Ratelimiter returns resource exhausted error

This is necessary so that when it is used with the backoff retry it will
allow for the backoff to continue to work as expected.

Signed-off-by: Nathan Zender <github@nathanzender.com>

pkg/util/grpcclient/ratelimit.go

@@ -5,6 +5,8 @@ import (
 
 	"golang.org/x/time/rate"
 	"google.golang.org/grpc"
+	"google.golang.org/grpc/codes"
+	"google.golang.org/grpc/status"
 )
 
 // NewRateLimiter creates a UnaryClientInterceptor for client side rate limiting.
@@ -17,7 +19,7 @@ func NewRateLimiter(cfg *Config) grpc.UnaryClientInterceptor {
 	return func(ctx context.Context, method string, req, reply interface{}, cc *grpc.ClientConn, invoker grpc.UnaryInvoker, opts ...grpc.CallOption) error {
 		err := limiter.Wait(ctx)
 		if err != nil {
-			return err
+			return status.Error(codes.ResourceExhausted, err.Error())
 		}
 		return invoker(ctx, method, req, reply, cc, opts...)
 	}

pkg/util/grpcclient/ratelimit_test.go

@@ -0,0 +1,36 @@
+package grpcclient_test
+
+import (
+	"context"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+	"google.golang.org/grpc"
+	"google.golang.org/grpc/codes"
+	"google.golang.org/grpc/status"
+
+	"github.com/cortexproject/cortex/pkg/util/grpcclient"
+)
+
+func TestRateLimiterFailureResultsInResourceExhaustedError(t *testing.T) {
+	config := grpcclient.Config{
+		RateLimitBurst: 0,
+		RateLimit:      0,
+	}
+	conn := grpc.ClientConn{}
+	invoker := func(currentCtx context.Context, currentMethod string, currentReq, currentRepl interface{}, currentConn *grpc.ClientConn, currentOpts ...grpc.CallOption) error {
+		return nil
+	}
+
+	limiter := grpcclient.NewRateLimiter(&config)
+	err := limiter(context.Background(), "methodName", "", "expectedReply", &conn, invoker)
+
+	if se, ok := err.(interface {
+		GRPCStatus() *status.Status
+	}); ok {
+		assert.Equal(t, se.GRPCStatus().Code(), codes.ResourceExhausted)
+		assert.Equal(t, se.GRPCStatus().Message(), "rate: Wait(n=1) exceeds limiter's burst 0")
+	} else {
+		assert.Fail(t, "Could not convert error into expected Status type")
+	}
+}