[#160] Add internal/net package with multinet dialer source

Signed-off-by: Alex Vanin <a.vanin@yadro.com>

internal/net/dialer_source.go

@@ -0,0 +1,69 @@
+package net
+
+import (
+	"context"
+	"net"
+	"sync"
+
+	"git.frostfs.info/TrueCloudLab/multinet"
+)
+
+type DialerSource struct {
+	guard sync.RWMutex
+
+	c Config
+
+	md multinet.Dialer
+}
+
+func NewDialerSource(c Config) (*DialerSource, error) {
+	result := &DialerSource{}
+	if err := result.build(c); err != nil {
+		return nil, err
+	}
+	return result, nil
+}
+
+func (s *DialerSource) build(c Config) error {
+	if c.Enabled {
+		mc, err := c.toMultinetConfig()
+		if err != nil {
+			return err
+		}
+		md, err := multinet.NewDialer(mc)
+		if err != nil {
+			return err
+		}
+		s.md = md
+		s.c = c
+		return nil
+	}
+	s.md = nil
+	s.c = c
+	return nil
+}
+
+// GrpcContextDialer returns grpc.WithContextDialer func.
+// Returns nil if multinet disabled.
+func (s *DialerSource) GrpcContextDialer() func(context.Context, string) (net.Conn, error) {
+	s.guard.RLock()
+	defer s.guard.RUnlock()
+
+	if s.c.Enabled {
+		return func(ctx context.Context, address string) (net.Conn, error) {
+			network, address := parseDialTarget(address)
+			return s.md.DialContext(ctx, network, address)
+		}
+	}
+	return nil
+}
+
+func (s *DialerSource) Update(c Config) error {
+	s.guard.Lock()
+	defer s.guard.Unlock()
+
+	if s.c.equals(c) {
+		return nil
+	}
+	return s.build(c)
+}