fix: improve email validation using net/mail package (#60)

* fix: improve email validation using net/mail package

* fix: improve email validation using net/mail package

* fix: update test expectations for email validation behavior change

Invalid emails no longer persist their value after failed UnmarshalJSON
validation, since the new net/mail-based validation sets the value only
after successful parsing.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

---------

Co-authored-by: Marcin Romaszewicz <marcinr@gmail.com>
Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>

Author: 3 people

types/email.go

@@ -3,6 +3,7 @@ package types
 import (
 	"encoding/json"
 	"errors"
+	"net/mail"
 )
 
 // ErrValidationEmail is the sentinel error returned when an email fails validation
@@ -14,11 +15,12 @@ var ErrValidationEmail = errors.New("email: failed to pass regex validation")
 type Email string
 
 func (e Email) MarshalJSON() ([]byte, error) {
-	if !emailRegex.MatchString(string(e)) {
+	m, err := mail.ParseAddress(string(e))
+	if err != nil {
 		return nil, ErrValidationEmail
 	}
 
-	return json.Marshal(string(e))
+	return json.Marshal(m.Address)
 }
 
 func (e *Email) UnmarshalJSON(data []byte) error {
@@ -31,10 +33,11 @@ func (e *Email) UnmarshalJSON(data []byte) error {
 		return err
 	}
 
-	*e = Email(s)
-	if !emailRegex.MatchString(s) {
+	m, err := mail.ParseAddress(s)
+	if err != nil {
 		return ErrValidationEmail
 	}
 
+	*e = Email(m.Address)
 	return nil
 }

types/email_test.go

@@ -22,6 +22,11 @@ func TestEmail_MarshalJSON_Validation(t *testing.T) {
 			expectedJSON:  []byte(`{"email":"validemail@openapicodegen.com"}`),
 			expectedError: nil,
 		},
+		"it should succeed marshalling a valid email and return valid JSON populated with the email with valid separators": {
+			email:         Email("validemail+with_valid-separator{like}~these*ones@openapicodegen.com"),
+			expectedJSON:  []byte(`{"email":"validemail+with_valid-separator{like}~these*ones@openapicodegen.com"}`),
+			expectedError: nil,
+		},
 		"it should fail marshalling an invalid email and return a validation error": {
 			email:         Email("invalidemail"),
 			expectedJSON:  nil,
@@ -71,10 +76,7 @@ func TestEmail_UnmarshalJSON_RequiredEmail_Validation(t *testing.T) {
 		"it should fail validating an invalid email": {
 			jsonStr:       `{"email":"not-an-email"}`,
 			expectedError: ErrValidationEmail,
-			expectedEmail: func() Email {
-				e := Email("not-an-email")
-				return e
-			}(),
+			expectedEmail: Email(""),
 		},
 		"it should fail validating an empty email": {
 			jsonStr: `{"email":""}`,
@@ -134,7 +136,7 @@ func TestEmail_UnmarshalJSON_NullableEmail_Validation(t *testing.T) {
 			jsonStr:       `{"email":"not-an-email"}`,
 			expectedError: ErrValidationEmail,
 			expectedEmail: func() *Email {
-				e := Email("not-an-email")
+				e := Email("")
 				return &e
 			}(),
 		},