Building Subgraphs on Cosmos

This guide is an introduction on building subgraphs indexing Cosmos based blockchains.

What are Cosmos subgraphs?

The Graph allows developers to process blockchain events and make the resulting data easily available via an open GraphQL API, known as a subgraph. Graph Node is now able to process Cosmos events, which means Cosmos developers can now build subgraphs to easily index on-chain events.

There are currently three types of handlers supported for the Cosmos subgraphs:

• Block handlers: run whenever a new block is appended to the chain.

• Event handlers: run when a specific event is emitted.

• Transaction handlers: run when a transaction occurs.

Based on the official Cosmos documentation:

Events are objects that contain information about the execution of the application. They are mainly used by service providers like block explorers and wallets to track the execution of various messages and index transactions.

Transactions are objects created by end-users to trigger state changes in the application.

Building a Cosmos subgraph

Subgraph Dependencies

graph-cli is a CLI tool to build and deploy subgraphs, version >=0.30.0 is required in order to work with Cosmos subgraphs.

graph-ts is a library of subgraph-specific types, version >=0.27.0 is required in order to work with Cosmos subgraphs.

Subgraph Main Components

There are three main key parts or files when it comes to defining a subgraph:

subgraph.yaml: a YAML file containing the subgraph manifest, which identifies which events to track and how to process them.

schema.graphql: a GraphQL schema that defines what data is stored for your subgraph, and how to query it via GraphQL.

AssemblyScript Mappings: AssemblyScript code that translates from blockchain data to the entities defined in your schema.

Subgraph Manifest Definition

The subgraph manifest (subgraph.yaml) identifies the data sources for the subgraph, the triggers of interest, and the functions (handlers) that should be run in response to those triggers. See below for an example subgraph manifest for a Cosmos subgraph:

specVersion: 0.0.5description: Cosmos Subgraph Exampleschema:  file: ./schema.graphql # link to the schema filedataSources:  - kind: cosmos    name: CosmosHub    network: cosmoshub-4 # This will change for each cosmos-based blockchain. In this case, the example uses the CosmosHub mainnet.    source:      startBlock: 0 # Required for Cosmos, set this to 0 to start indexing from chain genesis    mapping:      apiVersion: 0.0.7      language: wasm/assemblyscript      blockHandlers:        - handler: handleNewBlock # the function name in the mapping file      eventHandlers:        - event: rewards # the type of the event that will be handled          handler: handleReward # the function name in the mapping file      transactionHandlers:        - handler: handleTransaction # the function name in the mapping file      file: ./src/mapping.ts # link to the file with the Assemblyscript mappings

• Cosmos subgraphs introduce a new kind of data source (cosmos).

• The network should correspond to a network on the hosting Graph Node. In the example, the CosmosHub mainnet is used.

Cosmos data sources support three types of handlers:

• blockHandlers: run on every new block appended to the chain. The handler will receive a full block and all its data containing, among other things, all the events and transactions.

• eventHandlers: run on every event contained in a block that matches the event type specified in the manifest. Block data is also passed onto the mapping in order to have the context of the event within the chain.

• transactionHandlers: run for every transaction executed. The mapping is provided with all the relevant data related to the transaction and a block abstraction that can be used to acquire the context of the transaction within a block and within the chain.

Event and Transaction handlers are a way to process meaningful data from the chain without the need of processing a whole block. The data processed by them can also be found in the block handlers, since events and transactions are also part of a block, but removes the need of processing unnecessary data.

Schema Definition

Schema definition describes the structure of the resulting subgraph database and the relationships between entities. This is agnostic of the original data source. There are more details on subgraph schema definition here.

AssemblyScript Mappings

The handlers for processing events are written in AssemblyScript.

Cosmos indexing introduces Cosmos-specific data types to the AssemblyScript API.

class Block {  header: Header  evidence: EvidenceList  resultBeginBlock: ResponseBeginBlock  resultEndBlock: ResponseEndBlock  transactions: Array<TxResult>  validatorUpdates: Array<Validator>}
class EventData {  event: Event  block: HeaderOnlyBlock}
class TransactionData {  tx: TxResult  block: HeaderOnlyBlock}
class HeaderOnlyBlock {  header: Header}
class Header {  version: Consensus  chainId: string  height: u64  time: Timestamp  lastBlockId: BlockID  lastCommitHash: Bytes  dataHash: Bytes  validatorsHash: Bytes  nextValidatorsHash: Bytes  consensusHash: Bytes  appHash: Bytes  lastResultsHash: Bytes  evidenceHash: Bytes  proposerAddress: Bytes  hash: Bytes}
class TxResult {  height: u64  index: u32  tx: Tx  result: ResponseDeliverTx  hash: Bytes}
class Event {  eventType: string  attributes: Array<EventAttribute>}

The types above are just the general ones that mappings use. You can find the full list of types for the Cosmos integration here.

Each type of handler will receive a different type based on the relevant data. For both event and transaction handlers, a reference to the block they are contained in is passed as well. These are the exact types that are passed as a parameter to each mapping function:

Block is passed to the blockHandler.

EventData is passed to the eventHandler.

TransactionData is passed to the transactionHandler. Transactions will need to be decoded in the subgraph, here is an example on how it can be done.

Creating and building a Cosmos subgraph

The first step before starting to write the subgraph mappings is to generate the type bindings based on the entities that have been defined in the subgraph schema file (schema.graphql). This will allow the mapping functions to create new objects of those types and save them to the store. This is done by using the codegen CLI command:

$ graph codegen

Once the mappings are ready, the subgraph needs to be built. This step will highlight any errors the manifest or the mappings might have. A subgraph needs to build successfully in order to be deployed to the Graph Node. It can be done using the build CLI command:

$ graph build

Deploying a Cosmos subgraph

Once your subgraph has been created, you can deploy your subgraph by using the graph deploy CLI command after running the graph create CLI command:

Local Graph Node (based on default configuration):

graph create subgraph-name --node http://localhost:8020

graph deploy --node http://localhost:8020/ --ipfs http://localhost:5001

Querying a Cosmos subgraph

The GraphQL endpoint for Cosmos subgraphs is determined by the schema definition, with the existing API interface. Please visit the GraphQL API documentation for more information.

Supported Cosmos Blockchains

Cosmos Hub

What is Cosmos Hub?

The Cosmos Hub blockchain is the first blockchain in the Cosmos ecosystem. You can visit the official documentation for more information.

Networks

Cosmos Hub mainnet is cosmoshub-4. Cosmos Hub current testnet is theta-testnet-001. Other Cosmos Hub networks, i.e. cosmoshub-3, are halted, therefore no data is provided for them.

What is Osmosis?

Osmosis is a decentralized, cross-chain automated market maker (AMM) protocol built on top of the Cosmos SDK. It allows users to create custom liquidity pools and trade IBC-enabled tokens. You can visit the official documentation for more information.

Networks

Osmosis mainnet is osmosis-1. Osmosis current testnet is osmo-test-4.

Example Subgraphs

Here are some example subgraphs for reference:

Block Filtering Example

Validator Rewards Example

Validator Delegations Example

Osmosis Token Swaps Example