package rfc

/*
 * ZLint Copyright 2020 Regents of the University of Michigan
 *
 * Licensed under the Apache License, Version 2.0 (the "License"); you may not
 * use this file except in compliance with the License. You may obtain a copy
 * of the License at http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or
 * implied. See the License for the specific language governing
 * permissions and limitations under the License.
 */

/******************************************************************
RFC 5280: 4.2.1.6
If the subjectAltName extension is present, the sequence MUST contain
at least one entry.  Unlike the subject field, conforming CAs MUST
NOT issue certificates with subjectAltNames containing empty
GeneralName fields.  For example, an rfc822Name is represented as an
IA5String.  While an empty string is a valid IA5String, such an
rfc822Name is not permitted by this profile.  The behavior of clients
that encounter such a certificate when processing a certification
path is not defined by this profile.
******************************************************************/

import (
	"encoding/asn1"

	"github.com/zmap/zcrypto/x509"
	"github.com/zmap/zlint/v2/lint"
	"github.com/zmap/zlint/v2/util"
)

type SANEmptyName struct{}

func (l *SANEmptyName) Initialize() error {
	return nil
}

func (l *SANEmptyName) CheckApplies(c *x509.Certificate) bool {
	return util.IsExtInCert(c, util.SubjectAlternateNameOID)
}

func (l *SANEmptyName) Execute(c *x509.Certificate) *lint.LintResult {
	value := util.GetExtFromCert(c, util.SubjectAlternateNameOID).Value
	var seq asn1.RawValue
	if _, err := asn1.Unmarshal(value, &seq); err != nil {
		return &lint.LintResult{Status: lint.Fatal}
	}
	if !seq.IsCompound || seq.Tag != 16 || seq.Class != 0 {
		return &lint.LintResult{Status: lint.Fatal}
	}

	rest := seq.Bytes
	for len(rest) > 0 {
		var v asn1.RawValue
		var err error
		rest, err = asn1.Unmarshal(rest, &v)
		if err != nil {
			return &lint.LintResult{Status: lint.NA}
		}
		if len(v.Bytes) == 0 {
			return &lint.LintResult{Status: lint.Error}
		}
	}
	return &lint.LintResult{Status: lint.Pass}
}

func init() {
	lint.RegisterLint(&lint.Lint{
		Name:          "e_ext_san_empty_name",
		Description:   "General name fields MUST NOT be empty in subjectAlternateNames",
		Citation:      "RFC 5280: 4.2.1.6",
		Source:        lint.RFC5280,
		EffectiveDate: util.RFC2459Date,
		Lint:          &SANEmptyName{},
	})
}
