vmod_constant(3)

📦 version 0.0~git20260330, in ubuntu stonking

💖 vmod_constant — constants for VCL 💖

okay bestie, gather round, because today we're talking about vmod_constant(3), a manual page from the Library Functions Manual, and honestly? it's giving "set it once, use it everywhere" and I'm obsessed. 🎀

✨ SYNOPSIS ✨

import constant [as name] [from "path"]

new xacl = constant.acl([ACL init])

    ACL xacl.get([ACL fallback])

    BOOL xacl.defined()

new xbackend = constant.backend([BACKEND init])

    BACKEND xbackend.get([BACKEND fallback])

    BOOL xbackend.defined()

new xblob = constant.blob([BLOB init])

    BLOB xblob.get([BLOB fallback])

    BOOL xblob.defined()

new xbody = constant.body([BODY init])

    BODY xbody.get([BODY fallback])

    BOOL xbody.defined()

new xbool = constant.bool([BOOL init])

    BOOL xbool.get([BOOL fallback])

    BOOL xbool.defined()

new xbytes = constant.bytes([BYTES init])

    BYTES xbytes.get([BYTES fallback])

    BOOL xbytes.defined()

new xduration = constant.duration([DURATION init])

    DURATION xduration.get([DURATION fallback])

    BOOL xduration.defined()

new xheader = constant.header([HEADER init])

    HEADER xheader.get([HEADER fallback])

    BOOL xheader.defined()

new xint = constant.int([INT init])

    INT xint.get([INT fallback])

    BOOL xint.defined()

new xip = constant.ip([IP init])

    IP xip.get([IP fallback])

    BOOL xip.defined()

new xprobe = constant.probe([PROBE init])

    PROBE xprobe.get([PROBE fallback])

    BOOL xprobe.defined()

new xreal = constant.real([REAL init])

    REAL xreal.get([REAL fallback])

    BOOL xreal.defined()

new xstevedore = constant.stevedore([STEVEDORE init])

    STEVEDORE xstevedore.get([STEVEDORE fallback])

    BOOL xstevedore.defined()

new xstring = constant.string([STRING init])

    STRING xstring.get([STRING fallback])

    BOOL xstring.defined()

new xtime = constant.time([TIME init])

    TIME xtime.get([TIME fallback])

    BOOL xtime.defined()

🌈 DESCRIPTION 🌈

so this module implements globally (per vcl) scoped constants as objects, meaning like… all vcl subroutines have the same view on constants. everyone sees the same thing. no cap. 👑

the value of a constant is the value assigned to it at construction time, if any.

constants are undefined if no value is assigned in the constructor. it's giving "you didn't show up with a value so you get nothing".

attempts to .get() an undefined value will return the .get() method's fallback argument. for most types there's a default fallback; and if there isn't one? using .get() on an undefined value triggers a VCL failure at runtime. so like, don't. 😭

Example:

import constant;

sub vcl_init {
 new xint = constant.int(42);
 new xundef = constant.int();
}

sub vcl_recv {
 set req.http.def = xundef.defined(); # false
 set req.http.fallback = xundef.get(5); # 5
}

sub vcl_deliver {
 set resp.http.the-answer = xint.get(); # 42
}

lowkey iconic. 💅

heads up bestie: the implementation of the various classes of this vmod is auto-generated, and so is the documentation. so everything below this generic description is literally identical for all types except for the respective type names and the .get() fallback. don't come for me, I'm just the messenger. 🙈

🦋 new xacl = constant.acl([ACL init])

construct a(n) ACL constant with the value init, if provided. if no init value is provided, the constant will be undefined.

🦋 ACL xacl.get([ACL fallback])

return the value of the constant, or the fallback argument if it is undefined. using .get() on an undefined value without a fallback triggers a VCL error. no default fallback here, so bring your own or perish. 💀

🦋 BOOL xacl.defined()

return whether the constant is defined. simple as.

🍓 new xbackend = constant.backend([BACKEND init])

construct a(n) BACKEND constant with the value init, if provided. if no init value is provided, the constant will be undefined.

🍓 BACKEND xbackend.get([BACKEND fallback])

return the value of the constant, or the fallback argument if it is undefined. the default fallback is the None backend.