FreeTDS API: Internals

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# Internals
[The db-lib API]

Functions called within `db-lib` for self-help. More...

## Classes
struct | _dblib_error_message
| For internal use only. More...
## Typedefs
typedef struct _dblib_error_message | DBLIB_ERROR_MESSAGE
## Functions
int | _dblib_check_and_handle_interrupt (void *vdbproc)
| check interrupts for libtds.
RETCODE | dbcmdrow (DBPROCESS *dbproc)
| For internal use only.
DBINT | dbcount (DBPROCESS *dbproc)
| For internal use only.
int | dbcurcmd (DBPROCESS *dbproc)
| For internal use only.
DBINT | dbcurrow (DBPROCESS *dbproc)
| For internal use only.
DBBOOL | dbdead (DBPROCESS *dbproc)
| For internal use only.
DBINT | dbfirstrow (DBPROCESS *dbproc)
| For internal use only.
int | dbiordesc (DBPROCESS *dbproc)
| For internal use only.
int | dbiowdesc (DBPROCESS *dbproc)
| For internal use only.
DBINT | dblastrow (DBPROCESS *dbproc)
| For internal use only.
int | dbperror (DBPROCESS *dbproc, DBINT msgno, long errnum,...)
| For internal use only.
RETCODE | dbrows (DBPROCESS *dbproc)
| For internal use only.
STATUS | dbrowtype (DBPROCESS *dbproc)
| For internal use only.
void | dbsetavail (DBPROCESS *dbproc)
| For internal use only.
RETCODE | dbsetlbool (LOGINREC *login, int value, int which)
| For internal use only.
RETCODE | dbsetllong (LOGINREC *login, long value, int which)
| For internal use only.
RETCODE | dbsetlname (LOGINREC *login, const char *value, int which)
| For internal use only.
RETCODE | dbsetlshort (LOGINREC *login, int value, int which)
| For internal use only.
int | dbtds (DBPROCESS *dbproc)
| For internal use only.
static int | default_err_handler (DBPROCESS *dbproc, int severity, int dberr, int oserr, char *dberrstr, char *oserrstr)
| For internal use only.
DBPROCESS * | tdsdbopen (LOGINREC *login, const char *server, int msdblib)
| For internal use only.

## Detailed Description

Functions called within `db-lib` for self-help.

These functions are of interest only to people hacking on the FreeTDS db-lib implementation.

## Function Documentation

int _dblib_check_and_handle_interrupt | ( | void * | vdbproc | ) |

check interrupts for libtds.

Parameters:

  | vdbproc | a DBPROCESS pointer, contains all information needed by db-lib to manage communications with the server.

See also:
  DBDEAD(), dbsetinterrupt().

RETCODE dbcmdrow | ( | DBPROCESS * | dbproc | ) |

For internal use only.

See if the current command can return rows.

Parameters:

  | dbproc | contains all information needed by db-lib to manage communications with the server.

Return values:

  | SUCCEED | Yes, it can.
  | FAIL | No, it can't.

Remarks:
  Use DBCMDROW() macro instead.

See also:
  DBCMDROW(), dbnextrow(), dbresults(), DBROWS(), DBROWTYPE().

DBINT dbcount | ( | DBPROCESS * | dbproc | ) |

For internal use only.

Get count of rows processed

Parameters:

  | dbproc | contains all information needed by db-lib to manage communications with the server.

Returns:
  - for insert/update/delete, count of rows affected.
  - for select, count of rows returned, after all rows have been fetched.

See also:
  DBCOUNT(), dbnextrow(), dbresults().

int dbcurcmd | ( | DBPROCESS * | dbproc | ) |

For internal use only.

Get number of the row just returned.

Parameters:

  | dbproc | contains all information needed by db-lib to manage communications with the server.

See also:
  DBCURROW().

Todo:
  Unimplemented.

DBINT dbcurrow | ( | DBPROCESS * | dbproc | ) |

For internal use only.

Get number of the row currently being read.

Parameters:

  | dbproc | contains all information needed by db-lib to manage communications with the server.

Returns:
  ostensibly the row number, or 0 if no rows have been read yet.

Return values:

  | 0 | Always.

See also:
  DBCURROW(), dbclrbuf(), DBFIRSTROW(), dbgetrow(), DBLASTROW(), dbnextrow(), dbsetopt(),.

Todo:
  Unimplemented.

DBBOOL dbdead | ( | DBPROCESS * | dbproc | ) |

For internal use only.

Check if dbproc is an ex-parrot.

Parameters:

  | dbproc | contains all information needed by db-lib to manage communications with the server.

Return values:

  | TRUE | process has been marked dead.
  | FALSE | process is OK.

Remarks:
  dbdead() does not communicate with the server. Unless a previously db-lib marked dbproc dead, dbdead() returns `FALSE`.

See also:
  dberrhandle().

DBINT dbfirstrow | ( | DBPROCESS * | dbproc | ) |

For internal use only.

Get number of the first row in the row buffer.

Parameters:

  | dbproc | contains all information needed by db-lib to manage communications with the server.

See also:
  DBFIRSTROW(), dbclrbuf(), DBCURROW(), dbgetrow(), DBLASTROW(), dbnextrow(), dbsetopt().

int dbiordesc | ( | DBPROCESS * | dbproc | ) |

For internal use only.

Get file descriptor of the socket used by a `DBPROCESS` to read data coming from the server. (!)

Parameters:

  | dbproc | contains all information needed by db-lib to manage communications with the server.

See also:
  dbcmd(), DBIORDESC(), DBIOWDESC(), dbnextrow(), dbpoll(), DBRBUF(), dbresults(), dbsqlok(), dbsqlsend().

int dbiowdesc | ( | DBPROCESS * | dbproc | ) |

For internal use only.

Get file descriptor of the socket used by a `DBPROCESS` to write data coming to the server. (!)

Parameters:

  | dbproc | contains all information needed by db-lib to manage communications with the server.

See also:
  dbcmd(), DBIORDESC(), DBIOWDESC(), dbnextrow(), dbpoll(), DBRBUF(), dbresults(), dbsqlok(), dbsqlsend().

DBINT dblastrow | ( | DBPROCESS * | dbproc | ) |

For internal use only.

Get number of the last row in the row buffer.

Parameters:

  | dbproc | contains all information needed by db-lib to manage communications with the server.

See also:
  DBLASTROW(), dbclrbuf(), DBCURROW(), DBFIRSTROW(), dbgetrow(), dbnextrow(), dbsetopt().

int dbperror | ( | DBPROCESS * | dbproc,
|  | DBINT | msgno,
|  | long | errnum,
|  |  | ... |
| ) |  |  |

For internal use only.

Call client-installed error handler

Parameters:

  | dbproc | contains all information needed by db-lib to manage communications with the server.
  | msgno | identifies the error message to be passed to the client's handler.
  | errnum | identifies the OS error (errno), if any. Use 0 if not applicable.

Returns:
  the handler's return code, subject to correction and adjustment for vendor style:
  - INT_CANCEL The db-lib function that encountered the error will return FAIL.
  - INT_TIMEOUT The db-lib function will cancel the operation and return FAIL. dbproc remains useable.
  - INT_CONTINUE The db-lib function will retry the operation.

Remarks:
  The client-installed handler may also return INT_EXIT. If Sybase semantics are used, this function notifies the user and calls exit(3). If Microsoft semantics are used, this function returns INT_CANCEL.

If the client-installed handler returns something other than these four INT_* values, or returns timeout-related value for anything but SYBETIME, it's treated here as INT_EXIT (see above).

Instead of sprinkling error text all over db-lib, we consolidate it here, where it can be translated (one day), and where it can be mapped to the TDS error number. The libraries don't use consistent error numbers or messages, so when libtds has to emit an error message, it can't include the text. It can pass its error number to a client-library function, which will interpret it, add the text, call the application's installed handler (if any) and return the handler's return code back to the caller.

The call stack may look something like this:

1. application
2. db-lib function (encounters error)
3. dbperror
4. error handler (installed by application)

The error handling in this case is unambiguous: the caller invokes this function, the client's handler returns its instruction, which the caller receives. Quite often the caller will get INT_CANCEL, in which case it should put its house in order and return FAIL.

The call stack may otherwise look something like this:

1. application
2. db-lib function
3. libtds function (encounters error)
4. _dblib_handle_err_message
5. dbperror
6. error handler (installed by application)

Because different client libraries specify their handler semantics differently, and because libtds doesn't know which client library is in charge of any given connection, it cannot interpret the raw return code from a db-lib error handler. For these reasons, libtds calls _dblib_handle_err_message, which translates between libtds and db-lib semantics.

See also:
  dberrhandle(), _dblib_handle_err_message().

RETCODE dbrows | ( | DBPROCESS * | dbproc | ) |

For internal use only.

Indicate whether a query returned rows.

Parameters:

  | dbproc | contains all information needed by db-lib to manage communications with the server.

See also:
  DBROWS(), DBCMDROW(), dbnextrow(), dbresults(), DBROWTYPE().

STATUS dbrowtype | ( | DBPROCESS * | dbproc | ) |

For internal use only.

Get returned row's type.

Parameters:

  | dbproc | contains all information needed by db-lib to manage communications with the server.

See also:
  DBROWTYPE().

void dbsetavail | ( | DBPROCESS * | dbproc | ) |

For internal use only.

Mark a `DBPROCESS` as "available".

Parameters:

  | dbproc | contains all information needed by db-lib to manage communications with the server.

Remarks:
  Basically bogus. `FreeTDS` behaves the way Sybase's implementation does, but so what? Many `db-lib` functions set the `DBPROCESS` to "not available", but only dbsetavail() resets it to "available".

See also:
  DBISAVAIL(). DBSETAVAIL().

RETCODE dbsetlbool | ( | LOGINREC * | login,
|  | int | value,
|  | int | which |
| ) |  |  |

For internal use only.

Set a boolean value in a `LOGINREC` structure.

Called by various macros to populate login.

Parameters:

  | login | the `LOGINREC*` to modify.
  | value | the value to set it to.
  | which | the field to set.

Remarks:
  Only DBSETBCP is implemented.

Return values:

  | SUCCEED | the value was set.
  | FAIL | invalid value passed for which.

Todo:
  DBSETNOSHORT, DBSETENCRYPT, DBSETLABELED

RETCODE dbsetllong | ( | LOGINREC * | login,
|  | long | value,
|  | int | which |
| ) |  |  |

For internal use only.

Set an integer value in a `LOGINREC` structure.

Called by various macros to populate login.

Parameters:

  | login | the `LOGINREC*` to modify.
  | value | the value to set it to.
  | which | the field to set.

Return values:

  | SUCCEED | the value was set.
  | FAIL | anything other than `DBSETPACKET` was passed for which.

RETCODE dbsetlname | ( | LOGINREC * | login,
|  | const char * | value,
|  | int | which |
| ) |  |  |

For internal use only.

Set the value of a string in a `LOGINREC` structure.

Called by various macros to populate login.

Parameters:

  | login | the `LOGINREC*` to modify.
  | value | the value to set it to.
  | which | the field to set.

Return values:

  | SUCCEED | the value was set.
  | FAIL | `DBSETHID` or other invalid which was tried.

RETCODE dbsetlshort | ( | LOGINREC * | login,
|  | int | value,
|  | int | which |
| ) |  |  |

For internal use only.

Set an integer value in a `LOGINREC` structure.

Called by various macros to populate login.

Parameters:

  | login | the `LOGINREC*` to modify.
  | value | the value to set it to.
  | which | the field to set.

Return values:

  | SUCCEED | the value was set.
  | FAIL | anything other than `DBSETHIER` was passed for which.

int dbtds | ( | DBPROCESS * | dbproc | ) |

For internal use only.

Get the TDS version in use for dbproc.

Parameters:

  | dbproc | contains all information needed by db-lib to manage communications with the server.

Returns:
  a `DBTDS*` token.

Remarks:
  The integer values of the constants are counterintuitive.

See also:
  DBTDS().

static int default_err_handler | ( | DBPROCESS * | dbproc,
|  | int | severity,
|  | int | dberr,
|  | int | oserr,
|  | char * | dberrstr,
|  | char * | oserrstr |
| ) |  |  | `[static]`

For internal use only.

default error handler for db-lib (handles library-generated errors)

The default error handler doesn't print anything. If you want to see your messages printed, install an error handler. If you think that should be an optional compile- or run-time default, submit a patch. It could be done.

See also:
  DBDEAD(), dberrhandle().

DBPROCESS* tdsdbopen | ( | LOGINREC * | login,
|  | const char * | server,
|  | int | msdblib |
| ) |  |  |

For internal use only.

Form a connection with the server.

Called by the `dbopen()` macro, normally. If FreeTDS was configured with `--enable-msdblib`, this function is called by (exported) `dbopen()` function. `tdsdbopen` is so-named to avoid namespace conflicts with other database libraries that use the same function name.

Parameters:

  | login | `LOGINREC*` carrying the account information.
  | server | name of the dataserver to connect to.

Returns:
  valid pointer on successful login.

Return values:

  | NULL | insufficient memory, unable to connect for any reason.

See also:
  dbopen()

Todo:
  use `asprintf()` to avoid buffer overflow.

Todo:
  separate error messages for no-such-server and no-such-user.