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From 金 戈 <>
Subject [users@httpd] What's the meaning of the FilterProtocol Directive change=1:1
Date Thu, 24 Jan 2013 09:43:14 GMT
Hi, everyone!Sorry, I'm newbie in apache.
After a few days of search. We use apache2.4 for our project.For some improve of our forward
proxy compatibility.
As we need hide some content from our client.So we use forward proxy and filter module.
First we use nginx as the proxy. And some key config below:

                location /
                        proxy_pass      $scheme://$http_host$request_uri;
                       sub_filter              thatsneedchange thatschangethat;
                       sub_filter_types        application/json application/xhtml+xml text/html
                       sub_filter_once         off;

so this can filte and replace the content on website for our client on the internet.
But we met some problem can't resolve:
	Some of clients application didn't support the standard RFC.As we found the sub_filter module
will delete every content-length header of the response. As the lack of the content-length,
our client wouldn't accept that response.
So we came up the apache module filter. As we find the document 

FilterProtocol Directive
This directs mod_filter to deal with ensuring the filter doesn't run when it shouldn't, and
that the HTTP response headers are correctly set taking into account the effects of the filter.

There are two forms of this directive. With three arguments, it applies specifically to a
filter-name and a provider-name for that filter. With two arguments it applies to a filter-name
whenever the filter runs any provider.

proto-flags is one or more of

The filter changes the content, including possibly the content length
The filter changes the content, but will not change the content length
The filter cannot work on byteranges and requires complete input
The filter should not run in a proxy context
The filter transforms the response in a manner incompatible with the HTTP Cache-Control: no-transform
The filter renders the output uncacheable (eg by introducing randomised content changes)

the change=1:1 says 
The filter changes the content, but will not change the content length, and we config our
apache like this
ErrorLog "/var/log/apache2/error.log"
FilterDeclare MYFILTER
FilterProvider  MYFILTER  SUBSTITUTE "%{CONTENT_TYPE} >= 'text/html'"
FilterProvider  MYFILTER  SUBSTITUTE "%{CONTENT_TYPE} >= 'text/plain'"
FilterProvider  MYFILTER  SUBSTITUTE "%{CONTENT_TYPE} >= 'application/json'"
FilterProvider  MYFILTER  SUBSTITUTE "%{CONTENT_TYPE} >= 'application/xhtml+xml'"
<IfModule mod_proxy.c>
ProxyRequests On
ProxyVia On
NoProxy localhost
ProxyBadHeader Ignore
ProxyPreserveHost On
FilterChain     MYFILTER
FilterTrace     MYFILTER 1
FilterProtocol  MYFILTER SUBSTITUTE change=1:1
Substitute "s|27.24.140|49.24.141|ni"
RequestHeader unset Accept-Encoding
But, as we test the apache module filter as add 
FilterProtocol  MYFILTER SUBSTITUTE change=1:1
He also delete the content-length header.
I don't know why. Or what i leave out?
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