[freetds] Status of UTF-8 support in 0.83 dev

Sebastien FLAESCH sf at 4js.com
Mon Sep 1 10:54:24 EDT 2008


While testing ParameterType = SQL_WVARCHAR, I faced a problem with ColumnSize...

According to MSDN, ColumnSize defines the precision of the type in *characters* (not bytes):


With attached example, when using a CHAR(2) column, I just bind with ParameterType=SQL_WVARCHAR and ColumnSize=2 ...

But I get an error:

SQL State: 42000
SQL code : 8016
Message  : [FreeTDS][SQL Server]The incoming tabular data stream (TDS) remote
            procedure call (RPC) protocol stream is incorrect.
            Parameter 3 (""): Data type 0xE7 has an invalid data length or metadata length.

Please could you have a look at this?

Note in my SQL Native Client driver, I do also use SQL_WVARCHAR and ColumnSize has to be passed as a number of characters.


Frediano Ziglio wrote:
> Il giorno gio, 14/08/2008 alle 11.53 -0400, James K. Lowden ha scritto:
>> Hi Sebastien, 
>>> James K. Lowden wrote:
>>>> "Wide" characters have a fixed width, usually 16 bits.  UTF-8 has a
>>>> variable width and for the most part can be treated like ASCII
>>>> (strlen(3) et al.).  Declaring UTF-8 as SQL_C_WCHAR incorrectly tells
>>>> the driver there's a character in every two bytes.
>>> Oh take care, actually there are 2 type specifications in
>>> SQLBindParameter:
>>> SQLRETURN SQLBindParameter(
>>>       SQLHSTMT     StatementHandle,
>>>       SQLUSMALLINT     ParameterNumber,
>>>       SQLSMALLINT     InputOutputType,
>>>       SQLSMALLINT     ValueType,          -- This is the C type
>>>       SQLSMALLINT     ParameterType,      -- This is the SQL equivalent
>>>       SQLULEN     ColumnSize,
>>>       SQLSMALLINT     DecimalDigits,
>>>       SQLPOINTER     ParameterValuePtr,
>>>       SQLINTEGER     BufferLength,
>>>       SQLLEN *     StrLen_or_IndPtr);
>>> For sure, when using (char *) / UTF-8, ValueType *must* be SQL_C_CHAR,
>>> not SQL_C_WCHAR... (that one is for wchar_t).
>>> I was talking about ParameterType...
>>> Should it be  SQL_W[VAR]CHAR  or  SQL_[VAR]CHAR  when binding UTF-8?
>> Oh, I see.  Your question surprises me, then, because IIUC the client-side
>> encoding doesn't matter for ParameterType.  ParameterType describes the
>> data type of the parameter as used in the query, not as represented in the
>> client buffer.  (I"m just an ODBC student.  Correct me if I'm wrong.) 
> ParameterType specify the type to use with the server so if SQL_VARCHAR
> is used a VARCHAR is sent to the server while using SQL_WVARCHAR an
> NVARCHAR is used. This cause the problem with japanese encoding,
> SQL_VARCHAR is not able to "contain" japanese so the error. Some
> updates:
> - I split my working patch for wide support committing support for
> server N(VAR)CHAR, very short and seems to work correctly with UTF-8
> (the other part is to support *W functions and SQL_C_WCHAR... and it's a
> very very long work)
> - I ported Sebastian tests in a new src/odbc/unittests/utf8.c test, it
> works correctly and it tests data inserted too. I used a trick to force
> client encoding (using SQLDriverConnect instead of SQLConnect)
> - I wrote a workaround for invalid TDS protocol if a conversion error
> happen. Now libTDS send an empty string... not correct but at least you
> get an error from library and you can continue to issue queries. The
> patch was backported to 0.82 too. I'll write a definitive fix for this
> (it require to handle correctly errors and cancel sending query).
>> For instance, any of these pairs works:
>> 	ValueType	ParameterType 
>> 	-------------	-------------
>> For character data parameters, the choice of SQL_W[VAR]CHAR or
>> SQL_[VAR]CHAR is governed by the data type of the parameter as understood
>> by the server.  For stored procedures, the parameter type is obvious: it's
>> declared within the procedure text.  For placeholders in open SQL text, I
>> would say the type is always SQL_[VAR]CHAR.  
> No, the client encodes the parameter type as specified by the
> application. The server converts the parameter as needed.
>> That is, if your query is, 
>> 	CREATE TABLE t (name nvarchar(30))
>> 	INSERT t values( ? )	
>> You would use SQL_[VAR]CHAR.  
>> Now, what to do when what you really want is equivalent to "INSERT t
>> values( N'string' )"?  I assume it's still SQL_[VAR]CHAR, but I won't know
>> for sure until either Frediano explains or I figure out how sp_execute
>> works.  
> sp_execute is a special store procedure witch is embedded in sql server
> and support variable parameters... let's say it's like a printf instead
> of a strcpy. You specify parameters you pass followed by parameters and
> server execute the query.
>> One thing you could try is SQLDescribeParam with various combinations
>> using Microsoft's driver.  We would follow whatever it says/expects.  
> SQLDescribeParam is a workaround on mssql... it parse the query to get
> parameters type. Obviously on complicated query it isn't able to tell
> the truth... Assuming query is "SELECT * FROM table WHERE x = ?" it
> build a "SET FMTONLY ON SELECT x FROM table" and get x type... this is
> the reason is still unsupported by our driver... nobody wants to write
> the sql parser :)
> bye
>   Frediano
> _______________________________________________
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> FreeTDS at lists.ibiblio.org
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