refactor: extract mount library package, add flake.nix

Move protocol and SCSI code into importable mount/ package with a
single public API (Config + Run). Restructure as multi-binary repo
with cmd/aten-mount/ CLI wrapper using context-based cancellation.
Add Nix flake with go_1_26 for builds and devshell.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

.gitignore

@@ -1 +1,2 @@
-aten-mount
+/aten-mount
+/result

cmd/aten-mount/main.go

@@ -0,0 +1,44 @@
+package main
+
+import (
+	"context"
+	"flag"
+	"fmt"
+	"log"
+	"os"
+	"os/signal"
+	"syscall"
+
+	"git.dsg.is/dsg/aten-ipmi-tools/mount"
+)
+
+func main() {
+	user := flag.String("u", "admin", "BMC username")
+	pass := flag.String("p", "admin", "BMC password")
+	port := flag.Int("port", 623, "BMC virtual media TCP port")
+	flag.Usage = func() {
+		fmt.Fprintf(os.Stderr, "Usage: %s [flags] <bmc-host> <image.iso>\n\nFlags:\n", os.Args[0])
+		flag.PrintDefaults()
+	}
+	flag.Parse()
+
+	if flag.NArg() != 2 {
+		flag.Usage()
+		os.Exit(1)
+	}
+
+	ctx, cancel := signal.NotifyContext(context.Background(), syscall.SIGINT, syscall.SIGTERM)
+	defer cancel()
+
+	cfg := mount.Config{
+		Host:     flag.Arg(0),
+		Port:     *port,
+		Username: *user,
+		Password: *pass,
+		ISOPath:  flag.Arg(1),
+	}
+
+	if err := mount.Run(ctx, cfg); err != nil {
+		log.Fatal(err)
+	}
+}

flake.lock

@@ -0,0 +1,27 @@
+{
+  "nodes": {
+    "nixpkgs": {
+      "locked": {
+        "lastModified": 1773110118,
+        "narHash": "sha256-mPAG8phMbCReKSiKAijjjd3v7uVcJOQ75gSjGJjt/Rk=",
+        "owner": "NixOS",
+        "repo": "nixpkgs",
+        "rev": "e607cb5360ff1234862ac9f8839522becb853bb9",
+        "type": "github"
+      },
+      "original": {
+        "owner": "NixOS",
+        "ref": "nixpkgs-unstable",
+        "repo": "nixpkgs",
+        "type": "github"
+      }
+    },
+    "root": {
+      "inputs": {
+        "nixpkgs": "nixpkgs"
+      }
+    }
+  },
+  "root": "root",
+  "version": 7
+}

flake.nix

@@ -0,0 +1,32 @@
+{
+  inputs = {
+    nixpkgs.url = "github:NixOS/nixpkgs/nixpkgs-unstable";
+  };
+
+  outputs = { self, nixpkgs }:
+    let
+      systems = [ "x86_64-linux" "aarch64-linux" "x86_64-darwin" "aarch64-darwin" ];
+      forAllSystems = f: nixpkgs.lib.genAttrs systems (system: f {
+        pkgs = nixpkgs.legacyPackages.${system};
+      });
+    in
+    {
+      packages = forAllSystems ({ pkgs }: {
+        aten-mount = pkgs.buildGoModule.override { go = pkgs.go_1_26; } {
+          pname = "aten-mount";
+          version = "0.1.0";
+          src = ./.;
+          vendorHash = null;
+          subPackages = [ "cmd/aten-mount" ];
+        };
+
+        default = self.packages.${pkgs.system}.aten-mount;
+      });
+
+      devShells = forAllSystems ({ pkgs }: {
+        default = pkgs.mkShell {
+          packages = [ pkgs.go_1_26 ];
+        };
+      });
+    };
+}

go.mod

@@ -1,3 +1,3 @@
-module github.com/example/aten-mount
+module git.dsg.is/dsg/aten-ipmi-tools
 
-go 1.25.7
+go 1.26

main.go

@@ -1,102 +0,0 @@
-package main
-
-import (
-	"flag"
-	"fmt"
-	"log"
-	"net"
-	"os"
-	"os/signal"
-	"syscall"
-	"time"
-)
-
-func main() {
-	user := flag.String("u", "admin", "BMC username")
-	pass := flag.String("p", "admin", "BMC password")
-	port := flag.Int("port", 623, "BMC virtual media TCP port")
-	flag.Usage = func() {
-		fmt.Fprintf(os.Stderr, "Usage: %s [flags] <bmc-host> <image.iso>\n\nFlags:\n", os.Args[0])
-		flag.PrintDefaults()
-	}
-	flag.Parse()
-
-	if flag.NArg() != 2 {
-		flag.Usage()
-		os.Exit(1)
-	}
-	host := flag.Arg(0)
-	isoPath := flag.Arg(1)
-
-	// Open and validate ISO file
-	isoFile, err := os.Open(isoPath)
-	if err != nil {
-		log.Fatalf("open ISO: %v", err)
-	}
-	defer isoFile.Close()
-
-	isoInfo, err := isoFile.Stat()
-	if err != nil {
-		log.Fatalf("stat ISO: %v", err)
-	}
-	isoSize := isoInfo.Size()
-	if isoSize < 0x8054 {
-		log.Fatalf("ISO file too small (%d bytes)", isoSize)
-	}
-	totalSectors := uint32(isoSize / 2048)
-	log.Printf("ISO: %s (%d bytes, %d sectors)", isoPath, isoSize, totalSectors)
-
-	// TCP connect
-	addr := net.JoinHostPort(host, fmt.Sprintf("%d", *port))
-	log.Printf("Connecting to %s...", addr)
-	conn, err := net.DialTimeout("tcp", addr, 10*time.Second)
-	if err != nil {
-		log.Fatalf("connect: %v", err)
-	}
-	defer conn.Close()
-	log.Printf("Connected")
-
-	// Send PlugIn packet
-	pluginPkt := buildPlugInPacket(*user, *pass)
-	if _, err := conn.Write(pluginPkt); err != nil {
-		log.Fatalf("send plugin: %v", err)
-	}
-	log.Printf("Sent PlugIn packet (%d bytes)", len(pluginPkt))
-
-	// Read mount status
-	status, err := readMountStatus(conn)
-	if err != nil {
-		log.Fatalf("mount status: %v", err)
-	}
-	if status != 0x00 {
-		log.Fatalf("mount failed: %s", mountStatusString(status))
-	}
-	log.Printf("Mount OK")
-
-	// Send SetEP command
-	if _, err := conn.Write(buildSetEPPacket()); err != nil {
-		log.Fatalf("send setep: %v", err)
-	}
-	log.Printf("Sent SetEP, entering SCSI command loop")
-
-	// Signal handling for clean unmount
-	sigCh := make(chan os.Signal, 1)
-	signal.Notify(sigCh, syscall.SIGINT, syscall.SIGTERM)
-
-	// SCSI command loop
-	dev := &SCSIDevice{
-		file:         isoFile,
-		totalSectors: totalSectors,
-		sense:        initialSenseData(),
-	}
-
-	err = commandLoop(conn, dev, sigCh)
-
-	// Clean unmount
-	log.Printf("Sending unmount...")
-	conn.Write(buildUnmountPacket())
-	if err != nil {
-		log.Fatalf("command loop: %v", err)
-	}
-	log.Printf("Unmounted cleanly")
-}

mount/mount.go

@@ -0,0 +1,87 @@
+package mount
+
+import (
+	"context"
+	"fmt"
+	"log"
+	"net"
+	"os"
+	"time"
+)
+
+// Config holds the parameters for a virtual media mount session.
+type Config struct {
+	Host     string
+	Port     int
+	Username string
+	Password string
+	ISOPath  string
+}
+
+// Run connects to the BMC, mounts the ISO, and serves SCSI commands
+// until ctx is cancelled or an error occurs. Sends unmount on return.
+func Run(ctx context.Context, cfg Config) error {
+	isoFile, err := os.Open(cfg.ISOPath)
+	if err != nil {
+		return fmt.Errorf("open ISO: %w", err)
+	}
+	defer isoFile.Close()
+
+	isoInfo, err := isoFile.Stat()
+	if err != nil {
+		return fmt.Errorf("stat ISO: %w", err)
+	}
+	isoSize := isoInfo.Size()
+	if isoSize < 0x8054 {
+		return fmt.Errorf("ISO file too small (%d bytes)", isoSize)
+	}
+	totalSectors := uint32(isoSize / 2048)
+	log.Printf("ISO: %s (%d bytes, %d sectors)", cfg.ISOPath, isoSize, totalSectors)
+
+	addr := net.JoinHostPort(cfg.Host, fmt.Sprintf("%d", cfg.Port))
+	log.Printf("Connecting to %s...", addr)
+
+	var d net.Dialer
+	d.Timeout = 10 * time.Second
+	conn, err := d.DialContext(ctx, "tcp", addr)
+	if err != nil {
+		return fmt.Errorf("connect: %w", err)
+	}
+	defer conn.Close()
+	log.Printf("Connected")
+
+	if _, err := conn.Write(buildPlugInPacket(cfg.Username, cfg.Password)); err != nil {
+		return fmt.Errorf("send plugin: %w", err)
+	}
+	log.Printf("Sent PlugIn packet")
+
+	status, err := readMountStatus(conn)
+	if err != nil {
+		return fmt.Errorf("mount status: %w", err)
+	}
+	if status != 0x00 {
+		return fmt.Errorf("mount failed: %s", mountStatusString(status))
+	}
+	log.Printf("Mount OK")
+
+	if _, err := conn.Write(buildSetEPPacket()); err != nil {
+		return fmt.Errorf("send setep: %w", err)
+	}
+	log.Printf("Sent SetEP, entering SCSI command loop")
+
+	dev := &scsiDevice{
+		file:         isoFile,
+		totalSectors: totalSectors,
+		sense:        initialSenseData(),
+	}
+
+	err = commandLoop(ctx, conn, dev)
+
+	log.Printf("Sending unmount...")
+	conn.Write(buildUnmountPacket())
+	if err != nil {
+		return fmt.Errorf("command loop: %w", err)
+	}
+	log.Printf("Unmounted cleanly")
+	return nil
+}

mount/protocol.go

@@ -1,13 +1,13 @@
-package main
+package mount
 
 import (
+	"context"
 	"crypto/rc4"
 	"encoding/binary"
 	"fmt"
 	"io"
 	"log"
 	"net"
-	"os"
 	"time"
 )
 
@@ -272,7 +272,7 @@ func buildCSW(ep byte, tag [4]byte, dataTransferLen uint32, actualLen uint32, st
 	pdu[3] = 0xFF
 	binary.LittleEndian.PutUint32(pdu[4:8], 13)
 	// CSW body
-	pdu[8] = 'U'  // dCSWSignature "USBS"
+	pdu[8] = 'U' // dCSWSignature "USBS"
 	pdu[9] = 'S'
 	pdu[10] = 'B'
 	pdu[11] = 'S'
@@ -282,7 +282,7 @@ func buildCSW(ep byte, tag [4]byte, dataTransferLen uint32, actualLen uint32, st
 		residue = dataTransferLen - actualLen
 	}
 	binary.LittleEndian.PutUint32(pdu[16:20], residue) // dCSWDataResidue
-	pdu[20] = status                                                     // bCSWStatus
+	pdu[20] = status                                    // bCSWStatus
 	return pdu
 }
 
@@ -307,22 +307,20 @@ func (h pduHeader) pduType() uint32 {
 	return binary.BigEndian.Uint32(h.typeOrTag[:])
 }
 
-// commandLoop reads PDU headers and dispatches commands until signal or error.
+// commandLoop reads PDU headers and dispatches commands until context
-func commandLoop(conn net.Conn, dev *SCSIDevice, sigCh <-chan os.Signal) error {
+// cancellation or error.
+func commandLoop(ctx context.Context, conn net.Conn, dev *scsiDevice) error {
 	for {
-		// Check for signal (non-blocking)
+		if err := ctx.Err(); err != nil {
-		select {
-		case <-sigCh:
 			return nil
-		default:
 		}
 
-		// Set read deadline so we can check signals periodically
+		// Set read deadline so we can check context periodically
 		conn.SetReadDeadline(time.Now().Add(1 * time.Second))
 		hdr, err := readPDUHeader(conn)
 		if err != nil {
 			if netErr, ok := err.(net.Error); ok && netErr.Timeout() {
-				continue // timeout, loop back to check signal
+				continue // timeout, loop back to check context
 			}
 			return fmt.Errorf("read PDU header: %w", err)
 		}

mount/protocol_test.go

@@ -1,4 +1,4 @@
-package main
+package mount
 
 import (
 	"encoding/binary"

mount/scsi.go

@@ -1,4 +1,4 @@
-package main
+package mount
 
 import (
 	"encoding/binary"
@@ -8,25 +8,25 @@ import (
 
 // SCSI opcodes
 const (
-	scsiTestUnitReady          = 0x00
+	scsiTestUnitReady        = 0x00
-	scsiRequestSense           = 0x03
+	scsiRequestSense         = 0x03
-	scsiInquiry                = 0x12
+	scsiInquiry              = 0x12
-	scsiStartStopUnit          = 0x1B
+	scsiStartStopUnit        = 0x1B
-	scsiMediumRemoval          = 0x1E
+	scsiMediumRemoval        = 0x1E
-	scsiReadFormatCapacities   = 0x23
+	scsiReadFormatCapacities = 0x23
-	scsiReadCapacity           = 0x25
+	scsiReadCapacity         = 0x25
-	scsiRead10                 = 0x28
+	scsiRead10               = 0x28
-	scsiReadToc                = 0x43
+	scsiReadToc              = 0x43
-	scsiGetConfiguration       = 0x46
+	scsiGetConfiguration     = 0x46
-	scsiGetEventStatusNotif    = 0x4A
+	scsiGetEventStatusNotif  = 0x4A
-	scsiModeSense10            = 0x5A
+	scsiModeSense10          = 0x5A
-	scsiRead12                 = 0xA8
+	scsiRead12               = 0xA8
 )
 
 // CSW status
 const (
-	cswStatusPassed    = 0x00
+	cswStatusPassed = 0x00
-	cswStatusFailed    = 0x01
+	cswStatusFailed = 0x01
 )
 
 // Sense keys
@@ -37,8 +37,8 @@ const (
 	senseIllegalRequest = 0x05
 )
 
-// SCSIDevice holds state for the virtual CD-ROM.
+// scsiDevice holds state for the virtual CD-ROM.
-type SCSIDevice struct {
+type scsiDevice struct {
 	file         *os.File
 	totalSectors uint32
 	sense        [18]byte
@@ -46,25 +46,25 @@ type SCSIDevice struct {
 
 func initialSenseData() [18]byte {
 	var s [18]byte
-	s[0] = 0x70  // Response code (current errors)
+	s[0] = 0x70 // Response code (current errors)
-	s[7] = 0x0A  // Additional sense length
+	s[7] = 0x0A // Additional sense length
 	return s
 }
 
-func (d *SCSIDevice) setSense(key, asc, ascq byte) {
+func (d *scsiDevice) setSense(key, asc, ascq byte) {
 	d.sense = initialSenseData()
 	d.sense[2] = key
 	d.sense[12] = asc
 	d.sense[13] = ascq
 }
 
-func (d *SCSIDevice) setOK() {
+func (d *scsiDevice) setOK() {
 	d.sense = initialSenseData()
 }
 
 // handleCBW parses a 31-byte CBW and returns the complete TCP response
 // (data PDU + CSW, or just CSW).
-func (d *SCSIDevice) handleCBW(ep byte, cbw []byte) []byte {
+func (d *scsiDevice) handleCBW(ep byte, cbw []byte) []byte {
 	// Parse CBW fields (offsets relative to 31-byte CBW body)
 	// CBW signature at 0-3 ("USBC")
 	var tag [4]byte
@@ -96,7 +96,7 @@ func (d *SCSIDevice) handleCBW(ep byte, cbw []byte) []byte {
 	return resp
 }
 
-func (d *SCSIDevice) executeSCSI(cdb []byte, transferLen uint32) (data []byte, status byte) {
+func (d *scsiDevice) executeSCSI(cdb []byte, transferLen uint32) (data []byte, status byte) {
 	if len(cdb) == 0 {
 		d.setSense(senseIllegalRequest, 0x20, 0x00) // Invalid command
 		return nil, cswStatusFailed
@@ -137,12 +137,12 @@ func (d *SCSIDevice) executeSCSI(cdb []byte, transferLen uint32) (data []byte, s
 	}
 }
 
-func (d *SCSIDevice) cmdTestUnitReady() ([]byte, byte) {
+func (d *scsiDevice) cmdTestUnitReady() ([]byte, byte) {
 	d.setOK()
 	return nil, cswStatusPassed
 }
 
-func (d *SCSIDevice) cmdRequestSense(cdb []byte) ([]byte, byte) {
+func (d *scsiDevice) cmdRequestSense(cdb []byte) ([]byte, byte) {
 	allocLen := int(cdb[4])
 	resp := make([]byte, 18)
 	copy(resp, d.sense[:])
@@ -153,7 +153,7 @@ func (d *SCSIDevice) cmdRequestSense(cdb []byte) ([]byte, byte) {
 	return resp, cswStatusPassed
 }
 
-func (d *SCSIDevice) cmdInquiry(cdb []byte) ([]byte, byte) {
+func (d *scsiDevice) cmdInquiry(cdb []byte) ([]byte, byte) {
 	evpd := cdb[1] & 0x01
 	pageCode := cdb[2]
 	allocLen := int(cdb[3])<<8 | int(cdb[4])
@@ -216,17 +216,17 @@ func (d *SCSIDevice) cmdInquiry(cdb []byte) ([]byte, byte) {
 	return nil, cswStatusFailed
 }
 
-func (d *SCSIDevice) cmdStartStopUnit() ([]byte, byte) {
+func (d *scsiDevice) cmdStartStopUnit() ([]byte, byte) {
 	d.setOK()
 	return nil, cswStatusPassed
 }
 
-func (d *SCSIDevice) cmdMediumRemoval() ([]byte, byte) {
+func (d *scsiDevice) cmdMediumRemoval() ([]byte, byte) {
 	d.setOK()
 	return nil, cswStatusPassed
 }
 
-func (d *SCSIDevice) cmdReadCapacity(cdb []byte) ([]byte, byte) {
+func (d *scsiDevice) cmdReadCapacity(cdb []byte) ([]byte, byte) {
 	// Validate reserved bytes 1-8 are zero (except byte 2 which is OK)
 	for i := 1; i <= 8; i++ {
 		if i >= 2 && i <= 5 {
@@ -246,7 +246,7 @@ func (d *SCSIDevice) cmdReadCapacity(cdb []byte) ([]byte, byte) {
 	return resp, cswStatusPassed
 }
 
-func (d *SCSIDevice) cmdReadFormatCapacities(cdb []byte) ([]byte, byte) {
+func (d *scsiDevice) cmdReadFormatCapacities(cdb []byte) ([]byte, byte) {
 	allocLen := int(cdb[7])<<8 | int(cdb[8])
 	resp := make([]byte, 12)
 	resp[3] = 0x08 // Capacity list length
@@ -263,7 +263,7 @@ func (d *SCSIDevice) cmdReadFormatCapacities(cdb []byte) ([]byte, byte) {
 	return resp, cswStatusPassed
 }
 
-func (d *SCSIDevice) cmdRead10(cdb []byte) ([]byte, byte) {
+func (d *scsiDevice) cmdRead10(cdb []byte) ([]byte, byte) {
 	lba := binary.BigEndian.Uint32(cdb[2:6])
 	count := uint32(cdb[7])<<8 | uint32(cdb[8])
 
@@ -286,7 +286,7 @@ func (d *SCSIDevice) cmdRead10(cdb []byte) ([]byte, byte) {
 	return data[:n], cswStatusPassed
 }
 
-func (d *SCSIDevice) cmdRead12(cdb []byte) ([]byte, byte) {
+func (d *scsiDevice) cmdRead12(cdb []byte) ([]byte, byte) {
 	lba := binary.BigEndian.Uint32(cdb[2:6])
 	count := binary.BigEndian.Uint32(cdb[6:10])
 
@@ -309,7 +309,7 @@ func (d *SCSIDevice) cmdRead12(cdb []byte) ([]byte, byte) {
 	return data[:n], cswStatusPassed
 }
 
-func (d *SCSIDevice) cmdReadToc(cdb []byte) ([]byte, byte) {
+func (d *scsiDevice) cmdReadToc(cdb []byte) ([]byte, byte) {
 	format := cdb[2] & 0x0F
 	if format != 0 {
 		d.setSense(senseIllegalRequest, 0x24, 0x00)
@@ -354,7 +354,7 @@ func (d *SCSIDevice) cmdReadToc(cdb []byte) ([]byte, byte) {
 	return resp, cswStatusPassed
 }
 
-func (d *SCSIDevice) cmdGetConfiguration(cdb []byte) ([]byte, byte) {
+func (d *scsiDevice) cmdGetConfiguration(cdb []byte) ([]byte, byte) {
 	allocLen := int(cdb[7])<<8 | int(cdb[8])
 	if allocLen == 0 {
 		d.setSense(senseIllegalRequest, 0x24, 0x00)
@@ -398,7 +398,7 @@ func (d *SCSIDevice) cmdGetConfiguration(cdb []byte) ([]byte, byte) {
 	return resp, cswStatusPassed
 }
 
-func (d *SCSIDevice) cmdGetEventStatus(cdb []byte) ([]byte, byte) {
+func (d *scsiDevice) cmdGetEventStatus(cdb []byte) ([]byte, byte) {
 	if cdb[1]&0x01 == 0 {
 		// Polled bit not set - async not supported
 		d.setSense(senseIllegalRequest, 0x24, 0x00)
@@ -424,7 +424,7 @@ func (d *SCSIDevice) cmdGetEventStatus(cdb []byte) ([]byte, byte) {
 	return resp, cswStatusPassed
 }
 
-func (d *SCSIDevice) cmdModeSense10(cdb []byte) ([]byte, byte) {
+func (d *scsiDevice) cmdModeSense10(cdb []byte) ([]byte, byte) {
 	pageCode := cdb[2] & 0x3F
 	allocLen := int(cdb[7])<<8 | int(cdb[8])
 

mount/scsi_test.go

@@ -1,4 +1,4 @@
-package main
+package mount
 
 import (
 	"encoding/binary"
@@ -6,16 +6,16 @@ import (
 	"testing"
 )
 
-func newTestDevice(t *testing.T) *SCSIDevice {
+func newTestDevice(t *testing.T) *scsiDevice {
 	t.Helper()
-	return &SCSIDevice{
+	return &scsiDevice{
 		file:         nil, // No file for most tests
 		totalSectors: 1000,
 		sense:        initialSenseData(),
 	}
 }
 
-func newTestDeviceWithFile(t *testing.T) (*SCSIDevice, func()) {
+func newTestDeviceWithFile(t *testing.T) (*scsiDevice, func()) {
 	t.Helper()
 	// Create a minimal fake ISO (just enough for reads)
 	f, err := os.CreateTemp("", "test-*.iso")
@@ -30,7 +30,7 @@ func newTestDeviceWithFile(t *testing.T) (*SCSIDevice, func()) {
 	f.Write(data)
 	f.Sync()
 
-	dev := &SCSIDevice{
+	dev := &scsiDevice{
 		file:         f,
 		totalSectors: 10,
 		sense:        initialSenseData(),
@@ -173,14 +173,14 @@ func TestHandleCBW(t *testing.T) {
 	dev := newTestDevice(t)
 	// Build a CBW for INQUIRY
 	cbw := make([]byte, 31)
-	copy(cbw[0:4], []byte("USBC"))       // Signature
+	copy(cbw[0:4], []byte("USBC"))                    // Signature
-	copy(cbw[4:8], []byte{1, 2, 3, 4})   // Tag
+	copy(cbw[4:8], []byte{1, 2, 3, 4})                // Tag
-	binary.LittleEndian.PutUint32(cbw[8:12], 36)  // Transfer length
+	binary.LittleEndian.PutUint32(cbw[8:12], 36)      // Transfer length
-	cbw[12] = 0x80                        // Flags: IN
+	cbw[12] = 0x80                                     // Flags: IN
-	cbw[14] = 6                           // CDB length
+	cbw[14] = 6                                        // CDB length
-	cbw[15] = 0x12                        // INQUIRY opcode
+	cbw[15] = 0x12                                     // INQUIRY opcode
-	cbw[18] = 0x00                        // Alloc len MSB (CDB byte 3)
+	cbw[18] = 0x00                                     // Alloc len MSB (CDB byte 3)
-	cbw[19] = 0x24                        // Alloc len LSB (CDB byte 4) = 36
+	cbw[19] = 0x24                                     // Alloc len LSB (CDB byte 4) = 36
 
 	resp := dev.handleCBW(0x20, cbw)
 	// Should have: 8 data PDU tag + 36 data + 8 CSW tag + 13 CSW body = 65