How to write out a literal backslash character?

[bodgit]

As part of #274 (which I'm trying to revive and get working), I have the fundamental problem that I cannot get Augeas to write out a literal \ character as part of a separator implemented with del.

My lens contains the following:

let sep = del /:([ \t]*\\\\\n[ \t]*:)?/ ":\\\n\t:"

which (if I've got it right) should match in the get direction at least a colon, optionally followed by any amount of whitespace, a backslash, a newline, any amount of whitespace and finally another colon. On create it should always write a colon, a backslash, a newline, a tab and another colon.

This reads in existing entries correctly but new entries are always written out minus the backslash, i.e. just the colon, newline, tab and colon. The backslash has somehow been swallowed.

I'm not sure if I'm over-escaping the backslashes or not, but if I change them on either side from what's above then I tend to get a lens error of the form:

exception: del: the default value ':\\\n\t:' does not match /:([ \t]*\\\n[ \t]*:)?/

Is this a bug perhaps? How do I write out a literal backslash?

[lutter]

That indeed seems strange. Just for my clarification, I put together this test; the put test is the behavior you are looking for, right ? I'll have a look at what is happening there.

module T =

let sep = del /:([ \t]*\\\\\n[ \t]*:)?/ ":\\\n\t:"

let lns = [ label "entry" . sep . store /[a-z]+/ ]*

test lns get ":a:\\\n:b" =
  { "entry" = "a" }
  { "entry" = "b" }

test lns put ":a" after
  set "/entry[last()+1]" "b" = ":a:\\\n\t:b"

[lutter]

Found the problem - backslashes in those strings were indeed interpreted twice. PR should be up in a minute

[bodgit]

Yep, I've just tested my lens against your PR changes and it now creates new entries correctly.

[bodgit]

I think this same issue is present elsewhere in the codebase, consider this test case (also from #274):

module Test_getcap =

  (* Taken from the standard /etc/login.conf *)
  let login_conf = "# Default allowed authentication styles
auth-defaults:auth=passwd,skey:

#
# The default values
# To alter the default authentication types change the line:
#       :tc=auth-defaults:\\
# to be read something like: (enables passwd, \"myauth\", and activ)
#       :auth=passwd,myauth,activ:\\
# Any value changed in the daemon class should be reset in default
# class.
#
default:\
        :path=/usr/bin /bin /usr/sbin /sbin /usr/X11R6/bin /usr/local/bin /usr/local/sbin:\
        :umask=022:\
        :datasize-max=512M:\
        :datasize-cur=512M:\
        :maxproc-max=256:\
        :maxproc-cur=128:\
        :openfiles-cur=512:\
        :stacksize-cur=4M:\
        :localcipher=blowfish,8:\
        :ypcipher=old:\
        :tc=auth-defaults:\
        :tc=auth-ftp-defaults:
"

test Getcap.lns get login_conf =
  { "#comment" = "Default allowed authentication styles" }
  { "record"
    { "name" = "auth-defaults" }
    { "capability" = "auth=passwd,skey" }
  }
  {  }
  {  }
  { "#comment" = "The default values" }
  { "#comment" = "To alter the default authentication types change the line:" }
  { "#comment" = ":tc=auth-defaults:\\" }
  { "#comment" = "to be read something like: (enables passwd, \"myauth\", and activ)" }
  { "#comment" = ":auth=passwd,myauth,activ:\\" }
  { "#comment" = "Any value changed in the daemon class should be reset in default" }
  { "#comment" = "class." }
  {  }
  { "record"
    { "name" = "default" }
    { "capability" = "path=/usr/bin /bin /usr/sbin /sbin /usr/X11R6/bin /usr/local/bin /usr/local/sbin" }
    { "capability" = "umask=022" }
    { "capability" = "datasize-max=512M" }
    { "capability" = "datasize-cur=512M" }
    { "capability" = "maxproc-max=256" }
    { "capability" = "maxproc-cur=128" }
    { "capability" = "openfiles-cur=512" }
    { "capability" = "stacksize-cur=4M" }
    { "capability" = "localcipher=blowfish,8" }
    { "capability" = "ypcipher=old" }
    { "capability" = "tc=auth-defaults" }
    { "capability" = "tc=auth-ftp-defaults" }
  }

I've backslash-escaped the \ and " characters in the comments from the original file as I figured at least the " characters will need them. However I can't seem to specify the backslashes in the expected output such as this line:

  { "#comment" = ":tc=auth-defaults:\\" }

I get errors like:

.../test_getcap.aug:42:17: Unexpected character #
.../test_getcap.aug:41.17-42.8:syntax error, unexpected LIDENT, expecting '}'
.../test_getcap.aug:syntax error

If I take the backslashes out of the expected output then there are no syntax errors but of course the test fails because actual/expected don't match.

[lutter]

I'll look into it. Could you rebase #274 onto the HEAD of master and make sure it has your latest changes to the lens and tests ? That'll make it easier for me to understand what's happening - I'll try in the meantime to repro this with a small example.

[lutter]

This is a manifestation of the bug fixed in 244c0ed; what happens is that the \\" on line 41 gets parsed as \ + \", and so augeas thinks the string on that line isn't terminated, and keeps reading until it finds the quotes on the next line starting "#comment" so that it thinks the # is outside a string. Things go south from there.

[bodgit]

I'm afraid I initially just merged your PR into my very ancient branch without also rebasing it onto the HEAD of master.

I've rebased my branch and for now pared down the tests so the only thing currently failing is the above test case and its backslashes.

[lutter]

The backslash part of the tests now work (in the sense that they do not cause syntax errors) What's failing now seem to be 'normal' typecheck errors.

[bodgit]

Yeah, I made the mistake of not using the compiled augparse from the source tree and instead using the one from the binary distribution I had installed. Now the tests are a bit more reliable I can debug and test the lens much easier.