How I can set a size of PDU dynamically for Californium server?
Context:
1) I have a device with implemented coap-client functionality.
This device is constrained by RAM, about 200 free bytes for rx/tx buffers.
In the request the device can sent a prefer PDU size. But I don't understand how to configure server responses with this PDU size. Is it possible?
2) Will be work a blockwise-functionality for this case?
Ok, I found how to do it.
It is not a Californium responsibility. The management of the PDU-size works via block-wise option Block2.
See the CoAP block-wise RFC Section 3.1:
In the second example (Figure 3), the client anticipates the block- wise transfer (e.g., because of a size indication in the link-format description [RFC6690]) and sends a block size proposal. All ACK messages except for the last carry 64 bytes of payload; the last one carries between 1 and 64 bytes.
Client Server
| |
| CON [MID=1234], GET, /status, 2:0/0/64 ------> |
| |
| <------ ACK [MID=1234], 2.05 Content, 2:0/1/64 |
| |
| CON [MID=1235], GET, /status, 2:1/0/64 ------> |
| |
| <------ ACK [MID=1235], 2.05 Content, 2:1/1/64 |
: :
: ... :
: :
| CON [MID=1238], GET, /status, 2:4/0/64 ------> |
| |
| <------ ACK [MID=1238], 2.05 Content, 2:4/1/64 |
| |
| CON [MID=1239], GET, /status, 2:5/0/64 ------> |
| |
| <------ ACK [MID=1239], 2.05 Content, 2:5/0/64 |
Figure 3: Block-Wise GET with Early Negotiation