Regular Expression to validate URI (RFC 3986 http://tools.ietf.org/html/rfc3986)

function.rfc3986_validate_uri.php

<?php

function rfc3986_validate_uri($uri)
{
    // Play around with this regexp online:
    // http://regex101.com/r/hZ5gU9/1

    // Links to relevant RFC documents:
    // RFC 3986: http://tools.ietf.org/html/rfc3986 (URI scheme)
    // RFC 2234: http://tools.ietf.org/html/rfc2234#section-6.1 (ABNF notation)
    $regex = '/

    # URI scheme RFC 3986

    (?(DEFINE)

      # ABNF notation of RFC 2234
    
      (?<ALPHA>     [\x41-\x5A\x61-\x7A] )    # Latin character (A-Z, a-z)
      (?<CR>        \x0D )                    # Carriage return (\r)
      (?<DIGIT>     [\x30-\x39] )             # Decimal number (0-9)
      (?<DQUOTE>    \x22 )                    # Double quote (")
      (?<HEXDIG>    (?&DIGIT) | [\x41-\x46] ) # Hexadecimal number (0-9, A-F)
      (?<LF>        \x0A )                    # Line feed (\n)
      (?<SP>        \x20 )                    # Space
    
      # RFC 3986 body
    
      (?<uri>    (?&scheme) \: (?&hier_part) (?: \? (?&query) )? (?: \# (?&fragment) )? )
    
      (?<hier_part>    \/\/ (?&authority) (?&path_abempty)
                     | (?&path_absolute)
                     | (?&path_rootless)
                     | (?&path_empty) )
    
      (?<uri_reference>    (?&uri) | (?&relative_ref) )
    
      (?<absolute_uri>    (?&scheme) \: (?&hier_part) (?: \? (?&query) )? )
    
      (?<relative_ref>    (?&relative_part) (?: \? (?&query) )? (?: \# (?&fragment) )? )
    
      (?<relative_part>     \/\/ (?&authority) (?&path_abempty)
                          | (?&path_absolute)
                          | (?&path_noscheme)
                          | (?&path_empty) )
    
      (?<scheme>    (?&ALPHA) (?: (?&ALPHA) | (?&DIGIT) | \+ | \- | \. )* )
    
      (?<authority>    (?: (?&userinfo) \@ )? (?&host) (?: \: (?&port) )? )
      (?<userinfo>     (?: (?&unreserved) | (?&pct_encoded) | (?&sub_delims) | \: )* )
      (?<host>         (?&ip_literal) | (?&ipv4_address) | (?&reg_name) )
      (?<port>         (?&DIGIT)* )
    
      (?<ip_literal>    \[ (?: (?&ipv6_address) | (?&ipv_future) ) \] )
    
      (?<ipv_future>    \x76 (?&HEXDIG)+ \. (?: (?&unreserved) | (?&sub_delims) | \: )+ )
    
      (?<ipv6_address>                                              (?: (?&h16) \: ){6} (?&ls32)
                        |                                      \:\: (?: (?&h16) \: ){5} (?&ls32)
                        |                           (?&h16)?   \:\: (?: (?&h16) \: ){4} (?&ls32)
                        | (?: (?: (?&h16) \: ){0,1} (?&h16) )? \:\: (?: (?&h16) \: ){3} (?&ls32)
                        | (?: (?: (?&h16) \: ){0,2} (?&h16) )? \:\: (?: (?&h16) \: ){2} (?&ls32)
                        | (?: (?: (?&h16) \: ){0,3} (?&h16) )? \:\:     (?&h16) \:      (?&ls32)
                        | (?: (?: (?&h16) \: ){0,4} (?&h16) )? \:\:                     (?&ls32)
                        | (?: (?: (?&h16) \: ){0,5} (?&h16) )? \:\:                     (?&h16)
                        | (?: (?: (?&h16) \: ){0,6} (?&h16) )? \:\: )
    
      (?<h16>             (?&HEXDIG){1,4} )
      (?<ls32>            (?: (?&h16) \: (?&h16) ) | (?&ipv4_address) )
      (?<ipv4_address>    (?&dec_octet) \. (?&dec_octet) \. (?&dec_octet) \. (?&dec_octet) )
    
      (?<dec_octet>    (?&DIGIT)
                     | [\x31-\x39] (?&DIGIT)
                     | \x31 (?&DIGIT){2}
                     | \x32 [\x30-\x34] (?&DIGIT)
                     | \x32\x35 [\x30-\x35] )
    
      (?<reg_name>     (?: (?&unreserved) | (?&pct_encoded) | (?&sub_delims) )* )
    
      (?<path>    (?&path_abempty)
                | (?&path_absolute)
                | (?&path_noscheme)
                | (?&path_rootless)
                | (?&path_empty) )
    
      (?<path_abempty>     (?: \/ (?&segment) )* )
      (?<path_absolute>    \/ (?: (?&segment_nz) (?: \/ (?&segment) )* )? )
      (?<path_noscheme>    (?&segment_nz_nc) (?: \/ (?&segment) )* )
      (?<path_rootless>    (?&segment_nz) (?: \/ (?&segment) )* )
      (?<path_empty>       (?&pchar){0} ) # For explicity only
    
      (?<segment>       (?&pchar)* )
      (?<segment_nz>    (?&pchar)+ )
      (?<segment_nz_nc> (?: (?&unreserved) | (?&pct_encoded) | (?&sub_delims) | \@ )+ )
    
      (?<pchar>    (?&unreserved) | (?&pct_encoded) | (?&sub_delims) | \: | \@ )
    
      (?<query>    (?: (?&pchar) | \/ | \? )* )
    
      (?<fragment>    (?: (?&pchar) | \/ | \? )* )
    
      (?<pct_encoded>    \% (?&HEXDIG) (?&HEXDIG) )
    
      (?<unreserved>    (?&ALPHA) | (?&DIGIT) | \- | \. | \_ | \~ )
      (?<reserved>      (?&gen_delims) | (?&sub_delims) )
      (?<gen_delims>    \: | \/ | \? | \# | \[ | \] | \@ )
      (?<sub_delims>    \! | \$ | \& | \' | \( | \)
                      | \* | \+ | \, | \; | \= )
    
    )

    ^(?&uri)$

    /x';

    return preg_match($regex, $uri) === 1;
}

The regex throws an unknown modifier '/' error. Here's my test script:

The error specifically is:

PHP Warning:  preg_match(): Unknown modifier '/' in /home/jaith/biz/erep/2017/05-12-url/function.rfc3986_validate_uri.php on line 112
PHP Stack trace:
PHP   1. {main}() /home/jaith/biz/erep/2017/05-12-url/test.php:0
PHP   2. rfc3986_validate_uri() /home/jaith/biz/erep/2017/05-12-url/test.php:38
PHP   3. preg_match() /home/jaith/biz/erep/2017/05-12-url/function.rfc3986_validate_uri.php:112

GitHub did not send me a notification to your comment :(

Apparently, newer versions of PHP do not ignore slashes within regex comments, and I had a couple of URLs there. So I've updated the code

I think since this is a Gist your comment is fine. Thanks.