Varnish basic config file throws "VCL compilation failed" when I try to use std.syslog. Why?

Question

I have a simple VCL file as follows:

vcl 4.0;

import std;

backend default {
    .host = "127.0.0.1";
    .port = "3333";
}

sub vcl_recv {
    std.log("req.host: "+req.host);
}

sub vcl_backend_response {

}

sub vcl_deliver {

}

When I try to start varnishd with this config on my Mac, I get the following error:

Error:
Message from VCC-compiler:
Symbol not found: 'req.host' (expected type STRING):
('/Users/jononomo/dev/my_project/deploy/testing.vcl' Line 30 Pos 26)
    std.log("req.host: "+req.host);
-------------------------########--

('/Users/jononomo/dev/my_project/deploy/testing.vcl' Line 30 Pos 5) -- ('/Users/jononomo/dev/my_project/deploy/testing.vcl' Line 30 Pos 25)
    std.log("req.host: "+req.host);
----#####################----------

Running VCC-compiler failed, exited with 2
VCL compilation failed

I have tried different variations of this line:

std.log("req.host: "+req.host);

such as:

std.log(req.host: '+req.host);
std.log("req.host: ",req.host);
std.log('req.host: ',req.host);
std.log('hello');

but none of them work.

How can I do simple logging from my VCL file?

Thanks.

UPDATE: std.log("hello") seems to compile... however, I need to log information about the request object and req, request, etc do not exist.

Answer 1

Use req.http.host instead:

vcl 4.0;

import std;

backend default {
    .host = "127.0.0.1";
    .port = "3333";
}

sub vcl_recv {
    std.log("req.host: " + req.http.host);
}

sub vcl_backend_response {

}

sub vcl_deliver {

}