Recursive Contents of HTML tag using regex

Question

I'm writing an application for my client that uses a WYSIWYG to allow employees to modify a letter template with certain variables that get parsed out to be information for the customer that the letter is written for.

The WYSIWYG generates HTML that I save to a SQL server database. I then use a PHP class to generate a PDF document with the template text.

Here's my issue. The PDF generation class can translate b,u,i HTML tags. That's it. This is mostly okay, except I need blockquote to be translated too. I figure the best solution would be to write a regex statement that is to take the contents of each blockquote HTML block, and replace each line within the block with five spaces. The trick is that some blockquotes might contain nested blockquotes (double indenting, and what not)

But unfortunately I have never been too well versed with regex, and I spent the last 1.5 hours experimenting with different patterns and got nothing working.

Here are the gotchyas:

String may or may not contain a blockquote block
String could contain multiple blockquotes
String could contain potentially any level of nesting of blockquotes blocks
We can rely on the HTML being properly formed

A sample input string would be look something like something like this:

Dear Charlie,<br><br>We are contacting you because blah blah blah blah.<br><br><br>To login, please use this information:<blockquote>Username: someUsername<br>Password: somePassword</blockquote><br><br>Thank you.

To simply the solution, I need to replace each HTML break inside each blockquote with 5 spaces and then the \n line break character.

Seems more practical to modify the PDF creator than mickey-mouse around the problem with RegEx. Is this a closed-source library you're using, or something modifiable? — Brad Christie
– Brad Christie, Commented Jan 31, 2011 at 16:45
@Brad It's this class -> ros.co.nz/pdf <- I originally used it to generate mailing labels for customers but am extending it to generating welcome letters for customers as well. — WhiskeyTangoFoxtrot
– WhiskeyTangoFoxtrot, Commented Jan 31, 2011 at 16:48
You do realized "blockquote indent" !== "intent 5 spaces at the beginning of the line" right? — timdream
– timdream, Commented Jan 31, 2011 at 16:54
While I realize it's not as easy as "5 spaces", this is perhaps the simplest way to simulate a blockquote in the PDF document as it prints out each space (unlike how HTML handles spaces). The amount of spaces I am going to use to simulate the effect is probably going to be tweaked or ultimately turned into using \t characters. I'm still in an experimenting phase and just need to get it "to work" — WhiskeyTangoFoxtrot
– WhiskeyTangoFoxtrot, Commented Jan 31, 2011 at 17:02

Rosh Oxymoron · Accepted Answer · 2011-01-31 17:17:31Z

4

You might want to check PHP Simple HTML DOM Parser out. You can use it to parse the input to an HTML DOM tree and use that.

edited Jan 31, 2011 at 17:17

answered Jan 31, 2011 at 16:45

Rosh Oxymoron

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1 Comment

Brad Christie Over a year ago

If all else fails, I agree with this. Parse to an HTML document, then "reverse parse" it back to the database.

NikiC · Accepted Answer · 2011-01-31 16:54:57Z

4

~<blockquote>((?:[^<]*+(?:(?!<blockquote>)|(?R))*+)*+)</blockquote>~

You will need to run this regex recursively using preg_replace_callback:

const REGEX_BLOCKQUOTE = '~<blockquote>((?:[^<]*+(?:(?!<blockquote>)|(?R))*+)*+)</blockquote>~';
function blockquoteCallback($matches) {
    return doIndent(preg_replace_callback(REGEX_BLOCKQUOTE, __FUNCTION__, $matches[1]));
}

$output = preg_replace_callback(REGEX_BLOCKQUOTE, 'blockQuoteCallback', $input);

My regex assumes, that there won't be any attributes on the blockquote or anywhere else.

(PS: I'll leave the "Use a DOM parser" comment to someone else.)

edited Jan 31, 2011 at 16:54

answered Jan 31, 2011 at 16:46

NikiC

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Comments

user414441 · Accepted Answer · 2011-01-31 16:54:28Z

1

Regular expressions have a theory behind them, and even though the modern day's regular expresison engine provide can provide a 'Type - 2.5' level language , some things are still not doable. In your partiular case, nesting is not achievable easily. A simple way way to explain this, is to say that regular expression can't keep a count .. i.e. they can't count the nesting level...

what is you need is a limited CFG ( the paren-counting types ) .. you need to somehow keep a count ..may be a stack or tree ...

answered Jan 31, 2011 at 16:54

user414441

2 Comments

NikiC Over a year ago

The regex flavor PHP uses (PCRE) allows recursion in multiple ways. Using backreferences to capturing groups (?n) or using the resursion subgroup (?R).

user414441 Over a year ago

@nikic by 'Type -2.5' i had pcre in mind .. i didn't knew php has switched to it .. however the regexp looks hairy ... if solution involved writing a function and recursing in it , tokenzing using <blockquote> and </blockquote> and \n as seperator, and doing simple scan may be a more readable solution !

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