ConfigurableConstants

CoAP constants that can be overridden. More...

Macros
#define	COAP_MAX_MESSAGE_SIZE   128U
	Maximum size of a CoAP message in bytes.
#define	COAP_MAX_CALLBACKS   10U
	Maximum number of callbacks that can be registered at runtime.
#define	COAP_MAX_OBSERVERS   4U
	Maximum number of observers that can be registered at runtime.
#define	COAP_OBSERVER_LEASE_MS   60000UL
#define	COAP_ACK_MIN_TIMEOUT_MS   2000UL
	Minimum ACK timeout in milliseconds. See RFC 7252, Section 4.8. Default to 2 seconds (2000 ms).
#define	COAP_ACK_RANDOM_FACTOR   1.5f
	ACK timeout random factor as per RFC 7252, Section 4.8. Default to 1.5. This value can be overridden.
#define	COAP_ACK_MAX_TIMEOUT_MS   (unsigned long)(COAP_ACK_MIN_TIMEOUT_MS * COAP_ACK_RANDOM_FACTOR)
	The precomputed maximum ACK timeout derived from the minimum timeout and the random factor.
#define	COAP_MAX_RETRANSMIT   4U
	The maximum number of retransmission attempts for confirmable messages. Default to 4 as per RFC 7252, Section 4.8. This value can be overridden.
#define	COAP_CONFIRMABLE_MESSAGE_QUEUE_SIZE   2U
	The maximum number of confirmable messages that are stored for retransmission.

Detailed Description

CoAP constants that can be overridden.

These constants can be overridden by defining them before including this header. Example:

#define COAP_MAX_OBSERVERS 8
#include <ProsecCoAP.h>

Refer to each constant's documentation for details.

Macro Definition Documentation

COAP_ACK_MAX_TIMEOUT_MS

#define COAP_ACK_MAX_TIMEOUT_MS   (unsigned long)(COAP_ACK_MIN_TIMEOUT_MS * COAP_ACK_RANDOM_FACTOR)

The precomputed maximum ACK timeout derived from the minimum timeout and the random factor.

COAP_ACK_MIN_TIMEOUT_MS

#define COAP_ACK_MIN_TIMEOUT_MS   2000UL

Minimum ACK timeout in milliseconds. See RFC 7252, Section 4.8. Default to 2 seconds (2000 ms).

This value can be overridden.

COAP_ACK_RANDOM_FACTOR

#define COAP_ACK_RANDOM_FACTOR   1.5f

ACK timeout random factor as per RFC 7252, Section 4.8. Default to 1.5. This value can be overridden.

COAP_CONFIRMABLE_MESSAGE_QUEUE_SIZE

#define COAP_CONFIRMABLE_MESSAGE_QUEUE_SIZE   2U

The maximum number of confirmable messages that are stored for retransmission.

The total memory used by the queue will be about: COAP_CONFIRMABLE_MESSAGE_QUEUE_SIZE * COAP_MAX_MESSAGE_SIZE bytes. The actual memory usage may be slightly higher due to the Message representation.

Reduce this value to save memory.

COAP_MAX_CALLBACKS

#define COAP_MAX_CALLBACKS   10U

Maximum number of callbacks that can be registered at runtime.

This limits the number of endpoints that can be served.

COAP_MAX_MESSAGE_SIZE

#define COAP_MAX_MESSAGE_SIZE   128U

Maximum size of a CoAP message in bytes.

As per CoAP specification, the recommended message size should fit within a single IP packet to avoid fragmentation. The recommended maximum size is therefore 1152 bytes. The absolute minimum size for a UDP payload (and thus, of a message) is 40 bytes.

This value applies to both incoming and outgoing messages. Keep this value small enough to reduce memory usage. Exceeding it will lead to errors when building outgoing messages or parsing incoming messages.

See https://datatracker.ietf.org/doc/html/rfc7252#section-4.6

Further considerations on the message size

The message structure is:

HEADER	TOKEN	OPTIONS	PAYLOAD
4 bytes	0-8b	variable	variable

COAP_MAX_OBSERVERS

#define COAP_MAX_OBSERVERS   4U

Maximum number of observers that can be registered at runtime.

COAP_MAX_RETRANSMIT

#define COAP_MAX_RETRANSMIT   4U

The maximum number of retransmission attempts for confirmable messages. Default to 4 as per RFC 7252, Section 4.8. This value can be overridden.

COAP_OBSERVER_LEASE_MS

#define COAP_OBSERVER_LEASE_MS   60000UL