Content Identifiers

The Cid library provides a pure OCaml interface to Content Identifiers. These are like pointers to bits of data derived from the data itself. They are based on the cryptographic hash of the data along with extra information describing things like the encoding of the data, the hash function used to produce the digest etc.

For a thorough handling of this information see the IPFS documentation.

Quick Example

A very small example using Cid.of_string and the human-readable pretty printer Cid.pp_human.

let s = "zb2rhe5P4gXftAwvA4eXQ5HJwsER2owDyS9sKaQRRVQPn93bA"
let cid = Cid.of_string s |> Result.get_ok
let () = Cid.pp_human Format.std_formatter cid

Which would print the following:

cidv1 - base58btc - raw - ident(sha2-256) length(32)
digest(6e 6f f7 95 0a 36 18 7a  80 16 13 42 6e 85 8d ce
       68 6c d7 d7 e3 c0 fc 42  ee 03 30 07 2d 24 5c 95)

If instead we used Cid.to_string this will base encode this for us producing the original input.

The repository also contains an example of using Irmin and CIDs together. This is similar to the idea of using CIDs in IPFS.