Express Error Log
A very simple logger for Express 4.x, based on
the errorlog
NPM module.
Install and use
Install as usual with NPM:
npm install --save express-errorlog
Then configure as the last routes of your Express app:
var errorlog = require('express-errorlog');
app.use(errorlog);
app.use(function(err, req, res, next) {
res.json(err);
})
The express-errorlog
handler will normalize whatever your application passed
to the next(...)
function and log an error message.
It will then pass the normalized error to the next error handler, which will
have the job of rendering the actual response to the client.
The examples below assume that the final error handler will simply send back
a JSON of the normalized error (no need to set the status again,
express-errorhandler
will set that for you already).
Logging and sample JSON responses
In order to trigger log entries, simply use Express' own next(...)
function,
passing one of the the following types of parameter:
Numbers
app.get('/test', function(req, res, next) {
next(400);
});
The number will be interpreted as the status code of the response. If the number
is less than zero or greater than 599, the response status will be normalized to
a 500 Internal Server Error.
The response sent back to the client will contain the following:
HTTP/1.1 400 Bad Request
Content-Type: application/json
{
"status": 400,
"message": "Bad Request"
}
And the log will written with
2015-03-30T16:45:01.661Z - GET /test (400) - Bad Request
Strings
app.get('/test', function(req, res, next) {
next("Something is wrong");
});
The number will be interpreted as the status message for the response, while the
status will be defaulted to a 500 Internal Server Error.
The response sent back to the client will contain the following:
HTTP/1.1 500 Internal Server Error
Content-Type: application/json
{
"status": 500,
"message": "Something is wrong"
}
And the log will written with
2015-03-30T16:45:01.661Z - GET /test (500) - Something is wrong
Objects
app.get('/test', function(req, res, next) {
var error = new Error('Invalid access for user');
error.user = 'pier@usrz.com';
error.token = 'c568019d-3c80-4685-8982-ed455a2c0cd1';
next({
status: 403,
message: 'You have no access, my friend',
error: error,
details: {
example: "... some extra token for the response ..."
},
});
});
Objects can also be passed directly to the next(...)
call, having the
following keys:
status
: A number representing the status code of the response.message
: The message to transmit to the client.error
: An Error
that will be logged, but not transmitted to the client.details
: Anything that will be serialized to JSON and sent back alongside
the response.
In the example above, the response will be:
HTTP/1.1 403 Forbidden
Content-Type: application/json
{
"status": 403,
"message": "You have no access, my friend",
"details": {
"example": "... some extra token for the response ..."
}
}
And the log will contain something along the following:
2015-03-30T16:45:01.718Z - GET /test (403) - You have no access, my friend
>>> {"example":"... some extra token for the response ..."}
>>> {"user":"pier@usrz.com","token":"c568019d-3c80-4685-8982-ed455a2c0cd1"}
Error: Invalid access for user
at Error (native)
at ... stacktrace continues ...
In other words, details
and error
will be logged and the Error
's stack
trace will be dumped in full. At the same time, note that there is no trace of
the error
in the response sent back to the client.
Errors
app.get('/test', function(req, res, next) {
var error = new Error('Something is amiss');
error.status = 410;
error.details = {
example: "... some extra token for the response ..."
};
throw error;
});
Whether thrown or passed to next(...)
, exceptions will produce a 500 Internal
Server Error unless they expose a status
property directly and their message
will be sent alongside the response, as:
HTTP/1.1 410 Gone
Content-Type: application/json
{
"status": 410,
"message": "Something is amiss",
"details": {
"example": "... some extra token for the response ..."
}
}
The log will contain the full details and stack trace of the error:
2015-03-30T16:45:01.718Z - GET /test (410) - Something is amiss
>>> {"example":"... some extra token for the response ..."}
Error: Something is amiss
at Error (native)
at ... stacktrace continues ...
Request IDs
If the Express' request
contains the special id
value (as for example when
using express-request-id
)
said id
will also be reported, for example:
2015-03-30T16:45:01.661Z - d7c32387-3feb-452b-8df1-2d8338b3ea22 - GET /test (500) - Something is wrong
Configuration
Configure accepts basically the same options as
errorlog
:
var errorlog = require('express-errorlog');
app.use(errorlog({
logger: function/stream,
}));
logger
may be one of the following:
- a
Writable
stream to which error messages will be written to (actually
an object offering a write(...)
function will do). - a simple
function
that will be invoked once with each message to log. - if unspecified this will default to
process.stderr
.
category
: a category name that will be inserted in the message to log.
As with errorlog
, use a package
like logrotate-stream
if
log rotation is necessary in your environment.
License (MIT)
Copyright (c) 2015 USRZ.com and Pier Paolo Fumagalli
Permission is hereby granted, free of charge, to any person obtaining a copy of
this software and associated documentation files (the "Software"), to deal in
the Software without restriction, including without limitation the rights to
use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of
the Software, and to permit persons to whom the Software is furnished to do so,
subject to the following conditions:
The above copyright notice and this permission notice shall be included in all
copies or substantial portions of the Software.
THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
SOFTWARE.