From 5e0cc956a3c422ab30f4cd3d02f8ee81ad4f4034 Mon Sep 17 00:00:00 2001
From: Jonathan Giannuzzi <jonathan@giannuzzi.me>
Date: Fri, 17 Jan 2025 13:54:02 +0000
Subject: [PATCH 1/2] Add support for Echo requests

---
 client.go                 |  5 +++++
 internal/smb2/request.go  | 42 +++++++++++++++++++++++++++++++++++++++
 internal/smb2/response.go | 42 +++++++++++++++++++++++++++++++++++++++
 session.go                | 18 +++++++++++++++++
 4 files changed, 107 insertions(+)

diff --git a/client.go b/client.go
index 863edde..05fde0c 100644
--- a/client.go
+++ b/client.go
@@ -135,6 +135,11 @@ func (c *Session) Logoff() error {
 	return c.s.logoff(c.ctx)
 }
 
+// Echo sends an echo request to the server.
+func (c *Session) Echo() error {
+	return c.s.echo(c.ctx)
+}
+
 // Mount mounts the SMB share.
 // sharename must follow format like `<share>` or `\\<server>\<share>`.
 // Note that the mounted share doesn't inherit session's context.
diff --git a/internal/smb2/request.go b/internal/smb2/request.go
index 943ba06..815559f 100644
--- a/internal/smb2/request.go
+++ b/internal/smb2/request.go
@@ -291,6 +291,48 @@ func (r LogoffRequestDecoder) StructureSize() uint16 {
 	return le.Uint16(r[:2])
 }
 
+// ----------------------------------------------------------------------------
+// SMB2 ECHO Request Packet
+//
+
+type EchoRequest struct {
+	PacketHeader
+}
+
+func (c *EchoRequest) Header() *PacketHeader {
+	return &c.PacketHeader
+}
+
+func (c *EchoRequest) Size() int {
+	return 64 + 4
+}
+
+func (c *EchoRequest) Encode(pkt []byte) {
+	c.Command = SMB2_ECHO
+	c.encodeHeader(pkt)
+
+	req := pkt[64:]
+	le.PutUint16(req[:2], 4) // StructureSize
+}
+
+type EchoRequestDecoder []byte
+
+func (r EchoRequestDecoder) IsInvalid() bool {
+	if len(r) < 4 {
+		return true
+	}
+
+	if r.StructureSize() != 4 {
+		return true
+	}
+
+	return false
+}
+
+func (r EchoRequestDecoder) StructureSize() uint16 {
+	return le.Uint16(r[:2])
+}
+
 // ----------------------------------------------------------------------------
 // SMB2 TREE_CONNECT Request Packet
 //
diff --git a/internal/smb2/response.go b/internal/smb2/response.go
index faf0a3c..e4dc876 100644
--- a/internal/smb2/response.go
+++ b/internal/smb2/response.go
@@ -631,6 +631,48 @@ func (r LogoffResponseDecoder) StructureSize() uint16 {
 	return le.Uint16(r[:2])
 }
 
+// ----------------------------------------------------------------------------
+// SMB2 ECHO Response
+//
+
+type EchoResponse struct {
+	PacketHeader
+}
+
+func (c *EchoResponse) Header() *PacketHeader {
+	return &c.PacketHeader
+}
+
+func (c *EchoResponse) Size() int {
+	return 64 + 4
+}
+
+func (c *EchoResponse) Encode(pkt []byte) {
+	c.Command = SMB2_ECHO
+	c.encodeHeader(pkt)
+
+	res := pkt[64:]
+	le.PutUint16(res[:2], 4) // StructureSize
+}
+
+type EchoResponseDecoder []byte
+
+func (r EchoResponseDecoder) IsInvalid() bool {
+	if len(r) < 4 {
+		return true
+	}
+
+	if r.StructureSize() != 4 {
+		return true
+	}
+
+	return false
+}
+
+func (r EchoResponseDecoder) StructureSize() uint16 {
+	return le.Uint16(r[:2])
+}
+
 // ----------------------------------------------------------------------------
 // SMB2 TREE_CONNECT Response
 //
diff --git a/session.go b/session.go
index ecf4630..3f184f6 100644
--- a/session.go
+++ b/session.go
@@ -291,6 +291,24 @@ func (s *session) logoff(ctx context.Context) error {
 	return nil
 }
 
+func (s *session) echo(ctx context.Context) error {
+	req := new(EchoRequest)
+
+	req.CreditCharge = 1
+
+	res, err := s.sendRecv(SMB2_ECHO, req, ctx)
+	if err != nil {
+		return err
+	}
+
+	r := EchoResponseDecoder(res)
+	if r.IsInvalid() {
+		return &InvalidResponseError{"broken echo response format"}
+	}
+
+	return nil
+}
+
 func (s *session) sendRecv(cmd uint16, req Packet, ctx context.Context) (res []byte, err error) {
 	rr, err := s.send(req, ctx)
 	if err != nil {

From f7a8a82f20b6ff8bfe8c072d6cb51b429691165c Mon Sep 17 00:00:00 2001
From: Jonathan Giannuzzi <jonathan@giannuzzi.me>
Date: Wed, 22 Jan 2025 10:52:20 +0000
Subject: [PATCH 2/2] Add test for Echo

---
 smb2_test.go | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/smb2_test.go b/smb2_test.go
index 5517f7b..cb77ae8 100644
--- a/smb2_test.go
+++ b/smb2_test.go
@@ -900,3 +900,11 @@ func TestGlob(t *testing.T) {
 		t.Errorf("unexpected matches: %v != %v", matches5, expected5)
 	}
 }
+
+func TestEcho(t *testing.T) {
+	if session == nil {
+		t.Skip()
+	}
+
+	require.NoError(t, session.Echo())
+}