#ifndef EVSQL_H

 #define EVSQL_H

 /**

  * @file src/evsql.h

  *

  * A SQL library designed for use with libevent and PostgreSQL's libpq. Provides support for queueing non-transactional

  * requests, transaction support, parametrized queries and result iteration.

  *

  * Currently, the API does not expose the underlying libpq data structures, but since it is currently the only

  * underlying implementation, there is no guarantee that the same API will actually work with other databases' interface

  * libraries...

  *

  * The order of function calls and callbacks goes something like this:

  *

  *  -   evsql_new_pq()

  *

  *  -   evsql_trans()

  *      -   evsql_trans_abort()

  *      -   evsql_trans_error_cb()

  *      -   evsql_trans_ready_cb()

  *

  *  -   evsql_query(), \ref evsql_param_ + evsql_query_params(), evsql_query_exec()

  *      -   evsql_query_abort()

  *      -   evsql_query_cb()

  *          -   \ref evsql_result_

  *          -   evsql_result_free()

  *

  *  -   evsql_trans_commit()

  *      -   evsql_trans_done_cb()

  *

  */

 /**

  * System includes

  */

 #include <stdint.h>

 #include <stdbool.h>

 #include <event2/event.h>

 /**

  * For err_t.

  */

 #include "lib/err.h"

 /**

  * @struct evsql

  *

  * The generic session handle used to manage a single "database connector" with multiple queries/transactions.

  *

  * @see \ref evsql_

  */

 struct evsql;

 /**

  * @struct evsql_trans

  *

  * Opaque transaction handle returned by evsql_trans() and used for the \ref evsql_query_ functions

  *

  * @see \ref evsql_trans_

  */

 struct evsql_trans;

 /**

  * @struct evsql_query

  *

  * Opaque query handle returned by the \ref evsql_query_ functions and used for evsql_query_abort()

  *

  * @see \ref evsql_query_

  */

 struct evsql_query;

 /**

  * @struct evsql_result

  *

  * Opaque result handle received by evsql_query_cb(), and used with the \ref evsql_result_ functions

  *

  * @see evsql_query_cb

  * @see \ref evsql_result_

  */

 struct evsql_result;

 /**

  * Various transaction isolation levels for conveniance

  *

  * @see evsql_trans

  */

 enum evsql_trans_type {

     EVSQL_TRANS_DEFAULT,

     EVSQL_TRANS_SERIALIZABLE,

     EVSQL_TRANS_REPEATABLE_READ,

     EVSQL_TRANS_READ_COMMITTED,

     EVSQL_TRANS_READ_UNCOMMITTED,

 };

 /**

  * An item can be in different formats, the classical text-based format (i.e. snprintf "1234") or a more low-level

  * binary format (i.e uint16_t 0x04F9 in network-byte order).

  */

 enum evsql_item_format {

     /** Format values as text strings */

     EVSQL_FMT_TEXT,

     /** Type-specific binary encoding */

     EVSQL_FMT_BINARY,

 };

 /**

  * An item has a specific type, these correspond somewhat to the native database types.

  */

 enum evsql_item_type {

     /** End marker, zero */

     EVSQL_TYPE_INVALID,

     /** A SQL NULL */

     EVSQL_TYPE_NULL_,

     /** A `struct evsql_item_binary` */

     EVSQL_TYPE_BINARY,

     /** A NUL-terminated char* */

     EVSQL_TYPE_STRING,

     /** A uint16_t value */

     EVSQL_TYPE_UINT16,

     /** A uint32_t value */

     EVSQL_TYPE_UINT32,

     /** A uint64_t value */

     EVSQL_TYPE_UINT64,

     EVSQL_TYPE_MAX

 };

 /**

  * Value for use with EVSQL_TYPE_BINARY, this just a non-NUL-terminated char* and an explicit length

  */

 struct evsql_item_binary {

     /** The binary data */

     const char *ptr;

     /** Number of bytes pointed to by ptr */

     size_t len;

 };

 /**

  * Metadata about the format and type of an item, this does not hold any actual value.

  */

 struct evsql_item_info {

     /** The format */

     enum evsql_item_format format;

     /** The type type */

     enum evsql_item_type type;

     /** Various flags */

     struct evsql_item_flags {

         /** The value may be NULL @see evsql_result_next */

         bool null_ok : 1;

     } flags;

 };

 /**

  * An union to provide storage for the values of small types

  *

  * @see evsql_item

  */

 union evsql_item_value {

     /** 16-bit unsigned integer */

     uint16_t uint16;

     /** 32-bit unsigned integer */

     uint32_t uint32;

     /** 64-bit unsigned integer */

     uint64_t uint64;

 };

 /**

  * A generic structure containing the type and value of a query parameter or a result field.

  *

  * @see evsql_query_info

  * @see evsql_query_params

  * @see evsql_result_info

  */

 struct evsql_item {

     /** The "header" containing the type and format */

     struct evsql_item_info info;

     /**

      * Pointer to the raw databytes. 

      * Set to NULL for SQL NULLs, otherwise &value or an external buf 

      */

     const char *bytes;

     /**

      * Size of the byte array pointed to by bytes, zero for EVSQL_FMT_TEXT data.

      */

     size_t length;

     /**

      * Inline storage for small values

      */

     union evsql_item_value value;

     /** Internal flags */

     struct {

         /**

          * The item has a value stored in `value`

          */

         bool has_value : 1;

     } flags;

 };

 /**

  * Query meta-info, similar to a prepared statement.

  *

  * Contains the literal SQL query and the types of the parameters, but no more.

  *

  * @see evsql_query_exec

  */

 struct evsql_query_info {

     /** The SQL query itself */

     const char *sql;

     /** 

      * A variable-length array of the item_info parameters, terminated by an EVSQL_TYPE_INVALID entry.

      */

     struct evsql_item_info params[];

 };

 /**

  * Contains the query parameter types and their actual values

  *

  * @see evsql_query_params

  */

 struct evsql_query_params {

     /** Requested result format for this query. XXX: move elsewhere */

     enum evsql_item_format result_format;

     /**

      * A variable-length array of the item parameter-values, terminated by an EVSQL_TYPE_INVALID entry.

      */

     struct evsql_item list[];

 };

 /**

  * Result layout metadata. This contains the stucture needed to decode result rows.

  *

  * @see evsql_result_begin

  */

 struct evsql_result_info {

     /** XXX: make up something useful to stick here */

     int _unused;

     /**

      * A variable-length array of the item_info column types.

      */

     struct evsql_item_info columns[];

 };

 /**

  * Magic macros for defining param/result info -lists

  *  

  * @code

  *  static struct evsql_query_params params = EVSQL_PARAMS(EVSQL_FMT_BINARY) {

  *      EVSQL_PARAM( UINT32 ),

  *      ...,

  *

  *      EVSQL_PARAMS_END

  *  };

  * @endcode

  *

  * @name EVSQL_TYPE/PARAM_*

  * @{

  */

 /**

  * A `struct evsql_item_info` initializer, using FMT_BINARY and the given EVSQL_TYPE_ -suffix.

  *

  * @param typenam the suffix of an evsql_item_type name

  *

  * @see struct evsql_item_info

  * @see enum evsql_item_type

  */

 #define EVSQL_TYPE(typenam)                     { EVSQL_FMT_BINARY, EVSQL_TYPE_ ## typenam  }

 /**

  * End marker for a `struct evsql_item_info` array.

  *

  * @see struct evsql_item_info

  */

 #define EVSQL_TYPE_END                          { EVSQL_FMT_BINARY, EVSQL_TYPE_INVALID      }

 /**

  * Initializer block for an evsql_query_params struct

  */

 #define EVSQL_PARAMS(result_fmt)            { result_fmt, 

 /**

  * An evsql_item initializer

  */

 #define EVSQL_PARAM(typenam)                    { EVSQL_TYPE(typenam) }

 /**

  * Include the ending item and terminate the pseudo-block started using #EVSQL_PARAMS

  */

 #define EVSQL_PARAMS_END                        { EVSQL_TYPE_END } \

                                               } // <<<

 // @}

 /**

  * Callback definitions

  *

  * @name evsql_*_cb

  * @{

  */

 /**

  * Callback for handling query results.

  *

  * The query has completed, either succesfully or unsuccesfully.

  *

  * Use the \ref evsql_result_ functions to manipulate the results, and call evsql_result_free() (or equivalent) once done.

  *

  * @param res The result handle that must be result_free'd after use

  * @param arg The void* passed to \ref evsql_query_

  *

  * @see evsql_query

  */

 typedef void (*evsql_query_cb)(struct evsql_result *res, void *arg);

 /**

  * Callback for handling global-level errors.

  *

  * The evsql is not useable anymore.

  *

  * XXX: this is not actually called yet, as no retry logic is implemented, so an evsql itself never fails.

  *

  * @see evsql_new_pq

  */

 typedef void (*evsql_error_cb)(struct evsql *evsql, void *arg);

 /**

  * Callback for handling transaction-level errors. This may be called at any time during a transaction's lifetime,

  * including from within the \ref evsql_query_ functions (but not always).

  *

  * The transaction is not useable anymore.

  *

  * @param trans the transaction in question

  * @param arg the void* passed to evsql_trans

  *

  * @see evsql_trans

  */

 typedef void (*evsql_trans_error_cb)(struct evsql_trans *trans, void *arg);

 /**

  * Callback for handling evsql_trans/evsql_query_abort completion. The transaction is ready for use with \ref evsql_query_.

  *

  * @param trans the transaction in question

  * @param arg the void* passed to evsql_trans

  *

  * @see evsql_trans

  * @see evsql_query_abort

  */

 typedef void (*evsql_trans_ready_cb)(struct evsql_trans *trans, void *arg);

 /**

  * Callback for handling evsql_trans_commit completion. The transaction was commited, and should not be used anymore.

  *

  * @param trans the transaction in question

  * @param arg the void* passed to evsql_trans

  *

  * @see evsql_trans

  * @see evsql_trans_commit

  */

 typedef void (*evsql_trans_done_cb)(struct evsql_trans *trans, void *arg);

 // @}

 /**

  * Session functions

  *

  * @defgroup evsql_* Session interface

  * @see evsql.h

  * @{

  */

 /**

  * Session creation functions

  *

  * @defgroup evsql_new_* Session creation interface

  * @see evsql.h

  * @{

  */

 /**

  * Create a new PostgreSQL/libpq (evpq) -based evsql using the given conninfo.

  *

  * The given \a pq_conninfo pointer must stay valid for the duration of the evsql's lifetime.

  *

  * See the libpq reference manual for the syntax of pq_conninfo

  *

  * @param ev_base the libevent base to use

  * @param pq_conninfo the libpq connection information

  * @param error_fn XXX: not used, may be NULL

  * @param cb_arg: XXX: not used, argument for error_fn

  * @return the evsql context handle for use with other functions

  */

 struct evsql *evsql_new_pq (struct event_base *ev_base, const char *pq_conninfo, 

     evsql_error_cb error_fn, 

     void *cb_arg

 );

 // @}

 /**

  * Close a connection. Callbacks for waiting queries will not be run.

  *

  * XXX: not implemented yet.

  *

  * @param evsql the context handle from \ref evsql_new_

  */

 void evsql_close (struct evsql *evsql);

 // @}

 /**

  * Query API

  *

  * @defgroup evsql_query_* Query interface

  * @see evsql.h

  * @{

  */

 /**

  * Queue the given query for execution.

  *

  * If \a trans is given (i.e. not NULL), then the transaction must be idle, and the query will be executed in that

  * transaction's context. Otherwise, the query will be executed without a transaction using an idle connection, or

  * enqueued for later execution.

  *

  * Once the query is complete (got a result, got an error, the connection failed), then \a query_fn will be called.

  * The callback can use the \ref evsql_result_ functions to manipulate the query results.

  *

  * The returned evsql_query handle can be passed to evsql_query_abort at any point before \a query_fn being called. 

  *

  * @param evsql the context handle from \ref evsql_new_

  * @param trans the optional transaction handle from evsql_trans

  * @param command the raw SQL command itself

  * @param query_fn the evsql_query_cb() to call once the query is complete

  * @param cb_arg the void* passed to the above

  * @return the evsql_query handle that can be used to abort the query

  */

 struct evsql_query *evsql_query (struct evsql *evsql, struct evsql_trans *trans, const char *command, evsql_query_cb query_fn, void *cb_arg);

 /**

  * Execute the given SQL query using the list of parameter types/values given via evsql_query_params.

  *

  * Use the EVSQL_PARAMS macros to declare \a params, and the \ref evsql_param_ functions to populate the values.

  *

  * See evsql_query() for more info about behaviour.

  *

  * See the <a href="http://www.postgresql.org/docs/8.3/static/libpq-exec.html#LIBPQ-EXEC-MAIN">libpq PQexecParams tip</a>

  * for the parameter syntax to use.

  *

  * @param evsql the context handle from \ref evsql_new_

  * @param trans the optional transaction handle from evsql_trans

  * @param command the SQL command to bind the parameters to

  * @param params the parameter types and values

  * @param query_fn the evsql_query_cb() to call once the query is complete

  * @param cb_arg the void* passed to the above

  * @see evsql_query

  */

 struct evsql_query *evsql_query_params (struct evsql *evsql, struct evsql_trans *trans, 

     const char *command, const struct evsql_query_params *params, 

     evsql_query_cb query_fn, void *cb_arg

 );

 /**

  * Execute the given \a query_info's SQL query with the values given as variable arguments, using the \a query_info to

  * resolve the types.

  *

  * See evsql_query() for more info about behaviour.

  *

  * @param evsql the context handle from \ref evsql_new_

  * @param trans the optional transaction handle from evsql_trans

  * @param query_info the SQL query information

  * @param query_fn the evsql_query_cb() to call once the query is complete

  * @param cb_arg the void* passed to the above

  * @see evsql_query

  */

 struct evsql_query *evsql_query_exec (struct evsql *evsql, struct evsql_trans *trans, 

     const struct evsql_query_info *query_info,

     evsql_query_cb query_fn, void *cb_arg,

     ...

 );

 /**

  * Abort a \a query returned by \ref evsql_query_ that has not yet completed (query_fn has not been called yet).

  *

  * The actual query itself may or may not be aborted (and hence may or may not be executed on the server), but \a query_fn

  * will not be called anymore, and the query will dispose of itself and any results returned.

  *

  * If the \a query is part of a transaction, then \a trans must be given, and the query must be the query that is currently

  * executing on that trans. The transaction's \a ready_fn will be called once the query has been aborted and the

  * transaction is now idle again.

  *

  * @param trans if the query is part of a transaction, then it MUST be given here

  * @param query the in-progress query to abort

  */

 void evsql_query_abort (struct evsql_trans *trans, struct evsql_query *query);

 /**

  * Print out a textual dump of the given \a sql query and \a params using DEBUG

  *

  * @param sql the SQL query command

  * @param params the list of parameter types and values

  */

 void evsql_query_debug (const char *sql, const struct evsql_query_params *params);

 // @}

 /**

  * Transaction API

  *

  * @defgroup evsql_trans_* Transaction interface

  * @see evsql.h

  * @{

  */

 /**

  * Create a new transaction.

  *

  * A transaction will be allocated its own connection, and the "BEGIN TRANSACTION ..." query will be sent (use the

  * \a type argument to specify this). 

  *

  * Once the transaction has been opened, the given \a ready_fn will be triggered, and the transaction can then

  * be used (see \ref evsql_query_).

  *

  * If, at any point, the transaction-connection fails, any pending query will be forgotten (i.e. the query callback

  * will NOT be called), and the given \a error_fn will be called. Note that this includes some, but not all,

  * cases where \ref evsql_query_ returns an error.

  *

  * Once you are done with the transaction, call either evsql_trans_commit() or evsql_trans_abort().

  *

  * @param evsql the context handle from \ref evsql_new_

  * @param type the type of transaction to create

  * @param error_fn the evsql_trans_error_cb() to call if this transaction fails

  * @param ready_fn the evsql_trans_ready_cb() to call once this transaction is ready for use

  * @param done_fn the evsql_trans_done_cb() to call once this transaction has been commmited

  * @param cb_arg the void* to pass to the above

  * @return the evsql_trans handle for use with other functions

  */

 struct evsql_trans *evsql_trans (struct evsql *evsql, enum evsql_trans_type type, 

     evsql_trans_error_cb error_fn, 

     evsql_trans_ready_cb ready_fn, 

     evsql_trans_done_cb done_fn, 

     void *cb_arg

 );

 /**

  * Commit a transaction using "COMMIT TRANSACTION".

  *

  * The transaction must be idle, just like for evsql_query. Once the transaction has been commited, the transaction's

  * \a done_fn will be called, after which the transaction must not be used anymore.

  *

  * You cannot abort a COMMIT, calling trans_abort() on trans after a succesful trans_commit is an error.

  *

  * Note that \a done_fn will never be called directly, always indirectly via the event loop.

  *

  * @param trans the transaction handle from evsql_trans to commit

  * @see evsql_trans

  */

 int evsql_trans_commit (struct evsql_trans *trans);

 /**

  * Abort a transaction, using "ROLLBACK TRANSACTION".

  *

  * No more transaction callbacks will be called. If there was a query running, it will be aborted, and the transaction

  * then rollback'd.

  *

  * You cannot abort a COMMIT, calling trans_abort on \a trans after a call to trans_commit is an error.

  * 

  * Do not call evsql_trans_abort from within evsql_trans_error_cb()!

  *

  * @param trans the transaction from evsql_trans to abort

  * @see evsql_trans

  */

 void evsql_trans_abort (struct evsql_trans *trans);

 /** 

  * Retrieve the transaction-specific error message from the underlying engine.

  *

  * Intended to be called from evsql_trans_error_cb()

  */

 const char *evsql_trans_error (struct evsql_trans *trans);

 // @}

 /**

  * Parameter-building functions.

  *

  * These manipulate the value of the given parameter index.

  *

  * @defgroup evsql_param_* Parameter interface

  * @see evsql.h

  * @{

  */

 /**

  * Sets the value of the parameter at the given index

  *

  * @param params the evsql_query_params struct

  * @param param the parameter index

  * @param ptr pointer to the binary data

  * @param len size of the binary data in bytes

  * @return zero on success, <0 on error

  */

 int evsql_param_binary (struct evsql_query_params *params, size_t param, const char *ptr, size_t len);

 /** @see evsql_param_binary */

 int evsql_param_string (struct evsql_query_params *params, size_t param, const char *ptr);

 /** @see evsql_param_binary */

 int evsql_param_uint16 (struct evsql_query_params *params, size_t param, uint16_t uval);

 /** @see evsql_param_binary */

 int evsql_param_uint32 (struct evsql_query_params *params, size_t param, uint32_t uval);

 /**

  * Sets the given parameter to NULL

  *

  * @param params the evsql_query_params struct

  * @param param the parameter index

  * @return zero on success, <0 on error

  */

 int evsql_param_null (struct evsql_query_params *params, size_t param);

 /**

  * Clears all the parameter values (sets them to NULL)

  *

  * @param params the evsql_query_params struct

  * @return zero on success, <0 on error

  */

 int evsql_params_clear (struct evsql_query_params *params);

 // @}

 /**

  * Result-handling functions

  *

  * @defgroup evsql_result_* Result interface

  * @see evsql.h

  * @see evsql_result

  * @{

  */

 /**

  * Check the result for errors. Intended for use with non-data queries, i.e. CREATE, etc.

  *

  * Returns zero if the query was OK, err otherwise. EIO indicates an SQL error, the error message can be retrived

  * using evsql_result_error.

  *

  * @param res the result handle passed to evsql_query_cb()

  * @return zero on success, EIO on SQL error, positive error code otherwise

  */

 err_t evsql_result_check (struct evsql_result *res);

 /**

  * The iterator-based interface results interface.

  *

  * Define an evsql_result_info struct that describes the columns returned by the query, and call evsql_result_begin on

  * the evsql_result. This verifies the query result, and then prepares it for iteration using evsql_result_next.

  *

  * Call evsql_result_end once you've stopped iteration.

  *

  * Returns zero if the evsql_result is ready for iteration, err otherwise. EIO indicates an SQL error, the error

  * message can be retreived using evsql_result_error. The result must be released in both cases.

  *

  * Note: currently the iterator state is simply stored in evsql_result, so only one iterator at a time per evsql_result.

  *

  * @param info the metadata to use to handle the result row columns

  * @param res the result handle passed to evsql_query_cb()

  * @return zero on success, +err on error

  */

 err_t evsql_result_begin (struct evsql_result_info *info, struct evsql_result *res);

 /**

  * Reads the next result row from the result prepared using evsql_result_begin. Stores the field values into to given

  * pointer arguments based on the evsql_result_info given to evsql_result_begin.

  *

  * If a field is NULL, and the result_info's evsql_item_type has flags.null_ok set, the given pointer is left

  * untouched, otherwise, an error is returned.

  *

  * @param res the result handle previous prepared using evsql_result_begin

  * @param ... a set of pointers corresponding to the evsql_result_info specified using evsql_result_begin

  * @return >0 when a row was read, zero when there are no more rows left, and -err on error

  */

 int evsql_result_next (struct evsql_result *res, ...);

 /**

  * Ends the result iteration, releasing any associated resources and the result itself.

  *

  * The result should not be iterated or accessed anymore.

  *

  * Note: this does the same thing as evsql_result_free, and works regardless of evsql_result_begin returning

  * succesfully or not.

  *

  * @param res the result handle passed to evsql_query_cb()

  * @see evsql_result_free

  */

 void evsql_result_end (struct evsql_result *res);

 /**

  * Get the error message associated with the result, intended for use after evsql_result_check/begin return an error

  * code.

  * 

  * @param res the result handle passed to evsql_query_cb()

  * @return a char* containing the NUL-terminated error string. Valid until evsql_result_free is called.

  */

 const char *evsql_result_error (const struct evsql_result *res);

 /**

  * Get the number of data rows returned by the query

  *

  * @param res the result handle passed to evsql_query_cb()

  * @return the number of rows, >= 0

  */

 size_t evsql_result_rows (const struct evsql_result *res);

 /**

  * Get the number of columns in the data results from the query

  *

  * @param res the result handle passed to evsql_query_cb()

  * @return the number of columns, presumeably zero if there were no results

  */

 size_t evsql_result_cols (const struct evsql_result *res);

 /**

  * Get the number of rows affected by an UPDATE/INSERT/etc query.

  *

  * @param res the result handle passed to evsql_query_cb()

  * @return the number of rows affected, >= 0

  */

 size_t evsql_result_affected (const struct evsql_result *res);

 /**

  * Fetch the raw binary value for the given field, returning it via ptr/size.

  *

  * The given row/col must be within bounds as returned by evsql_result_rows/cols.

  *

  * *ptr will point to *size bytes of read-only memory allocated internally.

  *

  * @param res the result handle passed to evsql_query_cb()

  * @param row the row index to access

  * @param col the column index to access

  * @param ptr where to store a pointer to the read-only field data, free'd upon evsql_result_free

  * @param size updated to the size of the field value pointed to by ptr

  * @param nullok when true and the field value is NULL, *ptr and *size are not modified, otherwise NULL means an error

  * @return zero on success, <0 on error

  */

 int evsql_result_binary (const struct evsql_result *res, size_t row, size_t col, const char **ptr, size_t *size, bool nullok);

 /**

  * Fetch the textual value of the given field, returning it via ptr.

  *

  * The given row/col must be within bounds as returned by evsql_result_rows/cols.

  *

  * *ptr will point to a NUL-terminated string allocated internally.

  *

  * @param res the result handle passed to evsql_query_cb()

  * @param row the row index to access

  * @param col the column index to access

  * @param ptr where to store a pointer to the read-only field data, free'd upon evsql_result_free

  * @param nullok when true and the field value is NULL, *ptr and *size are not modified, otherwise NULL means an error

  * @return zero on success, <0 on error

  */

 int evsql_result_string (const struct evsql_result *res, size_t row, size_t col, const char **ptr, int nullok);

 /**

  * Use evsql_result_binary to read a binary field value, and then convert it using ntoh[slq], storing the value in

  * *val.

  *

  * The given row/col must be within bounds as returned by evsql_result_rows/cols.

  *

  * @param res the result handle passed to evsql_query_cb()

  * @param row the row index to access

  * @param col the column index to access

  * @param uval where to store the decoded value

  * @param nullok when true and the field value is NULL, *ptr and *size are not modified, otherwise NULL means an error

  * @return zero on success, <0 on error

  */

 int evsql_result_uint16 (const struct evsql_result *res, size_t row, size_t col, uint16_t *uval, int nullok);

 /** @see evsql_result_uint16 */

 int evsql_result_uint32 (const struct evsql_result *res, size_t row, size_t col, uint32_t *uval, int nullok);

 /** @see evsql_result_uint16 */

 int evsql_result_uint64 (const struct evsql_result *res, size_t row, size_t col, uint64_t *uval, int nullok);

 /**

  * Every result handle passed to evsql_query_cb() MUST be released by the user, using this function.

  *

  * @param res the result handle passed to evsql_query_cb()

  */

 void evsql_result_free (struct evsql_result *res);

 // @}

 #endif /* EVSQL_H */