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MySQL 8.4 C API Developer Guide  /  ...  /  mysql_set_local_infile_handler()

5.4.78 mysql_set_local_infile_handler()

mysql_set_local_infile_handler(MYSQL *mysql,
  int (*local_infile_init)(void **, const char *, void *),
  int (*local_infile_read)(void *, char *, unsigned int),
  void (*local_infile_end)(void *),
  int (*local_infile_error)(void *, char*, unsigned int),
  void *userdata);


This function installs callbacks to be used during the execution of LOAD DATA LOCAL statements. It enables application programs to exert control over local (client-side) data file reading. The arguments are the connection handler, a set of pointers to callback functions, and a pointer to a data area that the callbacks can use to share information.

To use mysql_set_local_infile_handler(), you must write the following callback functions:

local_infile_init(void **ptr, const char *filename, void *userdata);

The initialization function. This is called once to do any setup necessary, open the data file, allocate data structures, and so forth. The first void** argument is a pointer to a pointer. You can set the pointer (that is, *ptr) to a value that will be passed to each of the other callbacks (as a void*). The callbacks can use this pointed-to value to maintain state information. The userdata argument is the same value that is passed to mysql_set_local_infile_handler().

Make the initialization function return zero for success, nonzero for an error.

local_infile_read(void *ptr, char *buf, unsigned int buf_len);

The data-reading function. This is called repeatedly to read the data file. buf points to the buffer where the read data is stored, and buf_len is the maximum number of bytes that the callback can read and store in the buffer. (It can read fewer bytes, but should not read more.)

The return value is the number of bytes read, or zero when no more data could be read (this indicates EOF). Return a value less than zero if an error occurs.

local_infile_end(void *ptr)

The termination function. This is called once after local_infile_read() has returned zero (EOF) or an error. Within this function, deallocate any memory allocated by local_infile_init() and perform any other cleanup necessary. It is invoked even if the initialization function returns an error.

local_infile_error(void *ptr,
                   char *error_msg,
                   unsigned int error_msg_len);

The error-handling function. This is called to get a textual error message to return to the user in case any of your other functions returns an error. error_msg points to the buffer into which the message is written, and error_msg_len is the length of the buffer. Write the message as a null-terminated string, at most error_msg_len−1 bytes long.

The return value is the error number.

Typically, the other callbacks store the error message in the data structure pointed to by ptr, so that local_infile_error() can copy the message from there into error_msg.

After calling mysql_set_local_infile_handler() in your C code and passing pointers to your callback functions, you can then issue a LOAD DATA LOCAL statement (for example, by using mysql_real_query() or mysql_query()). The client library automatically invokes your callbacks. The file name specified in LOAD DATA LOCAL will be passed as the second parameter to the local_infile_init() callback.

Return Values