Handle async pathRewrite function

[WestonThayer]

Is this a feature request?

Yes. I would like a pathRewrite function that returns a Promise to be handled. Currently it can only return a string.

My use case is: when a request for /api/foo?auth_token=xxx arrives, I need to:

1. Grab auth_token and check its validity. This is an async operation
2. If it is valid, use the token to look up some additional information that token has permission to access in a database (also an async operation)
3. Assuming all goes well, return a rewritten path, like /other-api/bar?db-field-1=abc&db-field-2=abc. If it did not go well, the path will be rewritten to /other-api/404

Similar to #318, but this covers the case where more than just the response headers/status needs to be modified.

I have this working and tested in a local fork, please let me know if you would accept a PR.

[sysoft]

same requestion!

[WestonThayer]

Workaround: I ended up just using the underlying http-proxy lib.

const http = require("http");
const httpProxy = require("http-proxy");
const url = require("url");

const proxy = httpProxy.createProxyServer({ target: "http://example.com" });
const server = http.createServer( /* handle HTTP requests */ );

server.on("upgrade", async (req, socket, head) => {
  const parsedUrl = url.parse(req.url, true /* also parse query params */);

  if (parsedUrl.pathname === "/api/foo") {
    // this should be in a try/catch for any situation in which the Promise could
    // reject
    const usr = await someAuthService.validate(parsedUrl.query.auth_token);
    const someVar = await someDbService.getField1(usr);
    const otherVar = await someDbService.getField2(usr);

    // Now do the path rewrite
    req.url = `/other-api/bar?db-field-1=${someVar}&db-field2=${otherVar}`;

    // let request through
    proxy.ws(req, socket, head);
  } else {
    // Invalid path, close the WebSocket
    socket.destroy();
    // Alternatively, could choose some other path rewrite, like:
    // req.url = "/other-api/404";
    // proxy.ws(req, socket, head);
  }
});

server.listen(3000);

[rsethc]

I also had a need for this (in my case, the path rewriting behavior is dependent on its own HTTP request, so async is needed). As such I have created a pull request with the fix.

[chimurai]

published http-proxy-middleware@0.21.0 with async pathRewrite

Thanks @rsethc !