list subject alternative name for dns

hostname.c

@@ -6,6 +6,7 @@
  */
 
 #include <openssl/x509.h>
+#include "hostname.h"
 
 #ifndef X509_CHECK_FLAG_ALWAYS_CHECK_SUBJECT
 
@@ -271,6 +272,30 @@ static int do_check_string(ASN1_STRING *a, int cmp_type, equal_fn equal,
 		}
 	}
 
+void list_x509_san(X509 *x, SanList *list)
+{
+    STACK_OF(GENERAL_NAME) *gens = NULL;
+    gens = X509_get_ext_d2i(x, NID_subject_alt_name, NULL, NULL);
+    if (gens)
+        {
+        int i;
+        int gens_length=sk_GENERAL_NAME_num(gens);
+        list->length = gens_length;
+        list->sans = (char**)realloc(list->sans, gens_length*sizeof(char*));
+        for (i = 0; i < gens_length; i++)
+            {
+            unsigned char *astr;
+            GENERAL_NAME *gen;
+            ASN1_STRING *cstr;
+
+            gen = sk_GENERAL_NAME_value(gens, i);
+            ASN1_STRING_to_UTF8(&astr, gen->d.dNSName);
+            list->sans[i] = astr;
+            }
+        GENERAL_NAMES_free(gens);
+        }
+}
+
 static int do_x509_check(X509 *x, const unsigned char *chk, size_t chklen,
 					unsigned int flags, int check_type)
 	{

hostname.go

@@ -18,6 +18,7 @@ package openssl
 #include <openssl/ssl.h>
 #include <openssl/conf.h>
 #include <openssl/x509.h>
+#include "hostname.h"
 
 #ifndef X509_CHECK_FLAG_ALWAYS_CHECK_SUBJECT
 #define X509_CHECK_FLAG_ALWAYS_CHECK_SUBJECT	0x1
@@ -29,13 +30,15 @@ extern int X509_check_email(X509 *x, const unsigned char *chk, size_t chklen,
     unsigned int flags);
 extern int X509_check_ip(X509 *x, const unsigned char *chk, size_t chklen,
 		unsigned int flags);
+extern void list_x509_san(X509 *x, SanList *sans);
 #endif
 */
 import "C"
 
 import (
 	"errors"
 	"net"
+	"reflect"
 	"unsafe"
 )
 
@@ -50,6 +53,25 @@ const (
 	NoWildcards        CheckFlags = C.X509_CHECK_FLAG_NO_WILDCARDS
 )
 
+func (c *Certificate) ListSanDns() []string {
+	list := C.SanList{}
+	list.sans = (**C.char)(C.malloc(100))
+	defer C.free(unsafe.Pointer(list.sans))
+	C.list_x509_san(c.x, &list)
+
+	var str []string
+	var pbuf []*C.char
+	header := (*reflect.SliceHeader)(unsafe.Pointer(&pbuf))
+	header.Cap = int(list.length)
+	header.Len = int(list.length)
+	header.Data = uintptr(unsafe.Pointer(list.sans))
+	for _, i := range pbuf {
+		str = append(str, C.GoString(i))
+	}
+
+	return str
+}
+
 // CheckHost checks that the X509 certificate is signed for the provided
 // host name. See http://www.openssl.org/docs/crypto/X509_check_host.html for
 // more. Note that CheckHost does not check the IP field. See VerifyHostname.

hostname.h

@@ -0,0 +1,6 @@
+#include <stdio.h>
+
+typedef struct _SanList {
+	int length;
+	char** sans;
+} SanList;