[#263] v2: Support new rpc library

Implement `message.Message` interface on all structures and use new methods
for conversion instead of functions. make `Unmarshal` and JSON methods to
use encoding functions from `message` library. Remove all per-service
clients and implement `rpc` library of the functions which execute NeoFS API
RPC through new RPC client. Remove no longer used gRPC per-service clients.

Signed-off-by: Leonard Lyubich <leonard@nspcc.ru>

v2/session/util.go

@@ -1,5 +1,9 @@
 package session
 
+import (
+	session "github.com/nspcc-dev/neofs-api-go/v2/session/grpc"
+)
+
 // RequestHeaders represents common part of
 // all NeoFS requests including headers.
 type RequestHeaders struct {
@@ -40,6 +44,49 @@ func (c *RequestHeaders) SetVerificationHeader(v *RequestVerificationHeader) {
 	}
 }
 
+func (c *RequestHeaders) ToMessage(m interface {
+	SetMetaHeader(*session.RequestMetaHeader)
+	SetVerifyHeader(*session.RequestVerificationHeader)
+}) {
+	m.SetMetaHeader(c.metaHeader.ToGRPCMessage().(*session.RequestMetaHeader))
+	m.SetVerifyHeader(c.verifyHeader.ToGRPCMessage().(*session.RequestVerificationHeader))
+}
+
+func (c *RequestHeaders) FromMessage(m interface {
+	GetMetaHeader() *session.RequestMetaHeader
+	GetVerifyHeader() *session.RequestVerificationHeader
+}) error {
+	metaHdr := m.GetMetaHeader()
+	if metaHdr == nil {
+		c.metaHeader = nil
+	} else {
+		if c.metaHeader == nil {
+			c.metaHeader = new(RequestMetaHeader)
+		}
+
+		err := c.metaHeader.FromGRPCMessage(metaHdr)
+		if err != nil {
+			return err
+		}
+	}
+
+	verifyHdr := m.GetVerifyHeader()
+	if verifyHdr == nil {
+		c.verifyHeader = nil
+	} else {
+		if c.verifyHeader == nil {
+			c.verifyHeader = new(RequestVerificationHeader)
+		}
+
+		err := c.verifyHeader.FromGRPCMessage(verifyHdr)
+		if err != nil {
+			return err
+		}
+	}
+
+	return nil
+}
+
 // ResponseHeaders represents common part of
 // all NeoFS responses including headers.
 type ResponseHeaders struct {
@@ -79,3 +126,46 @@ func (c *ResponseHeaders) SetVerificationHeader(v *ResponseVerificationHeader) {
 		c.verifyHeader = v
 	}
 }
+
+func (c *ResponseHeaders) ToMessage(m interface {
+	SetMetaHeader(*session.ResponseMetaHeader)
+	SetVerifyHeader(*session.ResponseVerificationHeader)
+}) {
+	m.SetMetaHeader(c.metaHeader.ToGRPCMessage().(*session.ResponseMetaHeader))
+	m.SetVerifyHeader(c.verifyHeader.ToGRPCMessage().(*session.ResponseVerificationHeader))
+}
+
+func (c *ResponseHeaders) FromMessage(m interface {
+	GetMetaHeader() *session.ResponseMetaHeader
+	GetVerifyHeader() *session.ResponseVerificationHeader
+}) error {
+	metaHdr := m.GetMetaHeader()
+	if metaHdr == nil {
+		c.metaHeader = nil
+	} else {
+		if c.metaHeader == nil {
+			c.metaHeader = new(ResponseMetaHeader)
+		}
+
+		err := c.metaHeader.FromGRPCMessage(metaHdr)
+		if err != nil {
+			return err
+		}
+	}
+
+	verifyHdr := m.GetVerifyHeader()
+	if verifyHdr == nil {
+		c.verifyHeader = nil
+	} else {
+		if c.verifyHeader == nil {
+			c.verifyHeader = new(ResponseVerificationHeader)
+		}
+
+		err := c.verifyHeader.FromGRPCMessage(verifyHdr)
+		if err != nil {
+			return err
+		}
+	}
+
+	return nil
+}