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The Protobuf ecosystem developed tools for different use cases, including code-generation from *.proto files into various languages. These tools allow clients to be built easily. Often, the client connection (i.e. the transport) can be plugged and replaced easily. Let’s explore a popular transport method, gRPC. Since the code generation library largely depends on your own tech stack, we will only present two alternatives:
  • grpcurl for generic debugging and testing
  • Programmatically via Go, Python, or TS

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grpcurl

grpcurl is like curl, but for gRPC. It is also available as a Go library, but we will use it only as a CLI command for debugging and testing purposes. Follow the instructions in the previous link to install it. Assuming you have a local node running (either a localnet, or connected to a live network), you should be able to run the following command to list the Protobuf services available. You can replace localhost:9090 by the gRPC server endpoint of another node, which is configured under the grpc.address field inside app.toml: 
grpcurl -plaintext localhost:9090 list
You should see a list of gRPC services, like cosmos.bank.v1beta1.Query. This is called reflection, which is a Protobuf endpoint returning a description of all available endpoints. Each of these represents a different Protobuf service, and each service exposes multiple RPC methods you can query against. In order to get a description of the service, you can run the following command: 
# Service we want to inspect
grpcurl \
    localhost:9090 \
    describe cosmos.bank.v1beta1.Query
It’s also possible to execute an RPC call to query the node for information: 
grpcurl \
    -plaintext
    -d '{"address":"$MY_VALIDATOR"}' \
    localhost:9090 \
    cosmos.bank.v1beta1.Query/AllBalances

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Query for historical state using grpcurl

You may also query for historical data by passing some gRPC metadata to the query: the x-cosmos-block-height metadata should contain the block to query. Using grpcurl as above, the command looks like: 
grpcurl \
    -plaintext \
    -H "x-cosmos-block-height: 279256" \
    -d '{"address":"$MY_VALIDATOR"}' \
    localhost:9090 \
    cosmos.bank.v1beta1.Query/AllBalances
Assuming the state at that block has not yet been pruned by the node, this query should return a non-empty response.

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Sending Transactions

Sending transactions using gRPC and REST requires some additional steps: generating the transaction, signing it, and finally broadcasting it. You can learn more in transactions.