MySQL Bugs: #30547: MyODBC 3 / ADO - Returning double the field size for blob types

Bug #30547	MyODBC 3 / ADO - Returning double the field size for blob types - regression
Submitted:	21 Aug 2007 21:26	Modified:	13 Sep 2007 11:34
Reporter:	Erica Moss	Email Updates:
Status:	Closed	Impact on me:	None
Category:	Connector / ODBC	Severity:	S2 (Serious)
Version:	3.51.19	OS:	Windows (XP sp2)
Assigned to:	Jim Winstead	CPU Architecture:	Any
Tags:	ADO definedSize blob

Description:
According to our manual these are the capacities of the blob types.  In 3.51.17 this is what was reported as the field size in the ADO.Field.DefinedSize property.  After this point the size is being reported as twice these values:

BLOB 	L + 2 bytes, where L <  2^16
MEDIUMBLOB L + 3 bytes, where L < 2^24

in .17
blob DefinedSize = 65535
mediumblob DefinedSize = 16777215
longblob DefinedSize = -1 (overflow)

Currently:
blob DefinedSize = 131070
medblob DefinedSize = 33554430
longblob DefinedSize = -2 (overflow again)

How to repeat:
Setup:
CREATE TABLE defsize (C1 INT PRIMARY KEY, C2 BLOB, C3 MEDIUMBLOB, C4 LONGBLOB);
INSERT INTO defsize VALUES (1, 'blob', 'medblob', 'longblob');

VB CODE:
Private Sub DefSizeTest()
    On Error GoTo EH
    Dim strSQL, strConn As String
    Dim connection1 As adodb.Connection
    Dim recset1 As adodb.Recordset
    Dim fld As Field

    Set connection1 = New adodb.Connection
    Set recset1 = New adodb.Recordset

    strSQL = "SELECT * FROM defsize"
                
    strConn = "DRIVER={MySQL ODBC 3.51 Driver};" & _
        "SERVER=localhost;DATABASE=ado" & _
        ";USER=root;PASSWORD=mypass;OPTION=3;"
        
    ' open connection
    connection1.ConnectionString = strConn
    connection1.CursorLocation = adUseClient
    connection1.Open
    
   ' open recordset
    recset1.Open strSQL, connection1, adOpenStatic, adLockOptimistic, adCmdText
        
    For Each fld In recset1.Fields
        Debug.Print fld.Name & " " & fld.Type & " " & fld.DefinedSize
    Next
                
    recset1.Close
    Set recset1 = Nothing
    connection1.Close
    Set connection1 = Nothing
    Exit Sub
EH:
    Debug.Print Err.Number & ":" & Err.Description
    recset1.Close
    Set recset1 = Nothing
    connection1.Close
    Set connection1 = Nothing
End Sub

This seems to be caused by a change for bug#27862.
If the character set is "binary" the size returned
is doubled.

The call to SQLDescribeCol() in "result.c" calls
get_column_size() in "utility.c" that contains

  case MYSQL_TYPE_TINY_BLOB:
  case MYSQL_TYPE_MEDIUM_BLOB:
  case MYSQL_TYPE_LONG_BLOB:
  case MYSQL_TYPE_BLOB:
  case MYSQL_TYPE_GEOMETRY:
    if (field->charsetnr == 63)
      return length * 2;
    else
      return length / mbmaxlen;
  }

Fix reported value of column size for binary fields

Attachment: bug30547.patch (text/plain), 4.22 KiB.

The fix for this bug has been committed to the repository, and will be included in the next release (3.51.20).

A note has been added to the .3.51.20 changelog: 

The wrong column size was returned for binary data.