[Feature]: Allow creation of AppGenesis without a file lookup

[chatton]

Summary

Provide an alternative to AppGenesisFromFile which does not depend on a file lookup to create an instance of AppGenesis.

Problem Definition

In the ibc-go e2e tests, we use interchain test which provides a hook to modify the genesis bytes. In order to provide modifications, we need to serialize the bytes, make changes, and return the new bytes.

The current implementation of AppGenesisFromFile does a direct os.ReadFile and so is not quite flexible enough to meet our use case.

Proposed Feature

I propose the method signature is changed (or a new fn is added is the original behaviour is still required!)

I think using an io.Reader is a nice ux for this.

// AppGenesisFromReader reads the AppGenesis from the reader.
func AppGenesisFromReader(reader io.Reader) (*AppGenesis, error) {
    jsonBlob, err := io.ReadAll(reader)
    if err != nil {
        return nil, err
    }

    var appGenesis AppGenesis
    if err := json.Unmarshal(jsonBlob, &appGenesis); err != nil {
        // fallback to CometBFT genesis
        var ctmGenesis cmttypes.GenesisDoc
        if err2 := cmtjson.Unmarshal(jsonBlob, &ctmGenesis); err2 != nil {
            return nil, fmt.Errorf("error unmarshalling AppGenesis: %w\n failed fallback to CometBFT GenDoc: %w", err, err2)
        }

        appGenesis = AppGenesis{
            AppName: version.AppName,
            // AppVersion is not filled as we do not know it from a CometBFT genesis
            GenesisTime:   ctmGenesis.GenesisTime,
            ChainID:       ctmGenesis.ChainID,
            InitialHeight: ctmGenesis.InitialHeight,
            AppHash:       ctmGenesis.AppHash,
            AppState:      ctmGenesis.AppState,
            Consensus: &ConsensusGenesis{
                Validators: ctmGenesis.Validators,
                Params:     ctmGenesis.ConsensusParams,
            },
        }
    }

    return &appGenesis, nil
}

// AppGenesisFromFile reads the AppGenesis from the provided file.
func AppGenesisFromFile(genFile string) (*AppGenesis, error) {
    file, err := os.Open(genFile)
    if err != nil {
        return nil, err
    }
    return AppGenesisFromReader(bufio.NewReader(file))
}

[tac0turtle]

want to open a pr and we can include it in 0.50 since its not api breaking?

[chatton]

can do! 👍