Knot Resolver library


  • 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.


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.


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 AWAIT_CUT forces driver to fetch zone cut information before the packet is consumed; setting a 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.AWAIT_CUT = true
        return state

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
                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.AWAIT_CUT = true
                        print('planned SOA query, yielding')
                        return kres.YIELD
                return state

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


FIXME: this dev-docs section is outdated! Better see comments in files instead, for now.

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


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.RESOLVED = true;
                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('')
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') }

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

local rrset = { ... }
local rr = rrset:get(0) -- Return first 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')

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

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.

-- Clear answer and write QUESTION
pkt:question('\7blocked', kres.class.IN, kres.type.SOA)
-- Start writing data
-- Nothing in answer
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 information about current query
        local current = req:current()
        print(current.stype, current.sclass,, current.flags)

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

local last = req:resolved()

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.AWAIT_CUT = true

-- Pop the query, this will erase it from resolution plan

Significant Lua API changes

Incompatible changes since 3.0.0

In the main kres.* lua binding, there was only change in struct knot_rrset_t:

  • constructor now accepts TTL as additional parameter (defaulting to zero)
  • add_rdata() doesn’t accept TTL anymore (and will throw an error if passed)

In case you used knot_* functions and structures bound to lua:

  • knot_dname_is_sub(a, b): knot_dname_in_bailiwick(a, b) > 0
  • knot_rdata_rdlen(): knot_rdataset_at().len
  • knot_rdata_data(): knot_rdataset_at().data
  • knot_rdata_array_size(): offsetof(struct knot_data_t, data) + knot_rdataset_at().len
  • struct knot_rdataset: field names were renamed to .count and .rdata
  • some functions got inlined from headers, but you can use their kr_* clones: kr_rrsig_sig_inception(), kr_rrsig_sig_expiration(), kr_rrsig_type_covered(). Note that these functions now accept knot_rdata_t* instead of a pair knot_rdataset_t* and size_t - you can use knot_rdataset_at() for that.
  • knot_rrset_add_rdata() doesn’t take TTL parameter anymore
  • knot_rrset_init_empty() was inlined, but in lua you can use the constructor
  • knot_rrset_ttl() was inlined, but in lua you can use :ttl() method instead
  • knot_pkt_qname(), _qtype(), _qclass(), _rr(), _section() were inlined, but in lua you can use methods instead, e.g. myPacket:qname()
  • knot_pkt_free() takes knot_pkt_t* instead of knot_pkt_t**, but from lua you probably didn’t want to use that; constructor ensures garbage collection.

API reference

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);

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



Initializer for an array of *_selected.


enum kr_rank

RRset rank - for cache and ranked_rr_*.

The rank meaning consists of one independent flag - KR_RANK_AUTH, and the rest have meaning of values where only one can hold at any time. You can use one of the enums as a safe initial value, optionally | KR_RANK_AUTH; otherwise it’s best to manipulate ranks via the kr_rank_* functions.

See also:
The representation is complicated by restrictions on integer comparison:
  • AUTH must be > than !AUTH
  • AUTH INSECURE must be > than AUTH (because it attempted validation)
  • !AUTH SECURE must be > than AUTH (because it’s valid)



Did not attempt to validate.

It’s assumed compulsory to validate (or prove insecure).


Do not attempt to validate.

(And don’t consider it a validation failure.)


Attempt to validate, but failures are non-fatal.


Unable to determine whether it should be secure.


Ought to be secure but isn’t.


Unable to obtain a good signature.


Proven to be insecure, i.e.

we have a chain of trust from TAs that cryptographically denies the possibility of existence of a positive chain of trust from the TAs to the record.


Authoritative data flag; the chain of authority was “verified”.

Even if not set, only in-bailiwick stuff is acceptable, i.e. almost authoritative (example: mandatory glue and its NS RR).


Verified whole chain of trust from the closest TA.


bool kr_rank_check(uint8_t rank)

Check that a rank value is valid.

Meant for assertions.

static bool kr_rank_test(uint8_t rank, uint8_t kr_flag)

Test the presence of any flag/state in a rank, i.e.

including KR_RANK_AUTH.

static void kr_rank_set(uint8_t * rank, uint8_t kr_flag)

Set the rank state.

The _AUTH flag is kept as it was.

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

Begin name resolution.

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.
CONSUME (expecting query)
  • 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())

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

any state
  • 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, const struct sockaddr * src, struct sockaddr * dst, int type, knot_pkt_t * packet)

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

The function must be called before actual sending of the request packet.
kr_ok() or error code
  • 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.

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

pointer to rplan
  • request: request state

KR_EXPORT KR_PURE knot_mm_t* kr_resolve_pool(struct kr_request * request)

Return memory pool associated with request.

  • request: request state

struct kr_context
#include <resolve.h>

Name resolution context.

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

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

Public Members

struct kr_qflags 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_rtt_lru_t* cache_rtt
unsigned cache_rtt_tout_retry_interval
kr_nsrep_lru_t* cache_rep
module_array_t* modules
struct kr_cookie_ctx cookie_ctx
int32_t tls_padding

See net.tls_padding in ../daemon/README.rst -1 is “true” (default policy), 0 is “false” (no padding)

knot_mm_t* pool
struct kr_request_qsource_flags

Public Members

bool tcp

true if the request is on TCP (or TLS); only meaningful if (dst_addr).

bool tls

true if the request is on TLS; only meaningful if (dst_addr).

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.

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 struct sockaddr* addr

Address that originated the request.

Current upstream address.

NULL for internal origin.

const struct sockaddr* dst_addr

Address that accepted the request.

NULL for internal origin.

const knot_pkt_t* packet
struct kr_request_qsource_flags flags

See definition above.

size_t size

query packet size

struct kr_request::@7 qsource
unsigned rtt

Current upstream RTT.

struct kr_request::@8 upstream

Upstream information, valid only in consume() phase.

struct kr_qflags options
int state
ranked_rr_array_t answ_selected
ranked_rr_array_t auth_selected
ranked_rr_array_t add_selected
rr_array_t additional
bool answ_validated

internal to validator; beware of caching, etc.

bool auth_validated

see answ_validated ^^ ; TODO

uint8_t rank

Overall rank for the request.

Values from kr_rank, currently just KR_RANK_SECURE and _INITIAL. Only read this in finish phase and after validator, please. Meaning of _SECURE: all RRs in answer+authority are _SECURE, including any negative results implied (NXDOMAIN, NODATA).

struct kr_rplan rplan
trace_log_f trace_log

Logging tracepoint.

trace_callback_f trace_finish

Request finish tracepoint.

int vars_ref

Reference to per-request variable table.

LUA_NOREF if not set.

knot_mm_t pool
unsigned int uid
void* daemon_context

for logging purposes only


typedef int32_t(* kr_stale_cb)(int32_t ttl, const knot_dname_t *owner, uint16_t type, const struct kr_query *qry)

Callback for serve-stale decisions.

the adjusted TTL (typically 1) or < 0.
  • ttl: the expired TTL (i.e. it’s < 0)


KR_EXPORT void kr_qflags_set(struct kr_qflags * fl1, struct kr_qflags fl2)

Combine flags together.

This means set union for simple flags.

KR_EXPORT void kr_qflags_clear(struct kr_qflags * fl1, struct kr_qflags fl2)

Remove flags.

This means set-theoretic difference.

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

Initialize resolution plan (empty).

  • 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.

  • 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)

true or false
  • 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.

This query serves as a cookie query only.
query instance or NULL
  • 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.

This means that this query takes precedence before all pending queries.
query instance or NULL
  • 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.

Popped queries are not discarded, but moved to the resolved list.
0 or an error
  • 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_last(struct kr_rplan * rplan)

Return last query (either currently being solved or last resolved).

This is necessary to retrieve the last query in case of resolution failures (e.g. time limit reached).

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

Check if a given query already resolved.

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

struct kr_qflags
#include <rplan.h>

Query flags.

Public Members


Don’t minimize QNAME.


No query/slow NS throttling.

bool NO_IPV6

Disable IPv6.

bool NO_IPV4

Disable IPv4.

bool TCP

Use TCP for this query.


Query is resolved.

Note that kr_query gets RESOLVED before following a CNAME chain; see .CNAME.


Query is waiting for A address.


Query is waiting for AAAA address.


Query is waiting for zone cut lookup.


Don’t use fancy stuff (EDNS, 0x20, …)


Query response is cached.


No cache for lookup; exception: finding NSs and subqueries.


Query response is cached, but expiring.


Allow queries to local or private address ranges.


Want DNSSEC secured answer; exception: +cd, i.e.



Query response is DNSSEC bogus.


Query response is DNSSEC insecure.


Instruction to set CD bit in request.

bool STUB

Stub resolution, accept received answer as solved.


Always recover zone cut (even if cached).


Query response has wildcard expansion.


Permissive resolver mode.


Strict resolver mode.


Query again because bad cookie returned.

bool CNAME

Query response contains CNAME in answer section.


Reorder cached RRs.

bool TRACE

Also log answers if verbose.

bool NO_0X20

Disable query case randomization .


DS non-existance is proven.


Closest encloser proof has optout.


Non-authoritative in-bailiwick records are enough.

TODO: utilize this also outside cache.


Forward all queries to upstream; validate answers.

bool DNS64_MARK

Internal mark for dns64 module.


Internal to cache module.


No valid NS found during last PRODUCE stage.

struct kr_query
#include <rplan.h>

Single query representation.

Public Members

struct kr_query* parent
knot_dname_t* sname

The name to resolve - lower-cased, uncompressed.

uint16_t stype
uint16_t sclass
uint16_t id
struct kr_qflags flags forward_flags
uint32_t secret
uint16_t fails
uint16_t reorder

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

uint64_t creation_time_mono
uint64_t timestamp_mono

Time of query created or time of query to upstream resolver (milliseconds).

struct timeval timestamp

Real time for TTL+DNSSEC checks (.tv_sec only).

struct kr_zonecut zone_cut
struct kr_layer_pickle* deferred
uint32_t uid

Query iteration number, unique within the kr_rplan.

struct kr_query* cname_parent

Pointer to the query that originated this one because of following a CNAME (or NULL).

struct kr_request* request

Parent resolution request.

kr_stale_cb stale_cb

See the type.

struct kr_nsrep ns
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.

Beware: order is significant ATM, as the last is the next one to solve, and they may be inter-dependent.

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).



int cache_peek(kr_layer_t * ctx, knot_pkt_t * pkt)
int cache_stash(kr_layer_t * ctx, knot_pkt_t * pkt)
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.

0 or an error code
  • 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.

This doesn’t clear the data, just closes the connection to the database.
  • cache: structure

KR_EXPORT int kr_cache_sync(struct kr_cache * cache)

Run after a row of operations to release transaction/lock if needed.

static bool kr_cache_is_open(struct kr_cache * cache)

Return true if cache is open and enabled.

static void kr_cache_make_checkpoint(struct kr_cache * cache)

(Re)set the time pair to the current values.

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

Insert RRSet into cache, replacing any existing data.

0 or an errcode
  • cache: cache structure
  • rr: inserted RRSet
  • rrsig: RRSIG for inserted RRSet (optional)
  • rank: rank of the data
  • timestamp: current time

KR_EXPORT int kr_cache_clear(struct kr_cache * cache)

Clear all items from the cache.

0 or an errcode
  • cache: cache structure

KR_EXPORT int kr_cache_peek_exact(struct kr_cache * cache, const knot_dname_t * name, uint16_t type, struct kr_cache_p * peek)
KR_EXPORT int32_t kr_cache_ttl(const struct kr_cache_p * peek, const struct kr_query * qry, const knot_dname_t * name, uint16_t type)
KR_EXPORT int kr_cache_materialize(knot_rdataset_t * dst, const struct kr_cache_p * ref, knot_mm_t * pool)
KR_EXPORT int kr_cache_remove(struct kr_cache * cache, const knot_dname_t * name, uint16_t type)

Remove an entry from cache.

number of deleted records, or negative error code
only “exact hits” are considered ATM, and some other information may be removed alongside.
  • cache: cache structure
  • name: dname
  • type: rr type

KR_EXPORT int kr_cache_match(struct kr_cache * cache, const knot_dname_t * name, bool exact_name, knot_db_val_t keyval[][2], int maxcount)

Get keys matching a dname lf prefix.

result count or an errcode
the cache keys are matched by prefix, i.e. it very much depends on their structure; CACHE_KEY_DEF.
  • cache: cache structure
  • name: dname
  • exact_name: whether to only consider exact name matches
  • keyval: matched key-value pairs
  • maxcount: limit on the number of returned key-value pairs

KR_EXPORT int kr_cache_remove_subtree(struct kr_cache * cache, const knot_dname_t * name, bool exact_name, int maxcount)

Remove a subtree in cache.

It’s like _match but removing them instead of returning.

number of deleted entries or an errcode

KR_EXPORT int kr_cache_closest_apex(struct kr_cache * cache, const knot_dname_t * name, bool is_DS, knot_dname_t ** apex)

Find the closest cached zone apex for a name (in cache).

the number of labels to remove from the name, or negative error code
timestamp is found by a syscall, and stale-serving is not considered
  • is_DS: start searching one name higher

KR_EXPORT int kr_unpack_cache_key(knot_db_val_t key, knot_dname_t * buf, uint16_t * type)

Unpack dname and type from db key.

length of dname or an errcode
only “exact hits” are considered ATM, moreover xNAME records are “hidden” as NS. (see comments in struct entry_h)
  • key: db key representation
  • buf: output buffer of domain name in dname format
  • type: output for type


const size_t PKT_SIZE_NOWIRE = -1

When knot_pkt is passed from cache without ->wire, this is the ->size.

KR_EXPORT const char* kr_cache_emergency_file_to_remove

Path to cache file to remove on critical out-of-space error.

(do NOT modify it)

struct kr_cache
#include <api.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

TTL limits.

struct timeval checkpoint_walltime

Wall time on the last check-point.

uint64_t checkpoint_monotime

Monotonic milliseconds on the last check-point.

struct kr_cache_p

Public Members

uint32_t time

The time of inception.

uint32_t ttl

TTL at inception moment.

Assuming it fits into int32_t ATM.

uint8_t rank

See enum kr_rank.

void* raw_data
void * raw_bound
struct kr_cache_p::@1 kr_cache_p::@2




See kr_nsrep_update_rtt()


If once NS was marked as “timeouted”, it won’t participate in NS elections at least KR_NS_TIMEOUT_RETRY_INTERVAL milliseconds (now: one second).



typedef struct kr_nsrep_rtt_lru_entry kr_nsrep_rtt_lru_entry_t


enum kr_ns_score

NS RTT score (special values).

RTT is measured in milliseconds.


KR_NS_FWD_TIMEOUT = (95 * 10000) / 100
enum kr_ns_rep

NS QoS flags.


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.

enum kr_ns_update_mode

NS RTT update modes.

First update is always KR_NS_RESET unless KR_NS_UPDATE_NORESET mode had choosen.



Update as smooth over last two measurements.


Same as KR_NS_UPDATE, but disable fallback to KR_NS_RESET on newly added entries.

Zero is used as initial value.


Set to given value.


Increment current value.


Set to maximum of current/proposed value.


typedef lru_t(kr_nsrep_rtt_lru_entry_t)

NS QoS tracking.

typedef lru_t(unsigned)

NS reputation tracking.

KR_EXPORT int kr_nsrep_set(struct kr_query * qry, size_t index, const struct sockaddr * sock)

Set given NS address.

(Very low-level access to the list.)

0 or an error code, in particular kr_error(ENOENT) for net.ipvX
  • qry: updated query
  • index: index of the updated target
  • sock: socket address to use (sockaddr_in or sockaddr_in6 or NULL)

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

Elect best nameserver/address pair from the nsset.

0 or an error code
  • 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.

0 or an error code
  • 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_rtt_lru_t * cache, int umode)

Update NS address RTT information.

In KR_NS_UPDATE mode reputation is smoothed over last N measurements.

0 on success, error code on failure
  • ns: updated NS representation
  • addr: chosen address (NULL for first)
  • score: new score (i.e. RTT), see enum kr_ns_score
  • cache: RTT 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.

0 on success, error code on failure
  • ns: updated NS representation
  • reputation: combined reputation flags, see enum kr_ns_rep
  • cache: LRU cache

int kr_nsrep_copy_set(struct kr_nsrep * dst, const struct kr_nsrep * src)

Copy NSSET reputation information and resets score.

0 on success, error code on failure
  • dst: updated NS representation
  • src: source NS representation

KR_EXPORT int kr_nsrep_sort(struct kr_nsrep * ns, struct kr_context * ctx)

Sort addresses in the query nsrep list by cached RTT.

if RTT is greater then KR_NS_TIMEOUT, address will placed at the beginning of the nsrep list once in cache.ns_tout() milliseconds. Otherwise it will be sorted as if it has cached RTT equal to KR_NS_MAX_SCORE + 1.

0 or an error code
ns reputation is zeroed and score is set to KR_NS_MAX_SCORE + 1.
  • ns: updated kr_nsrep
  • ctx: name resolution context.

struct kr_nsrep_rtt_lru_entry

Public Members

unsigned score
uint64_t tout_timestamp
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.

union inaddr kr_nsrep::addr[KR_NSREP_MAXADDR]

NS address(es)


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.

0 or error code
  • cut: zone cut
  • name:
  • pool:

KR_EXPORT void kr_zonecut_deinit(struct kr_zonecut * cut)

Clear the structure and free the address set.

  • cut: zone cut

KR_EXPORT void kr_zonecut_move(struct kr_zonecut * to, const struct kr_zonecut * from)

Move a zonecut, transferring ownership of any pointed-to memory.

  • to: the target - it gets deinit-ed
  • from: the source - not modified, but shouldn’t be used afterward

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.

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

0 or an error code; If it fails with kr_error(ENOMEM), it may be in a half-filled state, but it’s safe to deinit…
addresses for names in src get replaced and others are left as they were.
  • 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.

0 or an error code
  • dst: destination zone cut
  • src: source zone cut

KR_EXPORT int kr_zonecut_add(struct kr_zonecut * cut, const knot_dname_t * ns, const void * data, int len)

Add address record to the zone cut.

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

0 or error code
  • cut: zone cut to be populated
  • ns: nameserver name
  • data: typically knot_rdata_t::data
  • len: typically knot_rdata_t::len

KR_EXPORT int kr_zonecut_del(struct kr_zonecut * cut, const knot_dname_t * ns, const void * data, int len)

Delete nameserver/address pair from the zone cut.

0 or error code
  • cut:
  • ns: name server name
  • data: typically knot_rdata_t::data
  • len: typically knot_rdata_t::len

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

Delete all addresses associated with the given name.

0 or error code
  • 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.

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

0 or error code
  • 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, const struct kr_query * qry, bool *restrict secured)

Populate zone cut address set from cache.

0 or error code (ENOENT if it doesn’t find anything)
  • ctx: resolution context (to fetch data from LRU caches)
  • cut: zone cut to be populated
  • name: QNAME to start finding zone cut for
  • qry: query for timestamp and stale-serving decisions
  • secured: set to true if want secured zone cut, will return false if it is provably insecure

KR_EXPORT bool kr_zonecut_is_empty(struct kr_zonecut * cut)

Check if any address is present in the zone cut.

  • cut: zone cut to check

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.

trie_t* nsset

Map of nameserver => address_set (pack_t).

knot_mm_t* pool

Memory pool.


Module API definition and functions for (un)loading modules.



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

  • module: module name (f.e. hints)



typedef uint32_t( module_api_cb)(void)
typedef char*( kr_prop_cb)(void *env, struct kr_module *self, const char *input)

Module property callback.

Input and output is passed via a JSON encoded in a string.

a free-form JSON output (malloc-ated)
see l_trampoline() implementation for details about the input/output conversion.
  • env: pointer to the lua engine, i.e. struct engine *env (TODO: explicit type)
  • input: parameter (NULL if missing/nil on lua level)


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

Load a C module instance into memory.

0 or an error
  • module: module structure
  • name: module name
  • path: module search path

KR_EXPORT void kr_module_unload(struct kr_module * module)

Unload module instance.

  • module: module structure

KR_EXPORT const struct kr_module* kr_module_embedded(const char * name)

Get embedded module prototype by name (or NULL).

struct kr_module
#include <module.h>

Module representation.

The five symbols (init, …) may be defined by the module as name_init(), etc; all are optional and missing symbols are represented as NULLs;

Public Members

char* name
intinit)(struct kr_module *self)


Called after loading the module.

error code.

intdeinit)(struct kr_module *self)


Called before unloading the module.

error code.

intconfig)(struct kr_module *self, const char *input)

Configure with encoded JSON (NULL if missing).

error code.

const kr_layer_api_t*layer)(struct kr_module *self)

Get a pointer to packet processing API specs.

See docs on that type.

const struct kr_prop*props)(void)

Get a pointer to list of properties, terminated by { NULL, NULL, NULL }.

void* lib

Shared library handle or RTLD_DEFAULT.

void* data

Custom data context.

struct kr_prop
#include <module.h>

Module property (named callable).

Public Members

kr_prop_cb* cb
const char* name
const char* info




Return true if the query has request log handler installed.


Block run in verbose mode; optimized when not run.

KR_DNAME_GET_STR(dname_str, dname)
KR_RRTYPE_GET_STR(rrtype_str, rrtype)
static_assert(cond, msg)
SWAP(x, y)

Swap two places.

Note: the parameters need to be without side effects.


typedef void(* trace_callback_f)(struct kr_request *request)

Callback for request events.

typedef void(* trace_log_f)(const struct kr_query *query, const char *source, const char *msg)

Callback for request logging handler.


KR_EXPORT bool kr_verbose_set(bool status)

Set verbose mode.

Not available if compiled with -DNOVERBOSELOG.


Log a message if in verbose mode.


Utility for QRVERBOSE - use that instead.

Log a message through the request log handler.

true if the message was logged
  • query: current query
  • source: message source
  • fmt: message format

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

Return time difference in miliseconds.

based on the _BSD_SOURCE timersub() macro

KR_EXPORT char* kr_strcatdup(unsigned n, ...)

Concatenate N strings.

KR_EXPORT void kr_rnd_buffered(void * data, unsigned int size)

You probably want kr_rand_* convenience functions instead.

This is a buffered version of gnutls_rnd(GNUTLS_RND_NONCE, ..)

static uint64_t kr_rand_bytes(unsigned int size)

Return a few random bytes.

static bool kr_rand_coin(unsigned int nomin, unsigned int denomin)

Throw a pseudo-random coin, succeeding approximately with probability nomin/denomin.

  • low precision, only one byte of randomness (or none with extreme parameters)
  • tip: use !kr_rand_coin() to get the complementary probability

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 void kr_pkt_make_auth_header(knot_pkt_t * pkt)

Set packet header suitable for authoritative answer.

(for policy module)

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, i.e.

sizeof(struct in*_addr).

KR_EXPORT KR_PURE int kr_sockaddr_len(const struct sockaddr * addr)

Sockaddr length for given family, i.e.

sizeof(struct sockaddr_in*).

KR_EXPORT KR_PURE int kr_sockaddr_cmp(const struct sockaddr * left, const struct sockaddr * right)

Compare two given sockaddr.

return 0 - addresses are equal, error code otherwise.

KR_EXPORT KR_PURE uint16_t kr_inaddr_port(const struct sockaddr * addr)


KR_EXPORT void kr_inaddr_set_port(struct sockaddr * addr, uint16_t port)

Set port.

KR_EXPORT int kr_inaddr_str(const struct sockaddr * addr, char * buf, size_t * buflen)

Write string representation for given address as “<addr>#<port>”.

  • addr: the raw address
  • buf: the buffer for output string
  • buflen: the available(in) and utilized(out) length, including \0

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 (struct in*_addr).

KR_EXPORT struct sockaddr* kr_straddr_socket(const char * addr, int port)

Create a sockaddr* from string+port representation (also accepts IPv6 link-local).

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

Parse address and return subnet length (bits).

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

KR_EXPORT int kr_straddr_split(const char * addr, char * buf, size_t buflen, uint16_t * port)

Splits ip address specified as “addr@port” or “addr#port” into addr and port and performs validation.

if #port part isn’t present, then port will be set to 0. buf and port can be set to NULL.
kr_error(EINVAL) - addr part doesn’t contains valid ip address or #port part is out-of-range (either < 0 either > UINT16_MAX) kr_error(ENOSP) - buflen is too small

KR_EXPORT int kr_straddr_join(const char * addr, uint16_t port, char * buf, size_t * buflen)

Formats ip address and port in “addr#port” format.

and performs validation.

Port always formatted as five-character string with leading zeros.
kr_error(EINVAL) - addr or buf is NULL or buflen is 0 or addr doesn’t contain a valid ip address kr_error(ENOSP) - buflen is too small

KR_EXPORT KR_PURE int kr_bitcmp(const char * a, const char * b, int bits)

Compare memory bitwise.

The semantics is “the same” as for memcmp(). The partial byte is considered with more-significant bits first, so this is e.g. suitable for comparing IP prefixes.

static uint8_t KEY_FLAG_RANK(const char * key)
static bool KEY_COVERING_RRSIG(const char * key)
KR_EXPORT int kr_rrkey(char * key, uint16_t class, const knot_dname_t * owner, uint16_t type, uint16_t additional)

Create unique null-terminated string key for RR.

key length if successful or an error
  • key: Destination buffer for key size, MUST be KR_RRKEY_LEN or larger.
  • class: RR class.
  • owner: RR owner name.
  • type: RR type.
  • additional: flags (for instance can be used for storing covered type when RR type is RRSIG).

KR_EXPORT 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, bool check_dups, bool(*extraCheck)(const ranked_rr_array_entry_t *))
KR_PURE char* kr_pkt_text(const knot_pkt_t * pkt)
KR_PURE char* kr_rrset_text(const knot_rrset_t * rr)
static KR_PURE char* kr_dname_text(const knot_dname_t * name)
static KR_CONST char* kr_rrtype_text(const uint16_t rrtype)
KR_EXPORT char* kr_module_call(struct kr_context * ctx, const char * module, const char * prop, const char * input)

Call module property.

static uint16_t kr_rrset_type_maysig(const knot_rrset_t * rr)

Return the (covered) type of an nonempty RRset.

static const char* lua_push_printf(lua_State * L, const char * fmt, ...)

Printf onto the lua stack, avoiding additional copy (thin wrapper).

static char* kr_straddr(const struct sockaddr * addr)
KR_EXPORT uint64_t kr_now()

The current time in monotonic milliseconds.

it may be outdated in case of long callbacks; see uv_now().

int knot_dname_lf2wire(knot_dname_t * dst, uint8_t len, const uint8_t * lf)

Convert name from lookup format to wire.

See knot_dname_lf

len bytes are read and len+1 are written with normal LF, but it’s also allowed that the final zero byte is omitted in LF.
the number of bytes written (>0) or error code (<0)

static int kr_dname_lf(uint8_t * dst, const knot_dname_t * src, bool add_wildcard)

Patched knot_dname_lf.

LF for “.” has length zero instead of one, for consistency. (TODO: consistency?)

packet is always NULL
  • add_wildcard: append the wildcard label

KR_EXPORT const char* kr_strptime_diff(const char * format, const char * time1_str, const char * time0_str, double * diff)

Difference between two calendar times specified as strings.

  • format[in]: format for strptime
  • diff[out]: result from C difftime(time1, time0)

KR_EXPORT void kr_rrset_init(knot_rrset_t * rrset, knot_dname_t * owner, uint16_t type, uint16_t rclass, uint32_t ttl)
KR_EXPORT uint16_t kr_pkt_qclass(const knot_pkt_t * pkt)
KR_EXPORT uint16_t kr_pkt_qtype(const knot_pkt_t * pkt)
KR_EXPORT uint32_t kr_rrsig_sig_inception(const knot_rdata_t * rdata)
KR_EXPORT uint32_t kr_rrsig_sig_expiration(const knot_rdata_t * rdata)
KR_EXPORT uint16_t kr_rrsig_type_covered(const knot_rdata_t * rdata)


KR_EXPORT bool kr_verbose_status

Whether in verbose mode.

Only use this for reading.

KR_EXPORT KR_EXPORT const char* cls
KR_EXPORT const char const char * fmt
KR_EXPORT const char* source
const uint8_t KEY_FLAG_RRSIG = 0x02
union inaddr
#include <utils.h>

Simple storage for IPx address or AF_UNSPEC.

Public Members

struct sockaddr ip
struct sockaddr_in ip4
struct sockaddr_in6 ip6




typedef unsigned int uint


static int KR_COLD kr_error(int x)

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.
  • queue - a FIFO + LIFO queue.
  • map - a Crit-bit tree key-value map implementation (public domain) that comes with tests.
  • set - set abstraction implemented on top of map (unused now).
  • pack - length-prefixed list of objects (i.e. array-list).
  • lru - LRU-like hash table
  • trie - a trie-based key-value map, taken from knot-dns


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

MIN(array_push(arr, val), other)
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;

// 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) {

// Random delete
array_del(arr, 0);



Declare an array structure.


Zero-initialize the array.


Free and zero-initialize the array (plain malloc/free).

array_clear_mm(array, free, baton)

Make the array empty and free pointed-to memory.

Mempool usage: pass mm_free and a knot_mm_t* .

array_reserve(array, n)

Reserve capacity for at least n elements.

0 if success, <0 on failure

array_reserve_mm(array, n, reserve, baton)

Reserve capacity for at least n elements.

Mempool usage: pass kr_memreserve and a knot_mm_t* .

0 if success, <0 on failure

array_push_mm(array, val, reserve, baton)

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

Mempool usage: pass kr_memreserve and a knot_mm_t* .

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

array_push(array, val)

Push value at the end of the array, resize it if necessary (plain malloc/free).

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


Pop value from the end of the array.

array_del(array, i)

Remove value at given index.

0 on success, <0 on failure


Return last element of the array.

Undefined if the array is empty.


static size_t array_next_count(size_t want)

Simplified Qt containers growth strategy.

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


A queue, usable for FIFO and LIFO simultaneously.

Both the head and tail of the queue can be accessed and pushed to, but only the head can be popped from.

Example usage:

// define new queue type, and init a new queue instance
typedef queue_t(int) queue_int_t;
queue_int_t q;
// do some operations
queue_push(q, 1);
queue_push(q, 2);
queue_push(q, 3);
queue_push(q, 4);
assert(queue_head(q) == 2);
assert(queue_tail(q) == 4);

// you may iterate
typedef queue_it_t(int) queue_it_int_t;
for (queue_it_int_t it = queue_it_begin(q); !queue_it_finished(it);
     queue_it_next(it)) {
assert(queue_tail(q) == 5);

queue_push_head(q, 0);
assert(queue_tail(q) == 6);
// free it up

// you may use dynamic allocation for the type itself
queue_int_t *qm = malloc(sizeof(queue_int_t));
The implementation uses a singly linked list of blocks where each block stores an array of values (for better efficiency).



The type for queue, parametrized by value type.


Initialize a queue.

You can malloc() it the usual way.


De-initialize a queue: make it invalid and free any inner allocations.

queue_push(q, data)

Push data to queue’s tail.

(Type-safe version; use _impl() otherwise.)

queue_push_head(q, data)

Push data to queue’s head.

(Type-safe version; use _impl() otherwise.)


Remove the element at the head.

The queue must not be empty.


Return a “reference” to the element at the head (it’s an L-value).

The queue must not be empty.


Return a “reference” to the element at the tail (it’s an L-value).

The queue must not be empty.


Return the number of elements in the queue (very efficient).


Type for queue iterator, parametrized by value type.

It’s a simple structure that owns no other resources. You may NOT use it after doing any push or pop (without _begin again).


Initialize a queue iterator at the head of the queue.

If you use this in assignment (instead of initialization), you will unfortunately need to add corresponding type-cast in front. Beware: there’s no type-check between queue and iterator!


Return a “reference” to the current element (it’s an L-value) .


Test if the iterator has gone past the last element.

If it has, you may not use _val or _next.


Advance the iterator to the next element.


A Crit-bit tree key-value map implementation.

Example usage:

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

map_t map = map_make(NULL);

// 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) {

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

// 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_walk(map, callback, baton)


static map_t map_make(struct knot_mm * pool)

Creates an new empty critbit map.

Pass NULL for malloc+free.

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.

Note: NULL may mean two different things.

int map_set(map_t * map, const char * str, void * val)

Inserts str into map.

Returns 0 if new, 1 if replaced, or ENOMEM.

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(*callback)(const char *, void *, void *), void * baton)

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

Returns value immediately if a callback returns nonzero.

  • 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
struct knot_mm* pool


A set abstraction implemented on top of map.

Example usage:

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

set_t set = set_make(NULL);

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

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

// 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



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 if new, 1 if already present, or ENOMEM.

set_del(set, str)

Deletes str from the set, returns 0 on suceess


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


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


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:

Maximum object size is 2^16 bytes, see pack_objlen_t If some mistake happens somewhere, the access may end up in an infinite loop. (equality comparison on pointers)

pack_t 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);




Zero-initialize the pack.


Make the pack empty and free pointed-to memory (plain malloc/free).

pack_clear_mm(pack, free, baton)

Make the pack empty and free pointed-to memory.

Mempool usage: pass mm_free and a knot_mm_t* .

pack_reserve(pack, objs_count, objs_len)

Reserve space for additional objects in the pack (plain malloc/free).

0 if success, <0 on failure

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

Reserve space for additional objects in the pack.

Mempool usage: pass kr_memreserve and a knot_mm_t* .

0 if success, <0 on failure


Return pointer to first packed object.

Recommended way to iterate: for (uint8_t *it = pack_head(pack); it != pack_tail(pack); it = pack_obj_next(it))


Return pack end pointer.


typedef uint16_t pack_objlen_t

Packed object length type.


typedef array_t(uint8_t)

Pack is defined as an array of bytes.

static pack_objlen_t pack_obj_len(uint8_t * it)

Return packed object length.

static uint8_t* pack_obj_val(uint8_t * it)

Return packed object value.

static uint8_t* pack_obj_next(uint8_t * it)

Return pointer to next packed object.

static uint8_t* pack_last(pack_t pack)

Return pointer to the last packed object.

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

Push object to the end of the pack.

0 on success, negative number on failure

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

Returns a pointer to packed object.

pointer to packed object or NULL

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

Delete object from the pack.

0 on success, negative number on failure

static int pack_clone(pack_t ** dst, const pack_t * src, knot_mm_t * pool)

Clone a pack, replacing destination pack; (*dst == NULL) is valid input.

kr_error(ENOMEM) on allocation failure.


A lossy cache.

Example usage:

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

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

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

// Retrieve values
int *ret = lru_get_try(lru, "luke", strlen("luke"), NULL);
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]), NULL);
    if (val)
        *val = i;

// We're done
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.



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.

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


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


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.

pointer to data or NULL if not found
  • table: pointer to LRU
  • key_: lookup key
  • len_: key length

lru_get_new(table, key_, len_, is_new)

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

pointer to data or NULL (can be even if memory could be allocated!)
  • table: pointer to LRU
  • key_: lookup key
  • len_: key lengthkeys
  • is_new: pointer to bool to store result of operation (true if entry is newly added, false otherwise; can be NULL).

lru_apply(table, function, baton)

Apply a function to every item in LRU.

  • 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


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

  • table: pointer to LRU


enum lru_apply_do

Possible actions to do with an element.




static uint round_power(uint size, uint power)

Round the value up to a multiple of (1 << power).



typedef void* trie_val_t

Native API of QP-tries:

  • keys are char strings, not necessarily zero-terminated, the structure copies the contents of the passed keys
  • values are void* pointers, typically you get an ephemeral pointer to it
  • key lengths are limited by 2^32-1 ATM

XXX EDITORS: trie.{h,c} are synced from only with tiny adjustments, mostly #includes and KR_EXPORT.

Element value.

typedef struct trie trie_t

Opaque structure holding a QP-trie.

typedef struct trie_it trie_it_t

Opaque type for holding a QP-trie iterator.


KR_EXPORT trie_t* trie_create(knot_mm_t * mm)

Create a trie instance. Pass NULL to use malloc+free.

KR_EXPORT void trie_free(trie_t * tbl)

Free a trie instance.

KR_EXPORT void trie_clear(trie_t * tbl)

Clear a trie instance (make it empty).

KR_EXPORT size_t trie_weight(const trie_t * tbl)

Return the number of keys in the trie.

KR_EXPORT trie_val_t* trie_get_try(trie_t * tbl, const char * key, uint32_t len)

Search the trie, returning NULL on failure.

KR_EXPORT trie_val_t* trie_get_first(trie_t * tbl, char ** key, uint32_t * len)

Return pointer to the minimum. Optionally with key and its length.

KR_EXPORT trie_val_t* trie_get_ins(trie_t * tbl, const char * key, uint32_t len)

Search the trie, inserting NULL trie_val_t on failure.

KR_EXPORT int trie_get_leq(trie_t * tbl, const char * key, uint32_t len, trie_val_t ** val)

Search for less-or-equal element.

KNOT_EOK for exact match, 1 for previous, KNOT_ENOENT for not-found, or KNOT_E*.
  • tbl: Trie.
  • key: Searched key.
  • len: Key length.
  • val: Must be valid; it will be set to NULL if not found or errored.

int trie_apply(trie_t * tbl, int(*f)(trie_val_t *, void *), void * d)

Apply a function to every trie_val_t, in order.

First nonzero from f() or zero (i.e. KNOT_EOK).
  • d: Parameter passed as the second argument to f().

KR_EXPORT int trie_del(trie_t * tbl, const char * key, uint32_t len, trie_val_t * val)

Remove an item, returning KNOT_EOK if succeeded or KNOT_ENOENT if not found.

If val!=NULL and deletion succeeded, the deleted value is set.

KR_EXPORT int trie_del_first(trie_t * tbl, char * key, uint32_t * len, trie_val_t * val)

Remove the first item, returning KNOT_EOK on success.

You may optionally get the key and/or value. The key is copied, so you need to pass sufficient len, otherwise kr_error(ENOSPC) is returned.

KR_EXPORT trie_it_t* trie_it_begin(trie_t * tbl)

Create a new iterator pointing to the first element (if any).

KR_EXPORT void trie_it_next(trie_it_t * it)

Advance the iterator to the next element.

Iteration is in ascending lexicographical order. In particular, the empty string would be considered as the very first.

You may not use this function if the trie’s key-set has been modified during the lifetime of the iterator (modifying values only is OK).

KR_EXPORT bool trie_it_finished(trie_it_t * it)

Test if the iterator has gone past the last element.

KR_EXPORT void trie_it_free(trie_it_t * it)

Free any resources of the iterator. It’s OK to call it on NULL.

KR_EXPORT const char* trie_it_key(trie_it_t * it, size_t * len)

Return pointer to the key of the current element.

The optional len is uint32_t internally but size_t is better for our usage, as it is without an additional type conversion.

KR_EXPORT trie_val_t* trie_it_val(trie_it_t * it)

Return pointer to the value of the current element (writable).