Varnish: what does regsuball do? - caching

Question

All that I found about regsuball - it's description from docs: https://book.varnish-software.com/3.0/VCL_Basics.html#vcl-functions . But it still not clear for me what happens inside regsuball function. How does passed params (str, regex, sub) used? Is there a sandbox to test regsuball function online? Thanks!

Answer 1

Syntax
The regsuball() function will perform a regular expression match on a string and replace all occurences with another pattern.
regsuball(string, regex, sub)
The string argument is your input.
The regex argument is the regular expression you're using to match what you're looking for in the input string.
The sub argument is what the input string will be substituted with.
Example
The following example will look for cookies named original-cookie-123, where the numeric suffix could be any number. It replaces that with modified-cookie-123:
regsuball(req.http.Cookie, "original-cookie-([0-9+])", "modified-cookie-\1");
Imagine using passing the following cookie to Varnish:
Cookie: a=1; b=2; original-cookie-1=bla; c=3; original-cookie-2=test
The result after the find/replace would be:
Cookie: a=1; b=2; modified-cookie-1=bla; c=3; modified-cookie-2=test
Whereas regsub() matches and replaces the first occurrence of the pattern, regsuball() replaces all occurrences.
Sandbox
If you want to test regsuball() in a sandbox, the easiest way is by running varnishtest on a testcase. Here's an example:
varnishtest "Regsuball sandbox"
varnish v1 -vcl+backend {
vcl 4.1;
backend default none;
sub vcl_recv {
if (req.http.Cookie) {
set req.http.Cookie = regsuball(req.http.Cookie, "original-cookie-([0-9+])", "modified-cookie-\1");
return (synth(200, req.http.Cookie));
}
return (synth(400, "No cookie found"));
}
sub vcl_synth {
set resp.http.Content-Type = "text/plain; charset=utf-8";
set resp.body = req.http.Cookie;
return (deliver);
}
} -start
client c1 {
txreq -hdr "Cookie: a=1; b=2; original-cookie-1=bla; c=3; original-cookie-2=test"
rxresp
expect resp.body == "a=1; b=2; modified-cookie-1=bla; c=3; modified-cookie-2=test"
} -run
This test case uses the exact example mentioned earlier. After the find and replace, the VCL code in this test case will synthetically return the resulting value as output. There's no need for a backend server, all output is generated by the VCL code.
Running the test case, assuming it is stored in test.vtc can be done using the following command:
varnishtest test.vtc
You can also run this test case isolated within a Docker container. Just run the following command to bootstrap a Varnish Docker container and run the test:
docker run --rm --name varnishtest -v $(pwd)/test.vtc:/etc/varnish/test.vtc varnish:stable varnishtest /etc/varnish/test.vtc