Varnish trailing slash rewrite - varnish-vcl

Question

I'm trying to setup varnish to handle my default url which is example.url.co.uk.
If it hits example.url.co.uk or example.url.co.uk/ I want it to redirect or rewrite to example.url.co.uk/site which within the tomcat application sends it to a login page.
sub vcl_recv {
if ((req.url ~ "") || (req.url ~"^/")) {
set req.http.location = "https://example.url.co.uk/site" + req.url;
return (synth(750, "Found"));
}
}
sub vcl_synth {
if (resp.status == 301) {
set resp.http.Location = req.http.x-redir;
return (deliver);
}
if (resp.status == 750) {
set resp.http.Location = req.http.location;
set resp.status = 302;
return (deliver);
}
}
However when I use my attempt that this I get example.url.co.uk/site/site/site/site...
So I'm obviously stuck in a loop and I've been banging my head on this for a week trying to find the right solution! Please save me from my own stupidity I'm sure!

Answer 1

the problem is that req.url ~ "" matches everthing. as it is used as a regular expression. also your req.url ~ "^/" is too open.
changing it to:
if (req.url == "" || req.url ~"^/$") {
should fix it, verifying that it is either empty or / it self.
here is a simple varnishtest to verify the behaviour:
varnishtest "Test Redirect"
server s1 {
rxreq
txresp
rxreq
txresp
} -start
varnish v1 -vcl+backend {
sub vcl_recv {
if (req.url == "" || req.url ~"^/$") {
set req.http.location = "https://example.url.co.uk/site" + req.url;
return (synth(750, "Found"));
}
}
sub vcl_synth {
if (resp.status == 301) {
set resp.http.Location = req.http.x-redir;
return (deliver);
}
if (resp.status == 750) {
set resp.http.Location = req.http.location;
set resp.status = 302;
return (deliver);
}
}
} -start
client c1 {
txreq -url "/"
rxresp
expect resp.status == 302
} -run
client c1 {
txreq -url "/site"
rxresp
expect resp.status == 200
} -run
you can run it with varnishtest test.vtc