Set my own value in C for use in VCL

Philip Prince philip.prince at
Thu Jan 20 14:26:37 CET 2011

Dear List,

I am using Varnish 2.1.3 on Ubuntu 10.10.

I would like to use a C routine to set a value which I could pass on to VCL. I have made this simple start derived from examples I have seen on the web. I direct the request to a PHP file that streams out simulated data. If I comment out the VRT_SetHdr I get the expected data, otherwise I get an empty file.

  #include <stdlib.h>

# This is a basic VCL configuration file for varnish.  See the vcl(7)
# man page for details on VCL syntax and semantics.
# Default backend definition.  Set this to point to your content
# server.
backend default {
    .host = "";
    .port = "80";

sub vcl_miss {

    void setmyownvalue () {
      VRT_SetHdr(sp, HDR_REQ, "\013X-My-Own-Value:", "1", vrt_magic_string_end);

  if (req.http.X-My-Own-Value=="1"){
    error 418 "Short and Stout";

  return (fetch);

It has to be easy; my apologies for being so thick. I have looked for VRT documentation but I must be looking in all the wrong places...

Thank you,
Philip Prince 

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