Simplify X.509 extension handling code (#1855)

* Simplify X.509 extension handling code

The previous implementation had grown organically over time, as OpenSSL's API evolved.

* Delete even more code

Modules/_ssl.c

@@ -905,18 +905,15 @@ _get_peer_alt_names (X509 *certificate) {
        then iterates through the stack to add the
        names. */
 
-    int i, j;
+    int j;
     PyObject *peer_alt_names = Py_None;
     PyObject *v = NULL, *t;
-    X509_EXTENSION *ext = NULL;
     GENERAL_NAMES *names = NULL;
     GENERAL_NAME *name;
-    const X509V3_EXT_METHOD *method;
     BIO *biobuf = NULL;
     char buf[2048];
     char *vptr;
     int len;
-    const unsigned char *p;
 
     if (certificate == NULL)
         return peer_alt_names;
@@ -924,38 +921,15 @@ _get_peer_alt_names (X509 *certificate) {
     /* get a memory buffer */
     biobuf = BIO_new(BIO_s_mem());
 
-    i = -1;
-    while ((i = X509_get_ext_by_NID(
-                    certificate, NID_subject_alt_name, i)) >= 0) {
-
+    names = (GENERAL_NAMES *)X509_get_ext_d2i(
+        certificate, NID_subject_alt_name, NULL, NULL);
+    if (names != NULL) {
         if (peer_alt_names == Py_None) {
             peer_alt_names = PyList_New(0);
             if (peer_alt_names == NULL)
                 goto fail;
         }
 
-        /* now decode the altName */
-        ext = X509_get_ext(certificate, i);
-        if(!(method = X509V3_EXT_get(ext))) {
-            PyErr_SetString
-              (PySSLErrorObject,
-               ERRSTR("No method for internalizing subjectAltName!"));
-            goto fail;
-        }
-
-        p = X509_EXTENSION_get_data(ext)->data;
-        if (method->it)
-            names = (GENERAL_NAMES*)
-              (ASN1_item_d2i(NULL,
-                             &p,
-                             X509_EXTENSION_get_data(ext)->length,
-                             ASN1_ITEM_ptr(method->it)));
-        else
-            names = (GENERAL_NAMES*)
-              (method->d2i(NULL,
-                           &p,
-                           X509_EXTENSION_get_data(ext)->length));
-
         for(j = 0; j < sk_GENERAL_NAME_num(names); j++) {
             /* get a rendering of each name in the set of names */
             int gntype;