Expressjs Morgan dynamically format the logs

Question

Attempting to change the format of morgan's logging through the application run time.

The value will change pending on some remote value in a database and I would like morgan's output to change as a result. ie. If in the database the value is 1 morgan's formatting is 'dev', if the value is 3 the formatting is 'combined'

I have the been using the following line to set up morgan with formatting:

app.use(morgan(get_verbose()))
   .use ....

where get_verbose will correspond to the format options. However it is not giving the dynamic results I was wishing for - it's only setting the formatting once.

Am I going about this incorrectly or is morgan limited to only 1 format at run time?

Answer 1

One approach would be to create a middleware function that "wraps" the Morgan middleware:

var morganDev = mordan('dev');
var morganCombined = morgan('combined');

app.use(function(req, res, next) {
    var value = /* get value somehow */

    if (value === 1) {
        morganDev(req, res, next);
    } else if (value === 3) {
        morganCombined(req, res, next);
    }
});

Up front, you create one logger for each log format you would like, but don't attach either of them to the app. In their place, a custom function reads the value and chooses which logger should handle the processing for this request.

Safety update: There should be a catch-all else block to handle the case where value is neither 1 or 3. This block should call next() directly, otherwise the request handling will stall and never return a response to the client.