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Wes_98712's avatar
Wes_98712
Icon for Nimbostratus rankNimbostratus
Mar 30, 2007

rewrite HTML in response

Interesting dilemma we have here. We are about to release a new version of a site we own, but don't have time to change the HTML on a particular page, essentially the hyperlink points to site that will be going away after launch. So, what I want to do, is look for the hyperlink in the response and replace it with something else. I am not even sure if it is possible.

 

 

Right now the page links to a particular URL, upon response from any server, I want to replace www.foo.com/someuri with www.foofoo.com/somenewuri.

 

 

I thought HTTP_RESPONSE would be a good place to start, but I have a feeling I am going to have to inspect the body in order to do this, and I am really not sure what performance impact this will have.

 

 

I have a couple of options that I am playing with, 1 basically transfers the domain to us, then we handle requests as a redirect to the new destination, and of course replace the links in the code...course that all makes sense, but timing is critical, so if I can put this in place I'll be gold.

 

 

Not sure where to start with this, since it deals more with the body of the response rather than the header.

 

 

All comments would be appreciated.
application delivery
dev
devops
iRules

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  • Wes_98712's avatar
    Wes_98712
    Icon for Nimbostratus rankNimbostratus
    Mar 30, 2007
    BTW I had thought the following would work, but no dice, it doesn't find anything, so I must be misinterpreting the function of the regsub or possibly the HTTP::payload

    
when HTTP_RESPONSE {
    set old_link "www.somesite.com/someuri"
    set new_link "host.somesite.com/somenewuri"
 
    if { [regsub -all {$old_link} [HTTP::payload] $new_link newdata] } {
       log "Replacing $old_link with $new_link"  
       HTTP::payload replace 0 [HTTP::payload length] $newdata  
       HTTP::release
    } else {
       log "replacing nothing"
   } 
}

    What am I doing wrong here?
  • JRahm's avatar
    JRahm
    Icon for Admin rankAdmin
    Mar 30, 2007
    you'd need an HTTP::collect in the HTTP_RESPONSE event, then look at your payload in the HTTP_RESPONSE_DATA event.

     

     

    Are you on v9.2 or later? You could use the stream profile to search and replace host1 with host2
  • Wes_98712's avatar
    Wes_98712
    Icon for Nimbostratus rankNimbostratus
    Mar 30, 2007
    Something like as follows right?

    Taken from the creditcard scrubber.

    
when HTTP_RESPONSE {
   if { $scrub_content } {
      if { [HTTP::header exists "Content-Length"] } {
         set content_length [HTTP::header "Content-Length"]
         } else {
            set content_length 4294967295
         }
         if { $content_length > 0 } {
            HTTP::collect $content_length
         }
      }
}
when HTTP_RESPONSE_DATA {
    set old_link "www.somedomain.com/someuri"
    set new_link "www.somedomain1.com/somenewuri"
 
    if { [regsub -all {$old_link} [HTTP::payload] $new_link newdata] } {
       log "Replacing $old_link with $new_link"  
       HTTP::payload replace 0 [HTTP::payload length] $newdata  
    } else {
       log "replacing nothing"
   } 
}

    I think the issue is that I am not replacing the string correctly, the regsub seems like it should work, if it matches the old_link in the payload, replace etc. But I think I am off target.
  • Joe_Pruitt's avatar
    Joe_Pruitt
    Mar 30, 2007
    This is overlooked most of the time, but if you want a simple string replacement, the easiest solution is to use a Stream Profile associate with your virutal. There are no iRules involved. Just create a stream profile with the Source value as "www.somedomain.com/someuri" and the Target value as "www.somedomain1.com/somenewuri" and apply it to your virtual.

     

     

    Keep in mind that the stream profile will only work with fixed strings, regular expressions and wildcards are not supported.

     

     

    -Joe
  • Wes_98712's avatar
    Wes_98712
    Icon for Nimbostratus rankNimbostratus
    Mar 30, 2007
    Ok, so I tried both setting up a stream profile and looking for and replacing the string in question, and it gave me a page cannot be displayed error, I also tried it in a irule as follows:

    
when HTTP_RESPONSE {
STREAM::enable
STREAM::expression "@careers-24hourfit@24hr.e-selecsys@"
}

    It fails as well with the page cannot be displayed, which tells me it's either one of two things, either the response back from the client to the server is getting jacked up because this is a servlet object, or the stream profile isn't working as expected. I think it's the first theory, because I tried a simple string substitution of the following

    
when HTTP_RESPONSE {
STREAM::enable
STREAM::expression "@careers@24hr@"
}

    And the page loads for about a second then goes to a 503 error, or at least that is what it appears to be...cannot tell for sure since I'm on IE 7, I'll test with firefox and see if I can diagnose the problem.
  • Joe_Pruitt's avatar
    Joe_Pruitt
    Mar 30, 2007
    Do you have "Response Chunking" set to "Rechunk" in your HTTP Profile? That might be something to check as I believe that needs to be set for the stream profile to work when the response size changes.
  • Wes_98712's avatar
    Wes_98712
    Icon for Nimbostratus rankNimbostratus
    Mar 30, 2007
    Bammo, that did it, rechunk was the key, it replaces the string perfectly.
  • Wes_98712's avatar
    Wes_98712
    Icon for Nimbostratus rankNimbostratus
    Mar 30, 2007
    Forgot to ask, what if I have multiple static strings in the same page that I want to replace, would I have to have separate streams profiles, or could I reuse?

    On second thought, because rechunk was the problem, I could simply do the following right?

    
when HTTP_RESPONSE {
STREAM::enable
STREAM::expression "@http://www.somedomain.com/someuri@https://somehost.domain/somenewuri@ @http://www.someotherdomain.com/someuri@https://somehost.domain/somenewuri@""
}

    Let me know thoughts on this. Profile is great, if I can add multiple strings, if not I'll have to go with iRule.
  • Joe_Pruitt's avatar
    Joe_Pruitt
    Mar 30, 2007
    BTW, there is a good overview of the Stream Profile iRule components in this thread:

     

     

    http://devcentral.f5.com/Default.aspx?tabid=53&view=topic&forumid=5&postid=5097

     

    Click here

     

     

     

    -Joe
  • Wes_98712's avatar
    Wes_98712
    Icon for Nimbostratus rankNimbostratus
    Mar 30, 2007
    Yes, we are good to go. The back door comment is also documented in the following Solutions article:

    
https://tech.f5.com/home/solutions/sol7027.htmlAsk F5 Solution 7027

    The iRule worked great, but I think the profile is the way to go.