Apache module杂记
可以基于正则表达式修改文本内容的apache module:mod_sed:实现了类似sed功能的module,可以通过正则表达式修改文本内容。apache2.3中加入了这个module,但是这个module也可以用于apache 2.0版本。可以到http://src.opensolaris.org/source/xref/webstack/mod_sed/下载源代码,readme里有相应的编译命令：/http安装路径/bin/apxs -i -c mod_sed.c regexp.c sed0.c sed1.c
mod_substitute:功能和mod_sed类似，默认加入到apache2.2中http://httpd.apache.org/docs/2.2/mod/mod_substitute.html
mod_line_edit:也可以基于正则表达式替换文本内容，可以就该html/css/javascript。但是它和前两者不同的是mod_line_edit的to-pattern可以使用apache的环境变量http://apache.webthing.com/mod_line_edit/，这个功能正是我最近需要的。
例如下面的配置可以在<head>标签后插入一个<meta/>标签并且可以将环境变量unique_id的值添加到meta的属性中去（unique_id环境变量需要mod_unique_id的支持http://lamp.linux.gov.cn/apache/apachemenu/mod/mod_unique_id.html）
lerewriterule "<head>" "<head><meta http-equiv='request-id' content='${unique_id}' />" iv
mod_proxy_html:可以基于html标签进行比较比较精细的内容修改操作http://apache.webthing.com/mod_proxy_html/
以上这些module都是基于apache的过滤器的功能来完成对相应内容的修改（类似servlet里的filter）http://lamp.linux.gov.cn/apache/apachemenu/filter.html
http://lamp.linux.gov.cn/apache/apachemenu/images/filter_arch.gif
mod_line_edit使用经验:
1.mod_line_edit的性能问题：考虑到系统中有500-700k的html页面，因此我就对mod_line_edit在展现1m的静态html做了一下压力测试。测试结果非常不理想，在不添加mod_line_edit时tps在500+，加上mod_line_edit后tps只有1(狂汗...)。
2.mod_line_edit的代码分析：
/* mod_line_edit顾名思义就是对文本内容按行进行编辑， * 因此mod要先对输出流进行整理，每一行内容收集到一个apr_bucket里， * 然后将所有行数据放到bbline中，下面的代码实现的就是这个用途。 */bbline = apr_brigade_create(f->r->pool, f->c->bucket_alloc) ;/* first ensure we have no mid-line breaks that might be in the * middle of a search string causing us to miss it!at the same * time we split into lines to avoid pattern-matching over big * chunks of memory. */while ( b != apr_brigade_sentinel(bb) ) { if ( !apr_bucket_is_metadata(b) ) { if ( apr_bucket_read(b, &buf, &bytes, apr_block_read) == apr_success ) {if ( bytes == 0 ) {apr_bucket_remove(b) ;} else while ( bytes > 0 ) {switch (cfg->lineend) {case lineend_unix: le = memchr(buf, '\n', bytes) ; break ;case lineend_mac: le = memchr(buf, '\r', bytes) ; break ;case lineend_dos: /* edge-case issue: if a \r\n spans buckets it'll get missed. * not a problem for present purposes, but would be an issue * if we claimed to support pattern matching on the lineends. */ found = 0 ; le = memchr(buf+1, '\n', bytes-1) ; while ( le && !found ) { if ( le[-1] == '\r' ) { found = 1 ; } else { le = memchr(le+1, '\n', bytes-1 - (le+1 - buf)) ; } } if ( !found ) le = 0 ; break;case lineend_any:case lineend_unset: /* edge-case notabug: if a \r\n spans buckets it'll get seen as * two line-ends.it'll insert the \n as a one-byte bucket. */ le_n = memchr(buf, '\n', bytes) ; le_r = memchr(buf, '\r', bytes) ; if ( le_n != null ) if ( le_n == le_r + sizeof(char)) le = le_n ; else if ( (le_r < le_n) && (le_r != null) ) le = le_r ; else le = le_n ; else le = le_r ; break;case lineend_none: le = 0 ; break;case lineend_custom: le = memchr(buf, cfg->lechar, bytes) ; break;}if ( le ) { /* found a lineend in this bucket. */ offs = 1 + ((unsigned int)le-(unsigned int)buf) / sizeof(char) ; apr_bucket_split(b, offs) ; bytes -= offs ; buf += offs ; b1 = apr_bucket_next(b) ; apr_bucket_remove(b); /* is there any previous unterminated content ? */ if ( !apr_brigade_empty(ctx->bbsave) ) { /* append this to any content waiting for a lineend */ apr_brigade_insert_tail(ctx->bbsave, b) ; rv = apr_brigade_pflatten(ctx->bbsave, &fbuf, &fbytes, f->r->pool) ; /* make b a new bucket of the flattened stuff */ b = apr_bucket_pool_create(fbuf, fbytes, f->r->pool,f->r->connection->bucket_alloc) ; /* bbsave has been consumed, so clear it */ apr_brigade_cleanup(ctx->bbsave) ; } /* b now contains exactly one line */ apr_brigade_insert_tail(bbline, b); b = b1 ;} else { /* no lineend found.remember the dangling content */ apr_bucket_remove(b); apr_brigade_insert_tail(ctx->bbsave, b); bytes = 0 ;}} /* while bytes > 0 */ } else {/* bucket read failed - oops !let's remove it. */apr_bucket_remove(b); } } else if ( apr_bucket_is_eos(b) ) { /* if there's data to pass, send it in one bucket */ if ( !apr_brigade_empty(ctx->bbsave) ) { rv = apr_brigade_pflatten(ctx->bbsave, &fbuf, &fbytes, f->r->pool) ; b1 = apr_bucket_pool_create(fbuf, fbytes, f->r->pool,f->r->connection->bucket_alloc) ; apr_brigade_insert_tail(bbline, b1); } apr_brigade_cleanup(ctx->bbsave) ; /* start again rather than segfault if a seriously buggy * filter in front of us sent a bogus eos */ f->ctx = null ; /* move the eos to the new brigade */ apr_bucket_remove(b); apr_brigade_insert_tail(bbline, b); } else { /* chop flush or unknown metadata bucket types */ apr_bucket_delete(b); } /* ok, reset pointer to what's left (since we're not in a for-loop) */ b = apr_brigade_first(bb) ;}
/* 这里就是循环使用配置的规则处理整理好的每行apr_bucket */for (i = 0; i < ctx->rewriterules->nelts; ++i) { for ( b = apr_brigade_first(bbline) ;b != apr_brigade_sentinel(bbline) ;b = apr_bucket_next(b) ) { if ( !apr_bucket_is_metadata(b)&& (apr_bucket_read(b, &buf, &bytes, apr_block_read) == apr_success)) {if ( rules.flags & m_regex ) {bufp = apr_pstrmemdup(ctx->lpool, buf, bytes) ;while ( ! ap_regexec(rules.from.r, bufp, nmatch, pmatch, 0) ) { match = pmatch.rm_so ; subs = ap_pregsub(f->r->pool, rules.to, bufp, nmatch, pmatch) ; apr_bucket_split(b, match) ; b1 = apr_bucket_next(b) ; apr_bucket_split(b1, pmatch.rm_eo - match) ; b = apr_bucket_next(b1) ; apr_bucket_delete(b1) ; b1 = apr_bucket_pool_create(subs, strlen(subs), f->r->pool,f->r->connection->bucket_alloc) ; apr_bucket_insert_before(b, b1) ; bufp += pmatch.rm_eo ;}} else {bufp = buf ;while (subs = apr_strmatch(rules.from.s, bufp, bytes),subs != null) { match = ((unsigned int)subs - (unsigned int)bufp) / sizeof(char) ; bytes -= match ; bufp += match ; apr_bucket_split(b, match) ; b1 = apr_bucket_next(b) ; apr_bucket_split(b1, rules.length) ; b = apr_bucket_next(b1) ; apr_bucket_delete(b1) ; bytes -= rules.length ; bufp += rules.length ; b1 = apr_bucket_immortal_create(rules.to, strlen(rules.to),f->r->connection->bucket_alloc) ; apr_bucket_insert_before(b, b1) ;}} } } /* if we used a local pool, clear it now */ if ( (ctx->lpool != f->r->pool) && (rules.flags & m_regex) ) { apr_pool_clear(ctx->lpool) ; }}
正因为是这个filter对所有输出流会进行遍历、整理、拷贝，然后又将整理好的流按行进行处理。这样如果输出大文本势必会影响性能。
3.mod_line_edit的优化：针对我对mod_line_edit的需求比较简单，只是对<head>标记后面追加一些内容。所以没有必要对整个输出流进行遍历。只要对输出流中<head>标签处理以后就可以结束对输出流的处理，直接调用return ap_pass_brigade(f->next, bb) ;将流传递给下一个filter即可。
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