diff --git a/go/vendor/google.golang.org/grpc/service_config.go b/go/vendor/google.golang.org/grpc/service_config.go
new file mode 100644
index 0000000..a305fe0
--- /dev/null
+++ b/go/vendor/google.golang.org/grpc/service_config.go
@@ -0,0 +1,361 @@
+/*
+ *
+ * Copyright 2017 gRPC authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ */
+
+package grpc
+
+import (
+	"encoding/json"
+	"fmt"
+	"strconv"
+	"strings"
+	"time"
+
+	"google.golang.org/grpc/codes"
+	"google.golang.org/grpc/grpclog"
+)
+
+const maxInt = int(^uint(0) >> 1)
+
+// MethodConfig defines the configuration recommended by the service providers for a
+// particular method.
+//
+// Deprecated: Users should not use this struct. Service config should be received
+// through name resolver, as specified here
+// https://github.com/grpc/grpc/blob/master/doc/service_config.md
+type MethodConfig struct {
+	// WaitForReady indicates whether RPCs sent to this method should wait until
+	// the connection is ready by default (!failfast). The value specified via the
+	// gRPC client API will override the value set here.
+	WaitForReady *bool
+	// Timeout is the default timeout for RPCs sent to this method. The actual
+	// deadline used will be the minimum of the value specified here and the value
+	// set by the application via the gRPC client API.  If either one is not set,
+	// then the other will be used.  If neither is set, then the RPC has no deadline.
+	Timeout *time.Duration
+	// MaxReqSize is the maximum allowed payload size for an individual request in a
+	// stream (client->server) in bytes. The size which is measured is the serialized
+	// payload after per-message compression (but before stream compression) in bytes.
+	// The actual value used is the minimum of the value specified here and the value set
+	// by the application via the gRPC client API. If either one is not set, then the other
+	// will be used.  If neither is set, then the built-in default is used.
+	MaxReqSize *int
+	// MaxRespSize is the maximum allowed payload size for an individual response in a
+	// stream (server->client) in bytes.
+	MaxRespSize *int
+	// RetryPolicy configures retry options for the method.
+	retryPolicy *retryPolicy
+}
+
+// ServiceConfig is provided by the service provider and contains parameters for how
+// clients that connect to the service should behave.
+//
+// Deprecated: Users should not use this struct. Service config should be received
+// through name resolver, as specified here
+// https://github.com/grpc/grpc/blob/master/doc/service_config.md
+type ServiceConfig struct {
+	// LB is the load balancer the service providers recommends. The balancer specified
+	// via grpc.WithBalancer will override this.
+	LB *string
+
+	// Methods contains a map for the methods in this service.  If there is an
+	// exact match for a method (i.e. /service/method) in the map, use the
+	// corresponding MethodConfig.  If there's no exact match, look for the
+	// default config for the service (/service/) and use the corresponding
+	// MethodConfig if it exists.  Otherwise, the method has no MethodConfig to
+	// use.
+	Methods map[string]MethodConfig
+
+	// If a retryThrottlingPolicy is provided, gRPC will automatically throttle
+	// retry attempts and hedged RPCs when the client’s ratio of failures to
+	// successes exceeds a threshold.
+	//
+	// For each server name, the gRPC client will maintain a token_count which is
+	// initially set to maxTokens, and can take values between 0 and maxTokens.
+	//
+	// Every outgoing RPC (regardless of service or method invoked) will change
+	// token_count as follows:
+	//
+	//   - Every failed RPC will decrement the token_count by 1.
+	//   - Every successful RPC will increment the token_count by tokenRatio.
+	//
+	// If token_count is less than or equal to maxTokens / 2, then RPCs will not
+	// be retried and hedged RPCs will not be sent.
+	retryThrottling *retryThrottlingPolicy
+}
+
+// retryPolicy defines the go-native version of the retry policy defined by the
+// service config here:
+// https://github.com/grpc/proposal/blob/master/A6-client-retries.md#integration-with-service-config
+type retryPolicy struct {
+	// MaxAttempts is the maximum number of attempts, including the original RPC.
+	//
+	// This field is required and must be two or greater.
+	maxAttempts int
+
+	// Exponential backoff parameters. The initial retry attempt will occur at
+	// random(0, initialBackoffMS). In general, the nth attempt will occur at
+	// random(0,
+	//   min(initialBackoffMS*backoffMultiplier**(n-1), maxBackoffMS)).
+	//
+	// These fields are required and must be greater than zero.
+	initialBackoff    time.Duration
+	maxBackoff        time.Duration
+	backoffMultiplier float64
+
+	// The set of status codes which may be retried.
+	//
+	// Status codes are specified as strings, e.g., "UNAVAILABLE".
+	//
+	// This field is required and must be non-empty.
+	// Note: a set is used to store this for easy lookup.
+	retryableStatusCodes map[codes.Code]bool
+}
+
+type jsonRetryPolicy struct {
+	MaxAttempts          int
+	InitialBackoff       string
+	MaxBackoff           string
+	BackoffMultiplier    float64
+	RetryableStatusCodes []codes.Code
+}
+
+// retryThrottlingPolicy defines the go-native version of the retry throttling
+// policy defined by the service config here:
+// https://github.com/grpc/proposal/blob/master/A6-client-retries.md#integration-with-service-config
+type retryThrottlingPolicy struct {
+	// The number of tokens starts at maxTokens. The token_count will always be
+	// between 0 and maxTokens.
+	//
+	// This field is required and must be greater than zero.
+	MaxTokens float64
+	// The amount of tokens to add on each successful RPC. Typically this will
+	// be some number between 0 and 1, e.g., 0.1.
+	//
+	// This field is required and must be greater than zero. Up to 3 decimal
+	// places are supported.
+	TokenRatio float64
+}
+
+func parseDuration(s *string) (*time.Duration, error) {
+	if s == nil {
+		return nil, nil
+	}
+	if !strings.HasSuffix(*s, "s") {
+		return nil, fmt.Errorf("malformed duration %q", *s)
+	}
+	ss := strings.SplitN((*s)[:len(*s)-1], ".", 3)
+	if len(ss) > 2 {
+		return nil, fmt.Errorf("malformed duration %q", *s)
+	}
+	// hasDigits is set if either the whole or fractional part of the number is
+	// present, since both are optional but one is required.
+	hasDigits := false
+	var d time.Duration
+	if len(ss[0]) > 0 {
+		i, err := strconv.ParseInt(ss[0], 10, 32)
+		if err != nil {
+			return nil, fmt.Errorf("malformed duration %q: %v", *s, err)
+		}
+		d = time.Duration(i) * time.Second
+		hasDigits = true
+	}
+	if len(ss) == 2 && len(ss[1]) > 0 {
+		if len(ss[1]) > 9 {
+			return nil, fmt.Errorf("malformed duration %q", *s)
+		}
+		f, err := strconv.ParseInt(ss[1], 10, 64)
+		if err != nil {
+			return nil, fmt.Errorf("malformed duration %q: %v", *s, err)
+		}
+		for i := 9; i > len(ss[1]); i-- {
+			f *= 10
+		}
+		d += time.Duration(f)
+		hasDigits = true
+	}
+	if !hasDigits {
+		return nil, fmt.Errorf("malformed duration %q", *s)
+	}
+
+	return &d, nil
+}
+
+type jsonName struct {
+	Service *string
+	Method  *string
+}
+
+func (j jsonName) generatePath() (string, bool) {
+	if j.Service == nil {
+		return "", false
+	}
+	res := "/" + *j.Service + "/"
+	if j.Method != nil {
+		res += *j.Method
+	}
+	return res, true
+}
+
+// TODO(lyuxuan): delete this struct after cleaning up old service config implementation.
+type jsonMC struct {
+	Name                    *[]jsonName
+	WaitForReady            *bool
+	Timeout                 *string
+	MaxRequestMessageBytes  *int64
+	MaxResponseMessageBytes *int64
+	RetryPolicy             *jsonRetryPolicy
+}
+
+// TODO(lyuxuan): delete this struct after cleaning up old service config implementation.
+type jsonSC struct {
+	LoadBalancingPolicy *string
+	MethodConfig        *[]jsonMC
+	RetryThrottling     *retryThrottlingPolicy
+}
+
+func parseServiceConfig(js string) (ServiceConfig, error) {
+	if len(js) == 0 {
+		return ServiceConfig{}, fmt.Errorf("no JSON service config provided")
+	}
+	var rsc jsonSC
+	err := json.Unmarshal([]byte(js), &rsc)
+	if err != nil {
+		grpclog.Warningf("grpc: parseServiceConfig error unmarshaling %s due to %v", js, err)
+		return ServiceConfig{}, err
+	}
+	sc := ServiceConfig{
+		LB:              rsc.LoadBalancingPolicy,
+		Methods:         make(map[string]MethodConfig),
+		retryThrottling: rsc.RetryThrottling,
+	}
+	if rsc.MethodConfig == nil {
+		return sc, nil
+	}
+
+	for _, m := range *rsc.MethodConfig {
+		if m.Name == nil {
+			continue
+		}
+		d, err := parseDuration(m.Timeout)
+		if err != nil {
+			grpclog.Warningf("grpc: parseServiceConfig error unmarshaling %s due to %v", js, err)
+			return ServiceConfig{}, err
+		}
+
+		mc := MethodConfig{
+			WaitForReady: m.WaitForReady,
+			Timeout:      d,
+		}
+		if mc.retryPolicy, err = convertRetryPolicy(m.RetryPolicy); err != nil {
+			grpclog.Warningf("grpc: parseServiceConfig error unmarshaling %s due to %v", js, err)
+			return ServiceConfig{}, err
+		}
+		if m.MaxRequestMessageBytes != nil {
+			if *m.MaxRequestMessageBytes > int64(maxInt) {
+				mc.MaxReqSize = newInt(maxInt)
+			} else {
+				mc.MaxReqSize = newInt(int(*m.MaxRequestMessageBytes))
+			}
+		}
+		if m.MaxResponseMessageBytes != nil {
+			if *m.MaxResponseMessageBytes > int64(maxInt) {
+				mc.MaxRespSize = newInt(maxInt)
+			} else {
+				mc.MaxRespSize = newInt(int(*m.MaxResponseMessageBytes))
+			}
+		}
+		for _, n := range *m.Name {
+			if path, valid := n.generatePath(); valid {
+				sc.Methods[path] = mc
+			}
+		}
+	}
+
+	if sc.retryThrottling != nil {
+		if sc.retryThrottling.MaxTokens <= 0 ||
+			sc.retryThrottling.MaxTokens >= 1000 ||
+			sc.retryThrottling.TokenRatio <= 0 {
+			// Illegal throttling config; disable throttling.
+			sc.retryThrottling = nil
+		}
+	}
+	return sc, nil
+}
+
+func convertRetryPolicy(jrp *jsonRetryPolicy) (p *retryPolicy, err error) {
+	if jrp == nil {
+		return nil, nil
+	}
+	ib, err := parseDuration(&jrp.InitialBackoff)
+	if err != nil {
+		return nil, err
+	}
+	mb, err := parseDuration(&jrp.MaxBackoff)
+	if err != nil {
+		return nil, err
+	}
+
+	if jrp.MaxAttempts <= 1 ||
+		*ib <= 0 ||
+		*mb <= 0 ||
+		jrp.BackoffMultiplier <= 0 ||
+		len(jrp.RetryableStatusCodes) == 0 {
+		grpclog.Warningf("grpc: ignoring retry policy %v due to illegal configuration", jrp)
+		return nil, nil
+	}
+
+	rp := &retryPolicy{
+		maxAttempts:          jrp.MaxAttempts,
+		initialBackoff:       *ib,
+		maxBackoff:           *mb,
+		backoffMultiplier:    jrp.BackoffMultiplier,
+		retryableStatusCodes: make(map[codes.Code]bool),
+	}
+	if rp.maxAttempts > 5 {
+		// TODO(retry): Make the max maxAttempts configurable.
+		rp.maxAttempts = 5
+	}
+	for _, code := range jrp.RetryableStatusCodes {
+		rp.retryableStatusCodes[code] = true
+	}
+	return rp, nil
+}
+
+func min(a, b *int) *int {
+	if *a < *b {
+		return a
+	}
+	return b
+}
+
+func getMaxSize(mcMax, doptMax *int, defaultVal int) *int {
+	if mcMax == nil && doptMax == nil {
+		return &defaultVal
+	}
+	if mcMax != nil && doptMax != nil {
+		return min(mcMax, doptMax)
+	}
+	if mcMax != nil {
+		return mcMax
+	}
+	return doptMax
+}
+
+func newInt(b int) *int {
+	return &b
+}