Cada vez que nos enfrentamos a la programación de un sistema de usuarios, formulario de contacto o similar, inevitablemente encontramos el problema de validación de datos: Si bien es imposible validar un nombre y apellidos, si es común tener que validar el formato de DNI’s o teléfono y, en mi caso, la más temida de todas: el Email
Si ya de por si es pesado controlar todas las diferentes opciones (usuario@dominio.tld, nombre.apellido@dominio.tld, tlds de dos letras, de 3, de 4… o incluso de 6) encima nos encontramos «gracias» como la de las multicuentas de google, con los filtros usuario+filtro@gmail.com y similares.
Por documentarnos, nos vamos a ver el RFC 822, que define y delimita la validez del protocolo de mensajería en internet, y es aqui cuando, si pretendemos que nuestro sistema acepte toda posible combinación válida de emails, la pesadilla no ha hecho más que empezar: Escribir la expresión regular que filtre, limpie y de esplendor a semejante cantidad de normas y posibilidades es trabajo sólo al alcance de unas pocas mentes privilegiadas.
Y sin embargo, YA SE HA HECHO ANTES.
Concretamente, Paul Warren en 2002. Señores, señoras, gentuza varia… les presento la expresión regular para validar correos por excelencia:
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r\n)?[ \t])+|\Z|(?=[\[«()<>@,;:\\».\[\]]))|\[([^\[\]\r\\]|\\.)*\](?:(?:\r\n)?[
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«.\[\]]))|»(?:[^\»\r\\]|\\.|(?:(?:\r\n)?[ \t]))*»(?:(?:\r\n)?[ \t])*)(?:\.(?:(
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\[\]]))|»(?:[^\»\r\\]|\\.|(?:(?:\r\n)?[ \t]))*»(?:(?:\r\n)?[ \t])*)(?:\.(?:(?:
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+|\Z|(?=[\[«()<>@,;:\\».\[\]]))|\[([^\[\]\r\\]|\\.)*\](?:(?:\r\n)?[ \t])*)(?:\
.(?:(?:\r\n)?[ \t])*(?:[^()<>@,;:\\».\[\] \000-\031]+(?:(?:(?:\r\n)?[ \t])+|\Z
|(?=[\[«()<>@,;:\\».\[\]]))|\[([^\[\]\r\\]|\\.)*\](?:(?:\r\n)?[ \t])*))*\>(?:(
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