Express.js plugin for checking request and response with rho-contracts
You must use the Body Labs package, rho-contracts-fork
:
"dependencies": {
"rho-contracts-fork": "^1.3.0"
}
var c = require('rho-contracts-fork'),
ec = require('express-contracts');
var cc = {};
cc.request = c.object({
body: c.object({
foo: c.value('bar'),
}).strict(),
}).rename('request');
cc.responseBody = c.object({
baz: c.value('barbar'),
}).strict().rename('responseBody');
var exampleApplicationMiddleware = function (req, res, next) {
res.status(200).checkedJson({ baz: req.body.foo + req.body.foo });
};
var exampleErrorHandlingMiddleware = function (err, req, res, next) {
if (err) {
if (err instanceof ec.ValidationError) {
res.status(400).json({ error: err.message });
} else if (err instanceof c.ContractError) {
res.status(500).json({ error: 'Internal Contract Violation' });
} else {
res.status(500).json({ error: 'Internal Server Error' });
}
}
};
app.use(
require('body-parser').json(), // populates req.body
ec.useContracts(cc.request, cc.responseBody),
exampleApplicationMiddleware,
exampleErrorHandlingMiddleware
);
Note the middleware useContracts(requestContract, responseBodyContract)
distinguishes between ValidationError
(for failures of requestContract
) and
ContractError
(for failures of responseBodyContract
), which callers will
likely wish to handle differently.
Furthermore, note that the middleware works by extending res
with a method
checkedJson
which checks responseBodyContract
before calling res.json
,
thus it is easy to "jump out" of the contract e.g. to send an error.
Finally, there is an asymmetry between the requestContract
, which is run over
the whole request (but only body
, query
, and params
are actually
checked), and the responseBodyContract
, which is only run over the payload
that eventually becomes the res.body
.
As of 2.2.0, the exported ValidationError
says which of the three checked
fields caused the (first seen) error, under the key problemField
, e.g.
if (err.problemField === 'body') {
// do something
} else if (err.problemField === 'query') {
// do something else
} else if (err.problemField === 'params') {
// do yet something else
} else {
// should not happen unless we start checking more fields
}
npm install rho-contracts-fork express-contracts
- Issue Tracker: github.com/bodylabs/express-contracts/issues
- Source Code: github.com/bodylabs/express-contracts
Pull requests welcome!
If you are having issues, please let us know.
The project is licensed under the two-clause BSD license.