如何在Varnish 4中覆盖vcl_hash方法

Question

I have the following code snip-it for Varnish 2 to only include a subset of fields in it's hashing logic.

sub vcl_hash {
  set req.http.temp = regsub(req.url, "^.*[?&](q=[^&]*).*$", "\1");
  set req.http.temp2 = regsub(req.url, "^.*[?&](limit=[^&]*).*$", "\1");
  set req.http.temp3 = regsub(req.url, "^.*[?&](classes=[^&]*).*$", "\1");
  set req.http.temp3 = regsub(req.url, "^.*[?&](offset=[^&]*).*$", "\1");
  set req.hash += req.http.temp;
  set req.hash += req.http.temp2;
  set req.hash += req.http.temp3;
  set req.hash += req.http.temp4;
  return(hash); 
}

How can I convert this code to work with Varnish 4?

Answer 1

You can use the built-in function hash_data

First, call the hash_data function with your url but without the query string. Then call again the hash_data function for every fields you want to add to the hash logic.

You should end up with something like that :

sub vlc_hash {
  hash_data(__YOUR_REQUEST_WITHOUT_QUERY_STRING__);
  hash_data(regsub(req.url, "^.*[?&](q=[^&]*).*$", "\1"));
  hash_data(regsub(req.url, "^.*[?&](limit=[^&]*).*$", "\1"));
  hash_data(regsub(req.url, "^.*[?&](classes=[^&]*).*$", "\1"));
  hash_data(regsub(req.url, "^.*[?&](offset=[^&]*).*$", "\1"));
  return (lookup);
}

Note that your vlc_hash function must return lookup to abort the execution of the default VCL.

You can read the documentation of the Varnish 4 hashing logic at the following address https://www.varnish-cache.org/docs/4.0/users-guide/vcl-hashing.html