What's the meaning of the FilterProtocol Directive change=1:1

[金 戈 <altman87120@xxxxxxxxx>]

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 /

                {

                        resolver        192.168.10.1;

                        proxy_pass      $scheme://$http_host$request_uri;

                       sub_filter              thatsneedchange thatschangethat;

                       sub_filter_types        application/json application/xhtml+xml text/html text/plain;

                       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

change=yes

The filter changes the content, including possibly the content length

change=1:1

The filter changes the content, but will not change the content length

byteranges=no

The filter cannot work on byteranges and requires complete input

proxy=no

The filter should not run in a proxy context

proxy=transform

The filter transforms the response in a manner incompatible with the HTTP Cache-Control: no-transform header.

cache=no

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

</IfModule>

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?