eizo-pcap-decode.go: figure out USBHID

It is fairly dumb, but it allows to make more sense of what is
going on over the wires while using EIZO software.

README.adoc

@@ -20,7 +20,7 @@ and may not run at the same time, as it would contend for device access.
 eizoctltray
 ~~~~~~~~~~~
 _eizoctltray_ is a derived Windows utility that can stay in the systray.
-When holding the Shift or Control keys while switching singnal inputs,
+When holding the Shift or Control keys while switching signal inputs,
 it will also suspend or power off the system, respectively.
 
 image::eizoctltray.png["eizoctltray with expanded context menu", 343, 229]

eizo-pcap-decode.go

@@ -0,0 +1,212 @@
+// Usage: tshark { -r FILE | -i INTERFACE } -l -T ek --disable-protocol usbhid \
+// | go run eizo-pcap-decode.go [ | less -R]
+//
+// This cannot be done through -T json, because tshark doesn't immediately
+// flush the current object's trailing newline, but rather waits to decide
+// if it should follow it with a comma. Even with -l, it will flush it late.
+// It would be good if we could convince it not to wrap packets in a big array.
+package main
+
+import (
+	"encoding/binary"
+	"encoding/hex"
+	"encoding/json"
+	"errors"
+	"flag"
+	"fmt"
+	"io"
+	"os"
+	"strings"
+)
+
+type Packet struct {
+	Layers struct {
+		USB struct {
+			Source          string `json:"usb_usb_src"`
+			Destination     string `json:"usb_usb_dst"`
+			Direction       string `json:"usb_usb_endpoint_address_direction"`
+			MacEndpointType string `json:"usb_usb_darwin_endpoint_type"`
+			TransferType    string `json:"usb_usb_transfer_type"`
+		} `json:"usb"`
+		CapData         string `json:"usb_usb_capdata"`
+		ControlResponse string `json:"usb_usb_control_Response"`
+		DataFragment    string `json:"usb_usb_data_fragment"`
+	} `json:"layers"`
+}
+
+func (p *Packet) addr() string {
+	if p.Layers.USB.Source == "host" {
+		return p.Layers.USB.Destination
+	} else {
+		return p.Layers.USB.Source
+	}
+}
+
+func (p *Packet) isInterrupt() bool {
+	return p.Layers.USB.MacEndpointType == "3" ||
+		p.Layers.USB.TransferType == "0x01"
+}
+
+func (p *Packet) isControl() bool {
+	return p.Layers.USB.MacEndpointType == "0" ||
+		p.Layers.USB.TransferType == "0x02"
+}
+
+func (p *Packet) isIncoming() bool {
+	return p.Layers.USB.Direction == "1"
+}
+
+func hexDecode(encoded string) []byte {
+	decoded, err := hex.DecodeString(strings.ReplaceAll(encoded, ":", ""))
+	if err != nil {
+		panic(err)
+	}
+	return decoded
+}
+
+// - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
+
+var (
+	raw *bool
+	le  = binary.LittleEndian
+
+	fmtIn, fmtOut, fmtReset string
+)
+
+func decodeSubreport(data []byte) string {
+	if len(data) < 6 {
+		return fmt.Sprintf("%x", data)
+	}
+	usage := uint32(le.Uint16(data[:2]))<<16 | uint32(le.Uint16(data[2:4]))
+	filtered := make([]byte, len(data)-6)
+	for i, b := range data[6:] {
+		if b < 32 || b > 126 {
+			filtered[i] = '.'
+		} else {
+			filtered[i] = b
+		}
+	}
+	return fmt.Sprintf("<> %08x %04x %x %s", usage, le.Uint16(data[4:6]),
+		data[6:], string(filtered))
+}
+
+func decodeResult(data []byte) string {
+	if len(data) < 7 {
+		return fmt.Sprintf("%x", data)
+	}
+	usage := uint32(le.Uint16(data[:2]))<<16 | uint32(le.Uint16(data[2:4]))
+	return fmt.Sprintf(">< %08x %04x %02x", usage, le.Uint16(data[4:6]),
+		data[6])
+}
+
+func decodeMP(data []byte) string {
+	var out string
+	for i := 0; i+1 < len(data); {
+		sz := int(data[i+1])
+		if data[i] == 0xff || i+sz > len(data) {
+			break
+		}
+		if out != "" {
+			out += " "
+		}
+		out += fmt.Sprintf("[%02x] %x", data[i], data[i+2:i+2+sz])
+		i += 2 + sz
+	}
+	return out
+}
+
+func isSetSubreport(id byte) bool {
+	switch id {
+	case 2, 4, 11, 13:
+		return true
+	}
+	return false
+}
+
+func isGetSubreport(id byte) bool {
+	switch id {
+	case 3, 5, 12, 14:
+		return true
+	}
+	return false
+}
+
+func isSubreport(id byte) bool {
+	return isSetSubreport(id) || isGetSubreport(id)
+}
+
+func processInterrupt(p *Packet) {
+	data := hexDecode(p.Layers.CapData)
+	if len(data) < 1 {
+		return
+	}
+	if *raw {
+		fmt.Printf("%s INT %02x %x\n", p.addr(), data[0], data[1:])
+	} else if isSubreport(data[0]) {
+		fmt.Printf("%s INT %s\n", p.addr(), decodeSubreport(data[1:]))
+	}
+}
+
+func processControl(p *Packet) {
+	// macOS (Darwin) and Linux report Set_Feature differently.
+	data := hexDecode(p.Layers.ControlResponse)
+	if len(data) == 0 {
+		data = hexDecode(p.Layers.DataFragment)
+	}
+	if len(data) < 1 {
+		return
+	}
+	if p.isIncoming() {
+		if *raw {
+			fmt.Printf("%s IN  %02x %x\n", p.addr(), data[0], data[1:])
+		} else if data[0] == 1 {
+			fmt.Printf("%s IN  SR %x\n", p.addr(), data[5:])
+		} else if isGetSubreport(data[0]) {
+			fmt.Printf("%s IN  %s%s%s\n", p.addr(),
+				fmtIn, decodeSubreport(data[1:]), fmtReset)
+		} else if data[0] == 6 {
+			fmt.Printf("%s IN  PC %04x\n", p.addr(), le.Uint16(data[1:]))
+		} else if data[0] == 7 {
+			fmt.Printf("%s IN  %s\n", p.addr(), decodeResult(data[1:]))
+		} else if data[0] == 8 {
+			fmt.Printf("%s IN  ID %s %s\n", p.addr(), data[1:9], data[9:])
+		} else if data[0] == 9 {
+			fmt.Printf("%s IN  MP %s\n", p.addr(), decodeMP(data[1:]))
+		} else {
+			fmt.Printf("%s IN  %02x %x\n", p.addr(), data[0], data[1:])
+		}
+	} else {
+		if *raw {
+			fmt.Printf("%s OUT %02x %x\n", p.addr(), data[0], data[1:])
+		} else if isSetSubreport(data[0]) {
+			fmt.Printf("%s OUT %s%s%s\n", p.addr(),
+				fmtOut, decodeSubreport(data[1:]), fmtReset)
+		} else if data[0] != 1 && !isGetSubreport(data[0]) {
+			fmt.Printf("%s OUT %02x %x\n", p.addr(), data[0], data[1:])
+		}
+	}
+}
+
+func main() {
+	raw = flag.Bool("raw", false, "Do not decode EIZO packets")
+	flag.Parse()
+
+	if _, ok := os.LookupEnv("NO_COLOR"); !ok {
+		fmtIn, fmtOut, fmtReset = "\x1b[34m", "\x1b[31m", "\x1b[m"
+	}
+
+	decoder := json.NewDecoder(os.Stdin)
+	for {
+		var p Packet
+		if err := decoder.Decode(&p); err != nil {
+			if errors.Is(err, io.EOF) {
+				break
+			}
+			fmt.Fprintf(os.Stderr, "%v\n", err)
+		} else if p.isInterrupt() {
+			processInterrupt(&p)
+		} else if p.isControl() {
+			processControl(&p)
+		}
+	}
+}