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fix(parser): loop instead of recurse to avoid stack overflow #38

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fix(parser): loop instead of recurse to avoid stack overflow #38

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119 changes: 69 additions & 50 deletions src/parser.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -36,6 +36,7 @@ export default class Parser extends Emitter<ParserEvents> {
#messageSize = 0
#handshakeComplete = false
#isWaitingForData = true
#destroyed = false

constructor(socket: TLSSocket) {
super()
Expand All @@ -45,6 +46,7 @@ export default class Parser extends Emitter<ParserEvents> {
}

destroy(): void {
this.#destroyed = true
this.#isWaitingForData = false
this.#socket.removeListener('data', this.#handleData)
}
Expand All @@ -63,56 +65,67 @@ export default class Parser extends Emitter<ParserEvents> {
}
}

// Loop instead of recurse: each iteration checks the current state, ensures
// enough bytes are buffered, and dispatches to a handler. Handlers update
// #state / #data and return; they no longer call #waitForData() directly.
// The loop exits when the parser is destroyed or a handler sets
// #isWaitingForData = true (i.e. needs more bytes from the socket).
// The previous version recursed through #waitForData -> #handleGotMessageSize
// / #handleGotMessageBytes -> #getNextMessage -> #waitForData, which could
// blow the call stack on a burst of buffered messages or on a TCP segment
// that split a varint size header.
#waitForData() {
Logger.debug(`waitForData state: ${this.#state}`)
while (!this.#destroyed && !this.#isWaitingForData) {
Logger.debug(`waitForData state: ${this.#state}`)

let minBytesNeeded = 0
let minBytesNeeded = 0

switch (this.#state) {
case ProcessingState.MCS_VERSION_TAG_AND_SIZE:
minBytesNeeded += Variables.kVersionPacketLen
// eslint-disable-next-line no-fallthrough
case ProcessingState.MCS_TAG_AND_SIZE:
minBytesNeeded += Variables.kTagPacketLen
switch (this.#state) {
case ProcessingState.MCS_VERSION_TAG_AND_SIZE:
minBytesNeeded += Variables.kVersionPacketLen
// eslint-disable-next-line no-fallthrough
case ProcessingState.MCS_SIZE:
minBytesNeeded += Variables.kSizePacketLenMin
break
case ProcessingState.MCS_PROTO_BYTES:
minBytesNeeded = this.#messageSize
break
default:
this.#emitError(new Error(`Unexpected state: ${this.#state}`))
return
}

if (this.#data.length < minBytesNeeded) {
Logger.debug(`Waiting for ${minBytesNeeded - this.#data.length} more bytes. Got ${this.#data.length}`)
this.#isWaitingForData = true
return
}
case ProcessingState.MCS_TAG_AND_SIZE:
minBytesNeeded += Variables.kTagPacketLen
// eslint-disable-next-line no-fallthrough
case ProcessingState.MCS_SIZE:
minBytesNeeded += Variables.kSizePacketLenMin
break
case ProcessingState.MCS_PROTO_BYTES:
minBytesNeeded = this.#messageSize
break
default:
this.#emitError(new Error(`Unexpected state: ${this.#state}`))
return
}

Logger.debug(`Processing MCS data: state == ${this.#state}`)

switch (this.#state) {
case ProcessingState.MCS_VERSION_TAG_AND_SIZE:
this.#handleGotVersion()
this.#handleGotMessageTag()
this.#handleGotMessageSize()
break
case ProcessingState.MCS_TAG_AND_SIZE:
this.#handleGotMessageTag()
this.#handleGotMessageSize()
break
case ProcessingState.MCS_SIZE:
this.#handleGotMessageSize()
break
case ProcessingState.MCS_PROTO_BYTES:
this.#handleGotMessageBytes()
break
default:
this.#emitError(new Error(`Unexpected state: ${this.#state}`))
if (this.#data.length < minBytesNeeded) {
Logger.debug(`Waiting for ${minBytesNeeded - this.#data.length} more bytes. Got ${this.#data.length}`)
this.#isWaitingForData = true
return
}

Logger.debug(`Processing MCS data: state == ${this.#state}`)

switch (this.#state) {
case ProcessingState.MCS_VERSION_TAG_AND_SIZE:
this.#handleGotVersion()
this.#handleGotMessageTag()
this.#handleGotMessageSize()
break
case ProcessingState.MCS_TAG_AND_SIZE:
this.#handleGotMessageTag()
this.#handleGotMessageSize()
break
case ProcessingState.MCS_SIZE:
this.#handleGotMessageSize()
break
case ProcessingState.MCS_PROTO_BYTES:
this.#handleGotMessageBytes()
Comment on lines +111 to +123
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@Eneris Eneris May 6, 2026

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Copilot proposed change sounds a bit excessive, but it has a point. Can you check it out for the PR please? @zzorba

break
default:
this.#emitError(new Error(`Unexpected state: ${this.#state}`))
return
}
}
}

Expand Down Expand Up @@ -154,8 +167,13 @@ export default class Parser extends Emitter<ParserEvents> {
// NOTE(ibash) I could only test this case by manually cutting the buffer
// above to be mid-packet like: new ProtobufJS.BufferReader(this.#data.slice(0, 1))
if (incompleteSizePacket) {
// The varint extends past what's currently buffered; we need more
// bytes from the socket. Mark that we're waiting and bail -- do
// NOT re-enter #waitForData here, the length check would still
// pass (#data.length >= kSizePacketLenMin) and the recursive call
// would loop until it blew the stack across many TCP reads.
this.#state = ProcessingState.MCS_SIZE
this.#waitForData()
this.#isWaitingForData = true
return
}

Expand All @@ -165,10 +183,10 @@ export default class Parser extends Emitter<ParserEvents> {

if (this.#messageSize > 0) {
this.#state = ProcessingState.MCS_PROTO_BYTES
this.#waitForData()
} else {
this.#handleGotMessageBytes()
return
}

this.#handleGotMessageBytes()
}

#handleGotMessageBytes() {
Expand All @@ -190,7 +208,7 @@ export default class Parser extends Emitter<ParserEvents> {
// Continue reading data.
Logger.debug(`Continuing data read. Buffer size is ${this.#data.length}, expecting ${this.#messageSize}`)
this.#state = ProcessingState.MCS_PROTO_BYTES
this.#waitForData()
this.#isWaitingForData = true
return
}

Expand Down Expand Up @@ -223,7 +241,8 @@ export default class Parser extends Emitter<ParserEvents> {
this.#messageTag = 0
this.#messageSize = 0
this.#state = ProcessingState.MCS_TAG_AND_SIZE
this.#waitForData()
// No recursion: #waitForData's loop will pick up the new state on the
// next iteration.
}

#buildProtobufFromTag(tag) {
Expand Down