Difference between revisions of "OpenDBX/C API/odbx escape"

Latest revision as of 19:42, 17 July 2010

Prepare strings for inclusion in statements

#include <opendbx/api.h>

int odbx_escape(
    odbx_t* handle,
    const char* from,
    unsigned long fromlen,
    char* to,
    unsigned long* tolen )

Description

odbx_escape() neutralizes potentially dangerous characters of the string so it can be used as part of a statement. For security reasons every user input has to be passed to odbx_escape() to avoid SQL injection attacks which can have fatal consequences! It's also a good idea to escape strings returned from database fields again if you want to use them in a query because they don't stay escaped once they are returned as part of a record.

Most backends require the buffer to be more than twice as long as the input string. To be precise, the output buffer must be 2 * size of input + 1 bytes long. After successfully escaping the characters in from, they are written into the memory provided via to and the value/result parameter tolen is updated to the new length of to in the end.

The first parameter handle is the connection object created and returned by odbx_init() which becomes invalid as soon as it was supplied to odbx_finish().

from has to point to a character string containing the string which should be used as part of a statement. It doesn't have to be zero-terminated because the length of it is also given via fromlen. The backends may support variable width character sets like UTF-8 but this function doesn't support the wide char type (wchar_t) where each character has a fixed size of two or four bytes.

The value of the parameter fromlen must be the length in bytes of the string which from is pointing to. This is also true for variable width character sets like UTF-8 but the wide char type (wchar_t) is not supported. The terminating \0 character shouldn't be part of fromlen.

The calling function provides a buffer for storing the escaped string via to. In general, the length of the buffer should be more than twice as long as the string passed via from to be able to store the escaped string even if every character has to be escaped.

tolen is a value-result parameter which points to an integer variable in the calling function. It must contain the original length of the buffer given via to and if escaping the string in from suceeded, odbx_escape() will store the new length of the escaped string in this variable.

Return value

odbx_escape() returns ODBX_ERR_SUCCESS, or an error code whose value is less than zero if one of the operations couldn't be completed successfully. Possible error codes are listed in the error section and they can be feed to odbx_error() and odbx_error_type() to get further details.

Errors

-ODBX_ERR_BACKEND 

The native database library returned an error because it wasn't able to escape the given string to be suitable for a statement

-ODBX_ERR_PARAM 

One of the supplied parameters is invalid or is NULL and this isn't allowed in the used backend module or in the native database client library

-ODBX_ERR_SIZE 

The length of the escaped string exceeds or is likely to exeed the available buffer (before 1.1.4 the name of the label was ODBX_ERR_TOOLONG but the value is still the same)

See also

• odbx_error()
• odbx_error_type()
• odbx_query()