ENT-3417: Added allow_non_convergent to pattern_matching promise in edit_line

[victormlg]

Added a new attribute allow_non_convergent in replace_pattern promise to allow for idempotent non-convergent regex.

bundle agent __main__
{
  files:
      "/tmp/example.txt"
        content => "bash PORT=23 echo";

      "/tmp/example.txt"
        edit_line => regex_replace( "PORT=[0-9]+", "PORT=22" );

}
# From the stdlib:
bundle edit_line regex_replace(find,replace)
# @brief Find exactly a regular expression and replace exactly the match with a string.
# You can think of this like a PCRE powered sed.
# @param find The regular expression
# @param replace The replacement string
{
  replace_patterns:

      "$(find)"
        replace_with => value("$(replace)"),
        comment => "Search and replace string",
        allow_non_convergent => "true";
}

body replace_with value(x)
# @brief Replace matching lines
# @param x The replacement string
{
        replace_value => "$(x)";
        occurrences => "all";
}

I am a bit ensure on the implementation, but the idea is that we don't want to allow destructive non-convergent regex, such as:

bundle agent __main__
{
  files:
      "/tmp/example.txt"
        content => "PORT=23";

      "/tmp/example.txt"
        edit_line => regex_replace( "PORT=[0-9]+", "PORT=22 #Some comment" );

}

This will replace and rematch the same line indefinitely:
PORT=22 #Some comment #Some comment #Some comment [...]

So the idea was to let cfengine match and expand the pattern N times (as before), then we match and expand one more time (N+1), and if the total length of the line is greater, this means that the non-convergent regex is destructive and thus we need to error.

[larsewi]

Please add an acceptance test :)

[larsewi]

@nickanderson can you address the questions @victormlg posted in the PR description?

[larsewi]

Please make sure needed is not a negative integer before comparing it with an unsigned

[larsewi]

Please check for truncation

[larsewi]

Maybe avoid printing buffer overflow. Because you are avoiding it. The remaining message is sufficient in my opinion

[larsewi]

Since you are including default.cf.sub you can add the meta data with ticket number and description

[nickanderson]

@larsewi

@nickanderson can you address the questions @victormlg posted in the PR description?

Sorry, I had responded to @victormlg directly via slack.

I don't love the name use_non_convergent. Maybe allow_non_convergent? Semantically it's something we are allowing not a thing we are using.

I am unsure about the non-descructive thing.

Maybe it should be boxed in more specifically ... the use case is for the pattern similar to:

sed -i 's/PORT=.*/PORT=22/'

Basically, I don't know what is there now, but it should be PORT=22