Only escape the first character in a sequence of bytes that appears to be

a multibyte character, but was not a valid multibyte character. Refinement
of fix for Bug #8378.

mysys/charset.c

@@ -583,9 +583,10 @@ ulong escape_string_for_mysql(CHARSET_INFO *charset_info, char *to,
     }
     /*
      If the next character appears to begin a multi-byte character, we
-     escape all of the bytes of that apparent character. (The character just
-     looks like a multi-byte character -- if it were actually a multi-byte
-     character, it would have been passed through in the test above.)
+     escape that first byte of that apparent multi-byte character. (The
+     character just looks like a multi-byte character -- if it were actually
+     a multi-byte character, it would have been passed through in the test
+     above.)
 
      Without this check, we can create a problem by converting an invalid
      multi-byte character into a valid one. For example, 0xbf27 is not
@@ -593,12 +594,8 @@ ulong escape_string_for_mysql(CHARSET_INFO *charset_info, char *to,
     */
     if (use_mb_flag && (l= my_mbcharlen(charset_info, *from)) > 1)
     {
-      while (l--)
-      {
-        *to++= '\\';
-	*to++= *from++;
-      }
-      from--;
+      *to++= '\\';
+      *to++= *from;
       continue;
     }
 #endif

tests/mysql_client_test.c

@@ -11535,20 +11535,20 @@ static void test_bug6761(void)
 /*
  Test mysql_real_escape_string() with gbk charset
 
- The important part is that 0x27 (') is the second-byte in a invvalid
+ The important part is that 0x27 (') is the second-byte in a invalid
  two-byte GBK character here. But 0xbf5c is a valid GBK character, so
- it needs to be escaped as 0x5cbf5c27
+ it needs to be escaped as 0x5cbf27
 */
-#define TEST_BUG8317_IN  "\xef\xbb\xbf\x27"
-#define TEST_BUG8317_OUT "\xef\xbb\x5c\xbf\x5c\x27"
+#define TEST_BUG8378_IN  "\xef\xbb\xbf\x27\xbf\x10"
+#define TEST_BUG8378_OUT "\xef\xbb\x5c\xbf\x5c\x27\x5c\xbf\x10"
 
-static void test_bug8317()
+static void test_bug8378()
 {
   MYSQL *lmysql;
-  char out[9]; /* strlen(TEST_BUG8317)*2+1 */
+  char out[9]; /* strlen(TEST_BUG8378)*2+1 */
   int len;
 
-  myheader("test_bug8317");
+  myheader("test_bug8378");
 
   if (!opt_silent)
     fprintf(stdout, "\n Establishing a test connection ...");
@@ -11572,10 +11572,10 @@ static void test_bug8317()
   if (!opt_silent)
     fprintf(stdout, " OK");
 
-  len= mysql_real_escape_string(lmysql, out, TEST_BUG8317_IN, 4);
+  len= mysql_real_escape_string(lmysql, out, TEST_BUG8378_IN, 4);
 
   /* No escaping should have actually happened. */
-  DIE_UNLESS(memcmp(out, TEST_BUG8317_OUT, len) == 0);
+  DIE_UNLESS(memcmp(out, TEST_BUG8378_OUT, len) == 0);
 
   mysql_close(lmysql);
 }
@@ -11787,7 +11787,7 @@ static struct my_tests_st my_tests[]= {
   { "test_conversion", test_conversion },
   { "test_rewind", test_rewind },
   { "test_bug6761", test_bug6761 },
-  { "test_bug8317", test_bug8317 },
+  { "test_bug8378", test_bug8378 },
   { 0, 0 }
 };