grpcurl

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, by reading proto source files, or by loading in compiled "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 either need the proto source files that define the service or need protoset files that grpcurl can use.

Examples for how to set up server reflection can be found here.

This repo also provides a library package, github.com/fullstorydev/grpcurl, that has functions for simplifying the construction of other command-line tools that dynamically invoke gRPC endpoints. This code is 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 can supply the .proto source files or you can supply protoset files (containing compiled descriptors, produced by protoc) to grpcurl.

Installation

You can use the go tool to install grpcurl:

go get github.com/fullstorydev/grpcurl
go install github.com/fullstorydev/grpcurl/cmd/grpcurl

This installs the command into the bin sub-folder of wherever your $GOPATH environment variable points. If this directory is already in your $PATH, then you should be good to go.

If you have already pulled down this repo to a location that is not in your $GOPATH and want to build from the sources, you can cd into the repo and then run make install.

If you encounter compile errors, you could have out-dated versions of grpcurl's dependencies. You can update the dependencies by running make updatedeps.

Usage

The usage doc for the tool explains the numerous options:

grpcurl -help

In the sections below, you will find numerous examples demonstrating how to use grpcurl.

Invoking RPCs

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 send a non-empty request, use the -d argument. Note that all arguments must come before the server address and method name:

grpcurl -d '{"id": 1234, "tags": ["foo","bar"]}' \
    grpc.server.com:443 my.custom.server.Service/Method

As can be seen in the example, the supplied body must be in JSON format. The body will be parsed and then transmitted to the server in the protobuf binary format.

If you want to include grpcurl in a command pipeline, such as when using jq to create a request body, you can use -d @, which tells grpcurl to read the actual request body from stdin:

grpcurl -d @ grpc.server.com:443 my.custom.server.Service/Method <<<EOM
{
  "id": 1234,
  "tags": [
    "foor",
    "bar"
  ]
}
EOM

Listing Services

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

# Server supports reflection
grpcurl localhost:8787 list

# Using compiled protoset files
grpcurl -protoset my-protos.bin list

# Using proto sources
grpcurl -import-path ../protos -proto my-stuff.proto list

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

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

Describing Elements

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.

# Server supports reflection
grpcurl localhost:8787 describe my.custom.server.Service.MethodOne

# Using compiled protoset files
grpcurl -protoset my-protos.bin describe my.custom.server.Service.MethodOne

# Using proto sources
grpcurl -import-path ../protos -proto my-stuff.proto describe my.custom.server.Service.MethodOne

Proto Source Files

To use grpcurl on servers that do not support reflection, you can use .proto source files.

In addition to using -proto flags to point grpcurl at the relevant proto source file(s), you may also need to supply -import-path flags to tell grpcurl the folders from which dependencies can be imported.

Just like when compiling with protoc, you do not need to provide an import path for the location of the standard protos included with protoc (which contain various "well-known types" with a package definition of google.protobuf). These files are "known" by grpcurl as a snapshot of their descriptors is built into the grpcurl binary.

Protoset Files

You can also use compiled protoset files with grpcurl. If you are scripting grpcurl and need to re-use the same proto sources for many invocations, you will see better performance by using protoset files (since it skips the parsing and compilation steps with each invocation).

Protoset files contain binary encoded google.protobuf.FileDescriptorSet protos. To create a protoset file, invoke protoc with the *.proto files that describe the service:

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 argument is necessary for the protoset to contain everything that grpcurl needs to process and understand the schema.