Prohibit string changes by "s"/"z" specifier of `mrb_get_args()`

- The `s` specifier is a string pointer obtained without performing `mrb_str_modify()`, so it cannot be changed.
- The `z` specifier cannot be changed because it is a string pointer obtained by `RSTRING_CSTR()` which returns `const char *`.

include/mruby.h

@@ -876,8 +876,8 @@ MRB_API struct RClass * mrb_define_module_under(mrb_state *mrb, struct RClass *o
  * | `S`  | {String}       | {mrb_value}       | when `!` follows, the value may be `nil`           |
  * | `A`  | {Array}        | {mrb_value}       | when `!` follows, the value may be `nil`           |
  * | `H`  | {Hash}         | {mrb_value}       | when `!` follows, the value may be `nil`           |
- * | `s`  | {String}       | char *, {mrb_int} | Receive two arguments; `s!` gives (`NULL`,`0`) for `nil`        |
- * | `z`  | {String}       | char *            | `NULL` terminated string; `z!` gives `NULL` for `nil`           |
+ * | `s`  | {String}       | const char *, {mrb_int} | Receive two arguments; `s!` gives (`NULL`,`0`) for `nil` |
+ * | `z`  | {String}       | const char *      | `NULL` terminated string; `z!` gives `NULL` for `nil` |
  * | `a`  | {Array}        | {mrb_value} *, {mrb_int} | Receive two arguments; `a!` gives (`NULL`,`0`) for `nil` |
  * | `f`  | {Fixnum}/{Float} | {mrb_float}       |                                                    |
  * | `i`  | {Fixnum}/{Float} | {mrb_int}         |                                                    |

mrbgems/mruby-eval/src/eval.c

@@ -12,7 +12,7 @@ mrb_value mrb_obj_instance_eval(mrb_state *mrb, mrb_value self);
 void mrb_codedump_all(mrb_state*, struct RProc*);
 
 static struct RProc*
-create_proc_from_string(mrb_state *mrb, char *s, mrb_int len, mrb_value binding, const char *file, mrb_int line)
+create_proc_from_string(mrb_state *mrb, const char *s, mrb_int len, mrb_value binding, const char *file, mrb_int line)
 {
   mrbc_context *cxt;
   struct mrb_parser_state *p;
@@ -131,10 +131,10 @@ exec_irep(mrb_state *mrb, mrb_value self, struct RProc *proc)
 static mrb_value
 f_eval(mrb_state *mrb, mrb_value self)
 {
-  char *s;
+  const char *s;
   mrb_int len;
   mrb_value binding = mrb_nil_value();
-  char *file = NULL;
+  const char *file = NULL;
   mrb_int line = 1;
   struct RProc *proc;
 
@@ -154,9 +154,9 @@ f_instance_eval(mrb_state *mrb, mrb_value self)
   mrb_get_args(mrb, "*!&", &argv, &argc, &b);
 
   if (mrb_nil_p(b)) {
-    char *s;
+    const char *s;
     mrb_int len;
-    char *file = NULL;
+    const char *file = NULL;
     mrb_int line = 1;
     mrb_value cv;
     struct RProc *proc;

mrbgems/mruby-io/src/file.c

@@ -557,7 +557,8 @@ mrb_file_s_readlink(mrb_state *mrb, mrb_value klass) {
   mrb_raise(mrb, E_NOTIMP_ERROR, "readlink is not supported on this platform");
   return mrb_nil_value(); // unreachable
 #else
-  char *path, *buf, *tmp;
+  const char *path;
+  char *buf, *tmp;
   size_t bufsize = 100;
   ssize_t rc;
   mrb_value ret;

mrbgems/mruby-socket/src/socket.c

@@ -515,7 +515,8 @@ static mrb_value
 mrb_ipsocket_ntop(mrb_state *mrb, mrb_value klass)
 {
   mrb_int af, n;
-  char *addr, buf[50];
+  const char *addr;
+  char buf[50];
 
   mrb_get_args(mrb, "is", &af, &addr, &n);
   if ((af == AF_INET && n != 4) || (af == AF_INET6 && n != 16))
@@ -529,7 +530,8 @@ static mrb_value
 mrb_ipsocket_pton(mrb_state *mrb, mrb_value klass)
 {
   mrb_int af, n;
-  char *bp, buf[50];
+  const char *bp;
+  char buf[50];
 
   mrb_get_args(mrb, "is", &af, &bp, &n);
   if ((size_t)n > sizeof(buf) - 1)

mrbgems/mruby-string-ext/src/string.c

@@ -1072,7 +1072,8 @@ static mrb_value
 mrb_str_del_prefix_bang(mrb_state *mrb, mrb_value self)
 {
   mrb_int plen, slen;
-  char *ptr, *s;
+  const char *ptr;
+  char *s;
   struct RString *str = RSTRING(self);
 
   mrb_get_args(mrb, "s", &ptr, &plen);
@@ -1105,7 +1106,7 @@ static mrb_value
 mrb_str_del_prefix(mrb_state *mrb, mrb_value self)
 {
   mrb_int plen, slen;
-  char *ptr;
+  const char *ptr;
 
   mrb_get_args(mrb, "s", &ptr, &plen);
   slen = RSTRING_LEN(self);
@@ -1129,7 +1130,8 @@ static mrb_value
 mrb_str_del_suffix_bang(mrb_state *mrb, mrb_value self)
 {
   mrb_int plen, slen;
-  char *ptr, *s;
+  const char *ptr;
+  char *s;
   struct RString *str = RSTRING(self);
 
   mrb_get_args(mrb, "s", &ptr, &plen);
@@ -1160,7 +1162,7 @@ static mrb_value
 mrb_str_del_suffix(mrb_state *mrb, mrb_value self)
 {
   mrb_int plen, slen;
-  char *ptr;
+  const char *ptr;
 
   mrb_get_args(mrb, "s", &ptr, &plen);
   slen = RSTRING_LEN(self);

src/class.c

@@ -584,8 +584,8 @@ void mrb_hash_check_kdict(mrb_state *mrb, mrb_value self);
     S:      String         [mrb_value]            when ! follows, the value may be nil
     A:      Array          [mrb_value]            when ! follows, the value may be nil
     H:      Hash           [mrb_value]            when ! follows, the value may be nil
-    s:      String         [char*,mrb_int]        Receive two arguments; s! gives (NULL,0) for nil
-    z:      String         [char*]                NUL terminated string; z! gives NULL for nil
+    s:      String         [const char*,mrb_int]  Receive two arguments; s! gives (NULL,0) for nil
+    z:      String         [const char*]          NUL terminated string; z! gives NULL for nil
     a:      Array          [mrb_value*,mrb_int]   Receive two arguments; a! gives (NULL,0) for nil
     c:      Class/Module   [strcut RClass*]
     f:      Fixnum/Float   [mrb_float]
@@ -772,10 +772,10 @@ mrb_get_args(mrb_state *mrb, const char *format, ...)
     case 's':
       {
         mrb_value ss;
-        char **ps = 0;
+        const char **ps = 0;
         mrb_int *pl = 0;
 
-        ps = va_arg(ap, char**);
+        ps = va_arg(ap, const char**);
         pl = va_arg(ap, mrb_int*);
         if (i < argc) {
           ss = argv[i++];