Email

E-mail address validation per RFC 5321 and RFC 6531, plus canonical account identity IRIs per RFC 6068 and RFC 7565. More...

Functions
SOURCEMETA_CORE_EMAIL_EXPORT auto	sourcemeta::core::is_email (const std::string_view value) -> bool
SOURCEMETA_CORE_EMAIL_EXPORT auto	sourcemeta::core::is_idn_email (const std::string_view value) -> bool
SOURCEMETA_CORE_EMAIL_EXPORT auto	sourcemeta::core::is_idn_email_uts46 (const std::string_view value) -> bool
SOURCEMETA_CORE_EMAIL_EXPORT auto	sourcemeta::core::mailto_iri (const std::string_view value) -> std::optional< std::string >
SOURCEMETA_CORE_EMAIL_EXPORT auto	sourcemeta::core::acct_iri (const std::string_view value) -> std::optional< std::string >

Detailed Description

E-mail address validation per RFC 5321 and RFC 6531, plus canonical account identity IRIs per RFC 6068 and RFC 7565.

This functionality is included as follows:

#include <sourcemeta/core/email.h>

Function Documentation

acct_iri()

SOURCEMETA_CORE_EMAIL_EXPORT auto sourcemeta::core::acct_iri

(

const std::string_view

value

)

-> std::optional< std::string >

Produce the canonical RFC 7565 acct IRI that identifies the given user@host account, with no result when the input is not one. The host is lowercased, as RFC 7565 Section 4 compares these IRIs under RFC 3986 Section 6.2.2.1 case normalization, while the account name keeps its case.

The account name is limited to the printable ASCII repertoire of the PRECIS IdentifierClass (RFC 7564 Section 9.11) and the host to an ASCII DNS name, so internationalized forms yield no result. This restriction is deliberate and may be lifted later without re-minting any identity this function already produces.

For example:

#include <sourcemeta/core/email.h>
 
#include <cassert>
 
const auto iri{sourcemeta::core::acct_iri(
    "juliet@capulet.example@shoppingsite.example")};
assert(iri.has_value());
assert(iri.value() ==
       "acct:juliet%40capulet.example@shoppingsite.example");

is_email()

SOURCEMETA_CORE_EMAIL_EXPORT auto sourcemeta::core::is_email

(

const std::string_view

value

)

-> bool

Check whether the given string is a valid Mailbox per RFC 5321 Section 4.1.2, under the length constraints from Section 4.5.3.1.

The domain is validated slightly more strictly than the bare RFC 5321 Section 4.1.2 grammar, and one address-literal case follows the section prose over its ABNF. Both are deliberate stances rather than accidents.

A domain label beginning with the xn-- ACE prefix must be a valid IDNA A-label, not merely a letter-digit-hyphen string. The Section 4.1.2 grammar would accept any such label, but one that does not decode to a real internationalized label can never name a deliverable domain, so it is rejected. This is intentionally stricter than the grammar.

An [IPv6:...] address literal is validated per RFC 4291. The Section 4.1.3 prose specifies the IPv6 syntax as that of RFC 4291, while the IPv6-addr ABNF in the same section is stricter and conflicts with it, so the prose is followed. A bracketed [IPv6:...] whose body is not a valid address is still accepted, because Section 4.1.3 also permits any General-address-literal (a registered tag, a colon, and content) and ABNF alternatives are unordered.

For example:

#include <sourcemeta/core/email.h>
 
#include <cassert>
 
assert(sourcemeta::core::is_email("user@example.com"));
assert(sourcemeta::core::is_email("\"a b\"@example.com"));
assert(sourcemeta::core::is_email("user@[192.168.1.1]"));
assert(!sourcemeta::core::is_email("plain"));

is_idn_email()

SOURCEMETA_CORE_EMAIL_EXPORT auto sourcemeta::core::is_idn_email

(

const std::string_view

value

)

-> bool

Check whether the given string is a valid internationalized Mailbox per RFC 6531 Section 3.3 (extended Mailbox address syntax). Beyond the ASCII grammar accepted by is_email, the local-part atoms, quoted content, and domain labels may also contain valid UTF-8 non-ASCII byte sequences (RFC 6532 Section 3.1). For example:

#include <sourcemeta/core/email.h>
 
#include <cassert>
 
assert(sourcemeta::core::is_idn_email(
    "\xec\x8b\xa4\xeb\xa1\x80@\xec\x8b\xa4\xeb\xa1\x80.\xed\x85\x8c\xec\x8a\xa4\xed\x8a\xb8"));
assert(sourcemeta::core::is_idn_email("joe.bloggs@example.com"));
assert(!sourcemeta::core::is_idn_email("2962"));

is_idn_email_uts46()

SOURCEMETA_CORE_EMAIL_EXPORT auto sourcemeta::core::is_idn_email_uts46

(

const std::string_view

value

)

-> bool

Check whether the given string is a valid internationalized Mailbox per RFC 6531 Section 3.3, validating the domain under UTS #46 processing rather than strict IDNA 2008. The domain is mapped (case folding, compatibility mappings such as fullwidth to ASCII, and removal of ignorable characters) and NFC-normalised before validation, so forms that strict validation rejects, such as fullwidth characters and non-normalised (non-NFC) labels, are accepted. The local part carries no normalisation requirement (RFC 6531) and is validated as-is. See https://www.unicode.org/reports/tr46/ for the algorithm. For example:

#include <sourcemeta/core/email.h>
 
#include <cassert>
 
assert(sourcemeta::core::is_idn_email_uts46("joe.bloggs@example.com"));
// The fullwidth domain U+FF41 U+FF42 U+FF43 maps to "abc" and is accepted,
// whereas strict IDNA 2008 validation rejects it
assert(sourcemeta::core::is_idn_email_uts46(
    "user@\xef\xbd\x81\xef\xbd\x82\xef\xbd\x83"));
assert(!sourcemeta::core::is_idn_email_uts46("2962"));

mailto_iri()

SOURCEMETA_CORE_EMAIL_EXPORT auto sourcemeta::core::mailto_iri

(

const std::string_view

value

)

-> std::optional< std::string >

Produce the canonical RFC 6068 mailto IRI that identifies the given RFC 5321 Mailbox, with no result when the input is not one. The domain name is lowercased, the RFC 3986 Section 6.2.3 scheme-based case normalization that names this very scheme in its example, while the local part is case sensitive per RFC 5321 Section 2.4 and an address literal is not a DNS name, so both keep their spelling. For example:

#include <sourcemeta/core/email.h>
 
#include <cassert>
 
const auto iri{sourcemeta::core::mailto_iri("gorby%kremvax@example.com")};
assert(iri.has_value());
assert(iri.value() == "mailto:gorby%25kremvax@example.com");