py: Change vstr so that it doesn't null terminate buffer by default.

This cleans up vstr so that it's a pure "variable buffer", and the user
can decide whether they need to add a terminating null byte.  In most
places where vstr is used, the vstr did not need to be null terminated
and so this patch saves code size, a tiny bit of RAM, and makes vstr
usage more efficient.  When null termination is needed it must be
done explicitly using vstr_null_terminate.

3 files changed, 11 insertions, 9 deletions

diff --git a/stmhal/input.c b/stmhal/input.c
index b735ca2492..b1c8c1f78f 100644
--- a/stmhal/input.c
+++ b/stmhal/input.c
@@ -39,9 +39,7 @@ STATIC mp_obj_t mp_builtin_input(uint n_args, const mp_obj_t *args) {
     if (line.len == 0 && ret == CHAR_CTRL_D) {
         nlr_raise(mp_obj_new_exception(&mp_type_EOFError));
     }
-    mp_obj_t o = mp_obj_new_str(line.buf, line.len, false);
-    vstr_clear(&line);
-    return o;
+    return mp_obj_new_str_from_vstr(&mp_type_str, &line);
 }
 
 MP_DEFINE_CONST_FUN_OBJ_VAR_BETWEEN(mp_builtin_input_obj, 0, 1, mp_builtin_input);
diff --git a/stmhal/modusocket.c b/stmhal/modusocket.c
index b52a9c8e88..a2ec08f59e 100644
--- a/stmhal/modusocket.c
+++ b/stmhal/modusocket.c
@@ -217,7 +217,6 @@ STATIC mp_obj_t socket_recv(mp_obj_t self_in, mp_obj_t len_in) {
         return mp_const_empty_bytes;
     }
     vstr.len = ret;
-    vstr.buf[vstr.len] = '\0';
     return mp_obj_new_str_from_vstr(&mp_type_bytes, &vstr);
 }
 STATIC MP_DEFINE_CONST_FUN_OBJ_2(socket_recv_obj, socket_recv);
@@ -269,7 +268,6 @@ STATIC mp_obj_t socket_recvfrom(mp_obj_t self_in, mp_obj_t len_in) {
         tuple[0] = mp_const_empty_bytes;
     } else {
         vstr.len = ret;
-        vstr.buf[vstr.len] = '\0';
         tuple[0] = mp_obj_new_str_from_vstr(&mp_type_bytes, &vstr);
     }
     tuple[1] = mod_network_format_inet_addr(ip, port);
diff --git a/stmhal/pyexec.c b/stmhal/pyexec.c
index 1563dc8e4a..930c1c0191 100644
--- a/stmhal/pyexec.c
+++ b/stmhal/pyexec.c
@@ -248,11 +248,12 @@ int pyexec_friendly_repl_process_char(int c) {
             return 0;
         }
 
+        vstr_null_terminate(&repl.line);
         if (!mp_repl_continue_with_input(vstr_str(&repl.line))) {
             goto exec;
         }
 
-        vstr_add_char(&repl.line, '\n');
+        vstr_add_byte(&repl.line, '\n');
         repl.cont_line = true;
         stdout_tx_str("... ");
         readline_note_newline();
@@ -274,8 +275,9 @@ int pyexec_friendly_repl_process_char(int c) {
             return 0;
         }
 
+        vstr_null_terminate(&repl.line);
         if (mp_repl_continue_with_input(vstr_str(&repl.line))) {
-            vstr_add_char(&repl.line, '\n');
+            vstr_add_byte(&repl.line, '\n');
             stdout_tx_str("... ");
             readline_note_newline();
             return 0;
@@ -362,8 +364,12 @@ friendly_repl_reset:
             continue;
         }
 
-        while (mp_repl_continue_with_input(vstr_str(&line))) {
-            vstr_add_char(&line, '\n');
+        for (;;) {
+            vstr_null_terminate(&line);
+            if (!mp_repl_continue_with_input(vstr_str(&line))) {
+                break;
+            }
+            vstr_add_byte(&line, '\n');
             ret = readline(&line, "... ");
             if (ret == CHAR_CTRL_C) {
                 // cancel everything