do not depend on experimental API for balancer

Since this has been working just fine so far, I opted to copying the relevant
code over to avoid regressions from a change of implementation.
Fixes bazelbuild#499.

go/internal/balancer/BUILD.bazel

@@ -0,0 +1,16 @@
+load("@io_bazel_rules_go//go:def.bzl", "go_library")
+
+go_library(
+    name = "balancer",
+    srcs = ["balancer.go"],
+    importpath = "github.com/bazelbuild/remote-apis-sdks/go/internal/balancer",
+    visibility = ["//go:__subpackages__"],
+    deps = [
+        "//go/internal/resolver",
+        "@org_golang_google_grpc//channelz",
+        "@org_golang_google_grpc//connectivity",
+        "@org_golang_google_grpc//credentials",
+        "@org_golang_google_grpc//metadata",
+        "@org_golang_google_grpc//serviceconfig",
+    ],
+)

go/internal/resolver/BUILD.bazel

@@ -0,0 +1,13 @@
+load("@io_bazel_rules_go//go:def.bzl", "go_library")
+
+go_library(
+    name = "resolver",
+    srcs = ["resolver.go"],
+    importpath = "github.com/bazelbuild/remote-apis-sdks/go/internal/resolver",
+    visibility = ["//go:__subpackages__"],
+    deps = [
+        "@org_golang_google_grpc//attributes",
+        "@org_golang_google_grpc//credentials",
+        "@org_golang_google_grpc//serviceconfig",
+    ],
+)

go/internal/resolver/resolver.go

@@ -0,0 +1,319 @@
+// This file was copied from https://github.com/grpc/grpc-go/blob/b0a946cf0cf1adb094d7da9dbf2d054905702c73/resolver/resolver.go
+// to avoid depending on an experimental API. See #499.
+
+/*
+ *
+ * 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 resolver defines APIs for name resolution in gRPC.
+// All APIs in this package are experimental.
+package resolver
+
+import (
+	"context"
+	"fmt"
+	"net"
+	"net/url"
+	"strings"
+
+	"google.golang.org/grpc/attributes"
+	"google.golang.org/grpc/credentials"
+	"google.golang.org/grpc/serviceconfig"
+)
+
+var (
+	// m is a map from scheme to resolver builder.
+	m = make(map[string]Builder)
+	// defaultScheme is the default scheme to use.
+	defaultScheme = "passthrough"
+)
+
+// TODO(bar) install dns resolver in init(){}.
+
+// Register registers the resolver builder to the resolver map. b.Scheme will
+// be used as the scheme registered with this builder. The registry is case
+// sensitive, and schemes should not contain any uppercase characters.
+//
+// NOTE: this function must only be called during initialization time (i.e. in
+// an init() function), and is not thread-safe. If multiple Resolvers are
+// registered with the same name, the one registered last will take effect.
+func Register(b Builder) {
+	m[b.Scheme()] = b
+}
+
+// Get returns the resolver builder registered with the given scheme.
+//
+// If no builder is register with the scheme, nil will be returned.
+func Get(scheme string) Builder {
+	if b, ok := m[scheme]; ok {
+		return b
+	}
+	return nil
+}
+
+// SetDefaultScheme sets the default scheme that will be used. The default
+// default scheme is "passthrough".
+//
+// NOTE: this function must only be called during initialization time (i.e. in
+// an init() function), and is not thread-safe. The scheme set last overrides
+// previously set values.
+func SetDefaultScheme(scheme string) {
+	defaultScheme = scheme
+}
+
+// GetDefaultScheme gets the default scheme that will be used.
+func GetDefaultScheme() string {
+	return defaultScheme
+}
+
+// Address represents a server the client connects to.
+//
+// # Experimental
+//
+// Notice: This type is EXPERIMENTAL and may be changed or removed in a
+// later release.
+type Address struct {
+	// Addr is the server address on which a connection will be established.
+	Addr string
+
+	// ServerName is the name of this address.
+	// If non-empty, the ServerName is used as the transport certification authority for
+	// the address, instead of the hostname from the Dial target string. In most cases,
+	// this should not be set.
+	//
+	// WARNING: ServerName must only be populated with trusted values. It
+	// is insecure to populate it with data from untrusted inputs since untrusted
+	// values could be used to bypass the authority checks performed by TLS.
+	ServerName string
+
+	// Attributes contains arbitrary data about this address intended for
+	// consumption by the SubConn.
+	Attributes *attributes.Attributes
+
+	// BalancerAttributes contains arbitrary data about this address intended
+	// for consumption by the LB policy.  These attributes do not affect SubConn
+	// creation, connection establishment, handshaking, etc.
+	//
+	// Deprecated: when an Address is inside an Endpoint, this field should not
+	// be used, and it will eventually be removed entirely.
+	BalancerAttributes *attributes.Attributes
+
+	// Metadata is the information associated with Addr, which may be used
+	// to make load balancing decision.
+	//
+	// Deprecated: use Attributes instead.
+	Metadata any
+}
+
+// Equal returns whether a and o are identical.  Metadata is compared directly,
+// not with any recursive introspection.
+//
+// This method compares all fields of the address. When used to tell apart
+// addresses during subchannel creation or connection establishment, it might be
+// more appropriate for the caller to implement custom equality logic.
+func (a Address) Equal(o Address) bool {
+	return a.Addr == o.Addr && a.ServerName == o.ServerName &&
+		a.Attributes.Equal(o.Attributes) &&
+		a.BalancerAttributes.Equal(o.BalancerAttributes) &&
+		a.Metadata == o.Metadata
+}
+
+// String returns JSON formatted string representation of the address.
+func (a Address) String() string {
+	var sb strings.Builder
+	sb.WriteString(fmt.Sprintf("{Addr: %q, ", a.Addr))
+	sb.WriteString(fmt.Sprintf("ServerName: %q, ", a.ServerName))
+	if a.Attributes != nil {
+		sb.WriteString(fmt.Sprintf("Attributes: %v, ", a.Attributes.String()))
+	}
+	if a.BalancerAttributes != nil {
+		sb.WriteString(fmt.Sprintf("BalancerAttributes: %v", a.BalancerAttributes.String()))
+	}
+	sb.WriteString("}")
+	return sb.String()
+}
+
+// BuildOptions includes additional information for the builder to create
+// the resolver.
+type BuildOptions struct {
+	// DisableServiceConfig indicates whether a resolver implementation should
+	// fetch service config data.
+	DisableServiceConfig bool
+	// DialCreds is the transport credentials used by the ClientConn for
+	// communicating with the target gRPC service (set via
+	// WithTransportCredentials). In cases where a name resolution service
+	// requires the same credentials, the resolver may use this field. In most
+	// cases though, it is not appropriate, and this field may be ignored.
+	DialCreds credentials.TransportCredentials
+	// CredsBundle is the credentials bundle used by the ClientConn for
+	// communicating with the target gRPC service (set via
+	// WithCredentialsBundle). In cases where a name resolution service
+	// requires the same credentials, the resolver may use this field. In most
+	// cases though, it is not appropriate, and this field may be ignored.
+	CredsBundle credentials.Bundle
+	// Dialer is the custom dialer used by the ClientConn for dialling the
+	// target gRPC service (set via WithDialer). In cases where a name
+	// resolution service requires the same dialer, the resolver may use this
+	// field. In most cases though, it is not appropriate, and this field may
+	// be ignored.
+	Dialer func(context.Context, string) (net.Conn, error)
+}
+
+// An Endpoint is one network endpoint, or server, which may have multiple
+// addresses with which it can be accessed.
+type Endpoint struct {
+	// Addresses contains a list of addresses used to access this endpoint.
+	Addresses []Address
+
+	// Attributes contains arbitrary data about this endpoint intended for
+	// consumption by the LB policy.
+	Attributes *attributes.Attributes
+}
+
+// State contains the current Resolver state relevant to the ClientConn.
+type State struct {
+	// Addresses is the latest set of resolved addresses for the target.
+	//
+	// If a resolver sets Addresses but does not set Endpoints, one Endpoint
+	// will be created for each Address before the State is passed to the LB
+	// policy.  The BalancerAttributes of each entry in Addresses will be set
+	// in Endpoints.Attributes, and be cleared in the Endpoint's Address's
+	// BalancerAttributes.
+	//
+	// Soon, Addresses will be deprecated and replaced fully by Endpoints.
+	Addresses []Address
+
+	// Endpoints is the latest set of resolved endpoints for the target.
+	//
+	// If a resolver produces a State containing Endpoints but not Addresses,
+	// it must take care to ensure the LB policies it selects will support
+	// Endpoints.
+	Endpoints []Endpoint
+
+	// ServiceConfig contains the result from parsing the latest service
+	// config.  If it is nil, it indicates no service config is present or the
+	// resolver does not provide service configs.
+	ServiceConfig *serviceconfig.ParseResult
+
+	// Attributes contains arbitrary data about the resolver intended for
+	// consumption by the load balancing policy.
+	Attributes *attributes.Attributes
+}
+
+// ClientConn contains the callbacks for resolver to notify any updates
+// to the gRPC ClientConn.
+//
+// This interface is to be implemented by gRPC. Users should not need a
+// brand new implementation of this interface. For the situations like
+// testing, the new implementation should embed this interface. This allows
+// gRPC to add new methods to this interface.
+type ClientConn interface {
+	// UpdateState updates the state of the ClientConn appropriately.
+	//
+	// If an error is returned, the resolver should try to resolve the
+	// target again. The resolver should use a backoff timer to prevent
+	// overloading the server with requests. If a resolver is certain that
+	// reresolving will not change the result, e.g. because it is
+	// a watch-based resolver, returned errors can be ignored.
+	//
+	// If the resolved State is the same as the last reported one, calling
+	// UpdateState can be omitted.
+	UpdateState(State) error
+	// ReportError notifies the ClientConn that the Resolver encountered an
+	// error.  The ClientConn will notify the load balancer and begin calling
+	// ResolveNow on the Resolver with exponential backoff.
+	ReportError(error)
+	// NewAddress is called by resolver to notify ClientConn a new list
+	// of resolved addresses.
+	// The address list should be the complete list of resolved addresses.
+	//
+	// Deprecated: Use UpdateState instead.
+	NewAddress(addresses []Address)
+	// NewServiceConfig is called by resolver to notify ClientConn a new
+	// service config. The service config should be provided as a json string.
+	//
+	// Deprecated: Use UpdateState instead.
+	NewServiceConfig(serviceConfig string)
+	// ParseServiceConfig parses the provided service config and returns an
+	// object that provides the parsed config.
+	ParseServiceConfig(serviceConfigJSON string) *serviceconfig.ParseResult
+}
+
+// Target represents a target for gRPC, as specified in:
+// https://github.com/grpc/grpc/blob/master/doc/naming.md.
+// It is parsed from the target string that gets passed into Dial or DialContext
+// by the user. And gRPC passes it to the resolver and the balancer.
+//
+// If the target follows the naming spec, and the parsed scheme is registered
+// with gRPC, we will parse the target string according to the spec. If the
+// target does not contain a scheme or if the parsed scheme is not registered
+// (i.e. no corresponding resolver available to resolve the endpoint), we will
+// apply the default scheme, and will attempt to reparse it.
+type Target struct {
+	// URL contains the parsed dial target with an optional default scheme added
+	// to it if the original dial target contained no scheme or contained an
+	// unregistered scheme. Any query params specified in the original dial
+	// target can be accessed from here.
+	URL url.URL
+}
+
+// Endpoint retrieves endpoint without leading "/" from either `URL.Path`
+// or `URL.Opaque`. The latter is used when the former is empty.
+func (t Target) Endpoint() string {
+	endpoint := t.URL.Path
+	if endpoint == "" {
+		endpoint = t.URL.Opaque
+	}
+	// For targets of the form "[scheme]://[authority]/endpoint, the endpoint
+	// value returned from url.Parse() contains a leading "/". Although this is
+	// in accordance with RFC 3986, we do not want to break existing resolver
+	// implementations which expect the endpoint without the leading "/". So, we
+	// end up stripping the leading "/" here. But this will result in an
+	// incorrect parsing for something like "unix:///path/to/socket". Since we
+	// own the "unix" resolver, we can workaround in the unix resolver by using
+	// the `URL` field.
+	return strings.TrimPrefix(endpoint, "/")
+}
+
+// Builder creates a resolver that will be used to watch name resolution updates.
+type Builder interface {
+	// Build creates a new resolver for the given target.
+	//
+	// gRPC dial calls Build synchronously, and fails if the returned error is
+	// not nil.
+	Build(target Target, cc ClientConn, opts BuildOptions) (Resolver, error)
+	// Scheme returns the scheme supported by this resolver.  Scheme is defined
+	// at https://github.com/grpc/grpc/blob/master/doc/naming.md.  The returned
+	// string should not contain uppercase characters, as they will not match
+	// the parsed target's scheme as defined in RFC 3986.
+	Scheme() string
+}
+
+// ResolveNowOptions includes additional information for ResolveNow.
+type ResolveNowOptions struct{}
+
+// Resolver watches for the updates on the specified target.
+// Updates include address updates and service config updates.
+type Resolver interface {
+	// ResolveNow will be called by gRPC to try to resolve the target name
+	// again. It's just a hint, resolver can ignore this if it's not necessary.
+	//
+	// It could be called multiple times concurrently.
+	ResolveNow(ResolveNowOptions)
+	// Close closes the resolver.
+	Close()
+}

go/pkg/balancer/BUILD.bazel

@@ -11,11 +11,11 @@ go_library(
     visibility = ["//visibility:public"],
     deps = [
         "//go/pkg/balancer/proto",
+        "//go/internal/balancer",
+        "//go/internal/resolver",
         "@org_golang_google_grpc//:go_default_library",
-        "@org_golang_google_grpc//balancer:go_default_library",
         "@org_golang_google_grpc//connectivity:go_default_library",
         "@org_golang_google_grpc//grpclog:go_default_library",
-        "@org_golang_google_grpc//resolver:go_default_library",
         "@org_golang_google_protobuf//encoding/protojson:go_default_library",
     ],
 )
@@ -25,9 +25,9 @@ go_test(
     srcs = ["gcp_balancer_test.go"],
     embed = [":balancer"],
     deps = [
+        "//go/internal/balancer",
+        "//go/internal/resolver",
         "@com_github_pborman_uuid//:go_default_library",
-        "@org_golang_google_grpc//balancer:go_default_library",
         "@org_golang_google_grpc//connectivity:go_default_library",
-        "@org_golang_google_grpc//resolver:go_default_library",
     ],
 )

go/pkg/balancer/gcp_balancer.go

@@ -5,11 +5,11 @@ import (
 	"sync"
 	"sync/atomic"
 
-	"google.golang.org/grpc/balancer"
+	"github.com/bazelbuild/remote-apis-sdks/go/internal/balancer"
+	"github.com/bazelbuild/remote-apis-sdks/go/internal/resolver"
 
 	"google.golang.org/grpc/connectivity"
 	"google.golang.org/grpc/grpclog"
-	"google.golang.org/grpc/resolver"
 )
 
 const (