[Varnish] #1579: vcc: conversion to string with + operator incomplete

Varnish varnish-bugs at varnish-cache.org
Mon Sep 22 16:38:28 CEST 2014

#1579: vcc: conversion to string with + operator incomplete
 Reporter:  slink     |       Owner:  phk
     Type:  defect    |      Status:  closed
 Priority:  normal    |   Milestone:  Varnish 4.0 release
Component:  varnishd  |     Version:  trunk
 Severity:  normal    |  Resolution:  fixed
 Keywords:            |

Comment (by Lasse Karstensen <lkarsten@…>):

 In [7d99e1be1c0b772fb84db18bce12eb69c09a22f1]:
 #!CommitTicketReference repository=""
 Rework how we infer types in the VCC expresion evaluator.

 This mainly (only ?) changes things when we ask for an expression

 Previously addition and subtraction would follow the general rule,
 "first argument determines intial type" and that would make an
 expression like this fail:

         set resp.http.server_port_foo = std.port(server.ip) + "_foo";

 Because the addition tries to evaluate  "INT + STRING".

 The idea was that people would rewrite this as:

         set resp.http.server_port_foo = "" + std.port(server.ip) + "_foo";

 To make the first argument STRING and everything will then just work.

 However, this is needlessly strict in the case where we are actively
 desiring the expression to evaluate to STRING -- like above where
 resp.http.* has type STRING.

 With the new code, when an impossible addition is encountered, it
 will look at the type requested of the expression, and if it is
 STRING, convert the current subexpression to STRING and continue

 A large number of subtests which are designed to fail started working
 with this change, they have been fixed by not using *.http.* variables
 as scaffolding..

 You can still get into some weird corner-cases like the difference

         set resp.http.foobar = req.ttl + 1s + "_" + req.ttl + 1s;
         set resp.http.foobar = req.ttl + 1s + "_" + req.ttl + 1;
         set resp.http.foobar = req.ttl + 1s + "_" + (req.ttl + 1s);

 (Hint: The last one is the only one which does what you think)

 Fixes #1579

Ticket URL: <https://www.varnish-cache.org/trac/ticket/1579#comment:3>
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