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Error Handler
Thiago da Rosa de Bustamante edited this page Feb 6, 2018
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An ErrorHandler is a function that is called to handle all errors reported by the gateway.
The ErrorHandler middleware should be a valid expressjs error handler function.
Each errorHandler middleware must be defined on its own .js file.
Example:
module.exports = (err, req, res, next) => {
if (err && err.message) {
if (res.headersSent) { // important to allow default error handler to close connection if headers already sent
return next(err);
}
const mime = req.accepts('json', 'xml', 'html', 'text');
res.status(err.statusCode || err.status || 500);
switch (mime) {
case 'json':
res.set('Content-Type', 'application/json');
res.json({ error: err.message });
break;
case 'xml':
res.set('Content-Type', 'application/xml');
res.send(`<error>${err.message}</error>`);
break;
case 'html':
res.set('Content-Type', 'text/html');
res.send(`<html><head></head><body>${err.message}</body></html>`);
break;
default:
res.set('Content-Type', 'text/plain');
res.send(err.message);
}
} else {
next(err);
}
};If you need to receive some parameters to initialize your error handler, you can write a factory function, like:
module.exports = function(config) {
validateMustacheConfig(config);
const template = config.template;
return (err, req, res, next) => {
if (err && err.message) {
if (res.headersSent) {
return next(err);
}
res.set('Content-Type', config.contentType || 'text/html');
res.status(err.statusCode || err.status || 500);
let body;
try {
body = mustache.render(template, {
error: err,
req: req,
res: res
});
} catch (e) {
body = { error: err.message };
}
res.send(body);
} else {
next(err);
}
};
};
module.exports.factory = true;You can configure an errorHandler middleware through:
- Admin Rest API:
POST /midleware/errorhandler - SDK:
sdk.middleware.addErrorHandler(name, fileName); - CLI:
treeGatewayConfig middleware errorHandler -a <name> ./filename.js
Tree Gateway provide some error handler middlewares for common tasks already included in its distribution. Check the list here.