Adding debugger support to a v8-based application

[Petar Dobrev]

Hello!

I'd like to add debugger support to an application that uses v8 and tried following the resource on the topic from the wiki: https://code.google.com/p/v8/wiki/AddDebuggerSupport

However, it seems that in v8-debug.h in trunk (https://code.google.com/p/v8/source/browse/trunk/include/v8-debug.h) there is neither v8::Debug::EnableAgent, nor v8::Debug::SetDebugMessageDispatchHandler.

Does anyone know what the current API to achieve that is?

Thanks!

Petar

[Ben Noordhuis]

You feed in JSON debug commands[0] with v8::Debug::SendCommand().
It's safe to call from another thread; the main thread will interrupt
currently executing JS code in order to process the debug command.

If the main thread spends most of its time in native code, then call
v8::Debug::ProcessDebugMessages() periodically to flush queued
commands.

Everything else, like creating a listen socket and managing
connections from debugger clients, is up to the embedder. The wire
representation of the debug protocol looks a lot like HTTP, but with
the notable differences that:

1. There is no status or request line, and

2. The server (the process being debugged) sends headers first. They
look like this:

Type: connect
V8-Version: 3.26.33
Protocol-Version: 1
Embedding-Host: node v0.13.0-pre
Content-Length: 0

It should be noted that V8's native debugger protocol is being phased
out in favor of Chromium's remote debugger protocol; for a longer-term
solution, that's probably what you want to be looking at.

Hope that helps!

[0] https://code.google.com/p/v8/wiki/DebuggerProtocol

[1] https://developer.chrome.com/devtools/docs/debugger-protocol

[Bit Cortex]

Hi Ben,

A couple of questions:

1. How does the embedder know what reponse to send to the debugger? v8::Debug::SendCommand() doesn't return anything.

2. Do you know if the debug protocol change will affect V8's debugging API?

Thanks!

[Ben Noordhuis]

On Mon, Aug 25, 2014 at 10:02 PM, Bit Cortex <bitc...@gmail.com> wrote:
> 1. How does the embedder know what reponse to send to the debugger?
> v8::Debug::SendCommand() doesn't return anything.

You send or collect the response in the message handler that you
register with v8::Debug::SetMessageHandler():

void HandleMessage(const v8::Debug::Message& message) {
v8::String::Utf8Value response(message.GetJSON());
// do something with |response|

}

> 2. Do you know if the debug protocol change will affect V8's debugging API?

I'm not really the right person to answer that question but my guess
is no or not much. I understand Chromium talks to the debugger using
the C++ API so whatever functionality it uses, V8 needs to keep.
Chromium is of course continuously updated but I don't expect radical
changes in the short term.

[Bit Cortex]

Thank you very much, Ben!

[Petar Dobrev]

Thanks Ben, that's helpful!

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