ppsspp/docs/WebSocketDebugger.md

PPSSPP WebSocket Debugger

PPSSPP has a JSON/WebSocket-based debugger and automation API, served from the same HTTP server used for "Remote ISO" disc sharing and file upload. It lets an external tool (a script, a web page, another editor/IDE) inspect and control a running emulation session: read/write memory, set breakpoints, step the CPU, read GE/GPU state, send fake input, tail the log, etc.

This doc is a local reference; a version of it is planned to also live on the PPSSPP website (../ppsspp-site next to this repo).

Where the code lives

• Core/WebServer.cpp / Core/WebServer.h - the shared HTTP server (also used for Remote ISO and file upload). It owns the listening socket and dispatches /debugger requests.
• Core/Debugger/WebSocket.cpp - upgrades the HTTP request to a WebSocket and runs the per-connection event loop (HandleDebuggerRequest).
• Core/Debugger/WebSocket/*.cpp/.h - one "subscriber" or "broadcaster" per feature area (CPU, memory, GPU, HLE, input, breakpoints, ...). Each file's top comment documents its events in detail - this doc gives the overview and an index into those files.
• Core/Debugger/WebSocket/WebSocketUtils.h - shared DebuggerRequest helper (parameter parsing, response/error helpers) and DebuggerSubscriber base class.
• Common/Net/WebsocketServer.h/.cpp - the low-level WebSocket framing.

Transport

• Runs on the same port as Remote ISO sharing (g_Config.iRemoteISOPort; 0 means "pick a free port automatically" - the actual bound port is written back to that config value and logged: Listening on port N).
• URL path: /debugger.
• WebSocket subprotocol: debugger.ppsspp.org (required - a plain HTTP GET to /debugger without a websocket Upgrade just redirects to the bundled web UI at /debugger/index.html).
• Messages are JSON, both directions, always shaped as {"event": "NAME", ...}.
• One WebSocket connection = one client; PPSSPP does not limit the number of simultaneous debugger connections.
• The debugger only actually does anything while WebServerFlags::DEBUGGER is enabled (see "Enabling it" below) - the HTTP server itself may also be running for other reasons (Remote ISO, upload) without the debugger being reachable.

Message protocol

Requests you send:

{ "event": "cpu.status" }

Optionally include a "ticket" field (any JSON value) - PPSSPP echoes it back verbatim in the response/error, so you can correlate requests and responses when firing several at once. Tools/wsdbg (see below) assigns an incrementing integer ticket automatically.

Responses use the same event name as the request:

{ "event": "cpu.status", "ticket": 1, ... }

Responses are not always immediate - some handlers respond asynchronously (see DebuggerRequest::Finish() in WebSocketUtils.h/.cpp).

Errors look like this:

{ "event": "error", "message": "...", "level": 2, "ticket": 1 }

level is a LogLevel (1=NOTICE, 2=ERROR, 3=WARN, 4=INFO, 5=DEBUG, 6=VERBOSE).

PPSSPP also sends unsolicited ("broadcast") events with no request - see below.

By convention, send a version event right after connecting (see WebSocket/GameSubscriber.cpp):

{ "event": "version", "name": "my-tool", "version": "1.0" }

PPSSPP responds with its own name/version, and remembers yours (currently just for internal bookkeeping/future logging).

Broadcast (unsolicited) events

Sent without you asking, whenever the underlying state changes:

Event	Sent when	Source
log	A new log line is emitted	LogBroadcaster.cpp
game.start	A game finishes booting	GameBroadcaster.cpp
game.quit	The game is closed/reset	GameBroadcaster.cpp
game.pause / game.resume	User opens/leaves the pause menu	GameBroadcaster.cpp
cpu.stepping	CPU enters a stepping/break state	SteppingBroadcaster.cpp
cpu.resume	CPU resumes from stepping	SteppingBroadcaster.cpp
input.buttons	Any emulated button changes state	InputBroadcaster.cpp
input.analog	An analog stick position changes	InputBroadcaster.cpp

A client can opt out of specific broadcast categories with broadcast.config.set ({"disallowed": {"logger": true, "game": true, "stepping": true, "input": true}}), see ClientConfigSubscriber.cpp. gpu.stats.feed (see below) works the same way for periodic GPU stats.

Request/response event catalog

Full details (parameters, response shape) are documented as comments above each handler in the corresponding Core/Debugger/WebSocket/*Subscriber.cpp file - this is just an index.

Category	Events	File
Game/version	game.reset, game.status, version	GameSubscriber.cpp
CPU core	cpu.stepping, cpu.resume, cpu.status, cpu.getAllRegs, cpu.getReg, cpu.setReg, cpu.evaluate	CPUCoreSubscriber.cpp
Stepping	cpu.stepInto, cpu.stepOver, cpu.stepOut, cpu.runUntil, cpu.nextHLE	SteppingSubscriber.cpp
Breakpoints	cpu.breakpoint.add/update/remove/list, memory.breakpoint.add/update/remove/list	BreakpointSubscriber.cpp
Memory read/write	memory.read_u8/u16/u32, memory.read, memory.readString, memory.write_u8/u16/u32, memory.write	MemorySubscriber.cpp
Memory info/annotations	memory.mapping, memory.info.config/set/list/search	MemoryInfoSubscriber.cpp
Disassembly	memory.base, memory.disasm, memory.searchDisasm, memory.assemble	DisasmSubscriber.cpp
HLE	hle.thread.list/wake/stop, hle.func.list/add/remove/removeRange/rename/scan, hle.module.list, hle.backtrace	HLESubscriber.cpp
GPU stats	gpu.stats.get, gpu.stats.feed	GPUStatsSubscriber.cpp
GPU recording	gpu.record.dump	GPURecordSubscriber.cpp
GPU buffers	gpu.buffer.screenshot, gpu.buffer.renderColor/renderDepth/renderStencil, gpu.buffer.texture, gpu.buffer.clut	GPUBufferSubscriber.cpp
Input injection	input.buttons.send, input.buttons.press, input.analog.send	InputSubscriber.cpp
Replay	replay.begin/abort/flush/execute/status, replay.time.get/set	ReplaySubscriber.cpp
Client config	broadcast.config.get/set	ClientConfigSubscriber.cpp

Enabling it

• UI: Settings > Tools > Developer Tools > "Allow remote debugger" checkbox (UI/DeveloperToolsScreen.cpp). The "Local Server Port" slider on the Networking screen sets the port (shared with Remote ISO sharing; 0 = auto-pick).
• Config: RemoteDebuggerOnStartup=true in ppsspp.ini (g_Config.bRemoteDebuggerOnStartup) starts it automatically on launch (UI/NativeApp.cpp).
• Command line (application build only): --debugger - added in Core/CmdLine.cpp/.h as an Application-only auto-param, so it forces bRemoteDebuggerOnStartup on for that run without persisting it to the config file. It's deliberately not available in the headless build (CmdLineMode::Headless) - see caveat below.
• Headless build: has its own, separate, pre-existing mechanism - --debugger=PORT parsed directly in headless/Headless.cpp (not through Core/CmdLine.cpp's shared parser). It also forces startBreak = true so the CPU halts before running anything. This is currently known not to work properly - treat it as unreliable/needs investigation before depending on it, which is also why the new --debugger flag intentionally does not apply to CmdLineMode::Headless.

Discovery

For LAN auto-discovery (mainly used by the mobile Remote Play/debugger flow), the server periodically reports its (local ip, port) to report.ppsspp.org/match/update (see RegisterServer() in Core/WebServer.cpp). Clients can query report.ppsspp.org/match/list to get a list of candidate endpoints on the same network and try connecting to each in turn.

The bundled web-based JS debugger

assets/debugger/ is a git submodule (https://github.com/unknownbrackets/ppsspp-debugger.git, bundled branch - see .gitmodules) containing a prebuilt React app. PPSSPP serves it directly at /debugger/ (Core/WebServer.cpp's HandleFallback/ServeAssetFile), so opening http://<ip>:<port>/debugger/ in a browser gets you a full GUI debugger for free. The actual editable source lives in a different branch of that same repo (the bundled branch only holds the built output that gets checked in here).

From reading the minified bundle (assets/debugger/static/js/main.*.js), it connects like this:

• Manual connect: new WebSocket("ws://ip:port/debugger", "debugger.ppsspp.org").
• Auto connect: fetch("//report.ppsspp.org/match/list") for a list of {ip, p} candidates (as registered by RegisterServer() above), then tries each with the same WebSocket call until one succeeds.

Talking to it yourself

• scripts/websocket-test.py - old minimal Python one-shot script (needs the websocket-client pip package).
• Tools/wsdbg/ - a small Rust CLI/REPL client for this session's work (see Tools/wsdbg/README.md): connects, does the version handshake, and lets you fire off events by hand or from a one-shot command line, printing responses and broadcasts as they arrive. Built and smoke-tested against a live PPSSPP instance while writing this doc.