net/mail: allow empty quoted string name in address again

CL 12905 disallowed "Bob" <""@example.com> but inadvertently
also disallowed "" <bob@example.com>. Move the empty string
check to apply only in the addr-spec.

Fixes #14866.

Change-Id: Ia0b7a1a32810aa78157ae77bd0130b78154c460d
Reviewed-on: https://go-review.googlesource.com/32176Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

src/net/mail/message.go

@@ -346,6 +346,9 @@ func (p *addrParser) consumeAddrSpec() (spec string, err error) {
 		// quoted-string
 		debug.Printf("consumeAddrSpec: parsing quoted-string")
 		localPart, err = p.consumeQuotedString()
+		if localPart == "" {
+			err = errors.New("mail: empty quoted string in addr-spec")
+		}
 	} else {
 		// dot-atom
 		debug.Printf("consumeAddrSpec: parsing dot-atom")
@@ -463,9 +466,6 @@ Loop:
 		i += size
 	}
 	p.s = p.s[i+1:]
-	if len(qsb) == 0 {
-		return "", errors.New("mail: empty quoted-string")
-	}
 	return string(qsb), nil
 }
 

src/net/mail/message_test.go

@@ -315,6 +315,16 @@ func TestAddressParsing(t *testing.T) {
 				},
 			},
 		},
+		// Issue 14866
+		{
+			`"" <emptystring@example.com>`,
+			[]*Address{
+				{
+					Name:    "",
+					Address: "emptystring@example.com",
+				},
+			},
+		},
 	}
 	for _, test := range tests {
 		if len(test.exp) == 1 {