Multicast DNS

This module defines platform APIs for Multicast DNS (mDNS) socket.

Summary

Typedefs
otPlatMdnsAddressInfo typedef
Represents a socket address info.

Functions
otPlatMdnsHandleReceive(otInstance *aInstance, otMessage *aMessage, bool aIsUnicast, const otPlatMdnsAddressInfo *aAddress)
void
Callback to notify OpenThread mDNS module of a received message on UDP port 5353.
otPlatMdnsSendMulticast(otInstance *aInstance, otMessage *aMessage, uint32_t aInfraIfIndex)
void
Sends an mDNS message as multicast.
otPlatMdnsSendUnicast(otInstance *aInstance, otMessage *aMessage, const otPlatMdnsAddressInfo *aAddress)
void
Sends an mDNS message as unicast.
otPlatMdnsSetListeningEnabled(otInstance *aInstance, bool aEnable, uint32_t aInfraIfIndex)
Enables or disables listening for mDNS messages sent to mDNS port 5353.

Structs
otPlatMdnsAddressInfo

Represents a socket address info.

Typedefs

otPlatMdnsAddressInfo

struct otPlatMdnsAddressInfo otPlatMdnsAddressInfo

Represents a socket address info.

Functions

otPlatMdnsHandleReceive

void otPlatMdnsHandleReceive(
  otInstance *aInstance,
  otMessage *aMessage,
  bool aIsUnicast,
  const otPlatMdnsAddressInfo *aAddress
)

Callback to notify OpenThread mDNS module of a received message on UDP port 5353.

aMessage MUST contain DNS message starting with the DNS header at offset zero. This function passes the ownership of aMessage from the platform layer to the OpenThread stack. The OpenThread stack will free the message once processed.

The aAddress fields are as follows:

  • mAddress specifies the sender's address. IPv4-mapped IPv6 format is used to represent an IPv4 destination.
  • mPort specifies the sender's port.
  • mInfraIndex specifies the interface index.

Details
Parameters
[in] aInstance
The OpenThread instance.
[in] aMessage
The received mDNS message. Ownership is transferred to the OpenThread stack.
[in] aIsUnicast
Indicates whether the received message is unicast or multicast.
[in] aAddress
The sender's address info.

otPlatMdnsSendMulticast

void otPlatMdnsSendMulticast(
  otInstance *aInstance,
  otMessage *aMessage,
  uint32_t aInfraIfIndex
)

Sends an mDNS message as multicast.

The platform MUST multicast the prepared mDNS message in aMessage as a UDP message using the mDNS well-known port number 5353 for both source and destination ports. The message MUST be sent to the mDNS link-local multicast address 224.0.0.251 and/or its IPv6 equivalent ff02::fb.

aMessage contains the mDNS message starting with DNS header at offset zero. It does not include IP or UDP headers. This function passes the ownership of aMessage to the platform layer and platform implementation MUST free aMessage once sent and no longer needed.

The platform MUST allow multicast loopback, i.e., the multicast message aMessage MUST also be received and passed back to OpenThread stack using otPlatMdnsHandleReceive() callback. This behavior is essential for the OpenThread mDNS stack to process and potentially respond to its own queries, while allowing other mDNS receivers to also receive the query and its response.

Details
Parameters
[in] aInstance
The OpenThread instance.
[in] aMessage
The mDNS message to multicast. Ownership is transferred to the platform layer.
[in] aInfraIfIndex
The infrastructure network interface index.

otPlatMdnsSendUnicast

void otPlatMdnsSendUnicast(
  otInstance *aInstance,
  otMessage *aMessage,
  const otPlatMdnsAddressInfo *aAddress
)

Sends an mDNS message as unicast.

The platform MUST send the prepared mDNS message in aMessage as a UDP message using source UDP port 5353 to the destination address and port number specified by aAddress.

aMessage contains the DNS message starting with the DNS header at offset zero. It does not include IP or UDP headers. This function passes the ownership of aMessage to the platform layer and platform implementation MUST free aMessage once sent and no longer needed.

The aAddress fields are as follows:

  • mAddress specifies the destination address. IPv4-mapped IPv6 format is used to represent an IPv4 destination.
  • mPort specifies the destination port.
  • mInfraIndex specifies the interface index.

If the matches this devices address, the platform MUST ensure to receive and pass the message back to the OpenThread stack using otPlatMdnsHandleReceive() for processing.

Details
Parameters
[in] aInstance
The OpenThread instance.
[in] aMessage
The mDNS message to multicast. Ownership is transferred to platform layer.
[in] aAddress
The destination address info.

otPlatMdnsSetListeningEnabled

otError otPlatMdnsSetListeningEnabled(
  otInstance *aInstance,
  bool aEnable,
  uint32_t aInfraIfIndex
)

Enables or disables listening for mDNS messages sent to mDNS port 5353.

When listening is enabled, the platform MUST listen for multicast messages sent to UDP destination port 5353 at the mDNS link-local multicast address 224.0.0.251 and its IPv6 equivalent ff02::fb.

The platform SHOULD also listen for any unicast messages sent to UDP destination port 5353. If this is not possible, then OpenThread mDNS module can be configured to not use any "QU" questions requesting unicast response.

While enabled, all received messages MUST be reported back using otPlatMdnsHandleReceive() callback.

Details
Parameters
[in] aInstance
The OpernThread instance.
[in] aEnable
Indicate whether to enable or disable.
[in] aInfraInfIndex
The infrastructure network interface index.
Return Values
OT_ERROR_NONE
Successfully enabled/disabled listening for mDNS messages.
OT_ERROR_FAILED
Failed to enable/disable listening for mDNS messages.

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.