Invalid character in header content ["x-cypress-file-path"] in Cypress

Question

I have some strange issue in Cypress. When I go to the Cypress automation toll, click Settings and then try to click Project settings, I get the following error:

Invalid character in header content ["x-cypress-file-path"] TypeError [ERR_INVALID_CHAR]: Invalid character in header content ["x-cypress-file-path"] at ServerResponse.setHeader (node:_http_outgoing:666:3) at j (:4526:1236) at Server. (:4526:1875) at Server.emit (node:events:513:28) at parserOnIncoming (node:_http_server:1072:12) at HTTPParser.parserOnHeadersComplete (node:_http_common:119:17)

My Cypress version in 13.3.3 (the last one) but the issue appears in the oldest versions as well. Here is the screenshot of the problem. What could be the issue?

I have tried to use different versions of Cypress. I expect to resolve the issue and be able to click see Project settings.

Answer 1

This may be a problem in the configuration file cypress.config.js, specifically the fileServerFolder - root project folder setting.

This is used when the Cypress proxy handles a response, using this code:

const args = _.compact([
  fileServerFolder,            // from config 
  req.url,                     // from request
])

const file = decodeURI(url.parse(path.join(...args)).pathname)

res.setHeader('x-cypress-file-path', file)   // error occurs here

The other external value is the request URL, which you can check in the Network tab of devtools for anything suspicious (i.e odd characters)