config4gnu-developer Mailing List for Configuration for GNU (Page 8)

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For the apache & similar parsers, I've currently got the following XML:

<apache-style>
  <property>
    <name>Hostname</name>
    <value>myhost.com</value>
  </property>
  <section>
    <name>Directory</name>
    <value>/</value>
    ...
  </section>
  <property>
    <name>LoadModule</name>
    <value>cgi_module</value>
    <value>modules/mod_cgi.so</value>
  </property>
  ...
</apache-style>

The main issue is how to handle multiple value tags.  In most (but not all) cases, the order of the arguments to the various directives is important, as each position has a different meaning, such as with LoadModule.  There needs to be a way to preserve this in the XML.  With the passwd and group files, we use unique XML tags for each column in the file.  The only other option, which doesn't seem very good, is to put a position attribute on each value tag, i.e.:

<property>
  <name>LoadModule</name>
  <value pos="0">cgi_module</value>
  <value pos="1">modules/mod_cgi.so</value>
</property>

The only real advantage of this approach is that everything is still a "value" tag.

If we use unique XML tags, the problem is that since each directive has a different number and type of arguments, they won't be consistent as they are with group and passwd, i.e.:

<property>
  <name>LoadModule</name>
  <modulename>cgi_module</modulename>
  <modulepath>modules/mod_cgi.so</modulepath>
</property>
<property>
  <name>LogFormat</name>
  <logstring quoting="2">%{Referer}i -> %U</logstring>
  <identifier>agent</identifier>
</property>

In this case, we would have some problems:

1) not have a value tag to display in UI
2) can't make a "default" form that works for all directives

To solve this, there are a few solutions I've thought of:

A) make the parameter tags (modulename, modulepath, logstring, identifier, etc.) extend the type "value" and the UIs look for that instead of a "value" tag.  This solves problem #1, although the UI has to recognize that there could be >1 tag of type value.

B) copy some of all of the parameters into a read-only value tag, so the user can see the current value (although not displayed in a pretty way), but have to double-click on the form to edit the value, or even better do this automatically as is currently done with the multi-value control.  This solves problem #1.

C) give up on default form, make custom form for each multi-valued directive & use solution B to handle values.  A bad solution to #2

D) a variation on solution A where the first parameter tag extends the type "value1", the second "value2", etc.  value1, value2, value3, etc. would then extend value.  This way the UI has something of type "value" to display for the value if you just want to display the first, or you can use solution B to combine all of them into a fake read-only value.  This solves #1, and provided a default form could be made which only shows each of value1 thru valueN if they exist (otherwise no control would be shown at all for the missing valueN's).  This is again a slight variation on solution B but is adds the ability to locate a particular parameter by its position.

E) don't use custom tags for the parameters, just use value1, value2, value3, etc.  This makes things simpler, but for humans wanting to locate the "identifier" for a LogFormat directive, it is more difficult because they need to know its in a value2 tag instead of a "identifier" tag, i.e.:

resolve_path(".apache-style.logformat.identifier")

vs.

resolve_path(".apache-style.logformat.value2")

I think that solution D seems the best for this problem and can't come up with anything better, what do you think?

An additional thing I thought of (sorry this is getting so long) is that apache often has multiple directives (such as LoadModule or LogFormat) in a row.  How will we address them using resolve_path or similar API calls?  Right now resolve_path just returns the first match it finds right? 

I can't recall off hand, but I think XPath has a syntax for requesting all LogFormat directives, such as resolve_path(".apache-style.logformat[ALL]"), or just a particular one, such as resolve_path(".apache-style.logformat[2]").  I know thats not the right syntax, but it seems like we'll need something similar for apache.

Justin

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