Knot DNS Resolver library¶

Requirements¶

libknot 2.0 (Knot DNS high-performance DNS library.)

For users¶

The library as described provides basic services for name resolution, which should cover the usage, examples are in the resolve API documentation.

Tip

If you’re migrating from getaddrinfo(), see “synchronous” API, but the library offers iterative API as well to plug it into your event loop for example.

For developers¶

The resolution process starts with the functions in resolve.c, they are responsible for:

reacting to state machine state (i.e. calling consume layers if we have an answer ready)
interacting with the library user (i.e. asking caller for I/O, accepting queries)
fetching assets needed by layers (i.e. zone cut)

This is the driver. The driver is not meant to know “how” the query resolves, but rather “when” to execute “what”.

On the other side are layers. They are responsible for dissecting the packets and informing the driver about the results. For example, a produce layer generates query, a consume layer validates answer.

Tip

Layers are executed asynchronously by the driver. If you need some asset beforehand, you can signalize the driver using returning state or current query flags. For example, setting a flag QUERY_AWAIT_CUT forces driver to fetch zone cut information before the packet is consumed; setting a QUERY_RESOLVED flag makes it pop a query after the current set of layers is finished; returning FAIL state makes it fail current query.

Layers can also change course of resolution, for example by appending additional queries.

consume = function (state, req, answer)
        answer = kres.pkt_t(answer)
        if answer:qtype() == kres.type.NS then
                req = kres.request_t(req)
                local qry = req:push(answer:qname(), kres.type.SOA, kres.class.IN)
                qry.flags = kres.query.AWAIT_CUT
        end
        return state
end

This doesn’t block currently processed query, and the newly created sub-request will start as soon as driver finishes processing current. In some cases you might need to issue sub-request and process it before continuing with the current, i.e. validator may need a DNSKEY before it can validate signatures. In this case, layers can yield and resume afterwards.

consume = function (state, req, answer)
        answer = kres.pkt_t(answer)
        if state == kres.YIELD then
                print('continuing yielded layer')
                return kres.DONE
        else
                if answer:qtype() == kres.type.NS then
                        req = kres.request_t(req)
                        local qry = req:push(answer:qname(), kres.type.SOA, kres.class.IN)
                        qry.flags = kres.query.AWAIT_CUT
                        print('planned SOA query, yielding')
                        return kres.YIELD
                end
                return state
        end
end

The YIELD state is a bit special. When a layer returns it, it interrupts current walk through the layers. When the layer receives it, it means that it yielded before and now it is resumed. This is useful in a situation where you need a sub-request to determine whether current answer is valid or not.

Writing layers¶

The resolver library leverages the processing API from the libknot to separate packet processing code into layers.

Note

This is only crash-course in the library internals, see the resolver library documentation for the complete overview of the services.

The library offers following services:

Cache - MVCC cache interface for retrieving/storing resource records.
Resolution plan - Query resolution plan, a list of partial queries (with hierarchy) sent in order to satisfy original query. This contains information about the queries, nameserver choice, timing information, answer and its class.
Nameservers - Reputation database of nameservers, this serves as an aid for nameserver choice.

A processing layer is going to be called by the query resolution driver for each query, so you’re going to work with struct kr_request as your per-query context. This structure contains pointers to resolution context, resolution plan and also the final answer.

int consume(kr_layer_t *ctx, knot_pkt_t *pkt)
{
        struct kr_request *req = ctx->req;
        struct kr_query *qry = req->current_query;
}

This is only passive processing of the incoming answer. If you want to change the course of resolution, say satisfy a query from a local cache before the library issues a query to the nameserver, you can use states (see the Static hints for example).

int produce(kr_layer_t *ctx, knot_pkt_t *pkt)
{
        struct kr_request *req = ctx->req;
        struct kr_query *qry = req->current_query;

        /* Query can be satisfied locally. */
        if (can_satisfy(qry)) {
                /* This flag makes the resolver move the query
                 * to the "resolved" list. */
                qry->flags |= QUERY_RESOLVED;
                return KR_STATE_DONE;
        }

        /* Pass-through. */
        return ctx->state;
}

It is possible to not only act during the query resolution, but also to view the complete resolution plan afterwards. This is useful for analysis-type tasks, or “per answer” hooks.

int finish(kr_layer_t *ctx)
{
        struct kr_request *req = ctx->req;
        struct kr_rplan *rplan = req->rplan;

        /* Print the query sequence with start time. */
        char qname_str[KNOT_DNAME_MAXLEN];
        struct kr_query *qry = NULL
        WALK_LIST(qry, rplan->resolved) {
                knot_dname_to_str(qname_str, qry->sname, sizeof(qname_str));
                printf("%s at %u\n", qname_str, qry->timestamp);
        }

        return ctx->state;
}

APIs in Lua¶

The APIs in Lua world try to mirror the C APIs using LuaJIT FFI, with several differences and enhancements. There is not comprehensive guide on the API yet, but you can have a look at the bindings file.

Elementary types and constants¶

States are directly in kres table, e.g. kres.YIELD, kres.CONSUME, kres.PRODUCE, kres.DONE, kres.FAIL.
DNS classes are in kres.class table, e.g. kres.class.IN for Internet class.
DNS types are in kres.type table, e.g. kres.type.AAAA for AAAA type.
DNS rcodes types are in kres.rcode table, e.g. kres.rcode.NOERROR.
Packet sections (QUESTION, ANSWER, AUTHORITY, ADDITIONAL) are in the kres.section table.

Working with domain names¶

The internal API usually works with domain names in label format, you can convert between text and wire freely.

local dname = kres.str2dname('business.se')
local strname = kres.dname2str(dname)

Working with resource records¶

Resource records are stored as tables.

local rr = { owner = kres.str2dname('owner'),
             ttl = 0,
             class = kres.class.IN,
             type = kres.type.CNAME,
             rdata = kres.str2dname('someplace') }
print(kres.rr2str(rr))

RRSets in packet can be accessed using FFI, you can easily fetch single records.

local rrset = { ... }
local rr = rrset:get(0) -- Return first RR
print(kres.dname2str(rr:owner()))
print(rr:ttl())
print(kres.rr2str(rr))

Working with packets¶

Packet is the data structure that you’re going to see in layers very often. They consists of a header, and four sections: QUESTION, ANSWER, AUTHORITY, ADDITIONAL. The first section is special, as it contains the query name, type, and class; the rest of the sections contain RRSets.

First you need to convert it to a type known to FFI and check basic properties. Let’s start with a snippet of a consume layer.

consume = function (state, req, pkt)
        pkt = kres.pkt_t(answer)
        print('rcode:', pkt:rcode())
        print('query:', kres.dname2str(pkt:qname()), pkt:qclass(), pkt:qtype())
        if pkt:rcode() ~= kres.rcode.NOERROR then
                print('error response')
        end
end

You can enumerate records in the sections.

local records = pkt:section(kres.section.ANSWER)
for i = 1, #records do
        local rr = records[i]
        if rr.type == kres.type.AAAA then
                print(kres.rr2str(rr))
        end
end

During produce or begin, you might want to want to write to packet. Keep in mind that you have to write packet sections in sequence, e.g. you can’t write to ANSWER after writing AUTHORITY, it’s like stages where you can’t go back.

pkt:rcode(kres.rcode.NXDOMAIN)
-- Clear answer and write QUESTION
pkt:clear()
pkt:question('\7blocked', kres.class.IN, kres.type.SOA)
-- Start writing data
pkt:begin(kres.section.ANSWER)
-- Nothing in answer
pkt:begin(kres.section.AUTHORITY)
local soa = { owner = '\7blocked', ttl = 900, class = kres.class.IN, type = kres.type.SOA, rdata = '...' }
pkt:put(soa.owner, soa.ttl, soa.class, soa.type, soa.rdata)

Working with requests¶

The request holds information about currently processed query, enabled options, cache, and other extra data. You primarily need to retrieve currently processed query.

consume = function (state, req, pkt)
        req = kres.request_t(req)
        print(req.options)
        print(req.state)

        -- Print information about current query
        local current = req:current()
        print(kres.dname2str(current.owner))
        print(current.stype, current.sclass, current.id, current.flags)
end

In layers that either begin or finalize, you can walk the list of resolved queries.

local last = req:resolved()
print(last.stype)

As described in the layers, you can not only retrieve information about current query, but also push new ones or pop old ones.

-- Push new query
local qry = req:push(pkt:qname(), kres.type.SOA, kres.class.IN)
qry.flags = kres.query.AWAIT_CUT

-- Pop the query, this will erase it from resolution plan
req:pop(qry)

Name resolution ¶

The API provides an API providing a “consumer-producer”-like interface to enable user to plug it into existing event loop or I/O code.

Example usage of the iterative API:

// Create request and its memory pool
struct kr_request req = {
    .pool = {
        .ctx = mp_new (4096),
        .alloc = (mm_alloc_t) mp_alloc
    }
};

// Setup and provide input query
int state = kr_resolve_begin(&req, ctx, final_answer);
state = kr_resolve_consume(&req, query);

// Generate answer
while (state == KR_STATE_PRODUCE) {

    // Additional query generate, do the I/O and pass back answer
    state = kr_resolve_produce(&req, &addr, &type, query);
    while (state == KR_STATE_CONSUME) {
        int ret = sendrecv(addr, proto, query, resp);

        // If I/O fails, make "resp" empty
        state = kr_resolve_consume(&request, addr, resp);
        knot_pkt_clear(resp);
    }
    knot_pkt_clear(query);
}

// "state" is either DONE or FAIL
kr_resolve_finish(&request, state);

Typedefs

typedef enum kr_validation_rank kr_validation_rank_t: Validation rank.

Enums

kr_validation_rank enum

Validation rank.

Values:

KR_VLDRANK_INITIAL = = 0 -
KR_VLDRANK_INSECURE = = 1 -
KR_VLDRANK_BAD = = 2 -
KR_VLDRANK_MISMATCH = = 3 -
KR_VLDRANK_UNKNOWN = = 4 -
KR_VLDRANK_SECURE = = 5 -

Functions

KR_EXPORT int kr_resolve_begin(struct kr_request * request, struct kr_context * ctx, knot_pkt_t * answer)

Begin name resolution.

Note

Expects a request to have an initialized mempool, the “answer” packet will be kept during the resolution and will contain the final answer at the end.

Return

CONSUME (expecting query)

Parameters

request -
request state with initialized mempool
ctx -
resolution context
answer -
allocated packet for final answer

KR_EXPORT int kr_resolve_consume(struct kr_request * request, const struct sockaddr * src, knot_pkt_t * packet)

Consume input packet (may be either first query or answer to query originated from kr_resolve_produce())

Note

If the I/O fails, provide an empty or NULL packet, this will make iterator recognize nameserver failure.

Return

any state

Parameters

request -
request state (awaiting input)
src -
[in] packet source address
packet -
[in] input packet

KR_EXPORT int kr_resolve_produce(struct kr_request * request, struct sockaddr ** dst, int * type, knot_pkt_t * packet)

Produce either next additional query or finish.

If the CONSUME is returned then dst, type and packet will be filled with appropriate values and caller is responsible to send them and receive answer. If it returns any other state, then content of the variables is undefined.

Return

any state

Parameters

request -
request state (in PRODUCE state)
dst -
[out] possible address of the next nameserver
type -
[out] possible used socket type (SOCK_STREAM, SOCK_DGRAM)
packet -
[out] packet to be filled with additional query

KR_EXPORT int kr_resolve_checkout(struct kr_request * request, struct sockaddr * src, struct sockaddr * dst, int type, knot_pkt_t * packet)

Finalises the outbound query packet with the knowledge of the IP addresses.

Note

The function must be called before actual sending of the request packet.

Return

kr_ok() or error code

Parameters

request -
request state (in PRODUCE state)
src -
address from which the query is going to be sent
dst -
address of the name server
type -
used socket type (SOCK_STREAM, SOCK_DGRAM)
packet -
[in,out] query packet to be finalised

KR_EXPORT int kr_resolve_finish(struct kr_request * request, int state)

Finish resolution and commit results if the state is DONE.

Note

The structures will be deinitialized, but the assigned memory pool is not going to be destroyed, as it’s owned by caller.

Return

DONE

Parameters

request -
request state
state -
either DONE or FAIL state

KR_EXPORT KR_PURE struct kr_rplan * kr_resolve_plan(struct kr_request * request)

Return resolution plan.

Return

pointer to rplan

Parameters

request -
request state

KR_EXPORT KR_PURE knot_mm_t * kr_resolve_pool(struct kr_request * request)

Return memory pool associated with request.

Return

mempool

Parameters

request -
request state

struct kr_context

#include <resolve.h>

Name resolution context.

Resolution context provides basic services like cache, configuration and options.

Note: This structure is persistent between name resolutions and may be shared between threads.

Public Members

uint32_t options

knot_rrset_t * opt_rr

map_t trust_anchors

map_t negative_anchors

struct kr_zonecut root_hints

struct kr_cache cache

kr_nsrep_lru_t * cache_rtt

kr_nsrep_lru_t * cache_rep

module_array_t * modules

struct kr_cookie_ctx cookie_ctx

kr_cookie_lru_t * cache_cookie

uint32_t tls_padding: See net.tls_padding in ../daemon/README.rst.

knot_mm_t * pool

struct kr_request

#include <resolve.h>

Name resolution request.

Keeps information about current query processing between calls to processing APIs, i.e. current resolved query, resolution plan, ... Use this instead of the simple interface if you want to implement multiplexing or custom I/O.

Note: All data for this request must be allocated from the given pool.

Public Members

struct kr_context * ctx

knot_pkt_t * answer

struct kr_query * current_query: Current evaluated query.

const knot_rrset_t * key

const struct sockaddr * addr: Current upstream address.

const struct sockaddr * dst_addr

const knot_pkt_t * packet

const knot_rrset_t * opt

struct kr_request::@3 qsource

unsigned rtt: Current upstream RTT.

struct kr_request::@4 upstream: Upstream information, valid only in consume() phase.

uint32_t options

int state

ranked_rr_array_t answ_selected

ranked_rr_array_t auth_selected

rr_array_t additional

bool answ_validated

bool auth_validated

struct kr_rplan rplan

int has_tls

knot_mm_t pool

Defines

QUERY_FLAGS(X): Log answer with kr_verbose_log(), unless -DNDEBUG.

X(flag, val)

Enums

kr_query_flag enum

Query flags.

Values:

Functions

KR_EXPORT KR_CONST const knot_lookup_t * kr_query_flag_names(void): Query flag names table.

KR_EXPORT int kr_rplan_init(struct kr_rplan * rplan, struct kr_request * request, knot_mm_t * pool)

Initialize resolution plan (empty).

Parameters

rplan -
plan instance
request -
resolution request
pool -
ephemeral memory pool for whole resolution

KR_EXPORT void kr_rplan_deinit(struct kr_rplan * rplan)

Deinitialize resolution plan, aborting any uncommited transactions.

Parameters

rplan -
plan instance

KR_EXPORT KR_PURE bool kr_rplan_empty(struct kr_rplan * rplan)

Return true if the resolution plan is empty (i.e.

finished or initialized)

Return

true or false

Parameters

rplan -
plan instance

KR_EXPORT struct kr_query * kr_rplan_push_empty(struct kr_rplan * rplan, struct kr_query * parent)

Push empty query to the top of the resolution plan.

Note

This query serves as a cookie query only.

Return

query instance or NULL

Parameters

rplan -
plan instance
parent -
query parent (or NULL)

KR_EXPORT struct kr_query * kr_rplan_push(struct kr_rplan * rplan, struct kr_query * parent, const knot_dname_t * name, uint16_t cls, uint16_t type)

Push a query to the top of the resolution plan.

Note

This means that this query takes precedence before all pending queries.

Return

query instance or NULL

Parameters

rplan -
plan instance
parent -
query parent (or NULL)
name -
resolved name
cls -
resolved class
type -
resolved type

KR_EXPORT int kr_rplan_pop(struct kr_rplan * rplan, struct kr_query * qry)

Pop existing query from the resolution plan.

Note

Popped queries are not discarded, but moved to the resolved list.

Return

0 or an error

Parameters

rplan -
plan instance
qry -
resolved query

KR_EXPORT KR_PURE bool kr_rplan_satisfies(struct kr_query * closure, const knot_dname_t * name, uint16_t cls, uint16_t type): Return true if resolution chain satisfies given query.

KR_EXPORT KR_PURE struct kr_query * kr_rplan_resolved(struct kr_rplan * rplan): Return last resolved query.

KR_EXPORT KR_PURE struct kr_query * kr_rplan_next(struct kr_query * qry): Return query predecessor.

struct kr_query

#include <rplan.h>

Single query representation.

Public Members

struct kr_query * parent

knot_dname_t * sname

uint16_t stype

uint16_t sclass

uint16_t id

uint32_t flags

uint32_t secret

uint16_t fails

uint16_t reorder: Seed to reorder (cached) RRs in answer or zero.

struct timeval timestamp

struct kr_zonecut zone_cut

struct kr_nsrep ns

struct kr_layer_pickle * deferred

uint32_t uid: Query iteration number, unique within the kr_rplan.

struct kr_rplan

#include <rplan.h>

Query resolution plan structure.

The structure most importantly holds the original query, answer and the list of pending queries required to resolve the original query. It also keeps a notion of current zone cut.

Public Members

kr_qarray_t pending: List of pending queries.

kr_qarray_t resolved: List of resolved queries.

struct kr_request * request: Parent resolution request.

knot_mm_t * pool: Temporary memory pool.

uint32_t next_uid: Next value for kr_query::uid (incremental).

Cache ¶

Enums

kr_cache_tag enum

Cache entry tag.

Values:

KR_CACHE_RR = = 'R' -
KR_CACHE_PKT = = 'P' -
KR_CACHE_SIG = = 'G' -
KR_CACHE_USER = = 0x80 -

kr_cache_rank enum

Cache entry rank.

Ref: https://tools.ietf.org/html/rfc2181#section-5.4.1

Note

Be careful about chosen cache rank nominal values.

AUTH must be > than NONAUTH
AUTH INSECURE must be > than AUTH (because it attempted validation)
NONAUTH SECURE must be > than AUTH (because it’s valid)

Values:

KR_RANK_BAD = = 0 -
KR_RANK_INSECURE = = 1 -
KR_RANK_EXTRA = = 4 -
KR_RANK_NONAUTH = = 8 -
KR_RANK_AUTH = = 16 -
KR_RANK_SECURE = = 32 -

kr_cache_flag enum

Cache entry flags.

Values:

KR_CACHE_FLAG_NONE = = 0 -
KR_CACHE_FLAG_WCARD_PROOF = = 1 -

Functions

KR_EXPORT int kr_cache_open(struct kr_cache * cache, const struct kr_cdb_api * api, struct kr_cdb_opts * opts, knot_mm_t * mm)

Open/create cache with provided storage options.

Return

0 or an error code

Parameters

cache -
cache structure to be initialized
api -
storage engine API
opts -
storage-specific options (may be NULL for default)
mm -
memory context.

KR_EXPORT void kr_cache_close(struct kr_cache * cache)

Close persistent cache.

Note

This doesn’t clear the data, just closes the connection to the database.

Parameters

cache -
structure

KR_EXPORT void kr_cache_sync(struct kr_cache * cache)

Synchronise cache with the backing store.

Parameters

cache -
structure

bool kr_cache_is_open(struct kr_cache * cache): Return true if cache is open and enabled.

KR_EXPORT int kr_cache_peek(struct kr_cache * cache, uint8_t tag, const knot_dname_t * name, uint16_t type, struct kr_cache_entry ** entry, uint32_t * timestamp)

Peek the cache for asset (name, type, tag)

Note

The ‘drift’ is the time passed between the inception time and now (in seconds).

Return

0 or an errcode

Parameters

cache -
cache structure
tag -
asset tag
name -
asset name
type -
asset type
entry -
cache entry, will be set to valid pointer or NULL
timestamp -
current time (will be replaced with drift if successful)

KR_EXPORT int kr_cache_insert(struct kr_cache * cache, uint8_t tag, const knot_dname_t * name, uint16_t type, struct kr_cache_entry * header, knot_db_val_t data)

Insert asset into cache, replacing any existing data.

Return

0 or an errcode

Parameters

cache -
cache structure
tag -
asset tag
name -
asset name
type -
asset type
header -
filled entry header (count, ttl and timestamp)
data -
inserted data

KR_EXPORT int kr_cache_remove(struct kr_cache * cache, uint8_t tag, const knot_dname_t * name, uint16_t type)

Remove asset from cache.

Return

0 or an errcode

Parameters

cache -
cache structure
tag -
asset tag
name -
asset name
type -
record type

KR_EXPORT int kr_cache_clear(struct kr_cache * cache)

Clear all items from the cache.

Return

0 or an errcode

Parameters

cache -
cache structure

KR_EXPORT int kr_cache_match(struct kr_cache * cache, uint8_t tag, const knot_dname_t * name, knot_db_val_t * vals, int valcnt)

Prefix scan on cached items.

Return

number of retrieved keys or an error

Parameters

cache -
cache structure
tag -
asset tag
name -
asset prefix key
vals -
array of values to store the result
valcnt -
maximum number of retrieved keys

KR_EXPORT int kr_cache_peek_rank(struct kr_cache * cache, uint8_t tag, const knot_dname_t * name, uint16_t type, uint32_t timestamp)

Peek the cache for given key and retrieve it’s rank.

Return

rank (0 or positive), or an error (negative number)

Parameters

cache -
cache structure
tag -
asset tag
name -
asset name
type -
record type
timestamp -
current time

KR_EXPORT int kr_cache_peek_rr(struct kr_cache * cache, knot_rrset_t * rr, uint8_t * rank, uint8_t * flags, uint32_t * timestamp)

Peek the cache for given RRSet (name, type)

Note

The ‘drift’ is the time passed between the cache time of the RRSet and now (in seconds).

Return

0 or an errcode

Parameters

cache -
cache structure
rr -
query RRSet (its rdataset may be changed depending on the result)
rank -
entry rank will be stored in this variable
flags -
entry flags
timestamp -
current time (will be replaced with drift if successful)

KR_EXPORT int kr_cache_materialize(knot_rrset_t * dst, const knot_rrset_t * src, uint32_t drift, uint reorder, knot_mm_t * mm)

Clone read-only RRSet and adjust TTLs.

Return

0 or an errcode

Parameters

dst -
destination for materialized RRSet
src -
read-only RRSet (its rdataset may be changed depending on the result)
drift -
time passed between cache time and now
reorder -
(pseudo)-random seed to reorder the data or zero
mm -
memory context

KR_EXPORT int kr_cache_insert_rr(struct kr_cache * cache, const knot_rrset_t * rr, uint8_t rank, uint8_t flags, uint32_t timestamp)

Insert RRSet into cache, replacing any existing data.

Return

0 or an errcode

Parameters

cache -
cache structure
rr -
inserted RRSet
rank -
rank of the data
flags -
additional flags for the data
timestamp -
current time

KR_EXPORT int kr_cache_peek_rrsig(struct kr_cache * cache, knot_rrset_t * rr, uint8_t * rank, uint8_t * flags, uint32_t * timestamp)

Peek the cache for the given RRset signature (name, type)

Note

The RRset type must not be RRSIG but instead it must equal the type covered field of the sought RRSIG.

Return

0 or an errcode

Parameters

cache -
cache structure
rr -
query RRSET (its rdataset and type may be changed depending on the result)
rank -
entry rank will be stored in this variable
flags -
entry additional flags
timestamp -
current time (will be replaced with drift if successful)

KR_EXPORT int kr_cache_insert_rrsig(struct kr_cache * cache, const knot_rrset_t * rr, uint8_t rank, uint8_t flags, uint32_t timestamp)

Insert the selected RRSIG RRSet of the selected type covered into cache, replacing any existing data.

Note

The RRSet must contain RRSIGS with only the specified type covered.

Return

0 or an errcode

Parameters

cache -
cache structure
rr -
inserted RRSIG RRSet
rank -
rank of the data
flags -
additional flags for the data
timestamp -
current time

struct kr_cache_entry

#include <cache.h>

Serialized form of the RRSet with inception timestamp and maximum TTL.

Public Members

uint32_t timestamp

uint32_t ttl

uint16_t count

uint8_t rank

uint8_t flags

uint8_t data[]

struct kr_cache

#include <cache.h>

Cache structure, keeps API, instance and metadata.

Public Members

knot_db_t * db: Storage instance.

const struct kr_cdb_api * api: Storage engine.

uint32_t hit: Number of cache hits.

uint32_t miss: Number of cache misses.

uint32_t insert: Number of insertions.

uint32_t delete: Number of deletions.

struct kr_cache::@0 stats

uint32_t ttl_min

uint32_t ttl_max: Maximum TTL of inserted entries.

Nameservers ¶

Defines

KR_NSREP_MAXADDR

kr_nsrep_inaddr(addr)

kr_nsrep_inaddr_len(addr)

Enums

kr_ns_score enum

NS RTT score (special values).

Note: RTT is measured in milliseconds.

Values:

KR_NS_MAX_SCORE = = KR_CONN_RTT_MAX -
KR_NS_TIMEOUT = = (95 * KR_NS_MAX_SCORE) / 100 -
KR_NS_LONG = = (3 * KR_NS_TIMEOUT) / 4 -
KR_NS_UNKNOWN = = KR_NS_TIMEOUT / 2 -
KR_NS_PENALTY = = 100 -
KR_NS_GLUED = = 10 -

kr_ns_rep enum

NS QoS flags.

Values:

KR_NS_NOIP4 = = 1 << 0 -
NS has no IPv4.
KR_NS_NOIP6 = = 1 << 1 -
NS has no IPv6.
KR_NS_NOEDNS = = 1 << 2 -
NS has no EDNS support.

kr_ns_update_mode enum

NS RTT update modes.

Values:

KR_NS_UPDATE = = 0 -
Update as smooth over last two measurements.
KR_NS_RESET -
Set to given value.
KR_NS_ADD -
Increment current value.
KR_NS_MAX -
Set to maximum of current/proposed value.

Functions

typedef lru_t(unsigned): NS reputation/QoS tracking.

KR_EXPORT int kr_nsrep_set(struct kr_query * qry, size_t index, uint8_t * addr, size_t addr_len, int port)

Set given NS address.

Return

0 or an error code

Parameters

qry -
updated query
index -
index of the updated target
addr -
address bytes (struct in_addr or struct in6_addr)
addr_len -
address bytes length (type will be derived from this)
port -
address port (if <= 0, 53 will be used)

KR_EXPORT int kr_nsrep_elect(struct kr_query * qry, struct kr_context * ctx)

Elect best nameserver/address pair from the nsset.

Return

0 or an error code

Parameters

qry -
updated query
ctx -
resolution context

KR_EXPORT int kr_nsrep_elect_addr(struct kr_query * qry, struct kr_context * ctx)

Elect best nameserver/address pair from the nsset.

Return

0 or an error code

Parameters

qry -
updated query
ctx -
resolution context

KR_EXPORT int kr_nsrep_update_rtt(struct kr_nsrep * ns, const struct sockaddr * addr, unsigned score, kr_nsrep_lru_t * cache, int umode)

Update NS address RTT information.

In KR_NS_UPDATE mode reputation is smoothed over last N measurements.

Return

0 on success, error code on failure

Parameters

ns -
updated NS representation
addr -
chosen address (NULL for first)
score -
new score (i.e. RTT), see enum kr_ns_score
cache -
LRU cache
umode -
update mode (KR_NS_UPDATE or KR_NS_RESET or KR_NS_ADD)

KR_EXPORT int kr_nsrep_update_rep(struct kr_nsrep * ns, unsigned reputation, kr_nsrep_lru_t * cache)

Update NSSET reputation information.

Return

0 on success, error code on failure

Parameters

ns -
updated NS representation
reputation -
combined reputation flags, see enum kr_ns_rep
cache -
LRU cache

struct kr_nsrep

#include <nsrep.h>

Name server representation.

Contains extra information about the name server, e.g. score or other metadata.

Public Members

unsigned score: NS score.

unsigned reputation: NS reputation.

const knot_dname_t * name: NS name.

struct kr_context * ctx: Resolution context.

struct sockaddr ip

struct sockaddr_in ip4

struct sockaddr_in6 ip6

union kr_nsrep::@2 addr[KR_NSREP_MAXADDR]: NS address(es)

Functions

KR_EXPORT int kr_zonecut_init(struct kr_zonecut * cut, const knot_dname_t * name, knot_mm_t * pool)

Populate root zone cut with SBELT.

Return

0 or error code

Parameters

cut -
zone cut
name -
pool -

KR_EXPORT void kr_zonecut_deinit(struct kr_zonecut * cut)

Clear the structure and free the address set.

Parameters

cut -
zone cut

KR_EXPORT void kr_zonecut_set(struct kr_zonecut * cut, const knot_dname_t * name)

Reset zone cut to given name and clear address list.

Note

This clears the address list even if the name doesn’t change. TA and DNSKEY don’t change.

Parameters

cut -
zone cut to be set
name -
new zone cut name

KR_EXPORT int kr_zonecut_copy(struct kr_zonecut * dst, const struct kr_zonecut * src)

Copy zone cut, including all data.

Does not copy keys and trust anchor.

Return

0 or an error code

Parameters

dst -
destination zone cut
src -
source zone cut

KR_EXPORT int kr_zonecut_copy_trust(struct kr_zonecut * dst, const struct kr_zonecut * src)

Copy zone trust anchor and keys.

Return

0 or an error code

Parameters

dst -
destination zone cut
src -
source zone cut

KR_EXPORT int kr_zonecut_add(struct kr_zonecut * cut, const knot_dname_t * ns, const knot_rdata_t * rdata)

Add address record to the zone cut.

The record will be merged with existing data, it may be either A/AAAA type.

Return

0 or error code

Parameters

cut -
zone cut to be populated
ns -
nameserver name
rdata -
nameserver address (as rdata)

KR_EXPORT int kr_zonecut_del(struct kr_zonecut * cut, const knot_dname_t * ns, const knot_rdata_t * rdata)

Delete nameserver/address pair from the zone cut.

Return

0 or error code

Parameters

cut -
ns -
name server name
rdata -
name server address

KR_EXPORT int kr_zonecut_del_all(struct kr_zonecut * cut, const knot_dname_t * ns)

Delete all addresses associated with the given name.

Return

0 or error code

Parameters

cut -
ns -
name server name

KR_EXPORT KR_PURE pack_t * kr_zonecut_find(struct kr_zonecut * cut, const knot_dname_t * ns)

Find nameserver address list in the zone cut.

Note

This can be used for membership test, a non-null pack is returned if the nameserver name exists.

Return

pack of addresses or NULL

Parameters

cut -
ns -
name server name

KR_EXPORT int kr_zonecut_set_sbelt(struct kr_context * ctx, struct kr_zonecut * cut)

Populate zone cut with a root zone using SBELT :rfc:1034

Return

0 or error code

Parameters

ctx -
resolution context (to fetch root hints)
cut -
zone cut to be populated

KR_EXPORT int kr_zonecut_find_cached(struct kr_context * ctx, struct kr_zonecut * cut, const knot_dname_t * name, uint32_t timestamp, bool *restrict secured)

Populate zone cut address set from cache.

Return

0 or error code (ENOENT if it doesn’t find anything)

Parameters

ctx -
resolution context (to fetch data from LRU caches)
cut -
zone cut to be populated
name -
QNAME to start finding zone cut for
timestamp -
transaction timestamp
secured -
set to true if want secured zone cut, will return false if it is provably insecure

struct kr_zonecut

#include <zonecut.h>

Current zone cut representation.

Public Members

knot_dname_t * name: Zone cut name.

knot_rrset_t * key: Zone cut DNSKEY.

knot_rrset_t * trust_anchor: Current trust anchor.

struct kr_zonecut * parent: Parent zone cut.

map_t nsset: Map of nameserver => address_set.

knot_mm_t * pool: Memory pool.

Modules ¶

Defines

KR_MODULE_EXPORT(module)

Export module API version (place this at the end of your module).

Parameters

module -
module name (f.e. hints)

Functions

KR_EXPORT int kr_module_load(struct kr_module * module, const char * name, const char * path)

Load module instance into memory.

Return

0 or an error

Parameters

module -
module structure
name -
module name
path -
module search path

KR_EXPORT void kr_module_unload(struct kr_module * module)

Unload module instance.

Parameters

module -
module structure

struct kr_prop

#include <module.h>

Module property (named callable).

A module property has a free-form JSON output (and optional input).

Public Members

kr_prop_cb * cb

const char * name

const char * info

struct kr_module

#include <module.h>

Module representation.

Public Members

char * name: Name.

module_init_cb * init: Constructor.

module_deinit_cb * deinit: Destructor.

module_config_cb * config: Configuration.

module_layer_cb * layer: Layer getter.

struct kr_prop * props: Properties.

void * lib: Shared library handle or RTLD_DEFAULT.

void * data: Custom data context.

Utilities ¶

Defines

kr_log_info(fmt, ...)

kr_log_error(fmt, ...)

WITH_VERBOSE: Block run in verbose mode; optimized when not run.

kr_log_verbose

static_assert(cond, msg)

RDATA_ARR_MAX

kr_rdataset_next(rd)

KEY_FLAG_RRSIG

KEY_FLAG_RANK(key)

KEY_COVERING_RRSIG(key)

KR_RRKEY_LEN

SWAP(x, y)

Swap two places.

Note: the parameters need to be without side effects.

Functions

KR_EXPORT bool kr_verbose_set(bool status)

Set verbose mode.

Not available if compiled with -DNOVERBOSELOG.

KR_EXPORT void kr_log_verbose(const char * fmt, ...): Log a message if in verbose mode.

long time_diff(struct timeval * begin, struct timeval * end)

Return time difference in miliseconds.

Note: based on the _BSD_SOURCE timersub() macro

KR_EXPORT char * kr_strcatdup(unsigned n, ...): Concatenate N strings.

int kr_rand_reseed(void): Reseed CSPRNG context.

KR_EXPORT unsigned kr_rand_uint(unsigned max): Get pseudo-random value.

KR_EXPORT int kr_memreserve(void * baton, char ** mem, size_t elm_size, size_t want, size_t * have): Memory reservation routine for knot_mm_t.

KR_EXPORT int kr_pkt_recycle(knot_pkt_t * pkt)

KR_EXPORT int kr_pkt_clear_payload(knot_pkt_t * pkt)

KR_EXPORT int kr_pkt_put(knot_pkt_t * pkt, const knot_dname_t * name, uint32_t ttl, uint16_t rclass, uint16_t rtype, const uint8_t * rdata, uint16_t rdlen): Construct and put record to packet.

KR_EXPORT KR_PURE const char * kr_inaddr(const struct sockaddr * addr): Address bytes for given family.

KR_EXPORT KR_PURE int kr_inaddr_family(const struct sockaddr * addr): Address family.

KR_EXPORT KR_PURE int kr_inaddr_len(const struct sockaddr * addr): Address length for given family.

KR_EXPORT KR_PURE int kr_straddr_family(const char * addr): Return address type for string.

KR_EXPORT KR_CONST int kr_family_len(int family): Return address length in given family.

KR_EXPORT int kr_straddr_subnet(void * dst, const char * addr)

Parse address and return subnet length (bits).

Warning: ‘dst’ must be at least sizeof(struct in6_addr) long.

KR_EXPORT KR_PURE int kr_bitcmp(const char * a, const char * b, int bits): Compare memory bitwise.

KR_EXPORT int kr_rrkey(char * key, const knot_dname_t * owner, uint16_t type, uint8_t rank)

Create unique null-terminated string key for RR.

Return

key length if successful or an error

Parameters

key -
Destination buffer for key size, MUST be KR_RRKEY_LEN or larger.
owner -
RR owner domain name.
type -
RR type.
rank -
RR rank (8 bit tag usable for anything).

int kr_rrmap_add(map_t * stash, const knot_rrset_t * rr, uint8_t rank, knot_mm_t * pool)

int kr_rrarray_add(rr_array_t * array, const knot_rrset_t * rr, knot_mm_t * pool)

int kr_ranked_rrarray_add(ranked_rr_array_t * array, const knot_rrset_t * rr, uint8_t rank, bool to_wire, uint32_t qry_uid, knot_mm_t * pool)

int kr_ranked_rrarray_set_wire(ranked_rr_array_t * array, bool to_wire, uint32_t qry_uid)

void kr_rrset_print(const knot_rrset_t * rr, const char * prefix)

void kr_pkt_print(knot_pkt_t * pkt)

void kr_dname_print(const knot_dname_t * name, const char * prefix, const char * postfix)

void kr_rrtype_print(const uint16_t rrtype, const char * prefix, const char * postfix)

KR_EXPORT char * kr_module_call(struct kr_context * ctx, const char * module, const char * prop, const char * input): Call module property.

Variables

KR_EXPORT bool kr_verbose_status

Whether in verbose mode.

Only use this for reading.

Defines

KR_EXPORT

KR_CONST

KR_PURE

KR_NORETURN

KR_COLD

uint

kr_ok()

kr_strerror(x)

Typedefs

typedef unsigned int uint

Functions

int __attribute__((__cold__))

Generics library ¶

This small collection of “generics” was born out of frustration that I couldn’t find no such thing for C. It’s either bloated, has poor interface, null-checking is absent or doesn’t allow custom allocation scheme. BSD-licensed (or compatible) code is allowed here, as long as it comes with a test case in tests/test_generics.c.

array - a set of simple macros to make working with dynamic arrays easier.
map - a Crit-bit tree key-value map implementation (public domain) that comes with tests.
set - set abstraction implemented on top of map.
pack - length-prefixed list of objects (i.e. array-list).
lru - LRU-like hash table

array¶

A set of simple macros to make working with dynamic arrays easier.

MIN(array_push(arr, val), other)

Note: The C has no generics, so it is implemented mostly using macros. Be aware of that, as direct usage of the macros in the evaluating macros may lead to different expectations:

May evaluate the code twice, leading to unexpected behaviour. This is a price to pay for the absence of proper generics.

Example usage:

array_t(const char*) arr;
array_init(arr);

// Reserve memory in advance
if (array_reserve(arr, 2) < 0) {
    return ENOMEM;
}

// Already reserved, cannot fail
array_push(arr, "princess");
array_push(arr, "leia");

// Not reserved, may fail
if (array_push(arr, "han") < 0) {
    return ENOMEM;
}

// It does not hide what it really is
for (size_t i = 0; i < arr.len; ++i) {
    printf("%s\n", arr.at[i]);
}

// Random delete
array_del(arr, 0);

Defines

array_t(type): Declare an array structure.

array_init(array): Zero-initialize the array.

array_clear(array): Free and zero-initialize the array.

array_clear_mm(array, free, baton)

array_reserve(array, n)

Reserve capacity up to ‘n’ bytes.

Return: 0 if success, <0 on failure

array_reserve_mm(array, n, reserve, baton)

array_push(array, val)

Push value at the end of the array, resize it if necessary.

Note: May fail if the capacity is not reserved.
Return: element index on success, <0 on failure

array_pop(array): Pop value from the end of the array.

array_del(array, i)

Remove value at given index.

Return: 0 on success, <0 on failure

array_tail(array)

Return last element of the array.

Warning: Undefined if the array is empty.

Functions

size_t array_next_count(size_t want): Simplified Qt containers growth strategy.

int array_std_reserve(void * baton, char ** mem, size_t elm_size, size_t want, size_t * have)

void array_std_free(void * baton, void * p)

map¶

A Crit-bit tree key-value map implementation.

Example usage:

Warning: If the user provides a custom allocator, it must return addresses aligned to 2B boundary.

map_t map = map_make();

// Custom allocator (optional)
map.malloc = &mymalloc;
map.baton  = &mymalloc_context;

// Insert k-v pairs
int values = { 42, 53, 64 };
if (map_set(&map, "princess", &values[0]) != 0 ||
    map_set(&map, "prince", &values[1])   != 0 ||
    map_set(&map, "leia", &values[2])     != 0) {
    fail();
}

// Test membership
if (map_contains(&map, "leia")) {
    success();
}

// Prefix search
int i = 0;
int count(const char *k, void *v, void *ext) { (*(int *)ext)++; return 0; }
if (map_walk_prefixed(map, "princ", count, &i) == 0) {
    printf("%d matches\n", i);
}

// Delete
if (map_del(&map, "badkey") != 0) {
    fail(); // No such key
}

// Clear the map
map_clear(&map);

Defines

map_walk(map, callback, baton)

Typedefs

typedef void *(* map_alloc_f)(void *, size_t)

typedef void(* map_free_f)(void *baton, void *ptr)

Functions

map_t map_make(void): Creates an new, empty critbit map.

int map_contains(map_t * map, const char * str): Returns non-zero if map contains str.

void * map_get(map_t * map, const char * str): Returns value if map contains str.

int map_set(map_t * map, const char * str, void * val): Inserts str into map, returns 0 on suceess.

int map_del(map_t * map, const char * str): Deletes str from the map, returns 0 on suceess.

void map_clear(map_t * map): Clears the given map.

int map_walk_prefixed(map_t * map, const char * prefix, int(*)(const char *, void *, void *) callback, void * baton)

Calls callback for all strings in map with the given prefix.

Parameters

map -
prefix -
required string prefix (empty => all strings)
callback -
callback parameters are (key, value, baton)
baton -
passed uservalue

struct map_t

#include <map.h>

Main data structure.

Public Members

void * root

map_alloc_f malloc

map_free_f free

void * baton

set¶

A set abstraction implemented on top of map.

Example usage:

Note: The API is based on map.h, see it for more examples.

set_t set = set_make();

// Insert keys
if (set_add(&set, "princess") != 0 ||
    set_add(&set, "prince")   != 0 ||
    set_add(&set, "leia")     != 0) {
    fail();
}

// Test membership
if (set_contains(&set, "leia")) {
    success();
}

// Prefix search
int i = 0;
int count(const char *s, void *n) { (*(int *)n)++; return 0; }
if (set_walk_prefixed(set, "princ", count, &i) == 0) {
    printf("%d matches\n", i);
}

// Delete
if (set_del(&set, "badkey") != 0) {
    fail(); // No such key
}

// Clear the set
set_clear(&set);

Defines

set_make(): Creates an new, empty critbit set

set_contains(set, str): Returns non-zero if set contains str

set_add(set, str): Inserts str into set, returns 0 on suceess

set_del(set, str): Deletes str from the set, returns 0 on suceess

set_clear(set): Clears the given set

set_walk(set, callback, baton): Calls callback for all strings in map

set_walk_prefixed(set, prefix, callback, baton): Calls callback for all strings in set with the given prefix

Typedefs

typedef map_t set_t

typedef int( set_walk_cb)(const char *, void *)

pack¶

A length-prefixed list of objects, also an array list.

Each object is prefixed by item length, unlike array this structure permits variable-length data. It is also equivallent to forward-only list backed by an array.

Example usage:

Note: Maximum object size is 2^16 bytes, see pack_objlen_t

pack_t pack;
pack_init(pack);

// Reserve 2 objects, 6 bytes total
pack_reserve(pack, 2, 4 + 2);

// Push 2 objects
pack_obj_push(pack, U8("jedi"), 4)
pack_obj_push(pack, U8("\xbe\xef"), 2);

// Iterate length-value pairs
uint8_t *it = pack_head(pack);
while (it != pack_tail(pack)) {
    uint8_t *val = pack_obj_val(it);
    it = pack_obj_next(it);
}

// Remove object
pack_obj_del(pack, U8("jedi"), 4);

pack_clear(pack);

Defines

pack_init(pack): Zero-initialize the pack.

pack_clear(pack): Free and the pack.

pack_clear_mm(pack, free, baton)

pack_reserve(pack, objs_count, objs_len): Incrementally reserve objects in the pack.

pack_reserve_mm(pack, objs_count, objs_len, reserve, baton)

pack_head(pack): Return pointer to first packed object.

pack_tail(pack): Return pack end pointer.

Typedefs

typedef uint16_t pack_objlen_t: Packed object length type.

Functions

typedef array_t(uint8_t): Pack is defined as an array of bytes.

pack_objlen_t pack_obj_len(uint8_t * it): Return packed object length.

uint8_t * pack_obj_val(uint8_t * it): Return packed object value.

uint8_t * pack_obj_next(uint8_t * it): Return pointer to next packed object.

int pack_obj_push(pack_t * pack, const uint8_t * obj, pack_objlen_t len)

Push object to the end of the pack.

Return: 0 on success, negative number on failure

uint8_t * pack_obj_find(pack_t * pack, const uint8_t * obj, pack_objlen_t len)

Returns a pointer to packed object.

Return: pointer to packed object or NULL

int pack_obj_del(pack_t * pack, const uint8_t * obj, pack_objlen_t len)

Delete object from the pack.

Return: 0 on success, negative number on failure

lru¶

A lossy cache.

Example usage:

Note: The implementation tries to keep frequent keys and avoid others, even if “used recently”, so it may refuse to store it on lru_get_new(). It uses hashing to split the problem pseudo-randomly into smaller groups, and within each it tries to approximate relative usage counts of several most frequent keys/hashes. This tracking is done for more keys than those that are actually stored.

// Define new LRU type
typedef lru_t(int) lru_int_t;

// Create LRU
lru_int_t *lru;
lru_create(&lru, 5, NULL);

// Insert some values
int *pi = lru_get_new(lru, "luke", strlen("luke"));
if (pi)
    *pi = 42;
pi = lru_get_new(lru, "leia", strlen("leia"));
if (pi)
    *pi = 24;

// Retrieve values
int *ret = lru_get_try(lru, "luke", strlen("luke"));
if (!ret) printf("luke dropped out!\n");
    else  printf("luke's number is %d\n", *ret);

char *enemies[] = {"goro", "raiden", "subzero", "scorpion"};
for (int i = 0; i < 4; ++i) {
    int *val = lru_get_new(lru, enemies[i], strlen(enemies[i]));
    if (val)
        *val = i;
}

// We're done
lru_free(lru);

Defines

lru_t(type): The type for LRU, parametrized by value type.

lru_create(ptable, max_slots, mm_ctx_array, mm_ctx)

Allocate and initialize an LRU with default associativity.

The real limit on the number of slots can be a bit larger but less than double.

Note

The pointers to memory contexts need to remain valid during the whole life of the structure (or be NULL).

Parameters

ptable -
pointer to a pointer to the LRU
max_slots -
number of slots
mm_ctx_array -
memory context to use for the huge array, NULL for default
mm_ctx -
memory context to use for individual key-value pairs, NULL for default

lru_free(table): Free an LRU created by lru_create (it can be NULL).

lru_reset(table): Reset an LRU to the empty state (but preserve any settings).

lru_get_try(table, key_, len_)

Find key in the LRU and return pointer to the corresponding value.

Return

pointer to data or NULL if not found

Parameters

table -
pointer to LRU
key_ -
lookup key
len_ -
key length

lru_get_new(table, key_, len_)

Return pointer to value, inserting if needed (zeroed).

Return

pointer to data or NULL (can be even if memory could be allocated!)

Parameters

table -
pointer to LRU
key_ -
lookup key
len_ -
key lengthkeys

lru_apply(table, function, baton)

Apply a function to every item in LRU.

Parameters

table -
pointer to LRU
function -
enum lru_apply_do (*function)(const char *key, uint len, val_type *val, void *baton) See enum lru_apply_do for the return type meanings.
baton -
extra pointer passed to each function invocation

lru_capacity(table)

Return the real capacity - maximum number of keys holdable within.

Parameters

table -
pointer to LRU

Enums

lru_apply_do enum

Possible actions to do with an element.

Values:

LRU_APPLY_DO_NOTHING -
LRU_APPLY_DO_EVICT -

Functions

uint round_power(uint size, uint power): Round the value up to a multiple of (1 << power).

Knot DNS Resolver library¶

Requirements¶

For users¶

For developers¶

Writing layers¶

APIs in Lua¶

Elementary types and constants¶

Working with domain names¶

Working with resource records¶

Working with packets¶

Working with requests¶

API reference¶

Name resolution¶

Cache¶

Nameservers¶

Modules¶

Utilities¶

Generics library¶

array¶

map¶

set¶

pack¶

lru¶

Name resolution ¶

Cache ¶

Nameservers ¶

Modules ¶

Utilities ¶

Generics library ¶