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prevent domain.intercept passing 1st arg to cb
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GH nodejs#3379
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@wavded
wavded committed Jun 6, 2012
1 parent b9c5eee commit 61c0ee2
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Showing 3 changed files with 21 additions and 8 deletions.
9 changes: 6 additions & 3 deletions doc/api/domain.markdown
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Expand Up @@ -227,13 +227,16 @@ with a single error handler in a single place.
var d = domain.create();

function readSomeFile(filename, cb) {
fs.readFile(filename, d.intercept(function(er, data) {
fs.readFile(filename, d.intercept(function(data) {
// note, the first argument is never passed to the
// callback since it is assumed to be the 'Error' argument
// and thus intercepted by the domain.

// if this throws, it will also be passed to the domain
// additionally, we know that 'er' will always be null,
// so the error-handling logic can be moved to the 'error'
// event on the domain instead of being repeated throughout
// the program.
return cb(er, JSON.parse(data));
return cb(null, JSON.parse(data));
}));
}

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13 changes: 8 additions & 5 deletions lib/domain.js
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Expand Up @@ -149,15 +149,16 @@ Domain.prototype.bind = function(cb, interceptError) {
var b = function() {
// disposing turns functions into no-ops
if (self._disposed) return;
var args = Array.prototype.slice.call(arguments);

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@isaacs

isaacs Jun 6, 2012

This is extremely hazardous. I haven't benchmarked it yet, but in my experience in node, calling Array.prototype.slice.call(arguments) is an optimization killer.

Should be something like this:

var len = arguments.length;
switch (len) {
  case 0:
  case 1:
    // no args that we care about.
    args = [];
    break;
  case 2:
    // optimization for most common case: cb(er, data)
    args = [arguments[1]];
    break
  default:
    // slower for less common case: cb(er, foo, bar, baz, ...)
    var args = new Array(len - 1);
    for (var i = 1; i < len; i++) {
      args[i] = arguments[i - 1];
    }
    break;
}

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@isaacs

isaacs Jun 6, 2012

Whoops, premature send, sorry.

Then, once you've plucked off the non-error bits, just use the first argument as a named arg, and reference it by name.

  var b = function(er, data) {

If interceptError isn't set, then dont' do any of that monkey business, and instead just do cb.apply(this, arguments), but otherwise leave the arguments object alone.

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@wavded

wavded Jun 6, 2012

Author Owner

You are right, it is more optimized - see http://jsperf.com/arguments-slice2
I'll update the patch

if (this instanceof Domain) {
return cb.apply(this, arguments);
return cb.apply(this, args);
}

// only intercept first-arg errors if explicitly requested.
if (interceptError && arguments[0] &&
(arguments[0] instanceof Error)) {
var er = arguments[0];
if (interceptError && args[0] &&
(args[0] instanceof Error)) {
var er = args[0];
decorate(er, {
domain_bound: cb,
domain_thrown: false,
Expand All @@ -166,9 +167,11 @@ Domain.prototype.bind = function(cb, interceptError) {
self.emit('error', er);
return;
}
// remove first-arg if intercept as assumed to be the error-arg
if (interceptError && args.length) args.shift();

self.enter();
var ret = cb.apply(this, arguments);
var ret = cb.apply(this, args);
self.exit();
return ret;
};
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7 changes: 7 additions & 0 deletions test/simple/test-domain.js
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Expand Up @@ -127,6 +127,13 @@ function fn(er) {
var bound = d.intercept(fn);
bound(new Error('bound'));

// intercepted should never pass first argument to callback
function fn2(data) {
assert.equal(data, 'data', 'should not be null err argument')
}

var bound = d.intercept(fn2);
bound(null, 'data');


// throwing in a bound fn is also caught,
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