DNS Query

Detailed Description

DNS query is composed of a DNS request (question) and response (answer). This application only handles DNS query type "question", and provides a simple response. Implementation of DNS records database (zones) is not done as that is beyond the scope of purpose for this project.

Parsing EDNS opt RR is supported along with EDNS client subnet extension.

A single structure is used to hold query request and query response. Depending if query arrived over UDP or TCP, appropriate buffers are made available providing access to raw query data (as received or to be sent over the network).

Data Structures
struct	edns_client_subnet_s
struct	edns_s
struct	query_s
struct	query_log_s
struct	query_log_loop_args_s
struct	rr_record_s

Typedefs
typedef struct edns_client_subnet_s	edns_client_subnet_t
typedef struct edns_s	edns_t
typedef struct query_s	query_t
typedef struct query_log_s	query_log_t
typedef struct query_log_loop_args_s	query_log_loop_args_t
typedef struct rr_record_s	rr_record_t

Functions
void	query_init (query_t *q, config_t *cfg, uint8_t protocol)
void	query_reset (query_t *q)
void	query_clean (query_t *q)
int	query_tcp_response_buffer_increase (query_t *q)
int	query_parse_edns_ext_cs (edns_client_subnet_t *cs)
int	query_parse_edns_ext (query_t *q, unsigned char *buf, unsigned char *eobuf)
int	query_parse_request_rr_additional_edns (query_t *q, unsigned char *ptr)
int	query_parse_request_rr_question (query_t *q)
void	query_parse (query_t *q)
void	query_resolve (query_t *q)
int	query_pack_edns (uint8_t *buf, uint16_t buf_len, edns_t *edns)
int	query_pack_rr (const unsigned char *name, rr_record_t *rr, unsigned char *buf, uint16_t buf_len, const unsigned char **dnptrs, const unsigned char **lastdnptr)
int	query_response_pack (query_t *q)
int	query_log (char *buf, size_t buf_len, query_t *q)
void	query_log_rotate (query_log_t *query_log)
void *	query_log_loop (void *args)
void	query_report_metrics (query_t *, metrics_t *metrics)

Typedef Documentation

edns_client_subnet_t

typedef struct edns_client_subnet_s edns_client_subnet_t

Structure for EDNS client subnet option.

edns_t

typedef struct edns_s edns_t

Structure for EDNS optional resource record.

query_log_loop_args_t

typedef struct query_log_loop_args_s query_log_loop_args_t

Structure holds arguments passed to query_log_loop function.

query_log_t

typedef struct query_log_s query_log_t

Stucture describes a query log object.

Queries are logged into a buffer. There are two buffers, one is active, while the other one (inactive buffer) is having its data written to disk. This enables us to have no blocking operations (such as writing to disk) in the vectorloop.

Query logging thread uses channels to notify vectorloop thread when it should swap log buffers. Once VL thread swaps buffers, it sends a message back to query logging thread indicating so, which in turn signals the query logging thread that it should log data from VL inactive buffer to disk. Once data is written to disk the process repeats.

Each vectorloop thread has its own set of query log buffers.

Size of each buffer is set by configuration setting query_log_buffer_size.

query_t

typedef struct query_s query_t

Structure describes a DNS query.

rr_record_t

typedef struct rr_record_s rr_record_t

Structure describes a DNS Resource Record.

Function Documentation

query_clean()

void query_clean

(

query_t *

q

)

Clean a query object. This releases all memory owned by query object.

Parameters

q	Query to clean.

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query_init()

void query_init	(	query_t *	q,
		config_t *	cfg,
		uint8_t	protocol
	)

Initialize a query object.

Parameters

q	Query object to initialize.
cfg	Configuration with settings to use.
protocol	Transport protocol used for query. Valid options are 0 = UDP, 1 = TCP.

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query_log()

int query_log	(	char *	buf,
		size_t	buf_len,
		query_t *	q
	)

Log query to buffer.

Query log entry ends with new line "\n" (one query per line).

Parameters

buf	Buffer to log query to.
buf_len	Length of buffer (available space).
q	Query to log.

Returns

Returns number of bytes added to buf on success, otherwise returns 0 and error occurred (ie not enough room in buffer, or not a logable query end code) and nothing was added to buf.

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query_log_loop()

void * query_log_loop

(

void *

args

)

Function polls vectorloop threads for query log data and writes it to file. This function is meant to run in its own dedicated thread.

Parameters

args	Structure with settings to use.

Returns

Returns nULL just to abide by the pthread API.

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query_log_rotate()

void query_log_rotate

(

query_log_t *

query_log

)

Rotate query log.

Active log to write queries is switched to the other side.

Parameters

query_log

Query log to rotate.

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query_pack_edns()

int query_pack_edns	(	uint8_t *	buf,
		uint16_t	buf_len,
		edns_t *	edns
	)

Pack EDNS and it extensions into buffer.

Parameters

buf	Buffer to pack EDNS and extensions into.
buf_len	Length in bytes of available space in buffer.
edns	EDNS object to pack.

Returns

On success returns number of bytes packed into buffer. 0 is returned if edns object does not contain valid data. -1 is returned if there is not enough room in buffer to pack EDNS and all its extensions in which case buf is left untouched.

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query_pack_rr()

int query_pack_rr	(	const unsigned char *	name,
		rr_record_t *	rr,
		unsigned char *	buf,
		uint16_t	buf_len,
		const unsigned char **	dnptrs,
		const unsigned char **	lastdnptr
	)

Pack resource record into buffer, non-EDNS. TO pack EDNS use query_pack_edns.

Parameters

name	Name to use to when packing RR. If NULL name in rr is used.
rr	Resource record to pack.
buf	Buffer into which to pack the record.
buf_len	Length (in bytes) of available space in buffer.
dnptrs	Pointer to first entry in domain name array used to track names already packed.
lastdnptr	Last entry in domain name array.

Returns

On success returns number of bytes packed into buffer, Otherwise error occurred. Currently error can occur if there if not enough room in buffer to pack the record.

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query_parse()

void query_parse

(

query_t *

q

)

Parse query request from request buffer into query_t structure fields.

DNS request & response format is as per RFC 1035 https://datatracker.ietf.org/doc/html/rfc1035.

Parameters

q	Query to parse DNS request for.

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query_parse_edns_ext()

int query_parse_edns_ext	(	query_t *	q,
		unsigned char *	buf,
		unsigned char *	eobuf
	)

Parse EDNS extensions.

Format of EDNS option is: 2 bytes = Option code, 2 bytes = Option length (length that follows), Option length bytes = option specific

Parameters

q	Query to parse extensions into.
buf	Buffer to parse extensions from.
eobuf	End of buffer.

Returns

Returns 0 on success, otherwise an error occurred i.e. format error.

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query_parse_edns_ext_cs()

int query_parse_edns_ext_cs

(

edns_client_subnet_t *

cs

)

Parse EDNS extension client subnet.

Format is:
2 bytes = family
1 byte = source netmask
1 byte = scope netmask
remaining bytes = client subnet

Parameters

cs	EDNS client subnet object to parse data into.

Returns

Returns 0 on success, otherwise error occurred i.e. format error or unsupported address family.

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query_parse_request_rr_additional_edns()

int query_parse_request_rr_additional_edns	(	query_t *	q,
		unsigned char *	ptr
	)

Parse query request additional section looking for EDNS RR and if found parse EDNS RR.

Parameters

q	Query to parse request additional section EDNS opt RR.
ptr	Pointer in request buffer where additional section starts.

Returns

On success returns number of bytes consumed. On error returns -1 in which case query parameter end_code is set.

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query_parse_request_rr_question()

int query_parse_request_rr_question

(

query_t *

q

)

Parse query request question RR.

Format on the wire per RFC 1035 is:

0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 +–+–+–+–+–+–+–+–+–+–+–+–+–+–+–+–+ | | / QNAME / / / +–+–+–+–+–+–+–+–+–+–+–+–+–+–+–+–+ | QTYPE | +–+–+–+–+–+–+–+–+–+–+–+–+–+–+–+–+ | QCLASS | +–+–+–+–+–+–+–+–+–+–+–+–+–+–+–+–+

Parameters

q	Query for which to parse request question.

Returns

On success returns number of bytes from request buffer that are the question RR. On error returns -1 in which case query parameter end_code is set.

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query_report_metrics()

void query_report_metrics	(	query_t *	q,
		metrics_t *	metrics
	)

Report query metrics.

Parameters

q	Query to report metrics for.
metrics	Metrics object where to report metrics.

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query_reset()

void query_reset

(

query_t *

q

)

Reset query object so it is suitable to be reused for new query processing.

Parameters

q	Query to reset.

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query_resolve()

void query_resolve

(

query_t *

q

)

Resolve a query and if appropriate pack the answer into response buffer.

Parameters

q	Query to resolve.

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query_response_pack()

int query_response_pack

(

query_t *

q

)

Pack query response into query response buffer.

Parameters

q	Query to pack response for

Returns

Returns 0 on success otherwise error occurred: -1 indicates that there was not enough room to pack full response and response is truncated.

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query_tcp_response_buffer_increase()

int query_tcp_response_buffer_increase

(

query_t *

q

)

Increase the query response buffer size. This is only valid if query is used with TCP transport.

Response buffer size is increased via call to realloc() in increments of RIP_NS_UDP_MAXMSG up to max size of RIP_NS_MAXMSG.

Parameters

q	Query whose response buffer to increase.

Returns

Returns 0 on success, otherwise an error occurred and response buffer was untouched.

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