rpc: add generic dial methods to dial RPC clients

Introduce generic dial methods for creating RPC clients across services. This
consolidates code paths, reduces the number of places where the DRPC
experimental flag must be enabled, and simplifies adding version guards by
limiting them to only a few locations.

Epic: CRDB-48935
Informs: None
Release note: None

Author: cthumuluru-crdb

pkg/rpc/nodedialer/nodedialer.go

@@ -430,3 +430,32 @@ func (c *tracingInternalClient) Batch(
 	}
 	return c.RestrictedInternalClient.Batch(ctx, ba)
 }
+
+// DialRPCClient establishes a connection to a node identified by its ID and
+// returns a client for the requested service type. When DRPC is enabled, it
+// creates a DRPC client; otherwise, it falls back to a gRPC client.
+func DialRPCClient[C any](
+	nd *Dialer,
+	ctx context.Context,
+	nodeID roachpb.NodeID,
+	class rpcbase.ConnectionClass,
+	grpcClientFn func(*grpc.ClientConn) C,
+	drpcClientFn func(drpc.Conn) C,
+) (C, error) {
+	return rpcbase.DialRPCClient(nd, ctx, nodeID, class, grpcClientFn,
+		drpcClientFn, nd.rpcContext.Settings)
+}
+
+// DialRPCClientNoBreaker is like DialRPCClient, but will not check the
+// circuit breaker before trying to connect.
+func DialRPCClientNoBreaker[C any](
+	nd *Dialer,
+	ctx context.Context,
+	nodeID roachpb.NodeID,
+	class rpcbase.ConnectionClass,
+	grpcClientFn func(*grpc.ClientConn) C,
+	drpcClientFn func(drpc.Conn) C,
+) (C, error) {
+	return rpcbase.DialRPCClientNoBreaker(nd, ctx, nodeID, class, grpcClientFn,
+		drpcClientFn, nd.rpcContext.Settings)
+}

pkg/rpc/rpcbase/BUILD.bazel

@@ -26,6 +26,7 @@ go_library(
         "//pkg/roachpb",
         "//pkg/rpc/rpcpb",
         "//pkg/settings",
+        "//pkg/settings/cluster",
         "//pkg/util/buildutil",
         "//pkg/util/envutil",
         "@com_github_cockroachdb_errors//:errors",

pkg/rpc/rpcbase/nodedialer.go

@@ -10,6 +10,7 @@ import (
 
 	"github.com/cockroachdb/cockroach/pkg/roachpb"
 	"github.com/cockroachdb/cockroach/pkg/settings"
+	"github.com/cockroachdb/cockroach/pkg/settings/cluster"
 	"github.com/cockroachdb/cockroach/pkg/util/buildutil"
 	"github.com/cockroachdb/cockroach/pkg/util/envutil"
 	"github.com/cockroachdb/errors"
@@ -56,3 +57,62 @@ type NodeDialerNoBreaker interface {
 	DialNoBreaker(context.Context, roachpb.NodeID, ConnectionClass) (_ *grpc.ClientConn, err error)
 	DRPCDialNoBreaker(context.Context, roachpb.NodeID, ConnectionClass) (_ drpc.Conn, err error)
 }
+
+// DialRPCClient establishes a connection to a node identified by its ID and
+// returns a client for the requested service type. When DRPC is enabled, it
+// creates a DRPC client; otherwise, it falls back to a gRPC client.
+func DialRPCClient[C any](
+	nd NodeDialer,
+	ctx context.Context,
+	nodeID roachpb.NodeID,
+	class ConnectionClass,
+	grpcClientFn func(*grpc.ClientConn) C,
+	drpcClientFn func(drpc.Conn) C,
+	st *cluster.Settings,
+) (C, error) {
+	useDRPC := ExperimentalDRPCEnabled.Get(&st.SV)
+
+	var nilC C
+	if !TODODRPC && !useDRPC {
+		conn, err := nd.Dial(ctx, nodeID, class)
+		if err != nil {
+			return nilC, err
+		}
+		return grpcClientFn(conn), nil
+	}
+
+	conn, err := nd.DRPCDial(ctx, nodeID, class)
+	if err != nil {
+		return nilC, err
+	}
+	return drpcClientFn(conn), nil
+}
+
+// DialRPCClientNoBreaker is like DialRPCClient, but will not check the
+// circuit breaker before trying to connect.
+func DialRPCClientNoBreaker[C any](
+	nd NodeDialerNoBreaker,
+	ctx context.Context,
+	nodeID roachpb.NodeID,
+	class ConnectionClass,
+	grpcClientFn func(*grpc.ClientConn) C,
+	drpcClientFn func(drpc.Conn) C,
+	st *cluster.Settings,
+) (C, error) {
+	useDRPC := ExperimentalDRPCEnabled.Get(&st.SV)
+
+	var nilC C
+	if !TODODRPC && !useDRPC {
+		conn, err := nd.DialNoBreaker(ctx, nodeID, class)
+		if err != nil {
+			return nilC, err
+		}
+		return grpcClientFn(conn), nil
+	}
+
+	conn, err := nd.DRPCDialNoBreaker(ctx, nodeID, class)
+	if err != nil {
+		return nilC, err
+	}
+	return drpcClientFn(conn), nil
+}

pkg/server/testserver.go

@@ -334,7 +334,7 @@ func makeTestConfigFromParams(params base.TestServerArgs) Config {
 	}
 
 	if params.DefaultDRPCOption == base.TestDRPCEnabled {
-		rpc.ExperimentalDRPCEnabled.Override(context.Background(), &st.SV, true)
+		rpcbase.ExperimentalDRPCEnabled.Override(context.Background(), &st.SV, true)
 	}
 
 	return cfg

pkg/testutils/serverutils/BUILD.bazel

@@ -31,7 +31,6 @@ go_library(
         "//pkg/multitenant/tenantcapabilitiespb",
         "//pkg/roachpb",
         "//pkg/rpc",
-        "//pkg/rpc/rpcbase",
         "//pkg/security/securitytest",
         "//pkg/security/username",
         "//pkg/server/decommissioning",