Question：How I generate Cid before data stored?

I know the java-ipfs-api just invoke ipfs server. But now I want to get Cid of byte[] before invoke, I tried java-cid. But the Cid of java-ipfs-api is different from the Cid of java-cid(version 0).

this is my code.

        String ss = "123321";
        // 数据存储IPFS逻辑
        try {
            IPFS ipfs = new IPFS(Constants.IPFS_URL);//    "/ip4/0.0.0.0/tcp/5001"
            ipfs.refs.local();

            NamedStreamable.ByteArrayWrapper file = new NamedStreamable.ByteArrayWrapper(ss.getBytes());
            MerkleNode addResult = ipfs.add(file).get(0);
            if (null != addResult && null != addResult.hash) {
                System.out.println(addResult.hash.toString());
            }
            MessageDigest hasher = MessageDigest.getInstance("SHA-256");
            byte[] hash = hasher.digest(ss.getBytes());
            Multihash mhash = new Multihash(Multihash.Type.sha2_256, hash);
            Cid cid = Cid.buildCidV0(mhash);
            System.out.println(cid.toString());
        } catch (IOException | IllegalArgumentException | NoSuchAlgorithmException e) {
            e.printStackTrace();
        }

I get different result.

QmZE8aUxitmPdBjriC82rhhUmQbeh7KP4oEbgqBEATMct5
QmZKRiNkuVutGrvxWDr6dhp5zJa7sBM5HPWhuWF2mZgScm

Why? I doubt it maybe the ipfs server not only SHA256 byte[], but also other operation.

If anyone give advices. Thanks a lot!

[ianopolous]

In general you would need to implement the same chunking algorithm (rabin), encoding (protobufs) and data structures (unixfs) that ipfs uses internally.

[rmnvalera]

i have created a module which can generate the correct file hash: https://github.com/rmnvalera/java-cid-generate-hash