How can I serve static files like swagger ui in Cloud functions - go

Question

How can I serve swagger-ui-dist in Cloud Function with Go?
Out of Cloud Functions environment I would do:
package main
import (
"fmt"
"net/http"
)
func main() {
fs := http.FileServer(http.Dir("./swagger-ui-dist"))
http.Handle("/swaggerui/", http.StripPrefix("/swaggerui/", fs))
http.ListenAndServe(":8080", nil)
}
But since Cloud functions use a normal function as handler using the Standard http.HanlderFunc interface I don't know how to make it work.
I have tried to simulate this scenario to do my tests with http.ServeFile, but didn't work. Seems like is not downloading all the contents of the folder.
package main
import (
"fmt"
"net/http"
)
func cloudFunctionHandler(w http.ResponseWriter, r *http.Request) {
http.ServeFile(w, r, "./swagger-ui-dist")
}
func main() {
http.HanldeFunc("/swaggerui/", handler)
http.ListenAndServe(":8080", nil)
}

Answer 1

I tried it in several way and it worked locally with the same behavior as Cloud Function (same function signature), but it didn't work after deployment on Cloud Functions.
I understood why. In fact Buildpack (the tools develped by Google for building a container without a Dockerfile, and now in the CNCF sandbox) compiles the .go file and copy the binary to the final container layer. All the other files/directory are omitted. Thus, it can't work!
I recommend you to use Cloud Run (same underlying platform as Cloud Functions, and in some cases, cheaper. I wrote an article on this)
The other solution is to use a not compiled language such as NodeJS or Python.

Answer 2

It is actually possible in three ways (that I know):
Serve the static files from a CDN. E.g. from http://cdnjs.cloudflare.com/ajax/libs/swagger-ui/3.40.0/
Host the static files yourself on a different endpoint
Add the static files to the root folder of your cloud function. These will be packaged together with your code and therefore be available when deployed
(I went for option 3)
For options 2 and 3 you have to override the folder that swaggerui uses for its static assets. How you do this depends on how you configure the swagger ui.
In my case I was using the flask_restx Python package to generate the swagger.json and serve the swaggerui. So I monkeypatched like so:
from flask_restx.apidoc import apidoc
apidoc.static_folder = '<MY STATIC FOLDER PATH' # e.g. os.path.abspath('static/swaggerui')
Also, you need to copy the files from the swaggerui library to your function's root directory before running gcloud function deploy ....
I copy the static folder from flask_restx to my function's root directory during my CI pipeline.
Hope this helps anyone!