snapshot of https://github.com/grpc/grpc-go.git (master, 2026-09-15; blobs > 131072B omitted)

internal/resolver/config_selector.go

@@ -0,0 +1,100 @@
+/*
+ *
+ * Copyright 2020 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 provides internal resolver-related functionality.
+package resolver
+
+import (
+	"context"
+	"sync"
+
+	"google.golang.org/grpc/internal/serviceconfig"
+	"google.golang.org/grpc/resolver"
+)
+
+// ConfigSelector controls what configuration to use for every RPC.
+type ConfigSelector interface {
+	// Selects the configuration for the RPC, or terminates it using the error.
+	// This error will be converted by the gRPC library to a status error with
+	// code UNKNOWN if it is not returned as a status error.
+	SelectConfig(RPCInfo) (*RPCConfig, error)
+}
+
+// RPCInfo contains RPC information needed by a ConfigSelector.
+type RPCInfo struct {
+	// Context is the user's context for the RPC and contains headers and
+	// application timeout.  It is passed for interception purposes and for
+	// efficiency reasons.  SelectConfig should not be blocking.
+	Context context.Context
+	Method  string // i.e. "/Service/Method"
+	// Authority is the target authority (host) name of the RPC. This is required
+	// for HTTP filters (such as external processing) to populate request
+	// attributes.
+	Authority string
+}
+
+// RPCConfig describes the configuration to use for each RPC.
+type RPCConfig struct {
+	// The context to use for the remainder of the RPC; can pass info to LB
+	// policy or affect timeout or metadata.
+	Context      context.Context
+	MethodConfig serviceconfig.MethodConfig // configuration to use for this RPC
+	OnCommitted  func()                     // Called when the RPC has been committed (retries no longer possible)
+	Interceptor  any
+}
+
+type csKeyType string
+
+const csKey = csKeyType("grpc.internal.resolver.configSelector")
+
+// SetConfigSelector sets the config selector in state and returns the new
+// state.
+func SetConfigSelector(state resolver.State, cs ConfigSelector) resolver.State {
+	state.Attributes = state.Attributes.WithValue(csKey, cs)
+	return state
+}
+
+// GetConfigSelector retrieves the config selector from state, if present, and
+// returns it or nil if absent.
+func GetConfigSelector(state resolver.State) ConfigSelector {
+	cs, _ := state.Attributes.Value(csKey).(ConfigSelector)
+	return cs
+}
+
+// SafeConfigSelector allows for safe switching of ConfigSelector
+// implementations such that previous values are guaranteed to not be in use
+// when UpdateConfigSelector returns.
+type SafeConfigSelector struct {
+	mu sync.RWMutex
+	cs ConfigSelector
+}
+
+// UpdateConfigSelector swaps to the provided ConfigSelector and blocks until
+// all uses of the previous ConfigSelector have completed.
+func (scs *SafeConfigSelector) UpdateConfigSelector(cs ConfigSelector) {
+	scs.mu.Lock()
+	defer scs.mu.Unlock()
+	scs.cs = cs
+}
+
+// SelectConfig defers to the current ConfigSelector in scs.
+func (scs *SafeConfigSelector) SelectConfig(r RPCInfo) (*RPCConfig, error) {
+	scs.mu.RLock()
+	defer scs.mu.RUnlock()
+	return scs.cs.SelectConfig(r)
+}