"DESCRIPTION"
These are low-level routines for creating and parsing lightweight resolver no-op request and response messages.
The no-op message is analogous to a ping packet: a packet is sent to the resolver daemon and is simply echoed back. The opcode is intended to allow a client to determine if the server is operational or not.
There are four main functions for the no-op opcode. One render function converts a no-op request structure — lwres_nooprequest_t — to the lighweight resolver’s canonical format. It is complemented by a parse function that converts a packet in this canonical format to a no-op request structure. Another render function converts the no-op response structure — lwres_noopresponse_t to the canonical format. This is complemented by a parse function which converts a packet in canonical format to a no-op response structure.
These structures are defined in lwres/lwres.h. They are shown below.
#define LWRES_OPCODE_NOOP 0x00000000U
typedef struct {
lwres_uint16_t datalength;
unsigned char *data;
} lwres_nooprequest_t;
typedef struct {
lwres_uint16_t datalength;
unsigned char *data;
} lwres_noopresponse_t;
Although the structures have different types, they are identical. This is because the no-op opcode simply echos whatever data was sent: the response is therefore identical to the request.
lwres_nooprequest_render() uses resolver context ctx to convert no-op request structure req to canonical format. The packet header structure pkt is initialised and transferred to buffer b. The contents of *req are then appended to the buffer in canonical format. lwres_noopresponse_render() performs the same task, except it converts a no-op response structure lwres_noopresponse_t to the lightweight resolver’s canonical format.
lwres_nooprequest_parse() uses context ctx to convert the contents of packet pkt to a lwres_nooprequest_t structure. Buffer b provides space to be used for storing this structure. When the function succeeds, the resulting lwres_nooprequest_t is made available through *structp. lwres_noopresponse_parse() offers the same semantics as lwres_nooprequest_parse() except it yields a lwres_noopresponse_t structure.
lwres_noopresponse_free() and lwres_nooprequest_free() release the memory in resolver context ctx that was allocated to the lwres_noopresponse_t or lwres_nooprequest_t structures referenced via structp.
"RETURN VALUES"
The no-op opcode functions lwres_nooprequest_render(), lwres_noopresponse_render() lwres_nooprequest_parse() and lwres_noopresponse_parse() all return LWRES_R_SUCCESS on success. They return LWRES_R_NOMEMORY if memory allocation fails. LWRES_R_UNEXPECTEDEND is returned if the available space in the buffer b is too small to accommodate the packet header or the lwres_nooprequest_t and lwres_noopresponse_t structures. lwres_nooprequest_parse() and lwres_noopresponse_parse() will return LWRES_R_UNEXPECTEDEND if the buffer is not empty after decoding the received packet. These functions will return LWRES_R_FAILURE if pktflags in the packet header structure lwres_lwpacket_t indicate that the packet is not a response to an earlier query.
"SEE ALSO"
lwres_packet(3)
