I was searching something in the Varnish source code when I found a non documented (at least there is nothing in man varnishstat, for Varnish 2.1.2) feature.

Varnishstat can return statistics in XML. How to get this format ? That’s pretty simple, just add the -x argument to varnishstat, for example using :

varnishstat -x

will return something like :

<?xml version="1.0"?>
<varnishstat timestamp="2010-05-27T17:03:26">
 <stat>
 <name>client_conn</name>
 <value>33036</value>
 <description>Client connections accepted</description>
 </stat>
 <stat>
 <name>client_drop</name>
 <value>0</value>
 <description>Connection dropped, no sess/wrk</description>
 </stat>
 <stat>
 <name>client_req</name>
 <value>34740</value>
 <description>Client requests received</description>
 </stat>
 <stat>
 <name>cache_hit</name>
 <value>33580</value>
 <description>Cache hits</description>
 </stat>

[....]

</varnishstat>

So now, if you only want to get cache hits and cache_misses in XML so you can parse them easily on you can do :

varnishstat -f cache_hit,cache_miss -x

And you get something like

<?xml version="1.0"?>
<varnishstat timestamp="2010-05-27T17:05:41">
 <stat>
 <name>cache_hit</name>
 <value>33580</value>
 <description>Cache hits</description>
 </stat>
 <stat>
 <name>cache_miss</name>
 <value>1160</value>
 <description>Cache misses</description>
 </stat>
</varnishstat>

If you want to know more about that, have a look at the do_xml function in varnishstat.c

‘Hope that helps

A quick memo about useful informations I found on Varnish this afternoon after digging in the VCL system. I prefer writing them somewhere before forgetting…

The list of variables available in VCL for each context is available in libvcl/vcc_obj.c which seems to be generated by lib/libvcl/vcc_gen_fixed_token.tcl.

In vcc_gen_fixed_token.vcl the following code :

{ client.ip                IP
 RO
 all
 "const struct sess *"
}

Results in the following C code:

{ "client.ip", IP, 9,
 "VRT_r_client_ip(sp)",
 NULL,
 V_RO,        0,
 VCL_MET_RECV | VCL_MET_PIPE | VCL_MET_PASS | VCL_MET_HASH
 | VCL_MET_MISS | VCL_MET_HIT | VCL_MET_FETCH | VCL_MET_DELIVER
 | VCL_MET_ERROR
 },

“client.ip” is the directive available in a VCL file, “RO” means Read Only – “RW” (Read Write is available as well) – ‘all’ means it is available in all contexts in the VCL file :

VCL_MET_RECV | VCL_MET_PIPE | VCL_MET_PASS | VCL_MET_HASH | VCL_MET_MISS | VCL_MET_HIT | VCL_MET_FETCH | VCL_MET_DELIVER | VCL_MET_ERROR

The list of functions one can use directly (between C{ … }C tags) in VCL seems is available in include/vrt_obj.h VRT_SetHdr and VRT_GetHdr are available in include/vrt.h (for the declaration) and in bin/varnishd/cache_vrt.c.

It is possible to change the TTL of an item directly by using a few lines of C code, like for example :

if (obj.http.My-Header)
{
 C{
   char *ttl;
   ttl = VRT_GetHdr(sp, HDR_OBJ, "\012My-Header:");
   VRT_l_obj_ttl(sp, atoi(ttl));
 }C
   remove obj.http.My-Header;
 }
}

The “\012″ prepended to “My-Header” is the octal version of the length of the “My-Header” string.

The “sp” variable is the variable describing the current session.

HDR_OBJ is a constant available in in include/vrt.h :

enum gethdr_e { HDR_REQ, HDR_RESP, HDR_OBJ, HDR_BEREQ, HDR_BERESP };

It is possible to define custom HTTP headers by using the VRT_SetHdr function available in bin/varnishd/cache_vrt.c.

For example :

C{
 const char *contentMD5 = "12345";
 VRT_SetHdr(sp, HDR_RESP, "\014Content-MD5:", contentMD5, vrt_magic_string_end);
 }C

Reading the VCC code generated from a VCL file is available by running :

varnishd -d -f path/to/file.vcl -C

Useful links:

• Octal/Decimal converter (Yes, it is good to be lazy :p)

• Configuring varnish to use custom http headers