Knowing the current public hostname of a Netlify function

Support
1

Hello everyone,

tl;dr;
Is it possible, from inside a lambda handler, to know the public hostname this function is accessed from?

For example, if I have a function on http://foo.netlify.com/.netlify/functions/debug, how can I know, from inside this function handler, that it’s running on foo.netlify.com?

What I want to build:
My goal is to have one website available through multiple domain names. I added a redirect to my website so all incoming request to the root actually go through my lambda. Based on which domain is currently targeted, I want to return slightly different content.

What I tried
During development, I was using netlify-lambda to locally serve my functions. In that context, I could read event.headers.host and correctly get localhost:9000 so I assumed this was the way to go.

But once I deployed in production, I realized the headers exposed are totally different and do not include any mention of the public hostname.

Other workaround I thought of
I thought that maybe I could redirect each domain to a different subdirectory and then add redirect rules for each of this subdirectories to pass and additional header mirroring the domain name.

Something like www.foo1.com goes to foo.netlify.com/foo1 and www.foo2.com goes to foo.netlify.com/foo2 and then I add redirects such as /foo1 goes to my lambda with X-hostname: www.foo1.com as an additional header.

But I couldn’t find a way to have domains target anything else than the root, so I’m also blocked here.

Any idea, even an convoluted one, how I could have my lambdas aware of the url they’re running on?

1 Like
2

Hi, @pixelastic, thank you for your patience.

It might help to clarify something before we go further. Are the function calls themselves happening because of a Netlify redirect? Or is site javascript making the calls to the functions? It sounds like the former is the case but I wanted to be sure.

3

Oh, that’s an interesting point, I forgot about that part.

The functions is happening because of a redirect, namely:

[[redirects]]
  from = "/"
  to = "/.netlify/functions/index"
  status = 200
  force = true

So a visit to the root of the project does actually land on the lambda, and that’s where I’d like to read the hostname.

Thanks for your time,

4

So the hostname of the lambda function is available inside the context object. Here’s an example of how to do it: deploy-id-test/getdeploy.js at master · depadiernos/deploy-id-test · GitHub

function extractNetlifySiteFromContext(context) {
  data = context.clientContext.custom.netlify
  decoded = JSON.parse(Buffer.from(data, "base64").toString("utf-8"))
  return decoded
}

Let me know if that helps.

1 Like
5

How about if it’s called as an API endpoint?

Having the same issue where event.headers.host is available in dev but not in preview/production.

I don’t have any data in dev under context.clientContext at all.

Thank you!

6

Ah, I’m not sure there is a workaround for that. If you are invoking the function from somewhere that is not the site it is associated with, you could probably include a custom-header that includes the request host, so you can check a single place, since the context object is not available in ‘netlify dev’ and I doubt it would ever be.

7

This doesn’t seem to work locally with netlify-cli. Here is context.clientContext:

{ identity: [Object], user: [Object] },

Notice that there is not custom property.

8

Hi @donavon,

What version of the CLI are you using. This seems to work in 5.2.11:

context.clientContext logs this:

{
  identity: {
    url: '',
    token: ''
  },
  user: {
    exp: 12345,
    sub: '',
    email: '',
    app_metadata: { provider: 'email', roles: [Array] },
    user_metadata: { full_name: '' }
  }
}

As you can see, roles shows [Array] instead of actual array, so the logs is not going in dept. Seems like you might be logging something else? Object is the correct representation of what type it is.

9

Is there a solution for ntl dev AND prod to get the hostname in a function from a client js fetch call? Reading this thread I cannot see one. In dev, event.headers.host works, but likely not in prod. Is there a workaround? Maybe check if typeof(event.headers.host)!='undefined' before in prod to not get a functions error? In dev, context.clientContext for me results in {}, mentioned in the thread that it does not work.

10

Hey @tik9

When I log out event in a deployed function, I see event.headers.host. I see this regardless of the method used—browser, cURL, or JS fetch.

11

ok, I did ntl deploy --prod and can log the function:Sep 3, 10:27:38 AM: 38e15b75 INFO 1 { custom: { netlify: 'eyJzaXRlX3VybCI6Imh0dHBzOi8vNjMxMzBmZDM4MGZlMDU2OTI1OGYxZGEwLS10aWsyLm5ldGxpZnkuYXBwIn0=' } } 2 63130fd380fe0569258f1da0--tik2.netlify.app Sep 3, 10:27:38 AM: 38e15b75 Duration: 143.05 ms Memory Usage: 86 MB. So event.headers…
works on prod.