LWRES_CONTEXT(3)                     BIND9                    LWRES_CONTEXT(3)

       lwres_context_create, lwres_context_destroy, lwres_context_nextserial,
       lwres_context_initserial, lwres_context_freemem,
       lwres_context_allocmem, lwres_context_sendrecv - lightweight resolver
       context management

       #include <lwres/lwres.h>

       lwres_result_t lwres_context_create(lwres_context_t **contextp,
                                           void *arg,
                                           lwres_malloc_t malloc_function,
                                           lwres_free_t free_function);

       lwres_result_t lwres_context_destroy(lwres_context_t **contextp);

       void lwres_context_initserial(lwres_context_t *ctx,
                                     lwres_uint32_t serial);

       lwres_uint32_t lwres_context_nextserial(lwres_context_t *ctx);

       void lwres_context_freemem(lwres_context_t *ctx, void *mem,
                                  size_t len);

       void lwres_context_allocmem(lwres_context_t *ctx, size_t len);

       void * lwres_context_sendrecv(lwres_context_t *ctx, void *sendbase,
                                     int sendlen, void *recvbase, int recvlen,
                                     int *recvd_len);

       lwres_context_create() creates a lwres_context_t structure for use in
       lightweight resolver operations. It holds a socket and other data
       needed for communicating with a resolver daemon. The new
       lwres_context_t is returned through contextp, a pointer to a
       lwres_context_t pointer. This lwres_context_t pointer must initially be
       NULL, and is modified to point to the newly created lwres_context_t.

       When the lightweight resolver needs to perform dynamic memory
       allocation, it will call malloc_function to allocate memory and
       free_function to free it. If malloc_function and free_function are
       NULL, memory is allocated using malloc(3). and free(3). It is not
       permitted to have a NULL malloc_function and a non-NULL free_function
       or vice versa.  arg is passed as the first parameter to the memory
       allocation functions. If malloc_function and free_function are NULL,
       arg is unused and should be passed as NULL.

       Once memory for the structure has been allocated, it is initialized
       using lwres_conf_init(3) and returned via *contextp.

       lwres_context_destroy() destroys a lwres_context_t, closing its socket.
       contextp is a pointer to a pointer to the context that is to be
       destroyed. The pointer will be set to NULL when the context has been

       The context holds a serial number that is used to identify resolver
       request packets and associate responses with the corresponding
       requests. This serial number is controlled using
       lwres_context_initserial() and lwres_context_nextserial().
       lwres_context_initserial() sets the serial number for context *ctx to
       serial.  lwres_context_nextserial() increments the serial number and
       returns the previous value.

       Memory for a lightweight resolver context is allocated and freed using
       lwres_context_allocmem() and lwres_context_freemem(). These use
       whatever allocations were defined when the context was created with
       lwres_context_create().  lwres_context_allocmem() allocates len bytes
       of memory and if successful returns a pointer to the allocated storage.
       lwres_context_freemem() frees len bytes of space starting at location

       lwres_context_sendrecv() performs I/O for the context ctx. Data are
       read and written from the context's socket. It writes data from
       sendbase — typically a lightweight resolver query packet — and waits
       for a reply which is copied to the receive buffer at recvbase. The
       number of bytes that were written to this receive buffer is returned in

       lwres_context_create() returns LWRES_R_NOMEMORY if memory for the
       struct lwres_context could not be allocated, LWRES_R_SUCCESS otherwise.

       Successful calls to the memory allocator lwres_context_allocmem()
       return a pointer to the start of the allocated space. It returns NULL
       if memory could not be allocated.

       LWRES_R_SUCCESS is returned when lwres_context_sendrecv() completes
       successfully.  LWRES_R_IOERROR is returned if an I/O error occurs and
       LWRES_R_TIMEOUT is returned if lwres_context_sendrecv() times out
       waiting for a response.

       lwres_conf_init(3), malloc(3), free(3).

       Copyright © 2004, 2005, 2007 Internet Systems Consortium, Inc. ("ISC")
       Copyright © 2000, 2001, 2003 Internet Software Consortium.

BIND9                            Jun 30, 2000                 LWRES_CONTEXT(3)