Parsing e-mail-like headers (similar to RFC822)

Question

Problem / Question

There is a database of bot information that I would like to parse. It is said to be similar to RFC822 messages.

Before I re-invent the wheel and write a parser of my own, I figured I would see if something else was already available. I stumbled across imap_rfc822_parse_headers(), which seems to do exactly what I want. Unfortunately, the IMAP extension is not available in my environment.

I have seen many alternatives online and on Stack Overflow. Unfortunately, they are all built for e-mail and do more than I need... often times parsing out an entire e-mail and handling headers in special ways. I just want to simply parse those headers into a useful object or array.

Is there a straight PHP version of imap_rfc822_parse_headers() available, or something equivalent that will parse data like this? If not, I will write my own.

Sample Data

robot-id: abcdatos
robot-name: ABCdatos BotLink
robot-from: no
robot-useragent: ABCdatos BotLink/1.0.2 (test links)
robot-language: basic
robot-description: This robot is used to verify availability of the ABCdatos
                   directory entries (http://www.abcdatos.com), checking
                   HTTP HEAD. Robot runs twice a week. Under HTTP 5xx
                   error responses or unable to connect, it repeats
                   verification some hours later, verifiying if that was a
                   temporary situation.
robot-history: This robot was developed by ABCdatos team to help
               working in the directory maintenance.
robot-environment: commercial
modified-date: Thu, 29 May 2003 01:00:00 GMT
modified-by: ABCdatos

robot-id:                       acme-spider
robot-name:                     Acme.Spider
robot-cover-url:                http://www.acme.com/java/software/Acme.Spider.html
robot-exclusion:                yes
robot-exclusion-useragent:      Due to a deficiency in Java it's not currently possible to set the User-Agent.
robot-noindex:                  no
robot-host:                     *
robot-language:                 java
robot-description:              A Java utility class for writing your own robots.
robot-history:                  
robot-environment:              
modified-date:                  Wed, 04 Dec 1996 21:30:11 GMT
modified-by:                    Jef Poskanzer

...

Answer 1

Assuming that $data contains the sample data you pasted above, here is the parser:

<?php

/* 
 * $data = <<<'DATA'
 * <put-sample-data-here>
 * DATA;
 *
 */

$parsed  = array();
$blocks  = preg_split('/\n\n/', $data);
$lines   = array();
$matches = array();
foreach ($blocks as $i => $block) {
    $parsed[$i] = array();
    $lines = preg_split('/\n(([\w.-]+)\: *((.*\n\s+.+)+|(.*(?:\n))|(.*))?)/',
                        $block, -1, PREG_SPLIT_DELIM_CAPTURE);
    foreach ($lines as $line) {
        if(preg_match('/^\n?([\w.-]+)\: *((.*\n\s+.+)+|(.*(?:\n))|(.*))?$/',
                      $line, $matches)) {
            $parsed[$i][$matches[1]] = preg_replace('/\n +/', ' ',
                                                    trim($matches[2]));
        }
    }
}

print_r($parsed);

Answer 2

The message MIME type is pretty common. Parsers exist plenty, but are commonly hard to google. Personally I resort to regex here, if the format is somewhat consistent.

For example these two will do the trick:

  // matches a consecutive RFC821 style key:value list
define("RX_RFC821_BLOCK", b"/(?:^\w[\w.-]*\w:.*\R(?:^[ \t].*\R)*)++\R*/m");

  // break up Key: value lines
define("RX_RFC821_SPLIT", b"/^(\w+(?:[-.]?\w+)*)\s*:\s*(.*\n(?:^[ \t].*\n)*)/m");

Number one breaks out coherent blocks of message/* lines, and the second can be used to split up each such block. It needs post-processing to strip leading indendation from continued value lines though.