extmod/modssl_mbedtls: Fix cipher iteration in SSLContext.get_ciphers.

Prior to this commit it would skip every second cipher returned from
mbedtls.

The corresponding test is also updated and now passes on esp32, rp2, stm32
and unix.
Signed-off-by: Damien George <damien@micropython.org>

extmod/modssl_mbedtls.c

@@ -311,10 +311,6 @@ STATIC mp_obj_t ssl_context_get_ciphers(mp_obj_t self_in) {
     for (const int *cipher_list = mbedtls_ssl_list_ciphersuites(); *cipher_list; ++cipher_list) {
         const char *cipher_name = mbedtls_ssl_get_ciphersuite_name(*cipher_list);
         mp_obj_list_append(list, MP_OBJ_FROM_PTR(mp_obj_new_str(cipher_name, strlen(cipher_name))));
-        cipher_list++;
-        if (!*cipher_list) {
-            break;
-        }
     }
     return list;
 }

tests/extmod/ssl_sslcontext_ciphers.py

@@ -12,7 +12,9 @@ ctx = ssl.SSLContext(ssl.PROTOCOL_TLS_CLIENT)
 ciphers = ctx.get_ciphers()
 
 for ci in ciphers:
-    print(ci)
+    # Only print those ciphers know to exist on all ports.
+    if ("TLS-ECDHE-ECDSA-WITH-AES" in ci or "TLS-RSA-WITH-AES" in ci) and "CBC" in ci:
+        print(ci)
 
 ctx.set_ciphers(ciphers[:1])
 

tests/extmod/ssl_sslcontext_ciphers.py.exp

 TLS-ECDHE-ECDSA-WITH-AES-256-CBC-SHA384
+TLS-ECDHE-ECDSA-WITH-AES-256-CBC-SHA
 TLS-ECDHE-ECDSA-WITH-AES-128-CBC-SHA256
+TLS-ECDHE-ECDSA-WITH-AES-128-CBC-SHA
 TLS-RSA-WITH-AES-256-CBC-SHA256
+TLS-RSA-WITH-AES-256-CBC-SHA
 TLS-RSA-WITH-AES-128-CBC-SHA256
+TLS-RSA-WITH-AES-128-CBC-SHA
 object 'str' isn't a tuple or list
 (-24192, 'MBEDTLS_ERR_SSL_BAD_CONFIG')