Index: ChangeLog
===================================================================
--- ChangeLog	(revision 830)
+++ ChangeLog	(working copy)
@@ -1,6 +1,8 @@
 3.51.22
 
   Functionality added or changed:
+  * The wrong result was returned by SQLGetData() when the data was an
+    empty string and a zero-sized buffer was specified. (Bug #30958)
   * Added FLAG_COLUMN_SIZE_S32 to limit the reported column size to a
     signed 32-bit integer. This option is automatically enabled for ADO
     applications, in order to work around a bug in ADO. (Bug #13776)
Index: driver/utility.c
===================================================================
--- driver/utility.c	(revision 830)
+++ driver/utility.c	(working copy)
@@ -255,7 +255,8 @@
              !(((STMT FAR*)Handle)->dbc->flag & FLAG_PAD_SPACE) )
             fill_length= src_length;
     }
-    if ( *offset == (ulong) ~0L )
+
+    if (arg_length && *offset == (ulong) ~0L)
     {
       /*
         This is first call. Even if data has zero size, we don't
@@ -263,7 +264,7 @@
       */
       *offset= 0;
     }
-    else if ( *offset >= (ulong) fill_length )
+    else if (*offset != (ulong) ~0L && *offset >= (ulong) fill_length)
     {
       /*
         If not the first call, and we have no data left,
@@ -274,9 +275,12 @@
       return SQL_NO_DATA_FOUND;
     }
 
-    src+= *offset;
-    src_length-= (long) *offset;
-    fill_length-= *offset;
+    if (*offset != (ulong) ~0L)
+    {
+      src+= *offset;
+      src_length-= (long) *offset;
+      fill_length-= *offset;
+    }
 
     length= min(fill_length, cbValueMax);
     (*offset)+= length;        /* Fix for next call */
Index: test/my_result.c
===================================================================
--- test/my_result.c	(revision 830)
+++ test/my_result.c	(working copy)
@@ -1783,8 +1783,8 @@
   ok_stmt(hstmt, SQLFetch(hstmt));
 
   /*
-     check first that we get truncation, with zero bytes
-     available in out buffer, outbuffer should be untouched
+   check first that we get truncation, with zero bytes
+   available in out buffer, outbuffer should be untouched
   */
   outlen= 99;
   expect_stmt(hstmt, SQLGetData(hstmt, 1, SQL_C_CHAR, outbuf, outmax,
@@ -1793,7 +1793,7 @@
   is_num(outlen, 0);
   is(check_sqlstate(hstmt, "01004") == OK);
 
-  /* exact the same result, and not SQL_NO_DATA */
+  /* expect the same result, and not SQL_NO_DATA */
   outlen= 99;
   expect_stmt(hstmt, SQLGetData(hstmt, 1, SQL_C_CHAR, outbuf, outmax,
                                 &outlen), SQL_SUCCESS_WITH_INFO);
@@ -2008,7 +2008,7 @@
   ADD_TEST(bug6157)
   ADD_TEST(t_binary_collation)
   ADD_TODO(t_bug29239)
-  ADD_TODO(t_bug30958)
+  ADD_TEST(t_bug30958)
   ADD_TEST(t_bug31246)
   ADD_TEST(t_bug13776)
   ADD_TEST(t_bug13776_auto)