Follow our simple nameservice application tutorial to build your own decentralized application running on its own blockchain with the Cosmos SDK. Download the tutorial: github.com/cosmos/sdk-application-tutorial

1. Cosmos-SDK
Talkshop

2. Before we begin...
Talkshop: Talk + Workshop
(Interactive presentation)
Download the tutorial
github.com/cosmos/sdk-application-tutorial
goes in $GO_PATH/src/github.com/cosmos/
make get_tools && make get_vendor_deps && make install

3. Welcome!
Let’s use the Cosmos-SDK
To make a
Blockchain
Replicated State Machine
Hi, I’m Jack ✌

4. Replicated State Machine
What is the initial state?
What are the possible state transitions?
Is it Byzantine Fault Tolerant?

5. Cosmos Developer Kit
Golang toolset for building Replicated State Machines
Ruby-on-Rails for Blockchain
Focus on the Application
Proof-of-Stake 🍃 is better than Proof-of-Work ☠🔥
Tendermint for Consensus & Networking

6. Our Application!
Distributed Name Service
No one should be able to limit access to a public utility
Distribute the access and responsibility
● Ethereum Name Service
● Handshake
● Namecoin/Blockstack

7. Our Application!
● github.com/cosmos/sdk-application-tutorial
● Download the tutorial to follow along with code
● At the end I’ll spin up a node and give everyone money
● You can create and buy names from each other

8. The SDK is a Modular Framework
● Aggregates a collection of interoperable modules
● Each Module has its own Message/Transaction processor
● The SDK routes each message to the respective module

9. Modules in this Tutorial
● Auth
○ Access Control List (ACL) with Asymmetric Encryption
● Bank
○ Money Money Money
● NameService
○ Whois???

10. Modules NOT in this Tutorial
● Staking
○ Used for updating the set of validators
○ We use a fixed set from genesis
○ Private => Permissioned => Public
● Governance
○ Let’s Vote!

11. Modules are States & Messages

12. Modules: State
● All state goes in one store called multistore
● Contains multiple key/value stores called KVStores
● Our State
○ Accounts (auth)
○ Balances (bank)
○ Domain Names (nameservice)

13. Domain Names: nameStore
● Name => Value
○ What does the name resolve to (the zonefile)?
● Name => Owner
○ Who owns the name?
● Name => Price
○ How much to buy it?

14. Modules: Messages
● Messages Trigger State Transitions
● The Module Routes the Messages to Handlers
● The Handlers Hand them to Keepers
● The Keepers update the State

15. Domain Names: Messages
● MsgSetName
○ This message allows an owner to set the value of a name
● MsgBuyName
○ This message allows anyone to buy a name for some price

16. General Flow
● A Transaction contains a Message
● Tendermint nodes receive Transactions in Blocks
● They’re passed to the application via ABCI
○ Application Blockchain Interface
○ Socket Protocol between Tendermint and the application
● Decoded as Messages by baseapp & routed to correct Module
● Each Module has Handlers that decides what to do with them
● Each Handler calls Keepers to update the State

17. Let’s begin in ./app.go
● Imports
○ Log - for logs
○ Auth - for accounts and signing
○ Dbm - tendermint database
○ Codec - serialization
○ Baseapp - boilerplate
● Makes a new Type called nameservice
○ That’s our app!

18. Let’s begin in ./app.go
● Imports
○ Log - for logs
○ Auth - for accounts and signing
○ Dbm - tendermint database
○ Codec - serialization
○ Bam - Baseapp boilerplate
● Makes a new Type called nameservice
○ That’s our app!

19. Our nameservice module
● All modules go in the directory called ./x/
● Our module goes in the directory called ./x/nameservice/
● Inside ./x/nameservice/ we’ll have:
○ Handler.go
○ Keeper.go
○ Querier.go
○ Msgs.go
○ Codec.go
○ Client/ => for REST & CLI

20. ● Keepers manage the state
○ Like reducers/redux or mutations/vuex
● Handlers call the Keepers
○ Like actions in redux/vuex
The Keeper

21. ● nameStoreKey
○ map[name]value - like a Zonefile w traditional DNS
● ownerStoreKey
○ map[sdk_address]name - who owns what
● priceStoreKey
○ map[name]price - how much a name costs
Our Keeper has 3 New Keys

22. ● Getters
○ ResolveName
○ HasOwner
○ GetOwner
○ GetPrice
● Setters
○ SetName
○ SetOwner
○ SetPrice
Our Keeper has Getters & Setters

23. Our Keeper has Getters & Setters

24. Msgs & Handlers
● Msgs trigger Handlers
○ Like user initiated events
● Handlers call the Keepers
○ Like actions in redux/vuex
● Keepers manage the state
○ Like reducers/redux or mutations/vuex

25. Msgs go in ./x/nameservice/msgs.go

26. Two Msg Types Needed For Our App
● MsgSetName
○ Owners can set the name
● MsgBuyName
○ Names can be bought

27. MsgSetName
● Set all the Interfaces
● Example: ValidateBasic

28. handleMsgSetName
● Goes in ./x/nameservice/handler.go
● Utilizes the Keeper we made earlier

29. Queriers
● Queriers : Getters
● Handlers : Setters
● Goes inside ./x/nameservice/querier.go
● Uses the Keeper to access the KVStore

30. Our Queriers
● Resolve
○ Accepts name returns value
● Whois
○ Accepts name returns value, price, owner

31. Our Queriers: Whois

32. Codec
● Register new msg types for serialization (not whois?)
● Amino is an extension of protobuf
● Goes in ./x/nameservice/codec.go

33. Building Clients!
● From the Command Line
○ Utilizes the cobra library
○ Goes in ./x/nameservice/client/cli/query.go
○ Goes in ./x/nameservice/client/cli/tx.go
● From a REST server
○ Goes in ./x/nameservice/client/rest/rest.go
● Export both from Module Client
○ Goes in ./x/nameservice/client/module_client.go

34. Pull it all back into app.go
● Import and Initialize all our new pieces
● AddRoute for Handlers and Queriers
● Register the Codecs
● InitChainer for initial application state
○ Takes a genesis.json file that can be generated by the CLI
○ This is where I’ll add everyone’s public key and some
balance of token for buying names $ )

35. Build our Binaries!
● Wrap our app with commands we can use
● Wrap our client with commands we can use
● ./cmd/nsd/main.go
○ Name Service Daemon runs our node
● ./cmd/nscli/main.go
○ Name Service CLI

36. One last step
● Makefile
○ Installs and builds
● Gopkg
○ keeps our versions constrained
● Build!
○ dep ensure -update -v
○ make install

37. Claim Your Name!
Go to talkshop.name/