中间件中的ExpressJS和域错误处理

Question

I had an expectation that middleware that is bound to a Domain would be handled by the error handler for that domain.

In Express this did not turn out to be true.

I created a repository to illustrate this issue

https://github.com/rook2pawn/express-domains-issue

var app = express(); 
app.get('/',d.bind(function(req,res,next) {
    throw new Error("error")
}));
var server = http.createServer(app);

Will not route the error to the domain error handler registered at d

whereas

var app = d.bind(function(req,res,next) {
    throw new Error("error")
});
var server = http.createServer(app);

Will properly route the error to the domain without express.

Requesting any comments or thoughts about this?

Answer 1

It's just a bad example, because express wraps middleware in try-catch. This works:

app.get('/',d.bind(function(req,res,next) {
    process.nextTick(function () {
      throw new Error("error")
    })
}));

Answer 2

By document of node js:

"This method is almost identical to domain.bind(callback). However, in addition to catching thrown errors, it will also intercept Error objects sent as the first argument to the function."

and I write a demo code:

var domain = require('domain');
var fs = require('fs');

var d = domain.create();

require('http').createServer(function(req, res, next) {

d.on('error', function (err) {
    console.log(err);
    res.writeHead(500, "content-type: plain/text");
    res.end("Something missing!");
});


// This is for async
function readFile(filename, cb) {
    fs.readFile(filename, 'utf8', d.bind(function (er, data) {
        return cb(er, data ? JSON.parse(data) : null);
    }));
}
readFile("unknow file");


// This is for sync
(d.bind(function() {
    throw new Error();
}))();

}).listen(1337);

=> d.bind total can resolve all error sync and async to domain. That is the definition