DNS

This module includes functions that control DNS communication.

Summary

The functions in this module are available only if feature OPENTHREAD_CONFIG_DNS_CLIENT_ENABLE is enabled.

Enumerations
otDnsNat64Mode{
  OT_DNS_NAT64_UNSPECIFIED = 0,
  OT_DNS_NAT64_ALLOW = 1,
  OT_DNS_NAT64_DISALLOW = 2
} 		enum
Type represents the NAT64 mode in an otDnsQueryConfig.
otDnsRecursionFlag{
  OT_DNS_FLAG_UNSPECIFIED = 0,
  OT_DNS_FLAG_RECURSION_DESIRED = 1,
  OT_DNS_FLAG_NO_RECURSION = 2
} 		enum
Type represents the "Recursion Desired" (RD) flag in an otDnsQueryConfig.
otDnsServiceMode{
  OT_DNS_SERVICE_MODE_UNSPECIFIED = 0,
  OT_DNS_SERVICE_MODE_SRV = 1,
  OT_DNS_SERVICE_MODE_TXT = 2,
  OT_DNS_SERVICE_MODE_SRV_TXT = 3,
  OT_DNS_SERVICE_MODE_SRV_TXT_SEPARATE = 4,
  OT_DNS_SERVICE_MODE_SRV_TXT_OPTIMIZE = 5
} 		enum
Type represents the service resolution mode in an otDnsQueryConfig.
otDnsTransportProto{
  OT_DNS_TRANSPORT_UDP = 1,
  OT_DNS_TRANSPORT_TCP = 2
} 		enum
Type represents the DNS transport protocol in an otDnsQueryConfig.

Typedefs
otDnsAddressCallback)(otError aError, const otDnsAddressResponse *aResponse, void *aContext) typedef
void(*
Pointer is called when a DNS response is received for an address resolution query.
otDnsAddressResponse typedef
An opaque representation of a response to an address resolution DNS query.
otDnsBrowseCallback)(otError aError, const otDnsBrowseResponse *aResponse, void *aContext) typedef
void(*
Pointer is called when a DNS response is received for a browse (service instance enumeration) query.
otDnsBrowseResponse typedef
An opaque representation of a response to a browse (service instance enumeration) DNS query.
otDnsQueryConfig typedef
Represents a DNS query configuration.
otDnsServiceCallback)(otError aError, const otDnsServiceResponse *aResponse, void *aContext) typedef
void(*
Pointer is called when a DNS response is received for a service instance resolution query.
otDnsServiceInfo typedef
Provides info for a DNS service instance.
otDnsServiceResponse typedef
An opaque representation of a response to a service instance resolution DNS query.
otDnsTxtEntry typedef
struct otDnsTxtEntry
Represents a TXT record entry representing a key/value pair (RFC 6763 - section 6.3).
otDnsTxtEntryIterator typedef
Represents an iterator for TXT record entries (key/value pairs).

Functions
otDnsAddressResponseGetAddress(const otDnsAddressResponse *aResponse, uint16_t aIndex, otIp6Address *aAddress, uint32_t *aTtl)
Gets an IPv6 address associated with an address resolution DNS response.
otDnsAddressResponseGetHostName(const otDnsAddressResponse *aResponse, char *aNameBuffer, uint16_t aNameBufferSize)
Gets the full host name associated with an address resolution DNS response.
otDnsBrowseResponseGetHostAddress(const otDnsBrowseResponse *aResponse, const char *aHostName, uint16_t aIndex, otIp6Address *aAddress, uint32_t *aTtl)
Gets the host IPv6 address from a DNS browse (service instance enumeration) response.
otDnsBrowseResponseGetServiceInfo(const otDnsBrowseResponse *aResponse, const char *aInstanceLabel, otDnsServiceInfo *aServiceInfo)
Gets info for a service instance from a DNS browse (service instance enumeration) response.
otDnsBrowseResponseGetServiceInstance(const otDnsBrowseResponse *aResponse, uint16_t aIndex, char *aLabelBuffer, uint8_t aLabelBufferSize)
Gets a service instance associated with a DNS browse (service instance enumeration) response.
otDnsBrowseResponseGetServiceName(const otDnsBrowseResponse *aResponse, char *aNameBuffer, uint16_t aNameBufferSize)
Gets the service name associated with a DNS browse (service instance enumeration) response.
otDnsClientBrowse(otInstance *aInstance, const char *aServiceName, otDnsBrowseCallback aCallback, void *aContext, const otDnsQueryConfig *aConfig)
Sends a DNS browse (service instance enumeration) query for a given service name.
otDnsClientGetDefaultConfig(otInstance *aInstance)
Gets the current default query config used by DNS client.
otDnsClientResolveAddress(otInstance *aInstance, const char *aHostName, otDnsAddressCallback aCallback, void *aContext, const otDnsQueryConfig *aConfig)
Sends an address resolution DNS query for AAAA (IPv6) record(s) for a given host name.
otDnsClientResolveIp4Address(otInstance *aInstance, const char *aHostName, otDnsAddressCallback aCallback, void *aContext, const otDnsQueryConfig *aConfig)
Sends an address resolution DNS query for A (IPv4) record(s) for a given host name.
otDnsClientResolveService(otInstance *aInstance, const char *aInstanceLabel, const char *aServiceName, otDnsServiceCallback aCallback, void *aContext, const otDnsQueryConfig *aConfig)
Starts a DNS service instance resolution for a given service instance.
otDnsClientResolveServiceAndHostAddress(otInstance *aInstance, const char *aInstanceLabel, const char *aServiceName, otDnsServiceCallback aCallback, void *aContext, const otDnsQueryConfig *aConfig)
Starts a DNS service instance resolution for a given service instance, with a potential follow-up address resolution for the host name discovered for the service instance.
otDnsClientSetDefaultConfig(otInstance *aInstance, const otDnsQueryConfig *aConfig)
void
Sets the default query config on DNS client.
otDnsGetNextTxtEntry(otDnsTxtEntryIterator *aIterator, otDnsTxtEntry *aEntry)
Parses the TXT data from an iterator and gets the next TXT record entry (key/value pair).
otDnsInitTxtEntryIterator(otDnsTxtEntryIterator *aIterator, const uint8_t *aTxtData, uint16_t aTxtDataLength)
void
Initializes a TXT record iterator.
otDnsIsNameCompressionEnabled(void)
bool
Indicates whether the "DNS name compression" mode is enabled or not.
otDnsServiceResponseGetHostAddress(const otDnsServiceResponse *aResponse, const char *aHostName, uint16_t aIndex, otIp6Address *aAddress, uint32_t *aTtl)
Gets the host IPv6 address from a DNS service instance resolution response.
otDnsServiceResponseGetServiceInfo(const otDnsServiceResponse *aResponse, otDnsServiceInfo *aServiceInfo)
Gets info for a service instance from a DNS service instance resolution response.
otDnsServiceResponseGetServiceName(const otDnsServiceResponse *aResponse, char *aLabelBuffer, uint8_t aLabelBufferSize, char *aNameBuffer, uint16_t aNameBufferSize)
Gets the service instance name associated with a DNS service instance resolution response.
otDnsSetNameCompressionEnabled(bool aEnabled)
void
Enables/disables the "DNS name compression" mode.

Structs
otDnsQueryConfig

Represents a DNS query configuration.

otDnsServiceInfo

Provides info for a DNS service instance.

otDnsTxtEntry

Represents a TXT record entry representing a key/value pair (RFC 6763 - section 6.3).

otDnsTxtEntryIterator

Represents an iterator for TXT record entries (key/value pairs).

Enumerations

otDnsNat64Mode

 otDnsNat64Mode

Type represents the NAT64 mode in an otDnsQueryConfig.

The NAT64 mode indicates whether to allow or disallow NAT64 address translation during DNS client address resolution. This mode is only used when OPENTHREAD_CONFIG_DNS_CLIENT_NAT64_ENABLE is enabled.

Properties
OT_DNS_NAT64_ALLOW

Allow NAT64 address translation during DNS client address resolution.

OT_DNS_NAT64_DISALLOW

Do not allow NAT64 address translation during DNS client address resolution.

OT_DNS_NAT64_UNSPECIFIED

NAT64 mode is not specified. Use default NAT64 mode.

otDnsRecursionFlag

 otDnsRecursionFlag

Type represents the "Recursion Desired" (RD) flag in an otDnsQueryConfig.

Properties
OT_DNS_FLAG_NO_RECURSION

Indicates DNS name server can not resolve the query recursively.

OT_DNS_FLAG_RECURSION_DESIRED

Indicates DNS name server can resolve the query recursively.

OT_DNS_FLAG_UNSPECIFIED

Indicates the flag is not specified.

otDnsServiceMode

 otDnsServiceMode

Type represents the service resolution mode in an otDnsQueryConfig.

This is only used during DNS client service resolution otDnsClientResolveService(). It determines which record types to query.

Properties
OT_DNS_SERVICE_MODE_SRV

Query for SRV record only.

OT_DNS_SERVICE_MODE_SRV_TXT

Query for both SRV and TXT records in same message.

OT_DNS_SERVICE_MODE_SRV_TXT_OPTIMIZE

Query for TXT/SRV together first, if fails then query separately.

OT_DNS_SERVICE_MODE_SRV_TXT_SEPARATE

Query in parallel for SRV and TXT using separate messages.

OT_DNS_SERVICE_MODE_TXT

Query for TXT record only.

OT_DNS_SERVICE_MODE_UNSPECIFIED

Mode is not specified. Use default service mode.

otDnsTransportProto

 otDnsTransportProto

Type represents the DNS transport protocol in an otDnsQueryConfig.

This OT_DNS_TRANSPORT_TCP is only supported when OPENTHREAD_CONFIG_DNS_CLIENT_OVER_TCP_ENABLE is enabled.

Properties
OT_DNS_TRANSPORT_TCP

DNS query should be sent via UDP.

OT_DNS_TRANSPORT_UDP

DNS transport is unspecified.

Typedefs

otDnsAddressCallback

void(* otDnsAddressCallback)(otError aError, const otDnsAddressResponse *aResponse, void *aContext)

Pointer is called when a DNS response is received for an address resolution query.

Within this callback the user can use otDnsAddressResponseGet{Item}() functions along with the aResponse pointer to get more info about the response.

The aResponse pointer can only be used within this callback and after returning from this function it will not stay valid, so the user MUST NOT retain the aResponse pointer for later use.

The aError can have the following:

Details
Parameters
[in] aError
The result of the DNS transaction.
[in] aResponse
A pointer to the response (it is always non-NULL).
[in] aContext
A pointer to application-specific context.

  • OT_ERROR_NONE A response was received successfully.
  • OT_ERROR_ABORT A DNS transaction was aborted by stack.
  • OT_ERROR_RESPONSE_TIMEOUT No DNS response has been received within timeout.

If the server rejects the address resolution request the error code from server is mapped as follow:

  • (0) NOERROR Success (no error condition) -> OT_ERROR_NONE
  • (1) FORMERR Server unable to interpret due to format error -> OT_ERROR_PARSE
  • (2) SERVFAIL Server encountered an internal failure -> OT_ERROR_FAILED
  • (3) NXDOMAIN Name that ought to exist, does not exist -> OT_ERROR_NOT_FOUND
  • (4) NOTIMP Server does not support the query type (OpCode) -> OT_ERROR_NOT_IMPLEMENTED
  • (5) REFUSED Server refused for policy/security reasons -> OT_ERROR_SECURITY
  • (6) YXDOMAIN Some name that ought not to exist, does exist -> OT_ERROR_DUPLICATED
  • (7) YXRRSET Some RRset that ought not to exist, does exist -> OT_ERROR_DUPLICATED
  • (8) NXRRSET Some RRset that ought to exist, does not exist -> OT_ERROR_NOT_FOUND
  • (9) NOTAUTH Service is not authoritative for zone -> OT_ERROR_SECURITY
  • (10) NOTZONE A name is not in the zone -> OT_ERROR_PARSE
  • (20) BADNAME Bad name -> OT_ERROR_PARSE
  • (21) BADALG Bad algorithm -> OT_ERROR_SECURITY
  • (22) BADTRUN Bad truncation -> OT_ERROR_PARSE
  • Other response codes -> OT_ERROR_FAILED

otDnsAddressResponse

struct otDnsAddressResponse otDnsAddressResponse

An opaque representation of a response to an address resolution DNS query.

Pointers to instance of this type are provided from callback otDnsAddressCallback.

otDnsBrowseCallback

void(* otDnsBrowseCallback)(otError aError, const otDnsBrowseResponse *aResponse, void *aContext)

Pointer is called when a DNS response is received for a browse (service instance enumeration) query.

Within this callback the user can use otDnsBrowseResponseGet{Item}() functions along with the aResponse pointer to get more info about the response.

The aResponse pointer can only be used within this callback and after returning from this function it will not stay valid, so the user MUST NOT retain the aResponse pointer for later use.

For the full list of possible values for aError, please see otDnsAddressCallback().

Details
Parameters
[in] aError
The result of the DNS transaction.
[in] aResponse
A pointer to the response (it is always non-NULL).
[in] aContext
A pointer to application-specific context.

otDnsBrowseResponse

struct otDnsBrowseResponse otDnsBrowseResponse

An opaque representation of a response to a browse (service instance enumeration) DNS query.

Pointers to instance of this type are provided from callback otDnsBrowseCallback.

otDnsQueryConfig

struct otDnsQueryConfig otDnsQueryConfig

Represents a DNS query configuration.

Any of the fields in this structure can be set to zero to indicate that it is not specified. How the unspecified fields are treated is determined by the function which uses the instance of otDnsQueryConfig.

otDnsServiceCallback

void(* otDnsServiceCallback)(otError aError, const otDnsServiceResponse *aResponse, void *aContext)

Pointer is called when a DNS response is received for a service instance resolution query.

Within this callback the user can use otDnsServiceResponseGet{Item}() functions along with the aResponse pointer to get more info about the response.

The aResponse pointer can only be used within this callback and after returning from this function it will not stay valid, so the user MUST NOT retain the aResponse pointer for later use.

For the full list of possible values for aError, please see otDnsAddressCallback().

Details
Parameters
[in] aError
The result of the DNS transaction.
[in] aResponse
A pointer to the response (it is always non-NULL).
[in] aContext
A pointer to application-specific context.

otDnsServiceInfo

struct otDnsServiceInfo otDnsServiceInfo

Provides info for a DNS service instance.

otDnsServiceResponse

struct otDnsServiceResponse otDnsServiceResponse

An opaque representation of a response to a service instance resolution DNS query.

Pointers to instance of this type are provided from callback otDnsAddressCallback.

otDnsTxtEntry

struct otDnsTxtEntry otDnsTxtEntry

Represents a TXT record entry representing a key/value pair (RFC 6763 - section 6.3).

The string buffers pointed to by mKey and mValue MUST persist and remain unchanged after an instance of such structure is passed to OpenThread (as part of otSrpClientService instance).

An array of otDnsTxtEntry entries are used in otSrpClientService to specify the full TXT record (a list of entries).

otDnsTxtEntryIterator

struct otDnsTxtEntryIterator otDnsTxtEntryIterator

Represents an iterator for TXT record entries (key/value pairs).

The data fields in this structure are intended for use by OpenThread core and caller should not read or change them.

Functions

otDnsAddressResponseGetAddress

otError otDnsAddressResponseGetAddress(
  const otDnsAddressResponse *aResponse,
  uint16_t aIndex,
  otIp6Address *aAddress,
  uint32_t *aTtl
)

Gets an IPv6 address associated with an address resolution DNS response.

MUST only be used from otDnsAddressCallback.

The response may include multiple IPv6 address records. aIndex can be used to iterate through the list of addresses. Index zero gets the first address and so on. When we reach end of the list, OT_ERROR_NOT_FOUND is returned.

Details
Parameters
[in] aResponse
A pointer to the response.
[in] aIndex
The address record index to retrieve.
[out] aAddress
A pointer to a IPv6 address to output the address (MUST NOT be NULL).
[out] aTtl
A pointer to an uint32_t to output TTL for the address. It can be NULL if caller does not want to get the TTL.
Return Values
OT_ERROR_NONE
The address was read successfully.
OT_ERROR_NOT_FOUND
No address record in aResponse at aIndex.
OT_ERROR_PARSE
Could not parse the records in the aResponse.
OT_ERROR_INVALID_STATE
No NAT64 prefix (applicable only when NAT64 is allowed).

otDnsAddressResponseGetHostName

otError otDnsAddressResponseGetHostName(
  const otDnsAddressResponse *aResponse,
  char *aNameBuffer,
  uint16_t aNameBufferSize
)

Gets the full host name associated with an address resolution DNS response.

MUST only be used from otDnsAddressCallback.

Details
Parameters
[in] aResponse
A pointer to the response.
[out] aNameBuffer
A buffer to char array to output the full host name (MUST NOT be NULL).
[in] aNameBufferSize
The size of aNameBuffer.
Return Values
OT_ERROR_NONE
The full host name was read successfully.
OT_ERROR_NO_BUFS
The name does not fit in aNameBuffer.

otDnsBrowseResponseGetHostAddress

otError otDnsBrowseResponseGetHostAddress(
  const otDnsBrowseResponse *aResponse,
  const char *aHostName,
  uint16_t aIndex,
  otIp6Address *aAddress,
  uint32_t *aTtl
)

Gets the host IPv6 address from a DNS browse (service instance enumeration) response.

MUST only be used from otDnsBrowseCallback.

The response can include zero or more IPv6 address records. aIndex can be used to iterate through the list of addresses. Index zero gets the first address and so on. When we reach end of the list, OT_ERROR_NOT_FOUND is returned.

Details
Parameters
[in] aResponse
A pointer to the response.
[in] aHostName
The host name to get the address (MUST NOT be NULL).
[in] aIndex
The address record index to retrieve.
[out] aAddress
A pointer to a IPv6 address to output the address (MUST NOT be NULL).
[out] aTtl
A pointer to an uint32_t to output TTL for the address. It can be NULL if caller does not want to get the TTL.
Return Values
OT_ERROR_NONE
The address was read successfully.
OT_ERROR_NOT_FOUND
No address record for aHostname in aResponse at aIndex.
OT_ERROR_PARSE
Could not parse the records in the aResponse.

otDnsBrowseResponseGetServiceInfo

otError otDnsBrowseResponseGetServiceInfo(
  const otDnsBrowseResponse *aResponse,
  const char *aInstanceLabel,
  otDnsServiceInfo *aServiceInfo
)

Gets info for a service instance from a DNS browse (service instance enumeration) response.

MUST only be used from otDnsBrowseCallback.

A browse DNS response can include SRV, TXT, and AAAA records for the service instances that are enumerated. This is a SHOULD and not a MUST requirement, and servers/resolvers are not required to provide this. This function attempts to retrieve this info for a given service instance when available.

  • If no matching SRV record is found in aResponse, OT_ERROR_NOT_FOUND is returned. In this case, no additional records (no TXT and/or AAAA) are read.
  • If a matching SRV record is found in aResponse, aServiceInfo is updated and OT_ERROR_NONE is returned.
  • If no matching TXT record is found in aResponse, mTxtDataSize in aServiceInfo is set to zero.
  • If TXT data length is greater than mTxtDataSize, it is read partially and mTxtDataTruncated is set to true.
  • If no matching AAAA record is found in aResponse, mHostAddress is set to all zero or unspecified address.
  • If there are multiple AAAA records for the host name in @p aResponse,mHostAddressis set to the first one. The other addresses can be retrieved usingotDnsBrowseResponseGetHostAddress()`.

Details
Parameters
[in] aResponse
A pointer to the response.
[in] aInstanceLabel
The service instance label (MUST NOT be NULL).
[out] aServiceInfo
A ServiceInfo to output the service instance information (MUST NOT be NULL).
Return Values
OT_ERROR_NONE
The service instance info was read. aServiceInfo is updated.
OT_ERROR_NOT_FOUND
Could not find a matching SRV record for aInstanceLabel.
OT_ERROR_NO_BUFS
The host name and/or TXT data could not fit in the given buffers.
OT_ERROR_PARSE
Could not parse the records in the aResponse.

otDnsBrowseResponseGetServiceInstance

otError otDnsBrowseResponseGetServiceInstance(
  const otDnsBrowseResponse *aResponse,
  uint16_t aIndex,
  char *aLabelBuffer,
  uint8_t aLabelBufferSize
)

Gets a service instance associated with a DNS browse (service instance enumeration) response.

MUST only be used from otDnsBrowseCallback.

The response may include multiple service instance records. aIndex can be used to iterate through the list. Index zero gives the the first record. When we reach end of the list, OT_ERROR_NOT_FOUND is returned.

Note that this function gets the service instance label and not the full service instance name which is of the form ...

Details
Parameters
[in] aResponse
A pointer to the response.
[in] aIndex
The service instance record index to retrieve.
[out] aLabelBuffer
A buffer to char array to output the service instance label (MUST NOT be NULL).
[in] aLabelBufferSize
The size of aLabelBuffer.
Return Values
OT_ERROR_NONE
The service instance was read successfully.
OT_ERROR_NO_BUFS
The name does not fit in aNameBuffer.
OT_ERROR_NOT_FOUND
No service instance record in aResponse at aIndex.
OT_ERROR_PARSE
Could not parse the records in the aResponse.

otDnsBrowseResponseGetServiceName

otError otDnsBrowseResponseGetServiceName(
  const otDnsBrowseResponse *aResponse,
  char *aNameBuffer,
  uint16_t aNameBufferSize
)

Gets the service name associated with a DNS browse (service instance enumeration) response.

MUST only be used from otDnsBrowseCallback.

Details
Parameters
[in] aResponse
A pointer to the response.
[out] aNameBuffer
A buffer to char array to output the service name (MUST NOT be NULL).
[in] aNameBufferSize
The size of aNameBuffer.
Return Values
OT_ERROR_NONE
The service name was read successfully.
OT_ERROR_NO_BUFS
The name does not fit in aNameBuffer.

otDnsClientBrowse

otError otDnsClientBrowse(
  otInstance *aInstance,
  const char *aServiceName,
  otDnsBrowseCallback aCallback,
  void *aContext,
  const otDnsQueryConfig *aConfig
)

Sends a DNS browse (service instance enumeration) query for a given service name.

Is available when OPENTHREAD_CONFIG_DNS_CLIENT_SERVICE_DISCOVERY_ENABLE is enabled.

The aConfig can be NULL. In this case the default config (from otDnsClientGetDefaultConfig()) will be used as the config for this query. In a non-NULL aConfig, some of the fields can be left unspecified (value zero). The unspecified fields are then replaced by the values from the default config.

Details
Parameters
[in] aInstance
A pointer to an OpenThread instance.
[in] aServiceName
The service name to query for (MUST NOT be NULL).
[in] aCallback
A function pointer that shall be called on response reception or time-out.
[in] aContext
A pointer to arbitrary context information.
[in] aConfig
A pointer to the config to use for this query.
Return Values
OT_ERROR_NONE
Query sent successfully. aCallback will be invoked to report the status.
OT_ERROR_NO_BUFS
Insufficient buffer to prepare and send query.

otDnsClientGetDefaultConfig

const otDnsQueryConfig * otDnsClientGetDefaultConfig(
  otInstance *aInstance
)

Gets the current default query config used by DNS client.

When OpenThread stack starts, the default DNS query config is determined from a set of OT config options such as OPENTHREAD_CONFIG_DNS_CLIENT_DEFAULT_SERVER_IP6_ADDRESS, _DEFAULT_SERVER_PORT, _DEFAULT_RESPONSE_TIMEOUT, etc. (see config/dns_client.h for all related config options).

Details
Parameters
[in] aInstance
A pointer to an OpenThread instance.
Returns
A pointer to the current default config being used by DNS client.

otDnsClientResolveAddress

otError otDnsClientResolveAddress(
  otInstance *aInstance,
  const char *aHostName,
  otDnsAddressCallback aCallback,
  void *aContext,
  const otDnsQueryConfig *aConfig
)

Sends an address resolution DNS query for AAAA (IPv6) record(s) for a given host name.

The aConfig can be NULL. In this case the default config (from otDnsClientGetDefaultConfig()) will be used as the config for this query. In a non-NULL aConfig, some of the fields can be left unspecified (value zero). The unspecified fields are then replaced by the values from the default config.

Details
Parameters
[in] aInstance
A pointer to an OpenThread instance.
[in] aHostName
The host name for which to query the address (MUST NOT be NULL).
[in] aCallback
A function pointer that shall be called on response reception or time-out.
[in] aContext
A pointer to arbitrary context information.
[in] aConfig
A pointer to the config to use for this query.
Return Values
OT_ERROR_NONE
Query sent successfully. aCallback will be invoked to report the status.
OT_ERROR_NO_BUFS
Insufficient buffer to prepare and send query.
OT_ERROR_INVALID_ARGS
The host name is not valid format.
OT_ERROR_INVALID_STATE
Cannot send query since Thread interface is not up.

otDnsClientResolveIp4Address

otError otDnsClientResolveIp4Address(
  otInstance *aInstance,
  const char *aHostName,
  otDnsAddressCallback aCallback,
  void *aContext,
  const otDnsQueryConfig *aConfig
)

Sends an address resolution DNS query for A (IPv4) record(s) for a given host name.

Requires and is available when OPENTHREAD_CONFIG_DNS_CLIENT_NAT64_ENABLE is enabled.

When a successful response is received, the addresses are returned from aCallback as NAT64 IPv6 translated versions of the IPv4 addresses from the query response.

The aConfig can be NULL. In this case the default config (from otDnsClientGetDefaultConfig()) will be used as the config for this query. In a non-NULL aConfig, some of the fields can be left unspecified (value zero). The unspecified fields are then replaced by the values from the default config.

Details
Parameters
[in] aInstance
A pointer to an OpenThread instance.
[in] aHostName
The host name for which to query the address (MUST NOT be NULL).
[in] aCallback
A function pointer that shall be called on response reception or time-out.
[in] aContext
A pointer to arbitrary context information.
[in] aConfig
A pointer to the config to use for this query.
Return Values
OT_ERROR_NONE
Query sent successfully. aCallback will be invoked to report the status.
OT_ERROR_NO_BUFS
Insufficient buffer to prepare and send query.
OT_ERROR_INVALID_ARGS
The host name is not valid format or NAT64 is not enabled in config.
OT_ERROR_INVALID_STATE
Cannot send query since Thread interface is not up.

otDnsClientResolveService

otError otDnsClientResolveService(
  otInstance *aInstance,
  const char *aInstanceLabel,
  const char *aServiceName,
  otDnsServiceCallback aCallback,
  void *aContext,
  const otDnsQueryConfig *aConfig
)

Starts a DNS service instance resolution for a given service instance.

Is available when OPENTHREAD_CONFIG_DNS_CLIENT_SERVICE_DISCOVERY_ENABLE is enabled.

The aConfig can be NULL. In this case the default config (from otDnsClientGetDefaultConfig()) will be used as the config for this query. In a non-NULL aConfig, some of the fields can be left unspecified (value zero). The unspecified fields are then replaced by the values from the default config.

The function sends queries for SRV and/or TXT records for the given service instance. The mServiceMode field in otDnsQueryConfig determines which records to query (SRV only, TXT only, or both SRV and TXT) and how to perform the query (together in the same message, separately in parallel, or in optimized mode where client will try in the same message first and then separately if it fails to get a response).

The SRV record provides information about service port, priority, and weight along with the host name associated with the service instance. This function DOES NOT perform address resolution for the host name discovered from SRV record. The server/resolver may provide AAAA/A record(s) for the host name in the Additional Data section of the response to SRV/TXT query and this information can be retrieved using otDnsServiceResponseGetServiceInfo() in otDnsServiceCallback. Users of this API MUST NOT assume that host address will always be available from otDnsServiceResponseGetServiceInfo().

Details
Parameters
[in] aInstance
A pointer to an OpenThread instance.
[in] aInstanceLabel
The service instance label.
[in] aServiceName
The service name (together with aInstanceLabel form full instance name).
[in] aCallback
A function pointer that shall be called on response reception or time-out.
[in] aContext
A pointer to arbitrary context information.
[in] aConfig
A pointer to the config to use for this query.
Return Values
OT_ERROR_NONE
Query sent successfully. aCallback will be invoked to report the status.
OT_ERROR_NO_BUFS
Insufficient buffer to prepare and send query.
OT_ERROR_INVALID_ARGS
aInstanceLabel is NULL.

otDnsClientResolveServiceAndHostAddress

otError otDnsClientResolveServiceAndHostAddress(
  otInstance *aInstance,
  const char *aInstanceLabel,
  const char *aServiceName,
  otDnsServiceCallback aCallback,
  void *aContext,
  const otDnsQueryConfig *aConfig
)

Starts a DNS service instance resolution for a given service instance, with a potential follow-up address resolution for the host name discovered for the service instance.

Is available when OPENTHREAD_CONFIG_DNS_CLIENT_SERVICE_DISCOVERY_ENABLE is enabled.

The aConfig can be NULL. In this case the default config (from otDnsClientGetDefaultConfig()) will be used as the config for this query. In a non-NULL aConfig, some of the fields can be left unspecified (value zero). The unspecified fields are then replaced by the values from the default config. This function cannot be used with mServiceMode in DNS config set to OT_DNS_SERVICE_MODE_TXT (i.e., querying for TXT record only) and will return OT_ERROR_INVALID_ARGS.

Behaves similarly to otDnsClientResolveService() sending queries for SRV and TXT records. However, if the server/resolver does not provide AAAA/A records for the host name in the response to SRV query (in the Additional Data section), it will perform host name resolution (sending an AAAA query) for the discovered host name from the SRV record. The callback aCallback is invoked when responses for all queries are received (i.e., both service and host address resolutions are finished).

Details
Parameters
[in] aInstance
A pointer to an OpenThread instance.
[in] aInstanceLabel
The service instance label.
[in] aServiceName
The service name (together with aInstanceLabel form full instance name).
[in] aCallback
A function pointer that shall be called on response reception or time-out.
[in] aContext
A pointer to arbitrary context information.
[in] aConfig
A pointer to the config to use for this query.
Return Values
OT_ERROR_NONE
Query sent successfully. aCallback will be invoked to report the status.
OT_ERROR_NO_BUFS
Insufficient buffer to prepare and send query.
OT_ERROR_INVALID_ARGS
aInstanceLabel is NULL, or aConfig is invalid.

otDnsClientSetDefaultConfig

void otDnsClientSetDefaultConfig(
  otInstance *aInstance,
  const otDnsQueryConfig *aConfig
)

Sets the default query config on DNS client.

Note:Any ongoing query will continue to use the config from when it was started. The new default config will be used for any future DNS queries. The aConfig can be NULL. In this case the default config will be set to the defaults from OT config options OPENTHREAD_CONFIG_DNS_CLIENT_DEFAULT_{}. This resets the default query config back to to the config when the OpenThread stack starts.

In a non-NULL aConfig, caller can choose to leave some of the fields in otDnsQueryConfig instance unspecified (value zero). The unspecified fields are replaced by the corresponding OT config option definitions OPENTHREAD_CONFIG_DNS_CLIENT_DEFAULT_{} to form the default query config.

When OPENTHREAD_CONFIG_DNS_CLIENT_DEFAULT_SERVER_ADDRESS_AUTO_SET_ENABLE is enabled, the server's IPv6 address in the default config is automatically set and updated by DNS client. This is done only when user does not explicitly set or specify it. This behavior requires SRP client and its auto-start feature to be enabled. SRP client will then monitor the Thread Network Data for DNS/SRP Service entries to select an SRP server. The selected SRP server address is also set as the DNS server address in the default config.

Details
Parameters
[in] aInstance
A pointer to an OpenThread instance.
[in] aConfig
A pointer to the new query config to use as default.

otDnsGetNextTxtEntry

otError otDnsGetNextTxtEntry(
  otDnsTxtEntryIterator *aIterator,
  otDnsTxtEntry *aEntry
)

Parses the TXT data from an iterator and gets the next TXT record entry (key/value pair).

The aIterator MUST be initialized using otDnsInitTxtEntryIterator() before calling this function and the TXT data buffer used to initialize the iterator MUST persist and remain unchanged. Otherwise the behavior of this function is undefined.

If the parsed key string length is smaller than or equal to OT_DNS_TXT_KEY_MAX_LENGTH (recommended max key length) the key string is returned in mKey in aEntry. But if the key is longer, then mKey is set to NULL and the entire encoded TXT entry string is returned in mValue and mValueLength.

Details
Parameters
[in] aIterator
A pointer to the iterator (MUST NOT be NULL).
[out] aEntry
A pointer to a otDnsTxtEntry structure to output the parsed/read entry (MUST NOT be NULL).
Return Values
OT_ERROR_NONE
The next entry was parsed successfully. aEntry is updated.
OT_ERROR_NOT_FOUND
No more entries in the TXT data.
OT_ERROR_PARSE
The TXT data from aIterator is not well-formed.

otDnsInitTxtEntryIterator

void otDnsInitTxtEntryIterator(
  otDnsTxtEntryIterator *aIterator,
  const uint8_t *aTxtData,
  uint16_t aTxtDataLength
)

Initializes a TXT record iterator.

The buffer pointer aTxtData and its content MUST persist and remain unchanged while aIterator object is being used.

Details
Parameters
[in] aIterator
A pointer to the iterator to initialize (MUST NOT be NULL).
[in] aTxtData
A pointer to buffer containing the encoded TXT data.
[in] aTxtDataLength
The length (number of bytes) of aTxtData.

otDnsIsNameCompressionEnabled

bool otDnsIsNameCompressionEnabled(
  void
)

Indicates whether the "DNS name compression" mode is enabled or not.

This is intended for testing only and available when OPENTHREAD_CONFIG_REFERENCE_DEVICE_ENABLE config is enabled.

Details
Returns
TRUE if the "DNS name compression" mode is enabled, FALSE otherwise.

otDnsServiceResponseGetHostAddress

otError otDnsServiceResponseGetHostAddress(
  const otDnsServiceResponse *aResponse,
  const char *aHostName,
  uint16_t aIndex,
  otIp6Address *aAddress,
  uint32_t *aTtl
)

Gets the host IPv6 address from a DNS service instance resolution response.

MUST only be used from otDnsServiceCallback.

The response can include zero or more IPv6 address records. aIndex can be used to iterate through the list of addresses. Index zero gets the first address and so on. When we reach end of the list, OT_ERROR_NOT_FOUND is returned.

Details
Parameters
[in] aResponse
A pointer to the response.
[in] aHostName
The host name to get the address (MUST NOT be NULL).
[in] aIndex
The address record index to retrieve.
[out] aAddress
A pointer to a IPv6 address to output the address (MUST NOT be NULL).
[out] aTtl
A pointer to an uint32_t to output TTL for the address. It can be NULL if caller does not want to get the TTL.
Return Values
OT_ERROR_NONE
The address was read successfully.
OT_ERROR_NOT_FOUND
No address record for aHostname in aResponse at aIndex.
OT_ERROR_PARSE
Could not parse the records in the aResponse.

otDnsServiceResponseGetServiceInfo

otError otDnsServiceResponseGetServiceInfo(
  const otDnsServiceResponse *aResponse,
  otDnsServiceInfo *aServiceInfo
)

Gets info for a service instance from a DNS service instance resolution response.

MUST only be used from a otDnsServiceCallback triggered from otDnsClientResolveService() or otDnsClientResolveServiceAndHostAddress().

When this is is used from a otDnsClientResolveService() callback, the DNS response from server/resolver may include AAAA records in its Additional Data section for the host name associated with the service instance that is resolved. This is a SHOULD and not a MUST requirement so servers/resolvers are not required to provide this. This function attempts to parse AAAA record(s) if included in the response. If it is not included mHostAddress is set to all zeros (unspecified address). To also resolve the host address, user can use the DNS client API function otDnsClientResolveServiceAndHostAddress() which will perform service resolution followed up by a host name address resolution query (when AAAA records are not provided by server/resolver in the SRV query response).

  • If a matching SRV record is found in aResponse, aServiceInfo is updated.
  • If no matching SRV record is found, OT_ERROR_NOT_FOUND is returned unless the query config for this query used OT_DNS_SERVICE_MODE_TXT for mServiceMode (meaning the request was only for TXT record). In this case, we still try to parse the SRV record from Additional Data Section of response (in case server provided the info).
  • If no matching TXT record is found in aResponse, mTxtDataSize in aServiceInfo is set to zero.
  • If TXT data length is greater than mTxtDataSize, it is read partially and mTxtDataTruncated is set to true.
  • If no matching AAAA record is found in aResponse, mHostAddress is set to all zero or unspecified address.
  • If there are multiple AAAA records for the host name in @p aResponse,mHostAddressis set to the first one. The other addresses can be retrieved usingotDnsServiceResponseGetHostAddress()`.

Details
Parameters
[in] aResponse
A pointer to the response.
[out] aServiceInfo
A ServiceInfo to output the service instance information (MUST NOT be NULL).
Return Values
OT_ERROR_NONE
The service instance info was read. aServiceInfo is updated.
OT_ERROR_NOT_FOUND
Could not find a required record in aResponse.
OT_ERROR_NO_BUFS
The host name and/or TXT data could not fit in the given buffers.
OT_ERROR_PARSE
Could not parse the records in the aResponse.

otDnsServiceResponseGetServiceName

otError otDnsServiceResponseGetServiceName(
  const otDnsServiceResponse *aResponse,
  char *aLabelBuffer,
  uint8_t aLabelBufferSize,
  char *aNameBuffer,
  uint16_t aNameBufferSize
)

Gets the service instance name associated with a DNS service instance resolution response.

MUST only be used from otDnsServiceCallback.

Details
Parameters
[in] aResponse
A pointer to the response.
[out] aLabelBuffer
A buffer to char array to output the service instance label (MUST NOT be NULL).
[in] aLabelBufferSize
The size of aLabelBuffer.
[out] aNameBuffer
A buffer to char array to output the rest of service name (can be NULL if user is not interested in getting the name.
[in] aNameBufferSize
The size of aNameBuffer.
Return Values
OT_ERROR_NONE
The service name was read successfully.
OT_ERROR_NO_BUFS
Either the label or name does not fit in the given buffers.

otDnsSetNameCompressionEnabled

void otDnsSetNameCompressionEnabled(
  bool aEnabled
)

Enables/disables the "DNS name compression" mode.

By default DNS name compression is enabled. When disabled, DNS names are appended as full and never compressed. This is applicable to OpenThread's DNS and SRP client/server modules.

This is intended for testing only and available when OPENTHREAD_CONFIG_REFERENCE_DEVICE_ENABLE config is enabled.

Note that in the case OPENTHREAD_CONFIG_MULTIPLE_INSTANCE_ENABLE is used, this mode applies to all OpenThread instances (i.e., calling this function enables/disables the compression mode on all OpenThread instances).

Details
Parameters
[in] aEnabled
TRUE to enable the "DNS name compression" mode, FALSE to disable.

Macros

OT_DNS_MAX_LABEL_SIZE

 OT_DNS_MAX_LABEL_SIZE 64

Maximum label string size (include null char at the end of string).

OT_DNS_MAX_NAME_SIZE

 OT_DNS_MAX_NAME_SIZE 255

Maximum name string size (includes null char at the end of string).

OT_DNS_TXT_KEY_MAX_LENGTH

 OT_DNS_TXT_KEY_MAX_LENGTH 9

Recommended maximum length of TXT record key string (RFC 6763 - section 6.4).

OT_DNS_TXT_KEY_MIN_LENGTH

 OT_DNS_TXT_KEY_MIN_LENGTH 1

Minimum length of TXT record key string (RFC 6763 - section 6.4).

Resources

OpenThread API Reference topics originate from the source code, available on GitHub. For more information, or to contribute to our documentation, refer to Resources.