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

[Raphaël Pinson]

You could also make a larger use of common modules (Util, Rx, Sep, Build)
to simply the lens. Here is my take for the lens:


module Gmetad =

autoload xfm

let quoted =
     let quote = Util.del_str "\""
  in quote . store Rx.word. quote

let data_source =
     let host = [ label "host" . store Rx.word ]
  in Build.key_value_line "data_source" Sep.space
      (quoted . Sep.space
      . Build.opt_list host Sep.space)


let gridname = Build.key_value_line "gridname" Sep.space quoted

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

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




and for the test file:

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_name"
     { "host" = "ds1" }
     { "host" = "ds2" }
     { "host" = "ds3.example.com" } }
   { "data_source" = "group_other"
     { "host" = "www1" }
     { "host" = "www2" }
     { "host" = "www3.example.com" } }



Raphaël



On Thu, May 31, 2012 at 4:57 PM, Raphaël Pinson <
raphael.pinson at camptocamp.com> wrote:

>
> On Thu, May 31, 2012 at 4:38 PM, Nathaniel Cook <nvcook42 at gmail.com>wrote:
>
>> 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 = ?
>>
>>
>
> An empty (or non existent) file is not an empty string, but a single
> carriage return. The test should thus be:
>
> test Gmetad.lns get "\n" = ?
>
> which fails since the lens cannot parse a single carriage return. This is
> the reason why it fails in augtool.
>
>
> Doesn't this format not support empty lines? If it does, I'd advise to use
> Util.eol in gridname and data_source, and write lns as:
>
> let lns = (gridname | data_source | Util.empty)*
>
> or does the order strictly matter?
>
>
> Raphaël
>
>
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