Module manifest 

Content manifests as macula 12’s macula_manifest builds them, byte for byte: fixed-size chunks (256 KiB by default), SHA-384 hashes, a 50-byte content id <<2, Codec, SHA-384>> (tag 2 names SHA-384, D24; codec 0x55 a raw block, 0x56 a manifest), and a Merkle fold that pairs an odd last hash with itself.

A manifest’s name has two encodings that must not be confused: its content id hashes the name as CBOR text, while the wire form a manifest travels in carries it as a byte string.

Structs

ChunkInfo

One chunk of a manifest.

Manifest

A chunked content’s manifest. name is bytes, as the wire carries it, and hash_algorithm the wire’s own text: a manifest read from a peer may name anything, and verify_mcid refuses what is not a UTF-8 name and sha384.

Enums

ManifestError

Why a manifest was refused.

Constants

DEFAULT_CHUNK_SIZE

256 KiB, macula_manifest’s default chunk size.

HASH_SIZE

A SHA-384 digest’s length.

SHA384

The one hash algorithm a manifest names.

Functions

block_mcid

The content id of a single block: <<2, 0x55, SHA-384(data)>>.

check_chunk_hashes

Checks that m’s chunk hashes make its root hash. The root hash is part of the content id and the chunk hashes are not, so after verify_mcid this is what ties each chunk, fetched by its hash, to the content id.

check_whole

Checks that m’s chunks describe its content whole, cut as create cuts it: a positive chunk size, ceil(size / chunk size) chunks, which is its chunk count, chunk i at offset i × chunk size and chunk size long but for the last, which holds what is left, between 1 and chunk size bytes.

chunk_mcid

The content id chunk index is stored and fetched under: the block id of its bytes, which a sharer derives from the manifest alone.

create

Splits data into chunks of chunk_size bytes and builds its manifest, created now; returns it with the chunks in order.

create_at

create with the manifest’s creation time given, in unix seconds.

from_wire

A manifest read from its wire form, as macula_manifest’s from_wire/1 reads it. One that names another hash algorithm than sha384 (as text or bytes), whose chunks do not describe its content whole, or holding a number outside its field, is refused. Nothing is allocated from the size or count it claims: only the chunks it lists are read.

mcid_for

The content id the manifest’s canonical fields describe: its name, size, chunk size and count, hash algorithm and root hash. Its creation time and chunk list are not part of it.

mcid_is_chunked

Whether a content id names a manifest (chunked content) rather than a single block, read from its codec byte.

to_wire

The manifest as it travels: the name as a byte string.

verify

Checks reassembled data against m: its size, then a root hash over data cut the same way.

verify_mcid

Whether m describes mcid, as macula_manifest’s verify_mcid/2 checks: a UTF-8 name, sha384, and the content id its canonical fields recompute to. The manifest’s own mcid field is not consulted.

Type Aliases

Hash

A SHA-384 digest.

Mcid

A content id: <<Tag:8, Codec:8, Hash:48/binary>>.