cURL

You can access a Twirp service with cURL, using either JSON or Protobuf.

Example

With the following HelloWorld service defined in this proto file:

syntax = "proto3";
package example.helloworld;

service HelloWorld {
  rpc Hello(HelloReq) returns (HelloResp);
}

message HelloReq {
   string subject = 1;
}

message HelloResp {
  string text = 1;
}

Assuming a service generated from this definition is running in http://localhost:8080 with the default "/twirp" prefix, you can call it with cURL by following the routing rules (see Routing)

JSON

Use the header Content-Type: application/json to signal that the request and response are JSON:

curl --request "POST" \
    --header "Content-Type: application/json" \
    --data '{"subject": "World"}' \
    http://localhost:8080/twirp/example.helloworld.HelloWorld/Hello

The service should respond with something like this:

{"text": "Hello World"}

NOTE: Twirp uses proto3-json mapping, which means that empty fields are excluded. If you specify an empty request --data '{}' it will be interpreted as zero-values. Zero-values are also excluded on responses. In this example, if the service responded with an empty "text" field, the response you will see is empty {}.

Protobuf

Use the header Content-Type: application/protobuf to signal that the request and response are Protobuf. Use the protoc tool to encode and decode the Protobuf messages into readable key-values:

echo 'subject:"World"' \
    | protoc --encode example.helloworld.HelloReq ./rpc/helloworld/service.proto \
    | curl -s --request POST \
      --header "Content-Type: application/protobuf" \
      --data-binary @- \
      http://localhost:8080/twirp/example.helloworld.HelloWorld/Hello \
    | protoc --decode example.helloworld.HelloResp ./rpc/haberdasher/service.proto

The service should respond with something like this:

text:"Hello World"

Errors

Twirp error responses are always JSON, even if the request is done in Protobuf. A Twirp error response looks like this:

{"code": "internal", "msg": "Something went wrong"}