CVE-2018-25057: Improper Neutralization of Special Elements used in an SQL Command ('SQL Injection') (CWE-89)
value: A vulnerability was found in simple_php_link_shortener. It has been classified as critical. Affected is an unknown function of the file index.php. The manipulation of the argument $link["id"] leads to sql injection. The name of the patch is b26ac6480761635ed94ccb0222ba6b732de6e53f. It is recommended to apply a patch to fix this issue. The identifier of this vulnerability is VDB-216996.
CWE description: The product constructs all or part of an SQL command using externally-influenced input from an upstream component, but it does not neutralize or incorrectly neutralizes special elements that could modify the intended SQL command when it is sent to a downstream component. Without sufficient removal or quoting of SQL syntax in user-controllable inputs, the generated SQL query can cause those inputs to be interpreted as SQL instead of ordinary user data.
CVSS v3 base score: 9.8
Published: 2022-12-28T21:15Z
Repository: https://github.com/mikebharris/simple_php_link_shortener
Language: Other
Files changed: LICENSE, README.md, apache.conf, index.php, robots.txt
Commit date: 2018-06-25 23:47:27 +0100
Commit message: Better protection against SQL injection

Diff: diff --git a/LICENSE b/LICENSE
new file mode 100644
index 0000000..d6a9326
--- /dev/null
+++ b/LICENSE
@@ -0,0 +1,340 @@
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diff --git a/README.md b/README.md
new file mode 100644
index 0000000..ce291b3
--- /dev/null
+++ b/README.md
@@ -0,0 +1,142 @@
+# PHP Link Shortener
+
+There's lots of web sites that provide link shorteners (bit.ly, tinyurl.com, imc.li, tiny.booki.cc; to name but a few).  In the past I'd always used tinyurl.com, but then I started working on a project to provide a book of useful technical tips for political activists and grassroots campaigners and some people on the project were concerned about the security implications of third parties logging the redirects, having to have a named account in order to edit the links and the potential of the links being taken down due to policy or petition.  The commercial offerings were therefore not fit for purpose for this project.
+
+And so we cunningly used a free, non-commercial link shortener for our links.  All seemed good, but then what happened was that the destination links changed (without notice I might add).  We were unable to change the shortened links as there was no management side, nor did we manage to get in touch with the authors to get them to do it for us.  Another link shortener being offered to us to use didn't offer any editing of the links either, so I thought to myself how hard could it be to write one?  Not very hard surely...?
+
+## The spec
+
+I decided that the important thing was the redirector: it needed to be simple so that I could get it up and running quickly.  I also didn't want those auto-generated URLs either; I wanted something with URLs (web addresses) that made sense, that I could speak out loud to someone and they'd be able to remember it in their head or write it down.  I guess that although we call them link shorteners, shortening is but one goal, another being simplifying the URL.  Therefore this was to be a link simplifier (in the sense of making the URL simple to communicate verbally and rememeber) as well as a shortener.
+
+I realised that providing for the administration side of it was going to be more complex and that I could get really bogged down with the specification for my amazing and fully featured Short Links Manager (should I even write it in Drupal perhaps and really create a behemoth to crack a nut? :P) 
+
+I therefore came up with this feature list:
+
+* Use query strings, for URLs likle /?shortlink
+* Accept URLs with or without a proceding question mark, so /shortlink is also allowed.
+* If there is no entry for the short link then return a 404 Not Found error.
+* If robots.txt is requested, provide it.
+* In any other case redirect to another web site.
+* No flashy admininistrator, as I haven't got time to write one!
+* No need for a home page: noone has to know about it (at least for now).
+* Keep track of the count of hits for each shortened/simplified URL.
+
+## Database
+
+My MySQL database table looks like this:
+
+    CREATE TABLE `short_links` (
+      `id` int(10) unsigned NOT NULL AUTO_INCREMENT,
+      `short_link` varchar(15) NOT NULL,
+      `redirect_to` varchar(255) NOT NULL,
+      `count` int(10) unsigned NOT NULL DEFAULT '0',
+      PRIMARY KEY (`id`)
+    ) ENGINE=MyISAM AUTO_INCREMENT=8 DEFAULT CHARSET=latin1 ;
+
+The column names for the table should, I hope, be self explanatory.  I decided that it would be useful to know how many times a given short link was requested, so that's what the count column is for.
+
+##Back-end administrator
+
+So, having decided to use a mySQL database to store the links, I decided that for the back-end I'd just use phpMyAdmin to do the job (or one could just use the command line mySQL console, or another tool).  Job done! ;)
+
+## .htaccess file
+
+Here's my .htaccess file, it does two things:
+
+* Allows the file robots.txt to be requested; search engines are happy and know not to bother indexing this site.
+* Rewrites any URL in the form http://mysite.com/short to http://mysite.com/?short
+
+```
+    <IfModule mod_rewrite.c>
+      RewriteEngine On
+      RewriteBase /
+      RewriteCond %{REQUEST_FILENAME} !robots.txt
+      RewriteCond %{QUERY_STRING} ^$
+      RewriteCond %{REQUEST_FILENAME} !-f
+      RewriteCond %{REQUEST_FILENAME} !-d
+      RewriteCond %{REQUEST_FILENAME} !-l
+      RewriteRule ^(.*)$ http://mysite.com/?$1 [L]
+   </IfModule>
+```
+
+## Main PHP link shortener script
+
+And here's the PHP script that does the redirect:
+
+    <?php
+    
+    $DEFAULT_REDIRECT = "https://someothersite.org";
+    
+    $db_conn = mysql_pconnect ("localhost", "user", "password") or die ("Could not connect to DB");
+    mysql_select_db("links_db");
+    
+    if (isset($_SERVER["QUERY_STRING"]) && ($_SERVER["QUERY_STRING"] != '')) {
+    
+      $query = sprintf("SELECT id, redirect_to FROM short_links WHERE short_link = '%s' 
+                        ORDER BY id DESC LIMIT 1", mysql_real_escape_string($_SERVER["QUERY_STRING"]));
+      $result = mysql_query($query);
+    
+      $fail = 0;
+    
+      if (!$result)  {
+        // query failed
+        error_log("Sent an error 404 having executed query $query and got an error of " . mysql_error());
+        $fail = 1;
+      }
+    
+      if (mysql_num_rows($result) < 1) {
+        // short link not found in db
+        error_log("Sent an error 404 having executed query $query and got no rows back");
+        $fail = 1;
+      }
+    
+      $link = mysql_fetch_assoc($result);
+        
+      $query = "UPDATE short_links SET count = count + 1 WHERE id = " . $link["id"];
+      $result = mysql_query($query);
+    
+      if (!$result)  {
+        // query failed updating db (this really shouldn't occur ever
+        error_log("Sent an error 404 having executed query $query and got an error of " . mysql_error());
+        $fail = 1;
+      }
+    
+      if ($fail == 1) {
+        header("HTTP/1.1 404 Not Found");
+        print "<html><body><p>The requested short link was not found.</p></body></html>";
+      } else {
+        header("HTTP/1.1 301 Moved Permanently");
+        header("Location: " . $link["redirect_to"]);
+      }
+        
+    } else {
+      // redirect to some default site
+      // I don't have a home page, but here you could just output some HTML
+      header("HTTP/1.1 301 Moved Permanently");
+      header("Location: " . $DEFAULT_REDIRECT);
+    }
+    
+    ?>
+
+There's some overkill in that script I think.  The first and third mySQL query checks are not really needed, I just wanted to fail gracefully and log it if my query didn't work.  Also you don't really need to log to the error log, that may simply hog or clog up your log files with spam requests.  Lastly, I decided not to have a home page, so my default fall back action is to redirect to another site: You may like to simply output some HTML instead.
+
+## Robots.txt
+
+Finally, let's create a robots.txt file that will tell any well-behaved search engine spiders not to index our site:
+
+    User-agent: *
+    Disallow: / 
+
+That's it
+
+## In Summary
+
+And that's all there is to it.  I works fine and I'm happy with phpMyAdmin to administrate it; no need to write some complex manager for it.  Obviously it's only for my use, so I don't need a home page, don't need to offer the service to anyone else, but do have the ability to change my redirects and count how many people visit them.
+
+Here's a summary list of the technology employed:
+
+* One single PHP script.
+* One single .htaccess file in Apache.
+* One single mySQL database table (could be Postgres, or a noSQL database of course).
+* One single robots.txt file (optional).
+* phpMyAdmin or mySQL console for adminsitration.
diff --git a/apache.conf b/apache.conf
new file mode 100644
index 0000000..f724735
--- /dev/null
+++ b/apache.conf
@@ -0,0 +1,10 @@
+<IfModule mod_rewrite.c>
+RewriteEngine On
+RewriteBase /
+RewriteCond %{REQUEST_FILENAME} !robots.txt
+RewriteCond %{QUERY_STRING} ^$
+RewriteCond %{REQUEST_FILENAME} !-f
+RewriteCond %{REQUEST_FILENAME} !-d
+RewriteCond %{REQUEST_FILENAME} !-l
+RewriteRule ^(.*)$ http://mysite.com/?$1 [L]
+</IfModule>
diff --git a/index.php b/index.php
new file mode 100644
index 0000000..867cf81
--- /dev/null
+++ b/index.php
@@ -0,0 +1,58 @@
+<?php
+
+$DEFAULT_REDIRECT = "https://someothersite.org";
+
+$mysqli = new mysqli("127.0.0.1", "db_username", "db_password", "db_name");
+
+if ($mysqli->connect_errno) {
+	printf("Connect failed: %s\n", $mysqli->connect_error);
+	exit();
+}
+
+if (isset($_SERVER["QUERY_STRING"]) && ($_SERVER["QUERY_STRING"] != '')) {
+
+  $query = sprintf("SELECT id, redirect_to FROM short_links WHERE short_link = '%s' 
+                    ORDER BY id DESC LIMIT 1", $mysqli->real_escape_string($_SERVER["QUERY_STRING"]));
+  $result = $mysqli->query($query);
+
+  $fail = 0;
+
+  if (!$result)  {
+    // query failed
+    error_log("Sent an error 404 having executed query $query and got an error of " . $mysqli->error());
+    $fail = 1;
+  }
+
+  if ($result->num_rows < 1) {
+    // short link not found in db
+    error_log("Sent an error 404 having executed query $query and got no rows back");
+    $fail = 1;
+  }
+
+  $link = $result->fetch_array(MYSQLI_ASSOC);
+  $query = sprintf("UPDATE short_links SET count = count + 1, last_request = NOW() WHERE id = ''%s''", $link["id"]);
+
+  $result = $mysqli->query($query);
+
+  if (!$result)  {
+    // query failed updating db (this really shouldn't occur ever
+    error_log("Sent an error 404 having executed query $query and got an error of " . $mysqli->error());
+    $fail = 1;
+  }
+
+  if ($fail == 1) {
+    header("HTTP/1.0 404 Not Found");
+    print "<html><body><p>The requested short link was not found.</p></body></html>";
+  } else {
+    header("HTTP/1.1 301 Moved Permanently");
+    header("Location: " . $link["redirect_to"]);
+  }
+    
+} else {
+  // redirect to some default site
+  // I don't have a home page, but here you could just output some HTML
+  header("HTTP/1.1 301 Moved Permanently");
+  header("Location: " . $DEFAULT_REDIRECT);
+}
+
+?>
diff --git a/robots.txt b/robots.txt
new file mode 100644
index 0000000..1f53798
--- /dev/null
+++ b/robots.txt
@@ -0,0 +1,2 @@
+User-agent: *
+Disallow: /

Fixed code: GNU GENERAL PUBLIC LICENSE
                       Version 2, June 1991

 Copyright (C) 1989, 1991 Free Software Foundation, Inc., <http://fsf.org/>
 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
 Everyone is permitted to copy and distribute verbatim copies
 of this license document, but changing it is not allowed.

                            Preamble

  The licenses for most software are designed to take away your
freedom to share and change it.  By contrast, the GNU General Public
License is intended to guarantee your freedom to share and change free
software--to make sure the software is free for all its users.  This
General Public License applies to most of the Free Software
Foundation's software and to any other program whose authors commit to
using it.  (Some other Free Software Foundation software is covered by
the GNU Lesser General Public License instead.)  You can apply it to
your programs, too.

  When we speak of free software, we are referring to freedom, not
price.  Our General Public Licenses are designed to make sure that you
have the freedom to distribute copies of free software (and charge for
this service if you wish), that you receive source code or can get it
if you want it, that you can change the software or use pieces of it
in new free programs; and that you know you can do these things.

  To protect your rights, we need to make restrictions that forbid
anyone to deny you these rights or to ask you to surrender the rights.
These restrictions translate to certain responsibilities for you if you
distribute copies of the software, or if you modify it.

  For example, if you distribute copies of such a program, whether
gratis or for a fee, you must give the recipients all the rights that
you have.  You must make sure that they, too, receive or can get the
source code.  And you must show them these terms so they know their
rights.

  We protect your rights with two steps: (1) copyright the software, and
(2) offer you this license which gives you legal permission to copy,
distribute and/or modify the software.

  Also, for each author's protection and ours, we want to make certain
that everyone understands that there is no warranty for this free
software.  If the software is modified by someone else and passed on, we
want its recipients to know that what they have is not the original, so
that any problems introduced by others will not reflect on the original
authors' reputations.

  Finally, any free program is threatened constantly by software
patents.  We wish to avoid the danger that redistributors of a free
program will individually obtain patent licenses, in effect making the
program proprietary.  To prevent this, we have made it clear that any
patent must be licensed for everyone's free use or not licensed at all.

  The precise terms and conditions for copying, distribution and
modification follow.

                    GNU GENERAL PUBLIC LICENSE
   TERMS AND CONDITIONS FOR COPYING, DISTRIBUTION AND MODIFICATION

  0. This License applies to any program or other work which contains
a notice placed by the copyright holder saying it may be distributed
under the terms of this General Public License.  The "Program", below,
refers to any such program or work, and a "work based on the Program"
means either the Program or any derivative work under copyright law:
that is to say, a work containing the Program or a portion of it,
either verbatim or with modifications and/or translated into another
language.  (Hereinafter, translation is included without limitation in
the term "modification".)  Each licensee is addressed as "you".

Activities other than copying, distribution and modification are not
covered by this License; they are outside its scope.  The act of
running the Program is not restricted, and the output from the Program
is covered only if its contents constitute a work based on the
Program (independent of having been made by running the Program).
Whether that is true depends on what the Program does.

  1. You may copy and distribute verbatim copies of the Program's
source code as you receive it, in any medium, provided that you
conspicuously and appropriately publish on each copy an appropriate
copyright notice and disclaimer of warranty; keep intact all the
notices that refer to this License and to the absence of any warranty;
and give any other recipients of the Program a copy of this License
along with the Program.

You may charge a fee for the physical act of transferring a copy, and
you may at your option offer warranty protection in exchange for a fee.

  2. You may modify your copy or copies of the Program or any portion
of it, thus forming a work based on the Program, and copy and
distribute such modifications or work under the terms of Section 1
above, provided that you also meet all of these conditions:

    a) You must cause the modified files to carry prominent notices
    stating that you changed the files and the date of any change.

    b) You must cause any work that you distribute or publish, that in
    whole or in part contains or is derived from the Program or any
    part thereof, to be licensed as a whole at no charge to all third
    parties under the terms of this License.

    c) If the modified program normally reads commands interactively
    when run, you must cause it, when started running for such
    interactive use in the most ordinary way, to print or display an
    announcement including an appropriate copyright notice and a
    notice that there is no warranty (or else, saying that you provide
    a warranty) and that users may redistribute the program under
    these conditions, and telling the user how to view a copy of this
    License.  (Exception: if the Program itself is interactive but
    does not normally print such an announcement, your work based on
    the Program is not required to print an announcement.)

These requirements apply to the modified work as a whole.  If
identifiable sections of that work are not derived from the Program,
and can be reasonably considered independent and separate works in
themselves, then this License, and its terms, do not apply to those
sections when you distribute them as separate works.  But when you
distribute the same sections as part of a whole which is a work based
on the Program, the distribution of the whole must be on the terms of
this License, whose permissions for other licensees extend to the
entire whole, and thus to each and every part regardless of who wrote it.

Thus, it is not the intent of this section to claim rights or contest
your rights to work written entirely by you; rather, the intent is to
exercise the right to control the distribution of derivative or
collective works based on the Program.

In addition, mere aggregation of another work not based on the Program
with the Program (or with a work based on the Program) on a volume of
a storage or distribution medium does not bring the other work under
the scope of this License.

  3. You may copy and distribute the Program (or a work based on it,
under Section 2) in object code or executable form under the terms of
Sections 1 and 2 above provided that you also do one of the following:

    a) Accompany it with the complete corresponding machine-readable
    source code, which must be distributed under the terms of Sections
    1 and 2 above on a medium customarily used for software interchange; or,

    b) Accompany it with a written offer, valid for at least three
    years, to give any third party, for a charge no more than your
    cost of physically performing source distribution, a complete
    machine-readable copy of the corresponding source code, to be
    distributed under the terms of Sections 1 and 2 above on a medium
    customarily used for software interchange; or,

    c) Accompany it with the information you received as to the offer
    to distribute corresponding source code.  (This alternative is
    allowed only for noncommercial distribution and only if you
    received the program in object code or executable form with such
    an offer, in accord with Subsection b above.)

The source code for a work means the preferred form of the work for
making modifications to it.  For an executable work, complete source
code means all the source code for all modules it contains, plus any
associated interface definition files, plus the scripts used to
control compilation and installation of the executable.  However, as a
special exception, the source code distributed need not include
anything that is normally distributed (in either source or binary
form) with the major components (compiler, kernel, and so on) of the
operating system on which the executable runs, unless that component
itself accompanies the executable.

If distribution of executable or object code is made by offering
access to copy from a designated place, then offering equivalent
access to copy the source code from the same place counts as
distribution of the source code, even though third parties are not
compelled to copy the source along with the object code.

  4. You may not copy, modify, sublicense, or distribute the Program
except as expressly provided under this License.  Any attempt
otherwise to copy, modify, sublicense or distribute the Program is
void, and will automatically terminate your rights under this License.
However, parties who have received copies, or rights, from you under
this License will not have their licenses terminated so long as such
parties remain in full compliance.

  5. You are not required to accept this License, since you have not
signed it.  However, nothing else grants you permission to modify or
distribute the Program or its derivative works.  These actions are
prohibited by law if you do not accept this License.  Therefore, by
modifying or distributing the Program (or any work based on the
Program), you indicate your acceptance of this License to do so, and
all its terms and conditions for copying, distributing or modifying
the Program or works based on it.

  6. Each time you redistribute the Program (or any work based on the
Program), the recipient automatically receives a license from the
original licensor to copy, distribute or modify the Program subject to
these terms and conditions.  You may not impose any further
restrictions on the recipients' exercise of the rights granted herein.
You are not responsible for enforcing compliance by third parties to
this License.

  7. If, as a consequence of a court judgment or allegation of patent
infringement or for any other reason (not limited to patent issues),
conditions are imposed on you (whether by court order, agreement or
otherwise) that contradict the conditions of this License, they do not
excuse you from the conditions of this License.  If you cannot
distribute so as to satisfy simultaneously your obligations under this
License and any other pertinent obligations, then as a consequence you
may not distribute the Program at all.  For example, if a patent
license would not permit royalty-free redistribution of the Program by
all those who receive copies directly or indirectly through you, then
the only way you could satisfy both it and this License would be to
refrain entirely from distribution of the Program.

If any portion of this section is held invalid or unenforceable under
any particular circumstance, the balance of the section is intended to
apply and the section as a whole is intended to apply in other
circumstances.

It is not the purpose of this section to induce you to infringe any
patents or other property right claims or to contest validity of any
such claims; this section has the sole purpose of protecting the
integrity of the free software distribution system, which is
implemented by public license practices.  Many people have made
generous contributions to the wide range of software distributed
through that system in reliance on consistent application of that
system; it is up to the author/donor to decide if he or she is willing
to distribute software through any other system and a licensee cannot
impose that choice.

This section is intended to make thoroughly clear what is believed to
be a consequence of the rest of this License.

  8. If the distribution and/or use of the Program is restricted in
certain countries either by patents or by copyrighted interfaces, the
original copyright holder who places the Program under this License
may add an explicit geographical distribution limitation excluding
those countries, so that distribution is permitted only in or among
countries not thus excluded.  In such case, this License incorporates
the limitation as if written in the body of this License.

  9. The Free Software Foundation may publish revised and/or new versions
of the General Public License from time to time.  Such new versions will
be similar in spirit to the present version, but may differ in detail to
address new problems or concerns.

Each version is given a distinguishing version number.  If the Program
specifies a version number of this License which applies to it and "any
later version", you have the option of following the terms and conditions
either of that version or of any later version published by the Free
Software Foundation.  If the Program does not specify a version number of
this License, you may choose any version ever published by the Free Software
Foundation.

  10. If you wish to incorporate parts of the Program into other free
programs whose distribution conditions are different, write to the author
to ask for permission.  For software which is copyrighted by the Free
Software Foundation, write to the Free Software Foundation; we sometimes
make exceptions for this.  Our decision will be guided by the two goals
of preserving the free status of all derivatives of our free software and
of promoting the sharing and reuse of software generally.

                            NO WARRANTY

  11. BECAUSE THE PROGRAM IS LICENSED FREE OF CHARGE, THERE IS NO WARRANTY
FOR THE PROGRAM, TO THE EXTENT PERMITTED BY APPLICABLE LAW.  EXCEPT WHEN
OTHERWISE STATED IN WRITING THE COPYRIGHT HOLDERS AND/OR OTHER PARTIES
PROVIDE THE PROGRAM "AS IS" WITHOUT WARRANTY OF ANY KIND, EITHER EXPRESSED
OR IMPLIED, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF
MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE.  THE ENTIRE RISK AS
TO THE QUALITY AND PERFORMANCE OF THE PROGRAM IS WITH YOU.  SHOULD THE
PROGRAM PROVE DEFECTIVE, YOU ASSUME THE COST OF ALL NECESSARY SERVICING,
REPAIR OR CORRECTION.

  12. IN NO EVENT UNLESS REQUIRED BY APPLICABLE LAW OR AGREED TO IN WRITING
WILL ANY COPYRIGHT HOLDER, OR ANY OTHER PARTY WHO MAY MODIFY AND/OR
REDISTRIBUTE THE PROGRAM AS PERMITTED ABOVE, BE LIABLE TO YOU FOR DAMAGES,
INCLUDING ANY GENERAL, SPECIAL, INCIDENTAL OR CONSEQUENTIAL DAMAGES ARISING
OUT OF THE USE OR INABILITY TO USE THE PROGRAM (INCLUDING BUT NOT LIMITED
TO LOSS OF DATA OR DATA BEING RENDERED INACCURATE OR LOSSES SUSTAINED BY
YOU OR THIRD PARTIES OR A FAILURE OF THE PROGRAM TO OPERATE WITH ANY OTHER
PROGRAMS), EVEN IF SUCH HOLDER OR OTHER PARTY HAS BEEN ADVISED OF THE
POSSIBILITY OF SUCH DAMAGES.

                     END OF TERMS AND CONDITIONS

            How to Apply These Terms to Your New Programs

  If you develop a new program, and you want it to be of the greatest
possible use to the public, the best way to achieve this is to make it
free software which everyone can redistribute and change under these terms.

  To do so, attach the following notices to the program.  It is safest
to attach them to the start of each source file to most effectively
convey the exclusion of warranty; and each file should have at least
the "copyright" line and a pointer to where the full notice is found.

    {description}
    Copyright (C) {year}  {fullname}

    This program is free software; you can redistribute it and/or modify
    it under the terms of the GNU General Public License as published by
    the Free Software Foundation; either version 2 of the License, or
    (at your option) any later version.

    This program is distributed in the hope that it will be useful,
    but WITHOUT ANY WARRANTY; without even the implied warranty of
    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
    GNU General Public License for more details.

    You should have received a copy of the GNU General Public License along
    with this program; if not, write to the Free Software Foundation, Inc.,
    51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.

Also add information on how to contact you by electronic and paper mail.

If the program is interactive, make it output a short notice like this
when it starts in an interactive mode:

    Gnomovision version 69, Copyright (C) year name of author
    Gnomovision comes with ABSOLUTELY NO WARRANTY; for details type `show w'.
    This is free software, and you are welcome to redistribute it
    under certain conditions; type `show c' for details.

The hypothetical commands `show w' and `show c' should show the appropriate
parts of the General Public License.  Of course, the commands you use may
be called something other than `show w' and `show c'; they could even be
mouse-clicks or menu items--whatever suits your program.

You should also get your employer (if you work as a programmer) or your
school, if any, to sign a "copyright disclaimer" for the program, if
necessary.  Here is a sample; alter the names:

  Yoyodyne, Inc., hereby disclaims all copyright interest in the program
  `Gnomovision' (which makes passes at compilers) written by James Hacker.

  {signature of Ty Coon}, 1 April 1989
  Ty Coon, President of Vice

This General Public License does not permit incorporating your program into
proprietary programs.  If your program is a subroutine library, you may
consider it more useful to permit linking proprietary applications with the
library.  If this is what you want to do, use the GNU Lesser General
Public License instead of this License.

# PHP Link Shortener

There's lots of web sites that provide link shorteners (bit.ly, tinyurl.com, imc.li, tiny.booki.cc; to name but a few).  In the past I'd always used tinyurl.com, but then I started working on a project to provide a book of useful technical tips for political activists and grassroots campaigners and some people on the project were concerned about the security implications of third parties logging the redirects, having to have a named account in order to edit the links and the potential of the links being taken down due to policy or petition.  The commercial offerings were therefore not fit for purpose for this project.

And so we cunningly used a free, non-commercial link shortener for our links.  All seemed good, but then what happened was that the destination links changed (without notice I might add).  We were unable to change the shortened links as there was no management side, nor did we manage to get in touch with the authors to get them to do it for us.  Another link shortener being offered to us to use didn't offer any editing of the links either, so I thought to myself how hard could it be to write one?  Not very hard surely...?

## The spec

I decided that the important thing was the redirector: it needed to be simple so that I could get it up and running quickly.  I also didn't want those auto-generated URLs either; I wanted something with URLs (web addresses) that made sense, that I could speak out loud to someone and they'd be able to remember it in their head or write it down.  I guess that although we call them link shorteners, shortening is but one goal, another being simplifying the URL.  Therefore this was to be a link simplifier (in the sense of making the URL simple to communicate verbally and rememeber) as well as a shortener.

I realised that providing for the administration side of it was going to be more complex and that I could get really bogged down with the specification for my amazing and fully featured Short Links Manager (should I even write it in Drupal perhaps and really create a behemoth to crack a nut? :P) 

I therefore came up with this feature list:

* Use query strings, for URLs likle /?shortlink
* Accept URLs with or without a proceding question mark, so /shortlink is also allowed.
* If there is no entry for the short link then return a 404 Not Found error.
* If robots.txt is requested, provide it.
* In any other case redirect to another web site.
* No flashy admininistrator, as I haven't got time to write one!
* No need for a home page: noone has to know about it (at least for now).
* Keep track of the count of hits for each shortened/simplified URL.

## Database

My MySQL database table looks like this:

    CREATE TABLE `short_links` (
      `id` int(10) unsigned NOT NULL AUTO_INCREMENT,
      `short_link` varchar(15) NOT NULL,
      `redirect_to` varchar(255) NOT NULL,
      `count` int(10) unsigned NOT NULL DEFAULT '0',
      PRIMARY KEY (`id`)
    ) ENGINE=MyISAM AUTO_INCREMENT=8 DEFAULT CHARSET=latin1 ;

The column names for the table should, I hope, be self explanatory.  I decided that it would be useful to know how many times a given short link was requested, so that's what the count column is for.

##Back-end administrator

So, having decided to use a mySQL database to store the links, I decided that for the back-end I'd just use phpMyAdmin to do the job (or one could just use the command line mySQL console, or another tool).  Job done! ;)

## .htaccess file

Here's my .htaccess file, it does two things:

* Allows the file robots.txt to be requested; search engines are happy and know not to bother indexing this site.
* Rewrites any URL in the form http://mysite.com/short to http://mysite.com/?short

```
    <IfModule mod_rewrite.c>
      RewriteEngine On
      RewriteBase /
      RewriteCond %{REQUEST_FILENAME} !robots.txt
      RewriteCond %{QUERY_STRING} ^$
      RewriteCond %{REQUEST_FILENAME} !-f
      RewriteCond %{REQUEST_FILENAME} !-d
      RewriteCond %{REQUEST_FILENAME} !-l
      RewriteRule ^(.*)$ http://mysite.com/?$1 [L]
   </IfModule>
```

## Main PHP link shortener script

And here's the PHP script that does the redirect:

    <?php
    
    $DEFAULT_REDIRECT = "https://someothersite.org";
    
    $db_conn = mysql_pconnect ("localhost", "user", "password") or die ("Could not connect to DB");
    mysql_select_db("links_db");
    
    if (isset($_SERVER["QUERY_STRING"]) && ($_SERVER["QUERY_STRING"] != '')) {
    
      $query = sprintf("SELECT id, redirect_to FROM short_links WHERE short_link = '%s' 
                        ORDER BY id DESC LIMIT 1", mysql_real_escape_string($_SERVER["QUERY_STRING"]));
      $result = mysql_query($query);
    
      $fail = 0;
    
      if (!$result)  {
        // query failed
        error_log("Sent an error 404 having executed query $query and got an error of " . mysql_error());
        $fail = 1;
      }
    
      if (mysql_num_rows($result) < 1) {
        // short link not found in db
        error_log("Sent an error 404 having executed query $query and got no rows back");
        $fail = 1;
      }
    
      $link = mysql_fetch_assoc($result);
        
      $query = "UPDATE short_links SET count = count + 1 WHERE id = " . $link["id"];
      $result = mysql_query($query);
    
      if (!$result)  {
        // query failed updating db (this really shouldn't occur ever
        error_log("Sent an error 404 having executed query $query and got an error of " . mysql_error());
        $fail = 1;
      }
    
      if ($fail == 1) {
        header("HTTP/1.1 404 Not Found");
        print "<html><body><p>The requested short link was not found.</p></body></html>";
      } else {
        header("HTTP/1.1 301 Moved Permanently");
        header("Location: " . $link["redirect_to"]);
      }
        
    } else {
      // redirect to some default site
      // I don't have a home page, but here you could just output some HTML
      header("HTTP/1.1 301 Moved Permanently");
      header("Location: " . $DEFAULT_REDIRECT);
    }
    
    ?>

There's some overkill in that script I think.  The first and third mySQL query checks are not really needed, I just wanted to fail gracefully and log it if my query didn't work.  Also you don't really need to log to the error log, that may simply hog or clog up your log files with spam requests.  Lastly, I decided not to have a home page, so my default fall back action is to redirect to another site: You may like to simply output some HTML instead.

## Robots.txt

Finally, let's create a robots.txt file that will tell any well-behaved search engine spiders not to index our site:

    User-agent: *
    Disallow: / 

That's it

## In Summary

And that's all there is to it.  I works fine and I'm happy with phpMyAdmin to administrate it; no need to write some complex manager for it.  Obviously it's only for my use, so I don't need a home page, don't need to offer the service to anyone else, but do have the ability to change my redirects and count how many people visit them.

Here's a summary list of the technology employed:

* One single PHP script.
* One single .htaccess file in Apache.
* One single mySQL database table (could be Postgres, or a noSQL database of course).
* One single robots.txt file (optional).
* phpMyAdmin or mySQL console for adminsitration.
<IfModule mod_rewrite.c>
RewriteEngine On
RewriteBase /
RewriteCond %{REQUEST_FILENAME} !robots.txt
RewriteCond %{QUERY_STRING} ^$
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteCond %{REQUEST_FILENAME} !-l
RewriteRule ^(.*)$ http://mysite.com/?$1 [L]
</IfModule>
<?php

$DEFAULT_REDIRECT = "https://someothersite.org";

$mysqli = new mysqli("127.0.0.1", "db_username", "db_password", "db_name");

if ($mysqli->connect_errno) {
	printf("Connect failed: %s\n", $mysqli->connect_error);
	exit();
}

if (isset($_SERVER["QUERY_STRING"]) && ($_SERVER["QUERY_STRING"] != '')) {

  $query = sprintf("SELECT id, redirect_to FROM short_links WHERE short_link = '%s' 
                    ORDER BY id DESC LIMIT 1", $mysqli->real_escape_string($_SERVER["QUERY_STRING"]));
  $result = $mysqli->query($query);

  $fail = 0;

  if (!$result)  {
    // query failed
    error_log("Sent an error 404 having executed query $query and got an error of " . $mysqli->error());
    $fail = 1;
  }

  if ($result->num_rows < 1) {
    // short link not found in db
    error_log("Sent an error 404 having executed query $query and got no rows back");
    $fail = 1;
  }

  $link = $result->fetch_array(MYSQLI_ASSOC);
  $query = sprintf("UPDATE short_links SET count = count + 1, last_request = NOW() WHERE id = ''%s''", $link["id"]);

  $result = $mysqli->query($query);

  if (!$result)  {
    // query failed updating db (this really shouldn't occur ever
    error_log("Sent an error 404 having executed query $query and got an error of " . $mysqli->error());
    $fail = 1;
  }

  if ($fail == 1) {
    header("HTTP/1.0 404 Not Found");
    print "<html><body><p>The requested short link was not found.</p></body></html>";
  } else {
    header("HTTP/1.1 301 Moved Permanently");
    header("Location: " . $link["redirect_to"]);
  }
    
} else {
  // redirect to some default site
  // I don't have a home page, but here you could just output some HTML
  header("HTTP/1.1 301 Moved Permanently");
  header("Location: " . $DEFAULT_REDIRECT);
}

?>
User-agent: *
Disallow: /