On Sun, 18 Oct 2015 00:07:13 +0200
PiBa-NL <[email protected]> wrote:
> Hi haproxy list,
>
> For testing purposes i am trying to 'modify' a response of a webserver
> but only having limited success. Is this supposed to work?
> As a more usefull goal than the current LAL to TST replacement i imagine
> rewriting absolute links on a webpage could be possible which is
> sometimes problematic with 'dumb' webapplications..
>
> Or is it outside of the current scope of implemented functionality? If
> so, it on the 'lua todo list' ?
>
> I tried for example a configuration like below. And get several
> different results in the browser.
> -Sometimes i get 4 times TSTA
> -Sometimes i see after the 8th TSTA- Connection: keep-alive << this
> happens most of the time..
> -Sometimes i get 9 times TSTA + STOP << this would be the desired
> outcome (only seen very few times..)
>
> Probably due to the response-buffer being filled differently due to
> 'timing'..
>
> The "connection: keep-alive" text is probably from the actual server
> reply which is 'appended' behind the response generated by my lua
> script.?. However shouldn't the .done() prevent that from being send to
> the client?
>
> Ive tried putting a loop into the lua script to call res:get() multiple
> times but that didnt seem to work..
>
> Also to properly modify a page i would need to know all changes before
> sending the headers with changed content-length back to the client..
>
> Can someone confirm this is or isn't (reliably) possible? Or how this
> can be scripted in lua differently?
Hello,
Your script replace 3 bytes by 3 bytes, this must run with HTTP, but if
your replacement change the length of the response, you can have some
difficulties with clients, or with keepalive.
The res:get(), returns the current content of the response buffer.
Maybe it not contains the full response. You must execute a loop with
regular "core.yield()" to get back the hand to HAProxy and wait for new
data. When all the data are read, res:get() returns an error.
The res:send() is dangerous because it send data directly to the client
without the end of haproxy analysis. Maybe it is the cause o your
problem.
Try to use res:set().
The difficulty is that another "res:get()" returns the same data that
these you put.
I don't known if you can modify an http response greater than one
buffer.
The function res:close() closes the connection even if HAProxy want to
keep the connection alive. I suggest that you don't use this function.
I reproduce the error message using curl. By default curl tries
to transfer data with keepalive, and it is not happy if the all the
announced data are not transfered.
Connection: keep-alive curl: (18) transfer closed with outstanding
read data remaining
It seems that i reproduce a bug. I'm looking for.
Thierry
> Thanks in advance,
> PiBa-NL
>
> ## haproxy.cfg
> listen proxyresponse
> bind :10006
> mode http
> http-response lua.luahttpresponse
> server x 192.168.0.40:302
>
> ## script.lua
> function luahttpresponse(txn)
> local response2 = txn.res:get()
> response2 = string.gsub(response2,"LAL","TST")
> txn.res:send(response2)
> txn.done()
> end
> core.register_action("luahttpresponse" , { "http-res" }, luahttpresponse);
>
> ## webpage.aspx , with 2.7KB output.
> ------------------
> <%@ Page Language="C#" %>
> <html><body>START
> <% var x = new String('x', 250);
> x = "<input type=\"hidden\" value=\""+x+"\" />"; %>
> 1 -LALA- <% Response.Write(x); %>
> 2 -LALA- <% Response.Write(x); %>
> 3 -LALA- <% Response.Write(x); %>
> 4 -LALA- <% Response.Write(x); %>
> 5 -LALA- <% Response.Write(x); %>
> 6 -LALA- <% Response.Write(x); %>
> 7 -LALA- <% Response.Write(x); %>
> 8 -LALA- <% Response.Write(x); %>
> 9 -LALA- <% Response.Write(x); %>
> STOP
> --------------------
>
>
