Represents the gRPC ServiceConfig parsed from JSON, which can come from DNS TXT records or xDS.

The gRPC ServiceConfig allows a client to configure per-service and per-method behaviors such as load balancing, timeouts, and retry policies.

Spec

According to the gRPC specification (service_config.md):

• loadBalancingConfig: a list of load balancing policies.
  The client should pick the first policy it supports. Common values are:

  • "pick_first": always pick the first server.
  • "round_robin": distribute calls across servers in round-robin.

• methodConfig: a list of configurations applied to specific methods or services.
  Each entry can include:

  • "name": a list of { "service": "<service_name>", "method": "<method_name>" } or { "service": "<service_name>" } to match all methods in the service.
  • "timeout": RPC timeout as a string (e.g., "1.000000001s").
  • "retryPolicy": optional retry policy map.
  • Other optional method-level settings.

Example TXT record

A DNS TXT record for a service my-service.local might look like this:

_grpc_config.my-service.local 3600 TXT
"grpc_config={
  "loadBalancingConfig":[{"round_robin":{}}],
  "methodConfig":[
    {
      "name":[
        {"service":"foo","method":"bar"},
        {"service":"baz"}
      ],
      "timeout":"1.000000001s"
    }
  ]
}"

This JSON will be parsed into a %GRPC.Client.ServiceConfig{} struct with:

%GRPC.Client.ServiceConfig{
  load_balancing_policy: :round_robin,
  method_configs: [
    %{
      "name" => [
        %{"service" => "foo", "method" => "bar"},
        %{"service" => "baz"}
      ],
      "timeout" => "1.000000001s"
    }
  ],
  raw: <original JSON map>
}

Usage

{:ok, config} = GRPC.Client.ServiceConfig.parse(txt_json)
IO.inspect(config.load_balancing_policy)
IO.inspect(config.method_configs)