gRPCurl

grpcurl is a command-line tool that lets you interact with gRPC servers. It's basically curl for gRPC servers.

The main purpose for this tool is to invoke RPC methods on a gRPC server from the command-line. gRPC servers use a binary encoding on the wire (protocol buffers, or "protobufs" for short). So they are basically impossible to interact with using regular curl (and older versions of curl that do not support HTTP/2 are of course non-starters). This program accepts messages using JSON encoding, which is much more friendly for both humans and scripts.

With this tool you can also browse the schema for gRPC services, either by querying a server that supports service reflection or by loading in "protoset" files (files that contain encoded file descriptor protos). In fact, the way the tool transforms JSON request data into a binary encoded protobuf is using that very same schema. So, if the server you interact with does not support reflection, you will need to build "protoset" files that grpcurl can use.

This code for this tool is also a great example of how to use the various packages of the protoreflect library, and shows off what they can do.

Features

grpcurl supports all kinds of RPC methods, including streaming methods. You can even operate bi-directional streaming methods interactively by running grpcurl from an interactive terminal and using stdin as the request body!

grpcurl supports both plain-text and TLS servers and has numerous options for TLS configuration. It also supports mutual TLS, where the client is required to present a client certificate.

As mentioned above, grpcurl works seamlessly if the server supports the reflection service. If not, you must use protoc to build protoset files and provide those to grpcurl.

Example Usage

Invoking an RPC on a trusted server (e.g. TLS without self-signed key or custom CA) that requires no client certs and supports service reflection is the simplest thing to do with grpcurl. This minimal invocation sends an empty request body:

grpcurl grpc.server.com:443 my.custom.server.Service/Method

To list all services exposed by a server, use the "list" verb. When using protoset files instead of server reflection, this lists all services defined in the protoset files.

grpcurl localhost:8787 list

grpcurl -protoset my-protos.bin list

The "list" verb also lets you see all methods in a particular service:

grpcurl localhost:8787 list my.custom.server.Service

The "describe" verb will print the type of any symbol that the server knows about or that is found in a given protoset file and also print the full descriptor for the symbol, in JSON.

grpcurl localhost:8787 describe my.custom.server.Service.MethodOne

grpcurl -protoset my-protos.bin describe my.custom.server.Service.MethodOne

The usage doc for the tool explains the numerous options:

grpcurl -help

Protoset Files

To use grpcurl on servers that do not support reflection, you need to compile the *.proto files that describe the service into files containing encoded FileDescriptorSet protos, also known as "protoset" files.

protoc --proto_path=. \
    --descriptor_set_out=myservice.protoset \
    --include_imports \
    my/custom/server/service.proto

The --descriptor_set_out argument is what tells protoc to produce a protoset, and the --include_imports arguments is necessary for the protoset to contain everything that grpcurl needs to process and understand the schema.