     // step 1: substitute back-references as appropriate.     newString= GenerateReplacementString(ts1, // current->Replacement,              &RuleMatchResult,               &CondMatchResult);     free(ts1);     FreeMatchResult(&CondMatchResult);     if (sizeof(MsgBuffer)-28> strlen(newString)) {  #if _WRITE_LOG      sprintf_s(MsgBuffer,512,"Result (length %d): %s", strlen(newString), newString);      LogMsg(2,MsgBuffer); #endif     }     else { #if _WRITE_LOG         LogMsg(2,"(Log Buffer too small to show new string)");      sprintf_s(MsgBuffer,512,"Result length: %d", strlen(newString));      LogMsg(3,MsgBuffer); #endif     }     // set output params     *result= newString;      // if the current rule asks to record the original URL, then set the OUT flag.      *pRecordOriginalUrl |= current->RecordOriginalUrl;     // check modifiers     if (current->IsRedirect) {      retVal = current->RedirectCode; // = redirect     }     else if (current->IsForbidden) {      // no recurse  #if _WRITE_LOG      LogMsg(2,"returning: Forbidden"); #endif      retVal = 403; // = forbidden     }     else if (current->IsNotFound) {      // no recurse  #if _WRITE_LOG         LogMsg(2,"returning: Not Found"); #endif       retVal = 404; // = not found     }     else {      // rewrite      retVal= 1;      if (current->IsLastIfMatch) {       // no recurse #if _WRITE_LOG       LogMsg(2,"Last if Match"); #endif       break;       //current= NULL; // as a way to stop the loop      }      else {       // by default, we recurse on the RewriteRules.       if (depth < config->IterationLimit) {        char * t;         int rv= ApplyRules(pfc, newString, depth+1, &t, pRecordOriginalUrl);        if (rv) {          *result= t; // a newly allocated string         retVal= rv; // for return to caller         free(newString); // free our string, we no longer need it        }        // else, no match on recursion, so dont free newString (keep the existing result).       }       else { #if _WRITE_LOG        sprintf_s(MsgBuffer,512,"Iteration stopped; reached limit of %d cycles.",           config->IterationLimit);        LogMsg(2,MsgBuffer); #endif       }      }     }     break; // break out of while loop on the first match    }   }   // We did not break out of the loop.    // Therefore, this rule did not apply.    // Therefore, go to the next rule.    if (current!=NULL)    current= current->next; } free(RuleMatchVector); #if _WRITE_LOG sprintf_s(MsgBuffer,512,"ApplyRules: returning %d", retVal); LogMsg(3,MsgBuffer); #endif return retVal; }

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