balancer: expose endpoint weight and hostname as experimental APIs

balancer/hostname/hostname.go

@@ -0,0 +1,73 @@
+/*
+ *
+ * Copyright 2026 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 hostname contains utilities for the endpoint hostname attribute
+// (used for per-endpoint :authority / SNI override).
+//
+// # Experimental
+//
+// Notice: This API is EXPERIMENTAL and may be changed or removed in a
+// later release.
+package hostname
+
+import "google.golang.org/grpc/resolver"
+
+type hostnameKey struct{}
+
+// Set returns a copy of the given endpoint with the hostname attribute set.
+// If hostname is empty the endpoint is returned unmodified.
+//
+// # Experimental
+//
+// Notice: This API is EXPERIMENTAL and may be changed or removed in a
+// later release.
+func Set(endpoint resolver.Endpoint, hostname string) resolver.Endpoint {
+	if hostname == "" {
+		return endpoint
+	}
+	endpoint.Attributes = endpoint.Attributes.WithValue(hostnameKey{}, hostname)
+	return endpoint
+}
+
+// Hostname returns the hostname attribute of endpoint. If this attribute is
+// not set, it returns the empty string.
+//
+// # Experimental
+//
+// Notice: This API is EXPERIMENTAL and may be changed or removed in a
+// later release.
+func Hostname(endpoint resolver.Endpoint) string {
+	h, _ := endpoint.Attributes.Value(hostnameKey{}).(string)
+	return h
+}
+
+// FromAddress returns the hostname attribute from a legacy
+// resolver.Address. It checks both the modern Attributes field and the
+// deprecated BalancerAttributes field for compatibility.
+//
+// # Experimental
+//
+// Notice: This API is EXPERIMENTAL and may be changed or removed in a
+// later release.
+func FromAddress(addr resolver.Address) string {
+	if h, ok := addr.Attributes.Value(hostnameKey{}).(string); ok && h != "" {
+		return h
+	}
+	h, _ := addr.BalancerAttributes.Value(hostnameKey{}).(string)
+	return h
+}

balancer/hostname/hostname_test.go

@@ -0,0 +1,44 @@
+/*
+ *
+ * Copyright 2026 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 hostname_test
+
+import (
+	"testing"
+
+	"google.golang.org/grpc/balancer/hostname"
+	"google.golang.org/grpc/resolver"
+)
+
+func TestHostname_SetAndGet(t *testing.T) {
+	ep := resolver.Endpoint{}
+	if h := hostname.Hostname(ep); h != "" {
+		t.Errorf("empty = %q", h)
+	}
+
+	ep2 := hostname.Set(ep, "myservice.example.com")
+	if h := hostname.Hostname(ep2); h != "myservice.example.com" {
+		t.Errorf("got %q", h)
+	}
+
+	// empty hostname returns same endpoint
+	ep3 := hostname.Set(ep2, "")
+	if hostname.Hostname(ep3) != "myservice.example.com" {
+		t.Error("empty should not overwrite")
+	}
+}

balancer/pickfirst/pickfirst.go

@@ -34,10 +34,10 @@ import (
 
 	"google.golang.org/grpc/balancer"
 	"google.golang.org/grpc/balancer/pickfirst/internal"
+	"google.golang.org/grpc/balancer/weight"
 	"google.golang.org/grpc/connectivity"
 	expstats "google.golang.org/grpc/experimental/stats"
 	"google.golang.org/grpc/grpclog"
-	"google.golang.org/grpc/internal/balancer/weight"
 	"google.golang.org/grpc/internal/envconfig"
 	internalgrpclog "google.golang.org/grpc/internal/grpclog"
 	"google.golang.org/grpc/internal/pretty"

balancer/pickfirst/pickfirst_ext_test.go

@@ -29,17 +29,18 @@ import (
 	"time"
 
 	"github.com/google/go-cmp/cmp"
+
 	"google.golang.org/grpc"
 	"google.golang.org/grpc/backoff"
 	"google.golang.org/grpc/balancer"
 	pfbalancer "google.golang.org/grpc/balancer/pickfirst"
 	pfinternal "google.golang.org/grpc/balancer/pickfirst/internal"
+	"google.golang.org/grpc/balancer/weight"
 	"google.golang.org/grpc/codes"
 	"google.golang.org/grpc/connectivity"
 	"google.golang.org/grpc/credentials/insecure"
 	"google.golang.org/grpc/internal"
 	"google.golang.org/grpc/internal/balancer/stub"
-	"google.golang.org/grpc/internal/balancer/weight"
 	"google.golang.org/grpc/internal/channelz"
 	"google.golang.org/grpc/internal/envconfig"
 	"google.golang.org/grpc/internal/grpcsync"

balancer/ringhash/ring_test.go

@@ -24,7 +24,8 @@ import (
 	"testing"
 
 	xxhash "github.com/cespare/xxhash/v2"
-	"google.golang.org/grpc/internal/balancer/weight"
+
+	"google.golang.org/grpc/balancer/weight"
 	"google.golang.org/grpc/resolver"
 )
 

balancer/ringhash/ringhash.go

@@ -41,8 +41,8 @@ import (
 	"google.golang.org/grpc/balancer/endpointsharding"
 	"google.golang.org/grpc/balancer/lazy"
 	"google.golang.org/grpc/balancer/pickfirst"
+	"google.golang.org/grpc/balancer/weight"
 	"google.golang.org/grpc/connectivity"
-	"google.golang.org/grpc/internal/balancer/weight"
 	"google.golang.org/grpc/internal/grpclog"
 	"google.golang.org/grpc/internal/pretty"
 	iringhash "google.golang.org/grpc/internal/ringhash"

balancer/ringhash/ringhash_test.go

@@ -25,8 +25,8 @@ import (
 	"time"
 
 	"google.golang.org/grpc/balancer"
+	"google.golang.org/grpc/balancer/weight"
 	"google.golang.org/grpc/connectivity"
-	"google.golang.org/grpc/internal/balancer/weight"
 	"google.golang.org/grpc/internal/grpctest"
 	iringhash "google.golang.org/grpc/internal/ringhash"
 	"google.golang.org/grpc/internal/testutils"

balancer/weight/weight.go

@@ -0,0 +1,81 @@
+/*
+ *
+ * Copyright 2026 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 weight contains utilities to manage endpoint weights. Weights are
+// used by LB policies such as ringhash to distribute load across multiple
+// endpoints.
+//
+// # Experimental
+//
+// Notice: This API is EXPERIMENTAL and may be changed or removed in a
+// later release.
+package weight
+
+import (
+	"fmt"
+
+	"google.golang.org/grpc/resolver"
+)
+
+// attributeKey is the type used as the key to store EndpointInfo in the
+// Attributes field of resolver.Endpoint.
+type attributeKey struct{}
+
+// EndpointInfo will be stored in the Attributes field of Endpoints in order to
+// use the ringhash balancer.
+type EndpointInfo struct {
+	Weight uint32
+}
+
+// Equal allows the values to be compared by Attributes.Equal.
+func (a EndpointInfo) Equal(o any) bool {
+	oa, ok := o.(EndpointInfo)
+	return ok && oa.Weight == a.Weight
+}
+
+// Set returns a copy of endpoint in which the Attributes field is updated with
+// EndpointInfo.
+//
+// # Experimental
+//
+// Notice: This API is EXPERIMENTAL and may be changed or removed in a
+// later release.
+func Set(endpoint resolver.Endpoint, epInfo EndpointInfo) resolver.Endpoint {
+	endpoint.Attributes = endpoint.Attributes.WithValue(attributeKey{}, epInfo)
+	return endpoint
+}
+
+// String returns a human-readable representation of EndpointInfo.
+// This method is intended for logging, testing, and debugging purposes only.
+// Do not rely on the output format, as it is not guaranteed to remain stable.
+func (a EndpointInfo) String() string {
+	return fmt.Sprintf("Weight: %d", a.Weight)
+}
+
+// FromEndpoint returns the EndpointInfo stored in the Attributes field of an
+// endpoint. It returns an empty EndpointInfo if attribute is not found.
+//
+// # Experimental
+//
+// Notice: This API is EXPERIMENTAL and may be changed or removed in a
+// later release.
+func FromEndpoint(endpoint resolver.Endpoint) EndpointInfo {
+	v := endpoint.Attributes.Value(attributeKey{})
+	ei, _ := v.(EndpointInfo)
+	return ei
+}

balancer/weight/weight_test.go

@@ -0,0 +1,84 @@
+/*
+ *
+ * Copyright 2026 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 weight_test
+
+import (
+	"testing"
+
+	"github.com/google/go-cmp/cmp"
+
+	"google.golang.org/grpc/attributes"
+	"google.golang.org/grpc/balancer/weight"
+	"google.golang.org/grpc/internal/grpctest"
+	"google.golang.org/grpc/resolver"
+)
+
+type s struct {
+	grpctest.Tester
+}
+
+func Test(t *testing.T) {
+	grpctest.RunSubTests(t, s{})
+}
+
+func (s) TestEndpointInfoToAndFromAttributes(t *testing.T) {
+	tests := []struct {
+		desc              string
+		inputEndpointInfo weight.EndpointInfo
+		inputAttributes   *attributes.Attributes
+		wantEndpointInfo  weight.EndpointInfo
+	}{
+		{
+			desc:              "empty_attributes",
+			inputEndpointInfo: weight.EndpointInfo{Weight: 100},
+			inputAttributes:   nil,
+			wantEndpointInfo:  weight.EndpointInfo{Weight: 100},
+		},
+		{
+			desc:              "non-empty_attributes",
+			inputEndpointInfo: weight.EndpointInfo{Weight: 100},
+			inputAttributes:   attributes.New("foo", "bar"),
+			wantEndpointInfo:  weight.EndpointInfo{Weight: 100},
+		},
+		{
+			desc:              "endpointInfo_not_present_in_empty_attributes",
+			inputEndpointInfo: weight.EndpointInfo{},
+			inputAttributes:   nil,
+			wantEndpointInfo:  weight.EndpointInfo{},
+		},
+		{
+			desc:              "endpointInfo_not_present_in_non-empty_attributes",
+			inputEndpointInfo: weight.EndpointInfo{},
+			inputAttributes:   attributes.New("foo", "bar"),
+			wantEndpointInfo:  weight.EndpointInfo{},
+		},
+	}
+
+	for _, test := range tests {
+		t.Run(test.desc, func(t *testing.T) {
+			endpoint := resolver.Endpoint{Attributes: test.inputAttributes}
+			endpoint = weight.Set(endpoint, test.inputEndpointInfo)
+			gotEndpointInfo := weight.FromEndpoint(endpoint)
+			if !cmp.Equal(gotEndpointInfo, test.wantEndpointInfo) {
+				t.Errorf("gotEndpointInfo: %v, wantEndpointInfo: %v", gotEndpointInfo, test.wantEndpointInfo)
+			}
+
+		})
+	}
+}

internal/balancer/weight/weight.go

@@ -19,6 +19,8 @@
 // Package weight contains utilities to manage endpoint weights. Weights are
 // used by LB policies such as ringhash to distribute load across multiple
 // endpoints.
+//
+// Deprecated: use google.golang.org/grpc/balancer/weight instead.
 package weight
 
 import (

internal/balancer/weight/weight_test.go

@@ -16,12 +16,14 @@
  *
  */
 
+// Deprecated: use google.golang.org/grpc/balancer/weight instead.
 package weight_test
 
 import (
 	"testing"
 
 	"github.com/google/go-cmp/cmp"
+
 	"google.golang.org/grpc/attributes"
 	"google.golang.org/grpc/internal/balancer/weight"
 	"google.golang.org/grpc/internal/grpctest"

internal/xds/balancer/cdsbalancer/configbuilder.go

@@ -24,7 +24,7 @@ import (
 	"maps"
 	"slices"
 
-	"google.golang.org/grpc/internal/balancer/weight"
+	"google.golang.org/grpc/balancer/weight"
 	"google.golang.org/grpc/internal/envconfig"
 	"google.golang.org/grpc/internal/hierarchy"
 	internalserviceconfig "google.golang.org/grpc/internal/serviceconfig"

internal/xds/balancer/cdsbalancer/configbuilder_test.go

@@ -27,12 +27,13 @@ import (
 	"time"
 
 	"github.com/google/go-cmp/cmp"
+
 	"google.golang.org/grpc/attributes"
 	"google.golang.org/grpc/balancer"
 	"google.golang.org/grpc/balancer/pickfirst"
 	"google.golang.org/grpc/balancer/ringhash"
 	"google.golang.org/grpc/balancer/roundrobin"
-	"google.golang.org/grpc/internal/balancer/weight"
+	"google.golang.org/grpc/balancer/weight"
 	"google.golang.org/grpc/internal/envconfig"
 	"google.golang.org/grpc/internal/hierarchy"
 	iringhash "google.golang.org/grpc/internal/ringhash"