correct truncation in my_vsnprintf %M format

(because of a width or a short buffer)

strings/my_vsnprintf.c

@@ -153,7 +153,7 @@ static const char *check_longlong(const char *fmt, uint *have_longlong)
     position in buffer which points on the end of escaped string
 */
 
-static char *backtick_string(CHARSET_INFO *cs, char *to, char *end,
+static char *backtick_string(CHARSET_INFO *cs, char *to, const char *end,
                              char *par, size_t par_len, char quote_char)
 {
   uint char_len;
@@ -196,7 +196,7 @@ static char *backtick_string(CHARSET_INFO *cs, char *to, char *end,
   Prints string argument
 */
 
-static char *process_str_arg(CHARSET_INFO *cs, char *to, char *end,
+static char *process_str_arg(CHARSET_INFO *cs, char *to, const char *end,
                              size_t width, char *par, uint print_type)
 {
   int well_formed_error;
@@ -257,7 +257,7 @@ static char *process_dbl_arg(char *to, char *end, size_t width,
   Prints integer argument
 */
 
-static char *process_int_arg(char *to, char *end, size_t length,
+static char *process_int_arg(char *to, const char *end, size_t length,
                              longlong par, char arg_type, uint print_type)
 {
   size_t res_length, to_length;
@@ -482,24 +482,26 @@ static char *process_args(CHARSET_INFO *cs, char *to, char *end,
       case 'M':
       {
         longlong larg;
-        char *org_to= to;
-        char errmsg_buff[MYSYS_STRERROR_SIZE];
+        const char *real_end;
 
-        length= (print_arr[i].flags & WIDTH_ARG)
+        width= (print_arr[i].flags & WIDTH_ARG)
           ? (size_t)args_arr[print_arr[i].width].longlong_arg
           : print_arr[i].width;
 
+        real_end= MY_MIN(to + width, end);
+
         larg = args_arr[print_arr[i].arg_idx].longlong_arg;
-        to= process_int_arg(to, end, 0, larg, 'd', print_arr[i].flags);
-        width-= (to - org_to);
-        if (width <= 4)
-          break;
-        *to++= ' ';
-        *to++= '"';
-        my_strerror(errmsg_buff, sizeof(errmsg_buff), (int) larg);
-        to= process_str_arg(cs, to, end, width-3, errmsg_buff,
-                            print_arr[i].flags);
-        *to++= '"';
+        to= process_int_arg(to, real_end, 0, larg, 'd', print_arr[i].flags);
+        if (real_end - to >= 3)
+        {
+          char errmsg_buff[MYSYS_STRERROR_SIZE];
+          *to++= ' ';
+          *to++= '"';
+          my_strerror(errmsg_buff, sizeof(errmsg_buff), larg);
+          to= process_str_arg(cs, to, real_end, width, errmsg_buff,
+                              print_arr[i].flags);
+          if (real_end > to) *to++= '"';
+        }
         break;
       }
       default:
@@ -666,18 +668,18 @@ size_t my_vsnprintf_ex(CHARSET_INFO *cs, char *to, size_t n,
     }
     else if (*fmt == 'M')
     {
-      const char *org_to= to;
       int larg= va_arg(ap, int);
-      to= process_int_arg(to, end, 0, larg, 'd', print_type);
-      width-= (to - org_to);
-      if ((end - to) >= 4 && (int) width >= 4)
+      const char *real_end= MY_MIN(to + width, end);
+
+      to= process_int_arg(to, real_end, 0, larg, 'd', print_type);
+      if (real_end - to >= 3)
       {
         char errmsg_buff[MYSYS_STRERROR_SIZE];
         *to++= ' ';
         *to++= '"';
         my_strerror(errmsg_buff, sizeof(errmsg_buff), larg);
-        to= process_str_arg(cs, to, end, width-3, errmsg_buff, print_type);
-        *to++= '"';
+        to= process_str_arg(cs, to, real_end, width, errmsg_buff, print_type);
+        if (real_end > to) *to++= '"';
       }
       continue;
     }

unittest/mysys/my_vsnprintf-t.c

@@ -19,6 +19,16 @@
 
 char buf[1024]; /* let's hope that's enough */
 
+static void test_w_len(const char *res, size_t buflen, const char *fmt, ...)
+{
+  va_list args;
+  size_t len;
+  va_start(args,fmt);
+  len= my_vsnprintf(buf, buflen, fmt, args);
+  va_end(args);
+  ok(strlen(res) == len && strcmp(buf, res) == 0, "\"%s\"", buf);
+}
+
 static void test1(const char *res, const char *fmt, ...)
 {
   va_list args;
@@ -51,7 +61,7 @@ static void test_many(const char **res, const char *fmt, ...)
 
 int main(void)
 {
-  plan(59);
+  plan(39);
 
   test1("Constant string",
         "Constant string");
@@ -141,62 +151,6 @@ int main(void)
   test1("G with a width (ignored) and precision: <12.35>",
         "G with a width (ignored) and precision: <%10.5g>", 12.3456789);
 
-  diag("================================================================");
-
-  test1("Hello",
-        "Hello");
-  test1("Hello int, 1",
-        "Hello int, %d", 1);
-  test1("Hello int, -1",
-        "Hello int, %d", -1);
-  test1("Hello int, 1",
-        "Hello int, %i", 1);
-  test1("Hello int, -1",
-        "Hello int, %i", -1);
-  test1("Hello string 'I am a string'",
-        "Hello string '%s'", "I am a string");
-  test1("Hello hack hack hack hack hack hack hack 1",
-        "Hello hack hack hack hack hack hack hack %d", 1);
-  test1("Hello 1 hack 4",
-        "Hello %d hack %d", 1, 4);
-  test1("Hello 1 hack hack hack hack hack 4",
-        "Hello %d hack hack hack hack hack %d", 1, 4);
-  test1("Hello 'hack' hhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhh",
-        "Hello '%s' hhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhh", "hack");
-  test1("Hello hhhhhhhhhhhhhh 1 sssssssssssssss",
-        "Hello hhhhhhhhhhhhhh %d sssssssssssssss", 1);
-  test1("Hello 1",
-        "Hello %u", 1);
-  test1("Hello 4294967295",
-        "Hello %u", -1);
-  test1("Hex:   20  '    41'",
-        "Hex:   %lx  '%6lx'", 32, 65);
-  test1("conn 1 to: '(null)' user: '(null)' host: '(null)' ((null))",
-        "conn %ld to: '%-.64s' user: '%-.32s' host: '%-.64s' (%-.64s)",
-                   1L,     NULL,          NULL,          NULL,    NULL);
-  test1("Hello string `I am a string`",
-        "Hello string %`s", "I am a string");
-  test1("Hello TEST",
-        "Hello %05s", "TEST");
-  test1("My `Q` test",
-        "My %1$`-.1s test", "QQQQ");
-  test1("My AAAA test done DDDD",
-        "My %2$s test done %1$s", "DDDD", "AAAA");
-  test1("My DDDD test CCCC, DDD",
-        "My %1$s test %2$s, %1$-.3s", "DDDD", "CCCC");
-  test1("My QQQQ test",
-        "My %1$`-.4b test", "QQQQ");
-  test1("My X test",
-        "My %1$c test", 'X');
-  test1("My <0000000010> test1 <   a> test2 <   A>",
-        "My <%010d> test1 <%4x> test2 <%4X>", 10, 10, 10);
-  test1("My <0000000010> test1 <   a> test2 <   a>",
-        "My <%1$010d> test1 <%2$4x> test2 <%2$4x>", 10, 10);
-  test1("My 00010 test",
-        "My %1$*02$d test", 10, 5);
-  test1("My `DDDD` test CCCC, `DDD`",
-        "My %1$`s test %2$s, %1$`-.3s", "DDDD", "CCCC");
-
   {
     /* Test that %M works */
     const char *results[]=
@@ -208,6 +162,22 @@ int main(void)
     test_many(results, "Error %M", 1);
   }
 
+  test1("M with 0 error code: 0 \"Internal error/check (Not system error)\"",
+        "M with 0 error code: %M", 0);
+
+  test1("M with positional: 0 \"Internal error/check (Not system error)\"",
+        "M with positional: %1$M", 0);
+
+  test1("M with width: 0 \"Internal error/ch",
+        "M with width: %.20M", 0);
+  test1("M with width positional: 0 \"Internal error/ch",
+        "M with width positional: %2$.*1$M", 20, 0);
+
+  test_w_len("M small buf: 0 \"In",
+         19, "M small buf: %M", 0);
+  test_w_len("M small buf positional: 0 \"In",
+         30, "M small buf positional: %1$M", 0);
+
   return exit_status();
 }