Email address validation is one of those topics that keep coming up again and again. It seems that we developers never get it quite right, but with good reason: the spec is downright insane. There are six RFCs involved, which obsolete some other RFCs, and in turn have some erratas. I hope the guys at the IETF had some very good reasons to make this so damn complex!
Anyway, you can validate all the RFCs you want and you can still get an invalid address. joe@example.com is syntactically correct yet there isn't any Joe that works at example.com :-)
What's interesting here is the different approaches taken to cope with such a monster:
- Validate lightly, trying not to incur into false negatives, then check it by actually sending a confirmation email to that address. This is IMO the only sensible way to do it.
- Perl's email validation includes (of course) a 6700 character regex and optionally does DNS validation of the domain.
- Phil Haack's validation (C#) uses just a regex, which can't technically handle all possible cases because the RFCs allow arbitrarily nested comments.
- Other single-regex implementations
- Dominic Sayers' PHP implementation includes what is probably the most thorough analysis and testcase for the various RFCs. The testcase has 228 tests, and (obviously) his implementation passes all the tests. Also includes optional DNS check.
- In comparison, System.Net.Mail.MailAddress does some quite poor validation, it passes 40% of Dominic's tests.
- George Pollard's Haskell validation uses Parsec which results in an interesting pseudotranslation of the ENBF to executable code.
The last one really caught my interest so I ported it (mostly as an exercise) to F# + FParsec. Then I grabbed Dominic's testcase and ran it with FsUnit. The result? It passes 84% of Dominic's tests (with no false negatives). Here's the code (updated to F# 2.0 / FParsec trunk 5/17/2010):
module EmailValidation.EmailValidator
open System
open FParsec
open FParsec.Primitives
open FParsec.CharParsers
let isValidEmail email =
let wsp = anyOf " \t" >>% ()
let crlf = pchar '\n' >>% ()
let nullChar = pchar (char 0) >>% ()
let ranges = Seq.map (Seq.map char) >> Seq.concat >> Seq.toArray >> (fun x -> String x) >> (fun x -> anyOf x >>% ())
let vchar = ranges [{0x21..0x7e}]
let obsNoWsCtl = ranges [{1..8};{11..12};{14..31};{127..127}]
let atomText = digit <|> letter <|> anyOf "!#$%&'*+-/=?^_`{|}~"
let atom = many1 atomText >>% ()
let fws = (many1 wsp >>. optional (crlf >>. many1 wsp)) <|> (many1 (crlf >>. many1 wsp) >>% ())
let commentText = ranges [{33..39};{42..91};{93..126}] <|> obsNoWsCtl
let quotedPair = pchar '\\' >>. (vchar <|> wsp <|> crlf <|> obsNoWsCtl <|> nullChar)
let rec commentContent x = (commentText <|> quotedPair <|> comment) x
and comment = between (pchar '(') (pchar ')') (many (commentContent <|> fws)) >>% ()
let cfws = many (comment <|> fws)
let quotedText = ranges [{33..33};{35..91};{93..126}] <|> obsNoWsCtl
let quotedContent = quotedText <|> quotedPair
let quotedString = between (pchar '"') (pchar '"') (many (optional fws >>. quotedContent) >>. optional fws)
let dottedAtoms = sepBy1 (optional cfws >>. (atom <|> quotedString) >>. optional cfws) (pchar '.') >>% ()
let localPart = dottedAtoms
let domainText = ranges [{33..90};{94..126}] <|> obsNoWsCtl
let domainLiteral = between (optional cfws >>. pchar '[') (pchar ']' >>. optional cfws) (many (optional fws >>. domainText) >>. optional fws)
let domain = dottedAtoms <|> domainLiteral
let addrSpec = localPart >>. pchar '@' >>. domain >>. eof
match run addrSpec email with
| Failure (msg, _, _) -> false
| Success _ -> true
Just for reference, here's the actual test output:
192 passed. 36 failed. 0 erred. ---- Failed: ID "21": "123456789012345678901234567890123456789012345678901234567890@1 2345678901234567890123456789012345678901234567890123456789.123456789012345678901 23456789012345678901234567890123456789.12345678901234567890123456789012345678901 234567890123456789.1234.example.com" Expected: false Actual: true ---- Failed: ID "23": "12345678901234567890123456789012345678901234567890123456789012 345@example.com" Expected: false Actual: true ---- Failed: ID "31": """@example.com" Expected: false Actual: true ---- Failed: ID "34": "x@x23456789.x23456789.x23456789.x23456789.x23456789.x23456789. x23456789.x23456789.x23456789.x23456789.x23456789.x23456789.x23456789.x23456789. x23456789.x23456789.x23456789.x23456789.x23456789.x23456789.x23456789.x23456789. x23456789.x23456789.x23456789.x23456" Expected: false Actual: true ---- Failed: ID "35": "first.last@[.12.34.56.78]" Expected: false Actual: true ---- Failed: ID "36": "first.last@[12.34.56.789]" Expected: false Actual: true ---- Failed: ID "37": "first.last@[::12.34.56.78]" Expected: false Actual: true ---- Failed: ID "38": "first.last@[IPv5:::12.34.56.78]" Expected: false Actual: true ---- Failed: ID "39": "first.last@[IPv6:1111:2222:3333::4444:5555:12.34.56.78]" Expected: false Actual: true ---- Failed: ID "40": "first.last@[IPv6:1111:2222:3333:4444:5555:12.34.56.78]" Expected: false Actual: true ---- Failed: ID "41": "first.last@[IPv6:1111:2222:3333:4444:5555:6666:7777:12.34.56.7 8]" Expected: false Actual: true ---- Failed: ID "42": "first.last@[IPv6:1111:2222:3333:4444:5555:6666:7777]" Expected: false Actual: true ---- Failed: ID "43": "first.last@[IPv6:1111:2222:3333:4444:5555:6666:7777:8888:9999] " Expected: false Actual: true ---- Failed: ID "44": "first.last@[IPv6:1111:2222::3333::4444:5555:6666]" Expected: false Actual: true ---- Failed: ID "45": "first.last@[IPv6:1111:2222:3333::4444:5555:6666:7777]" Expected: false Actual: true ---- Failed: ID "46": "first.last@[IPv6:1111:2222:333x::4444:5555]" Expected: false Actual: true ---- Failed: ID "47": "first.last@[IPv6:1111:2222:33333::4444:5555]" Expected: false Actual: true ---- Failed: ID "48": "first.last@example.123" Expected: false Actual: true ---- Failed: ID "49": "first.last@com" Expected: false Actual: true ---- Failed: ID "50": "first.last@-xample.com" Expected: false Actual: true ---- Failed: ID "51": "first.last@exampl-.com" Expected: false Actual: true ---- Failed: ID "52": "first.last@x23456789012345678901234567890123456789012345678901 2345678901234.example.com" Expected: false Actual: true ---- Failed: ID "97": "test@123.123.123.123" Expected: false Actual: true ---- Failed: ID "115": "test@12345678901234567890123456789012345678901234567890123456 78901234567890123456789012345678901234567890123456789012345678901234567890123456 78901234567890123456789012345678901234567890123456789012345678901234567890123456 789012345678901234567890123456789012.com" Expected: false Actual: true ---- Failed: ID "116": "test@example" Expected: false Actual: true ---- Failed: ID "153": "first."".last@example.com" Expected: false Actual: true ---- Failed: ID "158": "first.last@[IPv6:1111:2222:3333:4444:5555:6666:12.34.567.89]" Expected: false Actual: true ---- Failed: ID "159": ""test\ blah"@example.com" Expected: false Actual: true ---- Failed: ID "190": "a@b" Expected: false Actual: true ---- Failed: ID "199": "aaa@[123.123.123.333]" Expected: false Actual: true ---- Failed: ID "201": "a@bar" Expected: false Actual: true ---- Failed: ID "205": "a@-b.com" Expected: false Actual: true ---- Failed: ID "206": "a@b-.com" Expected: false Actual: true ---- Failed: ID "213": "invalid@special.museum-" Expected: false Actual: true ---- Failed: ID "216": "foobar@192.168.0.1" Expected: false Actual: true ---- Failed: ID "227": ""null \0"@char.com" Expected: false Actual: true
Great reaading your blog
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