cid

A dart implementation of cid ("content id") = human-friendly (readable/typeable) unique ID for distributed/decentralised systems.

Why 🤷

In a database that is distributed, creating IDs that reference records with virtually no risk of collision is a must. We need a standardized way of creating IDs for both the server and the client-side of our app, in an offline-first approach.

As we are using Flutter for developing our application, we needed a way to create these IDs using the Dart language.

What? 🔐

If you are a newbie when it comes to cids and how they are applicable to distributed scenarios, we highly encourage you to check the dwyl/cid repo. Although it was made for Elixir, you can find more about real-life situations of how these are used, especially with IPFS. And yes, it will answer the obvious question of Why are you not using UUIDs? 😉

How? 💡

Using this package is as easy as pie. You just need an input string that will be hashed and used to create a corresponding cid. This cid will be, as the name implies, the content identifier - something that will identify that string.

Let's see it in action.

Installing

Add the following to your pubspec.yaml file, under dependencies.

dependencies:
  cid: ^1.0.0

and run the following command to fetch the dependencies.

flutter pub get

Usage

Creating a CID

Now just call the createCid() function! You may decide what multibase you want to use. This library tries to support the official/default bases. If you see one that's missing, do open an issue.

import 'package:cid/cid.dart';

String input = 'hello world';
CIDInfo output = CID.createCid(input, Multibase.base58btc);

print(output.cid)
// "zb2rhj7crUKTQYRGCRATFaQ6YFLTde2YzdqbbhAASkL9uRDXn"

and you're done! 🎉 You just created your own fancy cid!

Note

Every cid generated with this package will use the raw codec and will be hashed using the sha2-256 algorithm. You may choose which base you want to encode it as, though.

Decoding a CID

If you're given a CID and you wish to decode it, you can use the decodeCid() function.

CIDInfo cidInfo = decodeCid("some_cid");

This function will return an instance of CIDInfo, holding relevant information of the provided CID.

Converting CIDv0 to CIDv1

If you've decoded a CIDv0 string, you can convert it to a CIDv1 object by calling toV1(). This function can receive a multibase parameter if you wish to encode it in a different base (e.g. toV1(Multibase.base58btc)). By default, it is encoded to base32.

// Decode a v0 cid.
CIDInfo cidInfo = decodeCid("QmcRD4wkPPi6dig81r5sLj9Zm1gDCL4zgpEj9CfuRrGbzF");

// Convert it to v1
cidInfo.toV1();
print(cidInfo.cid)
// "bafybeigrf2dwtpjkiovnigysyto3d55opf6qkdikx6d65onrqnfzwgdkfa"

Considerations

If you're interested in learning more about a given CID's components...

zb2rhj7crUKTQYRGCRATFaQ6YFLTde2YzdqbbhAASkL9uRDXn

...you can use the IPFS cid inspector to see the information that is hashed into the string.

Open https://cid.ipfs.tech/#zb2rhj7crUKTQYRGCRATFaQ6YFLTde2YzdqbbhAASkL9uRDXn and see it for yourself!

As you can see, the cid contains leading identifiers that clarify which representation is used, along with the content-hash. It includes:

• multibase prefix which specifies the encoding of the cid.
• cid version
• multicodec which indicates the format of the target content.

For more information about the format of cids, check this link -> https://docs.ipfs.tech/concepts/content-addressing/#cid-versions

I need help! ❓

If you have some feedback or have any question, do not hesitate and open an issue! We are here to help and are happy for your contribution!

License

MIT