Breakpoints are not hit on Windows

[DominicKramer]

Breakpoints don't appear to be hit on Windows (Tested on Windows Server 2019 with Node 12.13.1).

The following code isolates how the debug agent uses V8's inspector API. Either we are using the API incorrectly or there is a bug in the API.

index.js

const inspector = require('inspector');

const session = new inspector.Session();
session.connect();
session.post('Debugger.enable');
session.post('Debugger.setBreakpointsActive', {active: true});
session.on('Debugger.paused', message => {
	console.log('Paused with message', message);
});

const url = `file://${__filename}`
const line = 26;
const column = 1;

const options = {
  lineNumber: line - 1,
  url,
  columnNumber: column - 1,
  condition: undefined,
};

console.log('Setting breakpoing with options=', options);

session.post('Debugger.setBreakpointByUrl', options, (error, response) => {
  console.log('Setting breakpoint, error=', error, ', response=', response);
});

function f() {
	console.log('f() called');
	const a = 42;
}

setInterval(f, 1000);

Running node index.js on Linux causes the Paused with message ... callback to correctly get called. When running the code on Windows, the callback is never invoked. I think this is why breakpoints are not being hit by the debug agent on Windows.

The following is the output on Linux

$ node index.js 
Setting breakpoing with options= {
  lineNumber: 25,
  url: 'file:///xxxxx/index.js',
  columnNumber: 0,
  condition: undefined
}
Paused with message {
  method: 'Debugger.paused',
  params: {
    callFrames: [
      [Object], [Object],
      [Object], [Object],
      [Object], [Object],
      [Object], [Object],
      [Object], [Object],
      [Object]
    ],
    reason: 'other',
    hitBreakpoints: [
      '1:25:0:file:///xxxxx/index.js'
    ]
  }
}
Setting breakpoint, error= null , response= {
  breakpointId: '1:25:0:file:///xxxxx/index.js',
  locations: [ { scriptId: '51', lineNumber: 25, columnNumber: 2 } ]
}
f() called
f() called
f() called
f() called

while on Windows the output is

> node index.js
Setting breakpoing with options= {
  lineNumber: 24,
  url: 'file://C:\\xxxxx\\index.js',
  columnNumber: 0,
  condition: undefined
}
Setting breakpoint, error= null , response= {
  breakpointId: '1:24:0:file://C:\\xxxxx\\index.js',
  locations: []
}
f() called
f() called
f() called
f() called
f() called

Notice that the Setting breakpoint response returns a list of locations with zero elements.

[DominicKramer]

@hashseed I was wondering if you could help me out. Based on the repro above, is there a problem with how we are using the inspector API on Windows. Thanks.

[DominicKramer]

I have a potential fix in #815. The PR still has unit test failures, but I have verified that the modification I made works to debug on Windows 10.

It seems the inspector.setBreakpointByUrl method requires the url to start with file:/// (not file://, note the difference in the number of slashes). In addition, the url has to have all of its backslashes converted to forward slashes.