How to forward to a absolute PATH? because thenForwardTo() only accepts host url without PATH.

[rivudutta]

I want to forward requests to a particular path but I am not able to do it using thenForwardTo(). It is throwing error and it only accepts hostname (without path).

For example, I want to match one absolute URL & forward it to another absolute URL.

// Redirect any github/login requests to github.com/signup
server.anyRequest().forHost("https://github.com/login").thenForwardTo("https://github.com/signup");

[rivudutta]

Hi @pimterry , please let me know if it is possible?

[pimterry]

Hi @rivudutta. If you want to do this, you'll need to do so with a beforeRequest callback. Unfortunately it's not possible with thenForwardTo right now. You just need to provide a callback that returns { url: yourTargetUrl } and the request will be redirected. That way you can include any custom logic you like in that callback for all sorts of other advanced mappings 😄

[rivudutta]

@pimterry thanks for the solution, I have tried this but it also changes the URL with the targetURL in the chrome address bar.

For example,
If I redirect to "github.com/signup", browsers address bar URL is also getting changed, however while using .thenForwardTo() it doesn't change the URL in the browser addressbar. Any idea how to achieve the same behaviour with beforeRequest, where I can show "github.com/login" URL in the address bar but render "github.com/signup" as the body.

beforeRequest: (req) => {
 return {
        url: "https://github.com/signup/"
  };
}

[pimterry]

If the addressbar is being changed, that means the way you're rewriting the request is making github return a redirect response (e.g. a 301/302/307 status) for some reason. You'll probably be able to see that in the network inspector in the browser.

It's hard to know exactly why that might happen I'm afraid, I'd recommend testing out different requests and rewritings manually and see if you can tell what's causing that. As far as I'm aware though, returning a URL there should do almost exactly the same as using thenForwardTo.

The code for each is here:

• Forwarding:

  mockttp/src/rules/requests/request-handlers.ts

  Lines 433 to 467 in a5b0fc3

  	if (this.forwarding) {
  	const { targetHost, updateHostHeader } = this.forwarding;
  	if (!targetHost.includes('/')) {
  	// We're forwarding to a bare hostname
  	[hostname, port] = targetHost.split(':');
  	} else {
  	// We're forwarding to a fully specified URL; override the host etc, but never the path.
  	({ protocol, hostname, port } = url.parse(targetHost));
  	}
  	const hostHeaderName = isH2Downstream ? ':authority' : 'host';
  	let hostHeaderIndex = findRawHeaderIndex(rawHeaders, hostHeaderName);
  	let hostHeader: [string, string];
  	if (hostHeaderIndex === -1) {
  	// Should never happen really, but just in case:
  	hostHeader = [hostHeaderName, hostname!];
  	hostHeaderIndex = rawHeaders.length;
  	} else {
  	// Clone this - we don't want to modify the original headers, as they're used for events
  	hostHeader = _.clone(rawHeaders[hostHeaderIndex]);
  	}
  	rawHeaders[hostHeaderIndex] = hostHeader;
  	if (updateHostHeader === undefined || updateHostHeader === true) {
  	// If updateHostHeader is true, or just not specified, match the new target
  	hostHeader[1] = hostname + (port ? `:${port}` : '');
  	} else if (updateHostHeader) {
  	// If it's an explicit custom value, use that directly.
  	hostHeader[1] = updateHostHeader;
  	} // Otherwise: falsey means don't touch it.
  	reqUrl = new URL(`${protocol}//${hostname}${(port ? `:${port}` : '')}${path}`).toString();
  	}

• beforeRequest URL rewriting:

  mockttp/src/rules/requests/request-handlers.ts

  Line 597 in a5b0fc3

  reqUrl = modifiedReq?.url || reqUrl;

  +

  mockttp/src/rules/requests/request-handlers.ts

  Lines 613 to 617 in a5b0fc3

  	Object.assign(headers,
  	isH2Downstream
  	? getH2HeadersAfterModification(expectedTargetUrl, clientHeaders, modifiedReq?.headers)
  	: { 'host': getHostAfterModification(expectedTargetUrl, clientHeaders, modifiedReq?.headers) }
  	);

  +

  mockttp/src/rules/requests/request-handlers.ts

  Lines 636 to 640 in a5b0fc3

  	// Reparse the new URL, if necessary
  	if (modifiedReq?.url) {
  	if (!isAbsoluteUrl(modifiedReq?.url)) throw new Error("Overridden request URLs must be absolute");
  	({ protocol, hostname, port, path } = url.parse(reqUrl));
  	}

To debug this further, you might want to try logging the received & forwarded requests using mockttpServer.on(event, callback) to examine the raw traffic. The request event will tell you exactly what Mockttp receives, and the rule-event event will call the callback with a series of processing events, including a passthrough-request-head event with the final modified version of that request. There's more info in the docs here: https://httptoolkit.github.io/mockttp/interfaces/Mockttp.html#on. You could use that to compare exactly what gets sent in the forwarding & beforeRequest cases.

[rivudutta]

Thank you for the debugging steps, I will try them.