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This is an example showing a bug in RunKit's error handling for endpoints.
Specifically, while RunKit's use of Domains [0] is able to catch errors thrown directly by the exports.endpoint(req, res) function [1], RunKit is unable to catch errors thrown asynchronously [2]. This is not a language limitation, it's straightforward to manually use a Domain to catch the error [3], and RunKit should be doing exactly that.
[0]: https://nodejs.org/api/domain.html
[1]: https://runkit.io/laughinghan/58337152a62a08001304609a/branches/master/good_caught_error
(you can see the use of a Domain in the stacktrace)
[2]: https://runkit.io/laughinghan/58337152a62a08001304609a/branches/master/uncaught_error
[3]: https://runkit.io/laughinghan/58337152a62a08001304609a/branches/master/manually_caught_error
(The full workaround is slightly less straightforward, see the code for the full workaround including an edge case with an event handler and non-empty POST requests.)
const domain = require('domain')
exports.endpoint = (req, res) => {
const path = req.url.slice(process.env.RUNKIT_MOUNT_PATH.length)
if (path === '/good_caught_error') {
fail
} else if (path === '/uncaught_error') {
endpoint(req, res)
} else if (path === '/manually_caught_error') {
domain.create()
.on('error', function (e) {
res.statusCode = 500
res.end(`Manually caught error:\n${e.stack}\n`)
})
.run(endpoint, req, res)
} else if (path === '/surprising_caught_error') {
domain.create()
.on('error', function (e) {
res.statusCode = 500
res.end(`Manually caught error:\n${e.stack}\n`)
})
.run(() => fail)
} else if (path === '/unable_to_catch_error_if_nonempty_POST') {
// this fails if and only if a non-empty POST is submitted to it:
// curl -i -X POST https://runkit.io/laughinghan/58337152a62a08001304609a/branches/master/unable_to_catch_error_if_nonempty_POST -d body
// GET or empty POST works fine, weirdly enough
domain.create()
.on('error', function (e) {
res.statusCode = 500
res.end(`Manually caught error in event handler:\n${e.stack}\n`)
})
.run(() => {
req.on('end', () => fail)
req.resume()
})
} else if (path === '/manually_caught_error_in_event_handler') {
const d = domain.create()
d.on('error', function (e) {
res.statusCode = 500
res.end(`Manually caught error in event handler:\n${e.stack}\n`)
})
d.add(req) // this and
d.add(res) // this are added to fix the /unable_to_catch_error_if_nonempty_POST edge case
d.run(() => {
req.on('end', () => fail)
req.resume()
})
} else {
res.setHeader('Content-Type', 'text/html')
res.end(`Please go to <a href="${process.env.RUNKIT_MOUNT_PATH}/good_caught_error">/good_caught_error</a>, <a href="${process.env.RUNKIT_MOUNT_PATH}/uncaught_error">/uncaught_error</a>, or <a href="${process.env.RUNKIT_MOUNT_PATH}/manually_caught_error">/manually_caught_error</a>`)
}
}
function endpoint(req, res) {
process.nextTick(() => fail)
}
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