Apache :: How to stop a script tag from double insertion

apishdad · Joined: 01 Jul 2019 Posts: 52 Location: Canada, Toronto

Hi,
I have a situation where I am trying to insert a third party widget which is basically a <script> tag, but the script tag gets inserted twice.

My setup is very similar to the following

<Proxy balancer://MyServer>
require all granted
BalancerMember http://server1 loadfactor=1 max=100 retry=60 connectiontimeout=300 timeout=300 route=Route1
BalancerMember http://Servr2 loadfactor=2 max=150 retry=60 connectiontimeout=300 timeout=300 route=Route2
ProxySet lbmethod=bytraffic stickysession=JSESSIONID|jsessionid scolonpathdelim=On
</Proxy>

ProxyPass "/" "balancer://MyServer/"
ProxyPassReverse "/" "balancer://MyServer/"

<LocationMatch ^/(.*)$>
FilterChain Replace Compress
RequestHeader unset Accept-Encoding
RequestHeader set Accept-Encoding identity

SubstituteMaxLineLength 5M

Substitute "s#</head>#\
<script>\
alert('Testing')\
</script>\
</head>\
#inq"
</LocationMatch>

What is happening is that when the page loads and I go to "View Source" for the page. I see something like this in the page:

<head>
<script>\
alert('Testing')\
</script>\

<script>\
alert('Testing')\
</script>\
</head>

i believe this is because on the first Proxypass it replaces the </head> tag with the whole <script>...</script></head> and on proxypassrevrese it replaces the </head> tag that is already in the first pass with another script block similar to above.

My question is this :

How can I avoid a second replacement of my </head> element with the script tag.

Thanks and greatly appreciated for your help.

zhangdaoming · Joined: 08 Feb 2025 Posts: 3

<LocationMatch ^/(.*)$>
FilterChain Replace Compress
RequestHeader unset Accept-Encoding
RequestHeader set Accept-Encoding identity
SubstituteMaxLineLength 5M

RequestHeader set MY_REPLACE_HEAD "true"

Substitute "s#</head>#\
<script>\
alert('One~')\
</script>\
</head>\
#inq" env=MY_REPLACE_HEAD

# clear run tag
RequestHeader unset MY_REPLACE_HEAD
</LocationMatch>

apishdad · Joined: 01 Jul 2019 Posts: 52 Location: Canada, Toronto

Thanks for the great suggestion. But I am getting this error:

AH00526: Syntax error on line 106 of D:/MyCode/Apache_Code.conf:
Substitute takes one argument, Pattern to filter the response content (s/foo/bar/[inf])

This error appears when I put the
env=MY_REPLACE_HEADER at the location where it says

#inq" env=MY_REPLACE_HEADER

When I take the env part I get "Syntax OK" check.

Any ideas?

apishdad · Joined: 01 Jul 2019 Posts: 52 Location: Canada, Toronto

Does anyone else has any ideas?

substitute command is not very friendly with Environment variables.

James Blond

Maybe mod_proxy_html is your friend.

apishdad · Joined: 01 Jul 2019 Posts: 52 Location: Canada, Toronto

apishdad · Joined: 01 Jul 2019 Posts: 52 Location: Canada, Toronto

There is a different way to approach this too, but it leaves no </HEAD> tag.

The other way is to

use the substitute command as such without the </head> element in the .conf file but after that I am not quite sure how to just add a </HEAD> tag. So the code looks like

Substitute "s#</head>#\
<script>\
alert('One~')\
</script>\
#inq"

then I get

<script> alert('One~') </script>

in the HTML but I need a closing </head> tag. I dont know how to add that.

apishdad · Joined: 01 Jul 2019 Posts: 52 Location: Canada, Toronto

Figured it out...

At the beginning of my config file I had the following

FilterDeclare Replace
FilterProvider Replace Substitute "%{CONTENT_TYPE} =~ m#^application/(javascript|json|xml)#i"
FilterProvider Replace Substitute "%{CONTENT_TYPE} =~ m#^text/(css|html|javascript|plain|xml)#i"

I had to comment the line that says:

FilterProvider Replace Substitute "%{CONTENT_TYPE} =~ m#^text/(css|html|javascript|plain|xml)#i"

and it worked.