[augeas-devel] How to write lens so that it can parse empty file.

[Nathaniel Cook]

I have been working on writing a simplified lens for the ganglia
gmetad.conf file. I have the lens working as I like but when I try to
use augeas to add entries to the file I get errors on save if the file
doesn't exist or is empty. It says it cannot parse the entire input:

/augeas/files/etc/gmetad.conf/error = "parse_failed"
/augeas/files/etc/gmetad.conf/error/pos = "0"
/augeas/files/etc/gmetad.conf/error/line = "1"
/augeas/files/etc/gmetad.conf/error/char = "0"
/augeas/files/etc/gmetad.conf/error/lens =
"/usr/share/augeas/lenses/gmetad.aug:22.12-.56:"
/augeas/files/etc/gmetad.conf/error/message = "Get did not match entire input"


Here is the lens:


module Gmetad =
    autoload xfm

    let quote = Util.del_str "\""
    let space = del /[ \t]+/ " "
    let eol = Util.del_str "\n"
    let empty =  del /[ \t]*/ "" . eol

    let host = store /[a-zA-Z0-9._]+/
    let hosts = ( space . [ seq "hosts" . host ] )+
    let group = [ label "group" . quote . store /[a-zA-Z0-9._ ]+/ . quote ]
    let data_source = [ counter "hosts" .  label "data_source" .
Util.del_str "data_source" . space . group . [ label "hosts" . hosts ]
]

    let gridname = [ label "gridname" . Util.del_str "gridname" .
space . quote . store /[a-zA-Z0-9._]+/ . quote ]

    let lns  = (gridname . empty)* . (data_source . empty)*

    let filter = incl "/etc/gmetad.conf"
    let xfm = transform lns filter


Here is the test module:

module Test_gmetad =
    let conf = "gridname \"grid\"
data_source \"group_name\" ds1 ds2 ds3.example.com
data_source \"group_other\" www1 www2 www3.example.com
"
    test Gmetad.lns get  conf =
    { "gridname" = "grid" }
    { "data_source"
            { "group" = "group_name" }
            { "hosts"
                { "1" = "ds1" }
                { "2" = "ds2" }
                { "3" = "ds3.example.com" }
            }
    }
    { "data_source"
        { "group" = "group_other" }
        { "hosts"
            { "1" = "www1" }
            { "2" = "www2" }
            { "3" = "www3.example.com" }
        }
    }

    let empty = ""

    test Gmetad.lns get empty = ?


The lens can correctly parse the empty string returning a null tree.
Is their something I am doing wrong? I am new at this. Thanks

Nathaniel Cook