From 9253dac7533bd19be35e94e68c53b5192565737b Mon Sep 17 00:00:00 2001
From: Leonard Lyubich <leonard@nspcc.ru>
Date: Thu, 20 Aug 2020 12:28:00 +0300
Subject: [PATCH] v2: Add cross-service client package

Add package with cross-service client utilities for working with transport
protocols and basic network types.

Signed-off-by: Leonard Lyubich <leonard@nspcc.ru>
---
 v2/client/options.go | 108 +++++++++++++++++++++++++++++++++++++++++++
 v2/client/proto.go   |  23 +++++++++
 2 files changed, 131 insertions(+)
 create mode 100644 v2/client/options.go
 create mode 100644 v2/client/proto.go

diff --git a/v2/client/options.go b/v2/client/options.go
new file mode 100644
index 0000000..3dcdff1
--- /dev/null
+++ b/v2/client/options.go
@@ -0,0 +1,108 @@
+package client
+
+import (
+	"context"
+	"net"
+
+	"google.golang.org/grpc"
+)
+
+type Option func(*cfg)
+
+type cfg struct {
+	addr string
+
+	conn net.Conn
+
+	gRPC cfgGRPC
+}
+
+type cfgGRPC struct {
+	dialCtx context.Context
+
+	dialOpts []grpc.DialOption
+
+	conn *grpc.ClientConn
+}
+
+func defaultCfg() *cfg {
+	return &cfg{
+		gRPC: cfgGRPC{
+			dialCtx: context.Background(),
+			dialOpts: []grpc.DialOption{
+				grpc.WithInsecure(),
+			},
+		},
+	}
+}
+
+func NewGRPCClientConn(opts ...Option) (*grpc.ClientConn, error) {
+	cfg := defaultCfg()
+
+	for i := range opts {
+		opts[i](cfg)
+	}
+
+	var err error
+
+	if cfg.gRPC.conn == nil {
+		if cfg.conn != nil {
+			if cfg.addr == "" {
+				cfg.addr = cfg.conn.RemoteAddr().String()
+			}
+
+			cfg.gRPC.dialOpts = append(cfg.gRPC.dialOpts,
+				grpc.WithContextDialer(func(context.Context, string) (net.Conn, error) {
+					return cfg.conn, nil
+				}),
+			)
+		}
+
+		cfg.gRPC.conn, err = grpc.DialContext(cfg.gRPC.dialCtx, cfg.addr, cfg.gRPC.dialOpts...)
+		if err != nil {
+			return nil, err
+		}
+	}
+
+	return cfg.gRPC.conn, err
+}
+
+func WithNetworkAddress(v string) Option {
+	return func(c *cfg) {
+		if v != "" {
+			c.addr = v
+		}
+	}
+}
+
+func WithNetConn(v net.Conn) Option {
+	return func(c *cfg) {
+		if v != nil {
+			c.conn = v
+		}
+	}
+}
+
+func WithGRPCDialContext(v context.Context) Option {
+	return func(c *cfg) {
+		if v != nil {
+			c.gRPC.dialCtx = v
+		}
+	}
+}
+
+func WithGRPCDialOpts(v []grpc.DialOption) Option {
+	return func(c *cfg) {
+		if len(v) > 0 {
+			c.gRPC.dialOpts = v
+		}
+	}
+}
+
+func WithGRPCConn(v *grpc.ClientConn) Option {
+	return func(c *cfg) {
+		if v != nil {
+			c.gRPC.conn = v
+		}
+	}
+}
diff --git a/v2/client/proto.go b/v2/client/proto.go
new file mode 100644
index 0000000..f6a6aa6
--- /dev/null
+++ b/v2/client/proto.go
@@ -0,0 +1,23 @@
+package client
+
+import (
+	"github.com/pkg/errors"
+)
+
+type Protocol uint32
+
+const (
+	_ Protocol = iota
+	ProtoGRPC
+)
+
+var ErrProtoUnsupported = errors.New("unsupported protocol")
+
+func (p Protocol) String() string {
+	switch p {
+	case ProtoGRPC:
+		return "GRPC"
+	default:
+		return "UNKNOWN"
+	}
+}