mod_rewrite.c

            /* now make sure the request gets handled by the proxy handler */
            if (PROXYREQ_NONE == r->proxyreq) {
                r->proxyreq = PROXYREQ_REVERSE;
            }
            r->handler  = "proxy-server";

            rewritelog((r, 1, dconf->directory, "go-ahead with proxy request "
                        "%s [OK]", r->filename));
            return OK;
        }
        else if ((skip = is_absolute_uri(r->filename, NULL)) > 0) {
            /* it was finally rewritten to a remote URL */

            /* because we are in a per-dir context
             * first try to replace the directory with its base-URL
             * if there is a base-URL available
             */
            if (dconf->baseurl != NULL) {
                /* skip 'scheme://' */
                cp = r->filename + skip;

                if ((cp = ap_strchr(cp, '/')) != NULL && *(++cp)) {
                    rewritelog((r, 2, dconf->directory,
                                "trying to replace prefix %s with %s",
                                dconf->directory, dconf->baseurl));

                    /* I think, that hack needs an explanation:
                     * well, here is it:
                     * mod_rewrite was written for unix systems, were
                     * absolute file-system paths start with a slash.
                     * URL-paths _also_ start with slashes, so they
                     * can be easily compared with system paths.
                     *
                     * the following assumes, that the actual url-path
                     * may be prefixed by the current directory path and
                     * tries to replace the system path with the RewriteBase
                     * URL.
                     * That assumption is true if we use a RewriteRule like
                     *
                     * RewriteRule ^foo bar [R]
                     *
                     * (see apply_rewrite_rule function)
                     * However on systems that don't have a / as system
                     * root this will never match, so we skip the / after the
                     * hostname and compare/substitute only the stuff after it.
                     *
                     * (note that cp was already increased to the right value)
                     */
                    cp2 = subst_prefix_path(r, cp, (*dconf->directory == '/')
                                                   ? dconf->directory + 1
                                                   : dconf->directory,
                                            dconf->baseurl + 1);
                    if (strcmp(cp2, cp) != 0) {
                        *cp = '\0';
                        r->filename = apr_pstrcat(r->pool, r->filename,
                                                  cp2, NULL);
                    }
                }
            }

            /* now prepare the redirect... */
            if (rulestatus != ACTION_NOESCAPE) {
                rewritelog((r, 1, dconf->directory, "escaping %s for redirect",
                            r->filename));
                r->filename = escape_absolute_uri(r->pool, r->filename, skip);
            }

            /* append the QUERY_STRING part */
            if (r->args) {
                char *escaped_args = NULL;
                int noescape = (rulestatus == ACTION_NOESCAPE ||
                                (oargs && !strcmp(r->args, oargs)));

                r->filename = apr_pstrcat(r->pool, r->filename, "?",
                                          noescape
                                            ? r->args
                                            : (escaped_args = ap_escape_uri(r->pool, r->args)),
                                          NULL);

                rewritelog((r, 1, dconf->directory, "%s %s to query string for redirect %s",
                            noescape ? "copying" : "escaping",
                            r->args ,
                            noescape ? "" : escaped_args));
            }

            /* determine HTTP redirect response code */
            if (ap_is_HTTP_REDIRECT(r->status)) {
                n = r->status;
                r->status = HTTP_OK; /* make Apache kernel happy */
            }
            else {
                n = HTTP_MOVED_TEMPORARILY;
            }

            /* now do the redirection */
            apr_table_setn(r->headers_out, "Location", r->filename);
            rewritelog((r, 1, dconf->directory, "redirect to %s [REDIRECT/%d]",
                        r->filename, n));
            return n;
        }
        else {
            const char *tmpfilename = NULL;
            /* it was finally rewritten to a local path */

            /* if someone used the PASSTHROUGH flag in per-dir
             * context we just ignore it. It is only useful
             * in per-server context
             */
            if (l > 12 && strncmp(r->filename, "passthrough:", 12) == 0) {
                r->filename = apr_pstrdup(r->pool, r->filename+12);
            }

            /* the filename must be either an absolute local path or an
             * absolute local URL.
             */
            if (   *r->filename != '/'
                && !ap_os_is_path_absolute(r->pool, r->filename)) {
                return HTTP_BAD_REQUEST;
            }

            /* Check for deadlooping:
             * At this point we KNOW that at least one rewriting
             * rule was applied, but when the resulting URL is
             * the same as the initial URL, we are not allowed to
             * use the following internal redirection stuff because
             * this would lead to a deadloop.
             */
            if (ofilename != NULL && strcmp(r->filename, ofilename) == 0) {
                rewritelog((r, 1, dconf->directory, "initial URL equal rewritten"
                            " URL: %s [IGNORING REWRITE]", r->filename));
                return OK;
            }

            tmpfilename = r->filename;

            /* if there is a valid base-URL then substitute
             * the per-dir prefix with this base-URL if the
             * current filename still is inside this per-dir
             * context. If not then treat the result as a
             * plain URL
             */
            if (dconf->baseurl != NULL) {
                rewritelog((r, 2, dconf->directory, "trying to replace prefix "
                            "%s with %s", dconf->directory, dconf->baseurl));

                r->filename = subst_prefix_path(r, r->filename,
                                                dconf->directory,
                                                dconf->baseurl);
            }
            else {
                /* if no explicit base-URL exists we assume
                 * that the directory prefix is also a valid URL
                 * for this webserver and only try to remove the
                 * document_root if it is prefix
                 */
                if ((ccp = ap_document_root(r)) != NULL) {
                    /* strip trailing slash */
                    l = strlen(ccp);
                    if (ccp[l-1] == '/') {
                        --l;
                    }
                    if (!strncmp(r->filename, ccp, l) &&
                        r->filename[l] == '/') {
                        rewritelog((r, 2,dconf->directory, "strip document_root"
                                    " prefix: %s -> %s", r->filename,
                                    r->filename+l));

                        r->filename = apr_pstrdup(r->pool, r->filename+l);
                    }
                }
            }

            /* No base URL, or r->filename wasn't still under dconf->directory
             * or, r->filename wasn't still under the document root. 
             * If there's a context document root AND a context prefix, and 
             * the context document root is a prefix of r->filename, replace.
             * This allows a relative substitution on a path found by mod_userdir 
             * or mod_alias without baking in a RewriteBase.
             */
            if (tmpfilename == r->filename && 
                !(dconf->options & OPTION_IGNORE_CONTEXT_INFO)) { 
                if ((ccp = ap_context_document_root(r)) != NULL) { 
                    const char *prefix = ap_context_prefix(r);
                    if (prefix != NULL) { 
                        rewritelog((r, 2, dconf->directory, "trying to replace "
                                    "context docroot %s with context prefix %s",
                                    ccp, prefix));
                        r->filename = subst_prefix_path(r, r->filename,
                                ccp, prefix);
                    }
                }
            }

            /* now initiate the internal redirect */
            rewritelog((r, 1, dconf->directory, "internal redirect with %s "
                        "[INTERNAL REDIRECT]", r->filename));
            r->filename = apr_pstrcat(r->pool, "redirect:", r->filename, NULL);
            r->handler = REWRITE_REDIRECT_HANDLER_NAME;
            return OK;
        }
    }
    else {
        rewritelog((r, 1, dconf->directory, "pass through %s", r->filename));
        r->filename = ofilename;
        return DECLINED;
    }
}

/*
 * MIME-type hook
 * [T=...,H=...] execution
 */
static int hook_mimetype(request_rec *r)
{
    const char *t;

    /* type */
    t = apr_table_get(r->notes, REWRITE_FORCED_MIMETYPE_NOTEVAR);
    if (t && *t) {
        rewritelog((r, 1, NULL, "force filename %s to have MIME-type '%s'",
                    r->filename, t));

        ap_set_content_type(r, t);
    }

    /* handler */
    t = apr_table_get(r->notes, REWRITE_FORCED_HANDLER_NOTEVAR);
    if (t && *t) {
        rewritelog((r, 1, NULL, "force filename %s to have the "
                    "Content-handler '%s'", r->filename, t));

        r->handler = t;
    }

    return OK;
}


/*
 * "content" handler for internal redirects
 */
static int handler_redirect(request_rec *r)
{
    if (strcmp(r->handler, REWRITE_REDIRECT_HANDLER_NAME)) {
        return DECLINED;
    }

    /* just make sure that we are really meant! */
    if (strncmp(r->filename, "redirect:", 9) != 0) {
        return DECLINED;
    }

    /* now do the internal redirect */
    ap_internal_redirect(apr_pstrcat(r->pool, r->filename+9,
                                     r->args ? "?" : NULL, r->args, NULL), r);

    /* and return gracefully */
    return OK;
}


/*
 * +-------------------------------------------------------+
 * |                                                       |
 * |                Module paraphernalia
 * |                                                       |
 * +-------------------------------------------------------+
 */

static const command_rec command_table[] = {
    AP_INIT_FLAG(    "RewriteEngine",   cmd_rewriteengine,  NULL, OR_FILEINFO,
                     "On or Off to enable or disable (default) the whole "
                     "rewriting engine"),
    AP_INIT_ITERATE( "RewriteOptions",  cmd_rewriteoptions,  NULL, OR_FILEINFO,
                     "List of option strings to set"),
    AP_INIT_TAKE1(   "RewriteBase",     cmd_rewritebase,     NULL, OR_FILEINFO,
                     "the base URL of the per-directory context"),
    AP_INIT_RAW_ARGS("RewriteCond",     cmd_rewritecond,     NULL, OR_FILEINFO,
                     "an input string and a to be applied regexp-pattern"),
    AP_INIT_RAW_ARGS("RewriteRule",     cmd_rewriterule,     NULL, OR_FILEINFO,
                     "an URL-applied regexp-pattern and a substitution URL"),
    AP_INIT_TAKE23(   "RewriteMap",      cmd_rewritemap,      NULL, RSRC_CONF,
                     "a mapname and a filename and options"),
    { NULL }
};

static void ap_register_rewrite_mapfunc(char *name, rewrite_mapfunc_t *func)
{
    apr_hash_set(mapfunc_hash, name, strlen(name), (const void *)func);
}

static void register_hooks(apr_pool_t *p)
{
    /* fixup after mod_proxy, so that the proxied url will not
     * escaped accidentally by mod_proxy's fixup.
     */
    static const char * const aszPre[]={ "mod_proxy.c", NULL };

    /* make the hashtable before registering the function, so that
     * other modules are prevented from accessing uninitialized memory.
     */
    mapfunc_hash = apr_hash_make(p);
    APR_REGISTER_OPTIONAL_FN(ap_register_rewrite_mapfunc);

    ap_hook_handler(handler_redirect, NULL, NULL, APR_HOOK_MIDDLE);
    ap_hook_pre_config(pre_config, NULL, NULL, APR_HOOK_MIDDLE);
    ap_hook_post_config(post_config, NULL, NULL, APR_HOOK_MIDDLE);
    ap_hook_child_init(init_child, NULL, NULL, APR_HOOK_MIDDLE);

    ap_hook_fixups(hook_fixup, aszPre, NULL, APR_HOOK_FIRST);
    ap_hook_fixups(hook_mimetype, NULL, NULL, APR_HOOK_LAST);
    ap_hook_translate_name(hook_uri2file, NULL, NULL, APR_HOOK_FIRST);
}

    /* the main config structure */
AP_DECLARE_MODULE(rewrite) = {
   STANDARD20_MODULE_STUFF,
   config_perdir_create,        /* create per-dir    config structures */
   config_perdir_merge,         /* merge  per-dir    config structures */
   config_server_create,        /* create per-server config structures */
   config_server_merge,         /* merge  per-server config structures */
   command_table,               /* table of config file commands       */
   register_hooks               /* register hooks                      */
};

/*EOF*/