Module block 

CoAP block-wise transfer per RFC 7959.

EST payloads frequently exceed the CoAP datagram size limit, especially with post-quantum certificates (ML-DSA-87 certificates can exceed 7KB). Block-wise transfer splits large payloads into numbered blocks that are individually acknowledged.

Block Options

• Block1 (option 27): Controls request payload transfer (client to server). The client sends the request body in numbered chunks; the server acknowledges each chunk before the next is sent.

• Block2 (option 23): Controls response payload transfer (server to client). The server splits its response into numbered chunks; the client requests successive chunks.

SZX Encoding

Block sizes are encoded as szx where actual size = 2^(szx + 4):

• szx=0 → 16 bytes
• szx=1 → 32 bytes
• szx=2 → 64 bytes
• szx=3 → 128 bytes
• szx=4 → 256 bytes
• szx=5 → 512 bytes (default)
• szx=6 → 1024 bytes (maximum)

Structs

BlockAssembler

Reassembles Block1 fragments into a complete request payload.

BlockDisassembler

Splits a response payload into Block2 chunks for incremental delivery.

BlockOption

A decoded Block1 or Block2 option value.

Constants

DEFAULT_SZX

Default block size exponent (szx=5 → 512 bytes).

MAX_SZX

Maximum block size exponent (szx=6 → 1024 bytes).

Functions

block_size_from_szx

Converts an SZX exponent to the actual block size in bytes.

szx_from_block_size

Converts a block size in bytes to the corresponding SZX exponent.