xP: use the binary protocol for incoming events

And batch event messages together as much as possible.

JSON has proven itself to be really slow
(for example, encoding/json.Marshaler is a slow interface),
and browsers have significant overhead per WS message.

Commands are still sent as JSON, sending them in binary
would be a laborious rewrite without measurable merits.

The xP server now only prints debug output when requested,
because that was another source of major slowdowns.

5 files changed, 412 insertions, 138 deletions

diff --git a/xC-gen-proto-js.awk b/xC-gen-proto-js.awk
new file mode 100644
index 0000000..752fd18
--- /dev/null
+++ b/xC-gen-proto-js.awk
@@ -0,0 +1,223 @@
+# xC-gen-proto-js.awk: Javascript backend for xC-gen-proto.awk.
+#
+# Copyright (c) 2022, Přemysl Eric Janouch <p@janouch.name>
+# SPDX-License-Identifier: 0BSD
+#
+# This backend is currently for decoding the binary format only.
+# (JSON is way too expensive to process and transfer.)
+#
+# Import the resulting script as a Javascript module.
+
+function define_internal(name) {
+	Types[name] = "internal"
+}
+
+function define_sint(size,    shortname) {
+	shortname = "i" size
+	define_internal(shortname)
+	CodegenDeserialize[shortname] = "\t%s = r." shortname "()\n"
+
+	print ""
+	print "\t" shortname "() {"
+	if (size == "64") {
+		# XXX: 2^53 - 1 must be enough for anyone.  BigInts are a PITA.
+		print "\t\tconst " shortname \
+			" = Number(this.getBigInt" size "(this.offset))"
+	} else {
+		print "\t\tconst " shortname " = this.getInt" size "(this.offset)"
+	}
+	print "\t\tthis.offset += " (size / 8)
+	print "\t\treturn " shortname
+	print "\t}"
+}
+
+function define_uint(size,    shortname) {
+	shortname = "u" size
+	define_internal(shortname)
+	CodegenDeserialize[shortname] = "\t%s = r." shortname "()\n"
+
+	print ""
+	print "\t" shortname "() {"
+	if (size == "64") {
+		# XXX: 2^53 - 1 must be enough for anyone.  BigInts are a PITA.
+		print "\t\tconst " shortname \
+			" = Number(this.getBigUint" size "(this.offset))"
+	} else {
+		print "\t\tconst " shortname " = this.getUint" size "(this.offset)"
+	}
+	print "\t\tthis.offset += " (size / 8)
+	print "\t\treturn " shortname
+	print "\t}"
+}
+
+function codegen_begin() {
+	print "export class Reader extends DataView {"
+	print "\tconstructor() {"
+	print "\t\tsuper(...arguments)"
+	print "\t\tthis.offset = 0"
+	print "\t\tthis.decoder = new TextDecoder('utf-8', {fatal: true})"
+	print "\t}"
+	print ""
+	print "\tget empty() {"
+	print "\t\treturn this.byteLength <= this.offset"
+	print "\t}"
+	print ""
+	print "\trequire(len) {"
+	print "\t\tif (this.byteLength - this.offset < len)"
+	print "\t\t\tthrow `Premature end of data`"
+	print "\t\treturn this.byteOffset + this.offset"
+	print "\t}"
+
+	define_internal("string")
+	CodegenDeserialize["string"] = "\t%s = r.string()\n"
+
+	print ""
+	print "\tstring() {"
+	print "\t\tconst len = this.getUint32(this.offset)"
+	print "\t\tthis.offset += 4"
+	print "\t\tconst array = new Uint8Array("
+	print "\t\t\tthis.buffer, this.require(len), len)"
+	print "\t\tthis.offset += len"
+	print "\t\treturn this.decoder.decode(array)"
+	print "\t}"
+
+	define_internal("bool")
+	CodegenDeserialize["bool"] = "\t%s = r.bool()\n"
+
+	print ""
+	print "\tbool() {"
+	print "\t\tconst u8 = this.getUint8(this.offset)"
+	print "\t\tthis.offset += 1"
+	print "\t\treturn u8 != 0"
+	print "\t}"
+
+	define_sint("8")
+	define_sint("16")
+	define_sint("32")
+	define_sint("64")
+	define_uint("8")
+	define_uint("16")
+	define_uint("32")
+	define_uint("64")
+
+	print "}"
+}
+
+function codegen_constant(name, value) {
+	print ""
+	print "export const " decapitalize(snaketocamel(name)) " = " value
+}
+
+function codegen_enum_value(name, subname, value, cg) {
+	append(cg, "fields", "\t" snaketocamel(subname) ": " value ",\n")
+}
+
+function codegen_enum(name, cg) {
+	print ""
+	print "export const " name " = Object.freeze({"
+	print cg["fields"] "})"
+
+	CodegenDeserialize[name] = "\t%s = r.i8()\n"
+	for (i in cg)
+		delete cg[i]
+}
+
+function codegen_struct_field(d, cg,    camel, f, deserialize) {
+	camel = decapitalize(snaketocamel(d["name"]))
+	f = "s." camel
+	append(cg, "fields", "\t" camel "\n")
+
+	deserialize = CodegenDeserialize[d["type"]]
+	if (!d["isarray"]) {
+		append(cg, "deserialize", sprintf(deserialize, f))
+		return
+	}
+
+	append(cg, "deserialize",
+		"\t{\n" \
+		indent(sprintf(CodegenDeserialize["u32"], "const len")))
+	if (d["type"] == "u8") {
+		append(cg, "deserialize",
+			"\t\t" f " = new Uint8Array(\n" \
+			"\t\t\tr.buffer, r.require(len), len)\n" \
+			"\t\tr.offset += len\n" \
+			"\t}\n")
+		return
+	}
+	if (d["type"] == "i8") {
+		append(cg, "deserialize",
+			"\t\t" f " = new Int8Array(\n" \
+			"\t\t\tr.buffer, r.require(len), len)\n" \
+			"\t\tr.offset += len\n" \
+			"\t}\n")
+		return
+	}
+
+	append(cg, "deserialize",
+		"\t\t" f " = new Array(len)\n" \
+		"\t}\n" \
+		"\tfor (let i = 0; i < " f ".length; i++)\n" \
+		indent(sprintf(deserialize, f "[i]")))
+}
+
+function codegen_struct_tag(d, cg) {
+	append(cg, "fields", "\t" decapitalize(snaketocamel(d["name"])) "\n")
+	# Do not deserialize here, that is already done by the containing union.
+}
+
+function codegen_struct(name, cg) {
+	print ""
+	print "export class " name " {"
+	print cg["fields"] cg["methods"]
+	print "\tstatic deserialize(r) {"
+	print "\t\tconst s = new " name "()"
+	print indent(cg["deserialize"]) "\t\treturn s"
+	print "\t}"
+	print "}"
+
+	CodegenDeserialize[name] = "\t%s = " name ".deserialize(r)\n"
+	for (i in cg)
+		delete cg[i]
+}
+
+function codegen_union_tag(d, cg) {
+	cg["tagtype"] = d["type"]
+	cg["tagname"] = d["name"]
+}
+
+function codegen_union_struct(name, casename, cg, scg,     structname) {
+	append(scg, "methods",
+		"\n" \
+		"\tconstructor() {\n" \
+		"\t\tthis." decapitalize(snaketocamel(cg["tagname"])) \
+			" = " cg["tagtype"] "." snaketocamel(casename) "\n" \
+		"\t}\n")
+
+	# And thus not all generated structs are present in Types.
+	structname = name snaketocamel(casename)
+	codegen_struct(structname, scg)
+
+	append(cg, "deserialize",
+		"\tcase " cg["tagtype"] "." snaketocamel(casename) ":\n" \
+		"\t{\n" \
+		indent(sprintf(CodegenDeserialize[structname], "const s")) \
+		"\t\treturn s\n" \
+		"\t}\n")
+}
+
+function codegen_union(name, cg,    tagvar) {
+	tagvar = decapitalize(snaketocamel(cg["tagname"]))
+
+	print ""
+	print "export function deserialize" name "(r) {"
+	print sprintf(CodegenDeserialize[cg["tagtype"]], "const " tagvar) \
+		"\tswitch (" tagvar ") {"
+	print cg["deserialize"] "\tdefault:"
+	print "\t\tthrow `Unknown " cg["tagtype"] " (${tagvar})`"
+	print "\t}"
+	print "}"
+
+	CodegenDeserialize[name] = "\t%s = deserialize" name "(r)\n"
+	for (i in cg)
+		delete cg[i]
+}
diff --git a/xP/.gitignore b/xP/.gitignore
index 68c09f0..ba4d8c3 100644
--- a/xP/.gitignore
+++ b/xP/.gitignore
@@ -1,3 +1,4 @@
 /xP
 /proto.go
+/public/proto.js
 /public/mithril.js
diff --git a/xP/Makefile b/xP/Makefile
index 3c52146..eb0c8f5 100644
--- a/xP/Makefile
+++ b/xP/Makefile
@@ -1,13 +1,15 @@
 .POSIX:
 .SUFFIXES:
 
-outputs = xP proto.go public/mithril.js
+outputs = xP proto.go public/proto.js public/mithril.js
 all: $(outputs)
 
 xP: xP.go proto.go
 	go build -o $@
 proto.go: ../xC-gen-proto.awk ../xC-gen-proto-go.awk ../xC-proto
 	awk -f ../xC-gen-proto.awk -f ../xC-gen-proto-go.awk ../xC-proto > $@
+public/proto.js: ../xC-gen-proto.awk ../xC-gen-proto-js.awk ../xC-proto
+	awk -f ../xC-gen-proto.awk -f ../xC-gen-proto-js.awk ../xC-proto > $@
 public/mithril.js:
 	curl -Lo $@ https://unpkg.com/mithril/mithril.js
 clean:
diff --git a/xP/public/xP.js b/xP/public/xP.js
index d302a86..1362e22 100644
--- a/xP/public/xP.js
+++ b/xP/public/xP.js
@@ -1,6 +1,6 @@
 // Copyright (c) 2022, Přemysl Eric Janouch <p@janouch.name>
 // SPDX-License-Identifier: 0BSD
-'use strict'
+import * as Relay from './proto.js'
 
 // ---- RPC --------------------------------------------------------------------
 
@@ -31,6 +31,7 @@ class RelayRpc extends EventTarget {
 	}
 
 	_initialize() {
+		this.ws.binaryType = 'arraybuffer'
 		this.ws.onopen = undefined
 		this.ws.onmessage = event => {
 			this._process(event.data)
@@ -56,33 +57,30 @@ class RelayRpc extends EventTarget {
 	}
 
 	_process(data) {
-		if (typeof data !== 'string')
-			throw "Binary messages not supported"
+		if (typeof data === 'string')
+			throw "JSON messages not supported"
 
-		let message = JSON.parse(data)
-		if (typeof message !== 'object')
-			throw "Invalid message"
-		let e = message.data
-		if (typeof e !== 'object')
-			throw "Invalid message"
+		const r = new Relay.Reader(data)
+		while (!r.empty)
+			this._processOne(Relay.EventMessage.deserialize(r))
+	}
 
+	_processOne(message) {
+		let e = message.data
 		switch (e.event) {
-		case 'Error':
+		case Relay.Event.Error:
 			if (this.promised[e.commandSeq] !== undefined)
 				this.promised[e.commandSeq].reject(e.error)
 			else
 				console.error("Unawaited error")
 			break
-		case 'Response':
+		case Relay.Event.Response:
 			if (this.promised[e.commandSeq] !== undefined)
 				this.promised[e.commandSeq].resolve(e.data)
 			else
 				console.error("Unawaited response")
 			break
 		default:
-			if (typeof e.event !== 'string')
-				throw "Invalid event tag"
-
 			e.eventSeq = message.eventSeq
 			this.dispatchEvent(new CustomEvent('event', {detail: e}))
 			return
@@ -115,13 +113,6 @@ class RelayRpc extends EventTarget {
 			this.promised[seq] = {resolve, reject}
 		})
 	}
-
-	base64decode(str) {
-		const text = atob(str), bytes = new Uint8Array(text.length)
-		for (let i = 0; i < text.length; i++)
-			bytes[i] = text.charCodeAt(i)
-		return new TextDecoder().decode(bytes)
-	}
 }
 
 // ---- Utilities --------------------------------------------------------------
@@ -183,7 +174,7 @@ function updateIcon(highlighted) {
 // ---- Event processing -------------------------------------------------------
 
 let rpc = new RelayRpc(proxy)
-let rpcEventHandlers = {}
+let rpcEventHandlers = new Map()
 
 let buffers = new Map()
 let bufferLast = undefined
@@ -221,7 +212,7 @@ function bufferToggleLog() {
 		if (bufferCurrent !== name)
 			return
 
-		bufferLog = rpc.base64decode(resp.log)
+		bufferLog = utf8Decode(resp.log)
 		m.redraw()
 	})
 }
@@ -236,7 +227,7 @@ rpc.connect().then(result => {
 
 	servers.clear()
 
-	rpc.send({command: 'Hello', version: 1})
+	rpc.send({command: 'Hello', version: Relay.version})
 	connecting = false
 	m.redraw()
 }).catch(error => {
@@ -249,10 +240,11 @@ rpc.addEventListener('close', event => {
 })
 
 rpc.addEventListener('event', event => {
-	const handler = rpcEventHandlers[event.detail.event]
+	const handler = rpcEventHandlers.get(event.detail.event)
 	if (handler !== undefined) {
 		handler(event.detail)
-		if (bufferCurrent !== undefined || event.detail.event !== 'BufferLine')
+		if (bufferCurrent !== undefined ||
+			event.detail.event !== Relay.Event.BufferLine)
 			m.redraw()
 	}
 })
@@ -263,7 +255,7 @@ rpcEventHandlers['Ping'] = e => {
 
 // ~~~ Buffer events ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 
-rpcEventHandlers['BufferUpdate'] = e => {
+rpcEventHandlers.set(Relay.Event.BufferUpdate, e => {
 	let b = buffers.get(e.bufferName)
 	if (b === undefined) {
 		buffers.set(e.bufferName, (b = {
@@ -277,9 +269,9 @@ rpcEventHandlers['BufferUpdate'] = e => {
 	b.hideUnimportant = e.hideUnimportant
 	b.kind = e.context.kind
 	b.server = servers.get(e.context.serverName)
-}
+})
 
-rpcEventHandlers['BufferStats'] = e => {
+rpcEventHandlers.set(Relay.Event.BufferStats, e => {
 	let b = buffers.get(e.bufferName)
 	if (b === undefined)
 		return
@@ -287,20 +279,20 @@ rpcEventHandlers['BufferStats'] = e => {
 	b.newMessages = e.newMessages,
 	b.newUnimportantMessages = e.newUnimportantMessages
 	b.highlighted = e.highlighted
-}
+})
 
-rpcEventHandlers['BufferRename'] = e => {
+rpcEventHandlers.set(Relay.Event.BufferRename, e => {
 	buffers.set(e.new, buffers.get(e.bufferName))
 	buffers.delete(e.bufferName)
-}
+})
 
-rpcEventHandlers['BufferRemove'] = e => {
+rpcEventHandlers.set(Relay.Event.BufferRemove, e => {
 	buffers.delete(e.bufferName)
 	if (e.bufferName === bufferLast)
 		bufferLast = undefined
-}
+})
 
-rpcEventHandlers['BufferActivate'] = e => {
+rpcEventHandlers.set(Relay.Event.BufferActivate, e => {
 	let old = buffers.get(bufferCurrent)
 	if (old !== undefined)
 		bufferResetStats(old)
@@ -333,9 +325,9 @@ rpcEventHandlers['BufferActivate'] = e => {
 		textarea.value = b.input
 		textarea.setSelectionRange(b.inputStart, b.inputEnd, b.inputDirection)
 	}
-}
+})
 
-rpcEventHandlers['BufferLine'] = e => {
+rpcEventHandlers.set(Relay.Event.BufferLine, e => {
 	let b = buffers.get(e.bufferName), line = {...e}
 	delete line.event
 	delete line.eventSeq
@@ -372,37 +364,37 @@ rpcEventHandlers['BufferLine'] = e => {
 		}
 	}
 
-	if (line.isHighlight ||
-		(!visible && b.kind === 'PrivateMessage' && !line.isUnimportant)) {
+	if (line.isHighlight || (!visible && !line.isUnimportant &&
+			b.kind === Relay.BufferKind.PrivateMessage)) {
 		beep()
 		if (!visible)
 			b.highlighted = true
 	}
-}
+})
 
-rpcEventHandlers['BufferClear'] = e => {
+rpcEventHandlers.set(Relay.Event.BufferClear, e => {
 	let b = buffers.get(e.bufferName)
 	if (b !== undefined)
 		b.lines.length = 0
-}
+})
 
 // ~~~ Server events ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 
-rpcEventHandlers['ServerUpdate'] = e => {
+rpcEventHandlers.set(Relay.Event.ServerUpdate, e => {
 	let s = servers.get(e.serverName)
 	if (s === undefined)
 		servers.set(e.serverName, (s = {}))
 	s.state = e.state
-}
+})
 
-rpcEventHandlers['ServerRename'] = e => {
+rpcEventHandlers.set(Relay.Event.ServerRename, e => {
 	servers.set(e.new, servers.get(e.serverName))
 	servers.delete(e.serverName)
-}
+})
 
-rpcEventHandlers['ServerRemove'] = e => {
+rpcEventHandlers.set(Relay.Event.ServerRemove, e => {
 	servers.delete(e.serverName)
-}
+})
 
 // --- Colours -----------------------------------------------------------------
 
@@ -499,18 +491,19 @@ let Content = {
 		return a
 	},
 
-	view: vnode => {
-		let line = vnode.children[0]
-		let mark = undefined
+	makeMark: line => {
 		switch (line.rendition) {
-		case 'Indent': mark = m('span.mark',        {}, '');  break
-		case 'Status': mark = m('span.mark',        {}, '–'); break
-		case 'Error':  mark = m('span.mark.error',  {}, '⚠'); break
-		case 'Join':   mark = m('span.mark.join',   {}, '→'); break
-		case 'Part':   mark = m('span.mark.part',   {}, '←'); break
-		case 'Action': mark = m('span.mark.action', {}, '✶'); break
+		case Relay.Rendition.Indent: return m('span.mark',        {}, '')
+		case Relay.Rendition.Status: return m('span.mark',        {}, '–')
+		case Relay.Rendition.Error:  return m('span.mark.error',  {}, '⚠')
+		case Relay.Rendition.Join:   return m('span.mark.join',   {}, '→')
+		case Relay.Rendition.Part:   return m('span.mark.part',   {}, '←')
+		case Relay.Rendition.Action: return m('span.mark.action', {}, '✶')
 		}
+	},
 
+	view: vnode => {
+		let line = vnode.children[0]
 		let classes = new Set()
 		let flip = c => {
 			if (classes.has(c))
@@ -518,45 +511,49 @@ let Content = {
 			else
 				classes.add(c)
 		}
+
 		let fg = -1, bg = -1, inverse = false
-		return m('.content', vnode.attrs, [mark, line.items.flatMap(item => {
-			switch (item.kind) {
-			case 'Text':
-				return Content.linkify(item.text, {
-					class: Array.from(classes.keys()).join(' '),
-					style: Content.applyColor(fg, bg, inverse),
-				})
-			case 'Reset':
-				classes.clear()
-				fg = bg = -1
-				inverse = false
-				break
-			case 'FgColor':
-				fg = item.color
-				break
-			case 'BgColor':
-				bg = item.color
-				break
-			case 'FlipInverse':
-				inverse = !inverse
-				break
-			case 'FlipBold':
-				flip('b')
-				break
-			case 'FlipItalic':
-				flip('i')
-				break
-			case 'FlipUnderline':
-				flip('u')
-				break
-			case 'FlipCrossedOut':
-				flip('s')
-				break
-			case 'FlipMonospace':
-				flip('m')
-				break
-			}
-		})])
+		return m('.content', vnode.attrs, [
+			Content.makeMark(line),
+			line.items.flatMap(item => {
+				switch (item.kind) {
+				case Relay.Item.Text:
+					return Content.linkify(item.text, {
+						class: Array.from(classes.keys()).join(' '),
+						style: Content.applyColor(fg, bg, inverse),
+					})
+				case Relay.Item.Reset:
+					classes.clear()
+					fg = bg = -1
+					inverse = false
+					break
+				case Relay.Item.FgColor:
+					fg = item.color
+					break
+				case Relay.Item.BgColor:
+					bg = item.color
+					break
+				case Relay.Item.FlipInverse:
+					inverse = !inverse
+					break
+				case Relay.Item.FlipBold:
+					flip('b')
+					break
+				case Relay.Item.FlipItalic:
+					flip('i')
+					break
+				case Relay.Item.FlipUnderline:
+					flip('u')
+					break
+				case Relay.Item.FlipCrossedOut:
+					flip('s')
+					break
+				case Relay.Item.FlipMonospace:
+					flip('m')
+					break
+				}
+			}),
+		])
 	},
 }
 
@@ -669,8 +666,17 @@ let Status = {
 		let status = `${bufferCurrent}`
 		if (b.hideUnimportant)
 			status += `<H>`
-		if (b.server !== undefined)
-			status += ` (${b.server.state})`
+
+		// This should be handled differently, so don't mind the lookup.
+		if (b.server !== undefined) {
+			let state = b.server.state
+			for (const s in Relay.ServerState)
+				if (Relay.ServerState[s] == b.server.state) {
+					state = s
+					break
+				}
+			status += ` (${state})`
+		}
 		return m('.status', {}, status)
 	},
 }
diff --git a/xP/xP.go b/xP/xP.go
index 7e0285c..20117b2 100644
--- a/xP/xP.go
+++ b/xP/xP.go
@@ -8,6 +8,7 @@ import (
 	"context"
 	"encoding/binary"
 	"encoding/json"
+	"flag"
 	"fmt"
 	"html/template"
 	"io"
@@ -21,6 +22,8 @@ import (
 )
 
 var (
+	debug = flag.Bool("debug", false, "enable debug output")
+
 	addressBind    string
 	addressConnect string
 	addressWS      string
@@ -28,7 +31,7 @@ var (
 
 // -----------------------------------------------------------------------------
 
-func relayReadJSON(r io.Reader) []byte {
+func relayReadFrame(r io.Reader) []byte {
 	var length uint32
 	if err := binary.Read(r, binary.BigEndian, &length); err != nil {
 		log.Println("Event receive failed: " + err.Error())
@@ -40,32 +43,38 @@ func relayReadJSON(r io.Reader) []byte {
 		return nil
 	}
 
-	log.Printf("<? %v\n", b)
+	if *debug {
+		log.Printf("<? %v\n", b)
 
-	var m RelayEventMessage
-	if after, ok := m.ConsumeFrom(b); !ok {
-		log.Println("Event deserialization failed")
-		return nil
-	} else if len(after) != 0 {
-		log.Println("Event deserialization failed: trailing data")
-		return nil
-	}
+		var m RelayEventMessage
+		if after, ok := m.ConsumeFrom(b); !ok {
+			log.Println("Event deserialization failed")
+			return nil
+		} else if len(after) != 0 {
+			log.Println("Event deserialization failed: trailing data")
+			return nil
+		}
 
-	j, err := m.MarshalJSON()
-	if err != nil {
-		log.Println("Event marshalling failed: " + err.Error())
-		return nil
+		j, err := m.MarshalJSON()
+		if err != nil {
+			log.Println("Event marshalling failed: " + err.Error())
+			return nil
+		}
+
+		log.Printf("<- %s\n", j)
 	}
-	return j
+	return b
 }
 
 func relayMakeReceiver(ctx context.Context, conn net.Conn) <-chan []byte {
-	p := make(chan []byte, 1)
-	r := bufio.NewReader(conn)
+	// The usual event message rarely gets above 1 kilobyte,
+	// thus this is set to buffer up at most 1 megabyte or so.
+	p := make(chan []byte, 1000)
+	r := bufio.NewReaderSize(conn, 65536)
 	go func() {
 		defer close(p)
 		for {
-			j := relayReadJSON(r)
+			j := relayReadFrame(r)
 			if j == nil {
 				return
 			}
@@ -97,7 +106,9 @@ func relayWriteJSON(conn net.Conn, j []byte) bool {
 		return false
 	}
 
-	log.Printf("-> %v\n", b)
+	if *debug {
+		log.Printf("-> %v\n", b)
+	}
 	return true
 }
 
@@ -114,21 +125,23 @@ func clientReadJSON(ctx context.Context, ws *websocket.Conn) []byte {
 			"Command receive failed: " + "binary messages are not supported")
 		return nil
 	}
-	log.Printf("?> %s\n", j)
+
+	if *debug {
+		log.Printf("?> %s\n", j)
+	}
 	return j
 }
 
-func clientWriteJSON(ctx context.Context, ws *websocket.Conn, j []byte) bool {
-	if err := ws.Write(ctx, websocket.MessageText, j); err != nil {
+func clientWriteBinary(ctx context.Context, ws *websocket.Conn, b []byte) bool {
+	if err := ws.Write(ctx, websocket.MessageBinary, b); err != nil {
 		log.Println("Event send failed: " + err.Error())
 		return false
 	}
-	log.Printf("<- %s\n", j)
 	return true
 }
 
 func clientWriteError(ctx context.Context, ws *websocket.Conn, err error) bool {
-	j, err := (&RelayEventMessage{
+	b, ok := (&RelayEventMessage{
 		EventSeq: 0,
 		Data: RelayEventData{
 			Interface: RelayEventDataError{
@@ -137,12 +150,12 @@ func clientWriteError(ctx context.Context, ws *websocket.Conn, err error) bool {
 				Error:      err.Error(),
 			},
 		},
-	}).MarshalJSON()
-	if err != nil {
-		log.Println("Event marshalling failed: " + err.Error())
+	}).AppendTo(nil)
+	if ok {
+		log.Println("Event serialization failed")
 		return false
 	}
-	return clientWriteJSON(ctx, ws, j)
+	return clientWriteBinary(ctx, ws, b)
 }
 
 func handleWS(w http.ResponseWriter, r *http.Request) {
@@ -164,15 +177,36 @@ func handleWS(w http.ResponseWriter, r *http.Request) {
 
 	conn, err := net.Dial("tcp", addressConnect)
 	if err != nil {
+		log.Println("Connection failed: " + err.Error())
 		clientWriteError(ctx, ws, err)
 		return
 	}
 	defer conn.Close()
 
+	// To decrease latencies, events are received and decoded in parallel
+	// to their sending, and we try to batch them together.
+	relayFrames := relayMakeReceiver(ctx, conn)
+	batchFrames := func() []byte {
+		batch, ok := <-relayFrames
+		if !ok {
+			return nil
+		}
+	Batch:
+		for {
+			select {
+			case b, ok := <-relayFrames:
+				if !ok {
+					break Batch
+				}
+				batch = append(batch, b...)
+			default:
+				break Batch
+			}
+		}
+		return batch
+	}
+
 	// We don't need to intervene, so it's just two separate pipes so far.
-	// However, to decrease latencies, events are received and decoded
-	// in parallel to their sending.
-	relayJSON := relayMakeReceiver(ctx, conn)
 	go func() {
 		defer cancel()
 		for {
@@ -186,11 +220,11 @@ func handleWS(w http.ResponseWriter, r *http.Request) {
 	go func() {
 		defer cancel()
 		for {
-			j, ok := <-relayJSON
-			if !ok {
+			b := batchFrames()
+			if b == nil {
 				return
 			}
-			clientWriteJSON(ctx, ws, j)
+			clientWriteBinary(ctx, ws, b)
 		}
 	}()
 	<-ctx.Done()
@@ -214,7 +248,7 @@ var page = template.Must(template.New("/").Parse(`<!DOCTYPE html>
 	<script>
 	let proxy = '{{ . }}'
 	</script>
-	<script src="xP.js">
+	<script type="module" src="xP.js">
 	</script>
 </body>
 </html>`))
@@ -235,13 +269,21 @@ func handleDefault(w http.ResponseWriter, r *http.Request) {
 }
 
 func main() {
-	if len(os.Args) < 3 || len(os.Args) > 4 {
-		log.Fatalf("usage: %s BIND CONNECT [WSURI]\n", os.Args[0])
+	flag.Usage = func() {
+		fmt.Fprintf(flag.CommandLine.Output(),
+			"Usage: %s [OPTION...] BIND CONNECT [WSURI]\n\n", os.Args[0])
+		flag.PrintDefaults()
+	}
+
+	flag.Parse()
+	if flag.NArg() < 2 || flag.NArg() > 3 {
+		flag.Usage()
+		os.Exit(1)
 	}
 
-	addressBind, addressConnect = os.Args[1], os.Args[2]
-	if len(os.Args) > 3 {
-		addressWS = os.Args[3]
+	addressBind, addressConnect = flag.Arg(0), flag.Arg(1)
+	if flag.NArg() > 2 {
+		addressWS = flag.Arg(2)
 	}
 
 	http.Handle("/ws", http.HandlerFunc(handleWS))