Remove special characters that mess with formating

Question

I am currently creating a chat and can\'t seem to find a way to stop users from posting special characters that mess with formatting of the chat and lagging end users out of the

Answer 1

Contrary to many answers you'll find on StackOverflow, it is trivial to sanitize "Zalgo" text with a regex engine that supports matching on Unicode categories. PHP's preg_* functions use the PCRE library. If PCRE is compiled with --enable-unicode-properties, you can strip all Unicode combining marks using:

$sanitized = preg_replace('/\pM/u', '', $zalgo);

Or allow a certain maximum of consecutive combining marks, say one:

$sanitized = preg_replace('/(\pM)\pM+/u', '\1', $zalgo);

Or two:

$sanitized = preg_replace('/(\pM{2})\pM+/u', '\1', $zalgo);

This will turn Zalgo text like

T̫̺̳o̬̜ ì̬͎̲̟nv̖̗̻̣̹̕o͖̗̠̜̤k͍͚̹͖̼e̦̗̪͍̪͍ ̬ͅt̕h̠͙̮͕͓e̱̜̗͙̭ ̥͔̫͙̪͍̣͝ḥi̼̦͈̼v҉̩̟͚̞͎e͈̟̻͙̦̤-m̷̘̝̱í͚̞̦̳n̝̲̯̙̮͞d̴̺̦͕̫ ̗̭̘͎͖r̞͎̜̜͖͎̫͢ep͇r̝̯̝͖͉͎̺e̴s̥e̵̖̳͉͍̩̗n̢͓̪͕̜̰̠̦t̺̞̰i͟n҉̮̦̖̟g̮͍̱̻͍̜̳ ̳c̖̮̙̣̰̠̩h̷̗͍̖͙̭͇͈a̧͎̯̹̲̺̫ó̭̞̜̣̯͕s̶̤̮̩̘.̨̻̪̖͔ ̳̭̦̭̭̦̞́I̠͍̮n͇̹̪̬v̴͖̭̗̖o̸k҉̬̤͓͚̠͍i͜n̛̩̹͉̘̹g͙ ̠̥ͅt̰͖͞h̫̼̪e̟̩̝ ̭̠̲̫͔fe̤͇̝̱e͖̮̠̹̭͖͕l͖̲̘͖̠̪i̢̖͎̮̗̯͓̩n̸̰g̙̱̘̗͚̬ͅ ͍o͍͍̩̮͢f̖͓̦̥ ̘͘c̵̫̱̗͚͓̦h͝a̝͍͍̳̣͖͉o͙̟s̤̞.̙̝̭̣̳̼͟ ̢̻͖͓̬̞̰̦W̮̲̝̼̩̝͖i͖͖͡ͅt̘̯͘h̷̬̖̞̙̰̭̳ ̭̪̕o̥̤̺̝̼̰̯͟ṳ̞̭̤t̨͚̥̗ ̟̺̫̩̤̳̩o̟̰̩̖ͅr̞̘̫̩̼d̡͍̬͎̪̺͚͔e͓͖̝̙r̰͖̲̲̻̠.̺̝̺̟͈ ̣̭T̪̩̼h̥̫̪͔̀e̫̯͜ ̨N̟e҉͔̤zp̮̭͈̟é͉͈ṛ̹̜̺̭͕d̺̪̜͇͓i̞á͕̹̣̻n͉͘ ̗͔̭͡h̲͖̣̺̺i͔̣̖̤͎̯v̠̯̘͖̭̱̯e̡̥͕-m͖̭̣̬̦͈i͖n̞̩͕̟̼̺͜d̘͉ ̯o̷͇̹͕̦f̰̱ ̝͓͉̱̪̪c͈̲̜̺h̘͚a̞͔̭̰̯̗̝o̙͍s͍͇̱͓.̵͕̰͙͈ͅ ̯̞͈̞̱̖Z̯̮̺̤̥̪̕a͏̺̗̼̬̗ḻg͢o̥̱̼.̺̜͇͡ͅ ̴͓͖̭̩͎̗ ̧̪͈̱̹̳͖͙H̵̰̤̰͕̖e̛ ͚͉̗̼̞w̶̩̥͉̮h̩̺̪̩͘ͅọ͎͉̟ ̜̩͔̦̘ͅW̪̫̩̣̲͔̳a͏͔̳͖i͖͜t͓̤̠͓͙s̘̰̩̥̙̝ͅ ̲̠̬̥Be̡̙̫̦h̰̩i̛̫͙͔̭̤̗̲n̳͞d̸ ͎̻͘T̛͇̝̲̹̠̗ͅh̫̦̝ͅe̩̫͟ ͓͖̼W͕̳͎͚̙̥ą̙l̘͚̺͔͞ͅl̳͍̙̤̤̮̳.̢ ̟̺̜̙͉Z̤̲̙̙͎̥̝A͎̣͔̙͘L̥̻̗̳̻̳̳͢G͉̖̯͓̞̩̦O̹̹̺!̙͈͎̞̬ *

into something like

T̫o̬ ì̬nv̖o͖k͍e̦ ̬t̕h̠e̱ ̥ḥi̼v҉e͈-m̷í͚n̝d̴ ̗r̞ep͇r̝e̴s̥e̵n̢t̺i͟n҉g̮ ̳c̖h̷a̧ó̭s̶.̨ ̳I̠n͇v̴o̸k҉i͜n̛g͙ ̠t̰h̫e̟ ̭fe̤e͖l͖i̢n̸g̙ ͍o͍f̖ ̘c̵h͝a̝o͙s̤.̙ ̢W̮i͖t̘h̷ ̭o̥ṳ̞t̨ ̟o̟r̞d̡e͓r̰.̺ ̣T̪h̥e̫ ̨N̟e҉zp̮é͉ṛ̹d̺i̞á͕n͉ ̗h̲i͔v̠e̡-m͖i͖n̞d̘ ̯o̷f̰ ̝c͈h̘a̞o̙s͍.̵ ̯Z̯a͏ḻg͢o̥.̺ ̴ ̧H̵e̛ ͚w̶h̩ọ͎ ̜W̪a͏i͖t͓s̘ ̲Be̡h̰i̛n̳d̸ ͎T̛h̫e̩ ͓W͕ą̙l̘l̳.̢ ̟Z̤A͎L̥G͉O̹!̙ *