Yield object instead of string in cy.wait when request content-type is valid JSON Mime type (not only application/json)

[aethr]

Possibly a duplicate or related to #14273.

Our back-end services use JSON:API spec (https://jsonapi.org/) which recommends the media type application/vnd.api+json. They deliver valid JSON in the response body, which should be converted to an object by cy.wait to allow for deep assertions.

Current behavior

If request is intercepted with cy.intercept(), then cy.wait() yields a string for the response body (related issue: #14273.)

From this comment: #14273 (comment), I believe this is due to the check in

cypress/packages/driver/src/cy/net-stubbing/events/utils.ts

Lines 4 to 20 in 6ee7a9c

	export function hasJsonContentType (headers: { [k: string]: string }) {
	const contentType = find(headers, (v, k) => /^content-type$/i.test(k))
	return contentType && /^application\/json/i.test(contentType)
	}
	export function parseJsonBody (message: CyHttpMessages.BaseMessage) {
	if (!hasJsonContentType(message.headers)) {
	return
	}
	try {
	message.body = JSON.parse(message.body)
	} catch (e) {
	// invalid JSON
	}
	}

Due to our back-end sending content-type: application/vnd.api+json this check fails, and so the response body is not converted using JSON.parse.

Desired behavior

I believe that if the response to a request is valid JSON, it should be converted to a JS object regardless of the headers. This approach is taken elsewhere in Cypress, ie:

cypress/packages/server/lib/controllers/xhrs.js

Lines 9 to 23 in dae76a8

	const isValidJSON = function (text) {
	if (_.isObject(text)) {
	return true
	}
	try {
	const o = JSON.parse(text)
	return _.isObject(o)
	} catch (error) {
	false
	}
	return false
	}

Effectively if JSON.parse(text) succeeds without throwing, we can assume that text is valid JSON and return the resulting parsed object.

Test code to reproduce

describe('cy.intercept tests', () => {
  it('test cy.intercept() with application/json', () => {
    cy.intercept('POST', '/users', { foo: 'bar' }).as('postUrl');
    cy.visit('https://example.com');
    cy.then((win) => {
      Cypress.$.ajax({
        url: '/users',
        method: 'POST',
        contentType: 'application/json',
        data: JSON.stringify({ name: 'XYZ' }),
      });
    });

    cy.wait('@postUrl')
      .should((interception) => {
        expect(typeof interception.response.body).to.eq('object');
        expect(interception.response.body).to.deep.eq({ foo: 'bar' })
      });
  });

  it('test cy.intercept() with application/vnd.api+json', () => {
    // temporary API endpoint at mocky.io that responds with 'content-type: application/vnd.api+json'
    cy.intercept('GET', 'https://run.mocky.io/v3/5c528eae-f3c0-4dbe-b9cb-7b12a00320ad').as('jsonApiUrl');
    cy.visit('https://example.com');
    cy.then((win) => {
      Cypress.$.ajax({
        url: 'https://run.mocky.io/v3/5c528eae-f3c0-4dbe-b9cb-7b12a00320ad',
        method: 'GET',
      });
    });

    cy.wait('@jsonApiUrl')
      .should((interception) => {
        expect(interception.response.headers['content-type']).to.contain('application/vnd.api+json');
        // ❗️ fails
        expect(typeof interception.response.body).to.eq('object');
        // ❗️ fails
        expect(interception.response.body).to.deep.eq({ foo: 'bar' });
      });
  });
});

Versions

6.3.0

[flotwig]

Sounds like 'cypress/packages/driver/src/cy/net-stubbing/events/utils.ts' just needs to be updated to detect more valid JSON MIME types.

I don't think we should proactively JSON.parse all incoming request and response bodies, sounds like it could do more harm than good. For example, if you have an endpoint that returns plain text, the type of the response could be object or string depending on if the response happens to be JSON-parseable or not. Keep in mind that true, false, 1, and "foo" are all valid JSON bodies.

[aethr]

Good points. I did some testing and route in Cypress 5 and 6 are both consistent in not converting the response body to objects in this scenario, so my suggestion would probably be a breaking change for some.

A brief search on iana turned up a few likely JSON-compatible media types:

• https://www.iana.org/assignments/media-types/application/geo+json
• https://www.iana.org/assignments/media-types/application/scim+json
• https://www.iana.org/assignments/media-types/application/problem+json

Most seem to follow the same pattern:

• application/SOMETHING+json
• application/vnd.SOMETHING+json

Perhaps the check could be expanded to:

return contentType && /^application\/.*json/i.test(contentType)

[flotwig]

@aethr Sounds good. If it gets done by March we can squeeze it into the 7.0.0 release.

[github-actions]

Internal Jira issue: TR-681

[cypress-bot]

The code for this is done in cypress-io/cypress#15129, but has yet to be released.
We'll update this issue and reference the changelog when it's released.

[cypress-bot]

Released in 7.0.0.

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