Restrict email address validation

[lunny]

This didn't follow the RFC but it's a subset of that. I think we should narrow the allowed chars at first and discuss more possibility in future PRs.

Below are the rules to validate an email.

1. An email address should only contain [0-9a-zA-Z.!#$%&'*+-/=?^_{|}~@]`.
2. First char should only be [0-9a-zA-Z].
3. Strings after @ should only contains [0-9a-zA-Z.] charactors.

[Gusted]

What about a email address like [email protected]?

[Gusted]

Just a thought:

• This could be seen as too restrictive as other characters like ! { } & etc. are allowed and even more is allowed by escaping characters like IHaveASpace\ [email protected].
• Existing emails didn't go trough this check.

[wxiaoguang]

If we want to follow RFC, the rules are more complex.

https://stackoverflow.com/questions/2049502/what-characters-are-allowed-in-an-email-address

 addr-spec   =  local-part "@" domain        ; global address     
 local-part  =  word *("." word)             ; uninterpreted
                                             ; case-preserved
 
 domain      =  sub-domain *("." sub-domain)     
 sub-domain  =  domain-ref / domain-literal     
 domain-ref  =  atom                         ; symbolic reference

The local-part of the email address may use any of these ASCII characters:

    uppercase and lowercase Latin letters A to Z and a to z;
    digits 0 to 9;
    special characters !#$%&'*+-/=?^_`{|}~;
    dot ., provided that it is not the first or last character unless quoted, and provided also that it does not appear consecutively unless quoted (e.g. [email protected] is not allowed but "John..Doe"@example.com is allowed);
    space and "(),:;<>@[\] characters are allowed with restrictions (they are only allowed inside a quoted string, as described in the paragraph below, and in addition, a backslash or double-quote must be preceded by a backslash);
    comments are allowed with parentheses at either end of the local-part; e.g. john.smith(comment)@example.com and (comment)[email protected] are both equivalent to [email protected].

[silverwind]

How about using mail.ParseAddress? May need to pass Foo <$addr> to make it reject the long form with name.

Nevermind, I see the code does that, but it's probably deemed too lax.

[silverwind]

New test may be failing.

[lunny]

New test may be failing.

; is not accepted by mail.ParseAddress.

[zeripath]

Parsing email addresses with regexps seems like a bad idea.

If we want to follow RFC, the rules are more complex.

https://stackoverflow.com/questions/2049502/what-characters-are-allowed-in-an-email-address

 addr-spec   =  local-part "@" domain        ; global address     
 local-part  =  word *("." word)             ; uninterpreted
                                             ; case-preserved
 
 domain      =  sub-domain *("." sub-domain)     
 sub-domain  =  domain-ref / domain-literal     
 domain-ref  =  atom                         ; symbolic reference

The local-part of the email address may use any of these ASCII characters:

    uppercase and lowercase Latin letters A to Z and a to z;
    digits 0 to 9;
    special characters !#$%&'*+-/=?^_`{|}~;
    dot ., provided that it is not the first or last character unless quoted, and provided also that it does not appear consecutively unless quoted (e.g. [email protected] is not allowed but "John..Doe"@example.com is allowed);
    space and "(),:;<>@[\] characters are allowed with restrictions (they are only allowed inside a quoted string, as described in the paragraph below, and in addition, a backslash or double-quote must be preceded by a backslash);
    comments are allowed with parentheses at either end of the local-part; e.g. john.smith(comment)@example.com and (comment)[email protected] are both equivalent to [email protected].

Since 2012 you can include characters above U+007f if they're encoded as UTF-8.

---

Why are we doing this? Why not just parse the email address with mail.ParseAddress? What's the aim?

[lunny]

Parsing email addresses with regexps seems like a bad idea.

If we want to follow RFC, the rules are more complex.
https://stackoverflow.com/questions/2049502/what-characters-are-allowed-in-an-email-address

 addr-spec   =  local-part "@" domain        ; global address     
 local-part  =  word *("." word)             ; uninterpreted
                                             ; case-preserved
 
 domain      =  sub-domain *("." sub-domain)     
 sub-domain  =  domain-ref / domain-literal     
 domain-ref  =  atom                         ; symbolic reference

The local-part of the email address may use any of these ASCII characters:

    uppercase and lowercase Latin letters A to Z and a to z;
    digits 0 to 9;
    special characters !#$%&'*+-/=?^_`{|}~;
    dot ., provided that it is not the first or last character unless quoted, and provided also that it does not appear consecutively unless quoted (e.g. [email protected] is not allowed but "John..Doe"@example.com is allowed);
    space and "(),:;<>@[\] characters are allowed with restrictions (they are only allowed inside a quoted string, as described in the paragraph below, and in addition, a backslash or double-quote must be preceded by a backslash);
    comments are allowed with parentheses at either end of the local-part; e.g. john.smith(comment)@example.com and (comment)[email protected] are both equivalent to [email protected].

Since 2012 you can include characters above U+007f if they're encoded as UTF-8.

Why are we doing this? Why not just parse the email address with mail.ParseAddress? What's the aim?

The invisible unicode characters could pass mai.ParseAddress. Do we really want to allow them?

[adelowo]

Parsing email addresses with regexps seems like a bad idea.

If we want to follow RFC, the rules are more complex.
https://stackoverflow.com/questions/2049502/what-characters-are-allowed-in-an-email-address

 addr-spec   =  local-part "@" domain        ; global address     
 local-part  =  word *("." word)             ; uninterpreted
                                             ; case-preserved
 
 domain      =  sub-domain *("." sub-domain)     
 sub-domain  =  domain-ref / domain-literal     
 domain-ref  =  atom                         ; symbolic reference

The local-part of the email address may use any of these ASCII characters:

    uppercase and lowercase Latin letters A to Z and a to z;
    digits 0 to 9;
    special characters !#$%&'*+-/=?^_`{|}~;
    dot ., provided that it is not the first or last character unless quoted, and provided also that it does not appear consecutively unless quoted (e.g. [email protected] is not allowed but "John..Doe"@example.com is allowed);
    space and "(),:;<>@[\] characters are allowed with restrictions (they are only allowed inside a quoted string, as described in the paragraph below, and in addition, a backslash or double-quote must be preceded by a backslash);
    comments are allowed with parentheses at either end of the local-part; e.g. john.smith(comment)@example.com and (comment)[email protected] are both equivalent to [email protected].

Since 2012 you can include characters above U+007f if they're encoded as UTF-8.

Why are we doing this? Why not just parse the email address with mail.ParseAddress? What's the aim?

yes. Just using email verification links is a saner solution to be honest

[6543]

tests passed localy

[6543]

-> #19085