support reverse proxy with path rewrite

[eternal-flame-AD]

This fixes #122.

Changed the home path so that the page loads static assets relative to the page URL.

Also changed how API path is parsed so that the base path is considered.

[eternal-flame-AD]

The nginx configuration I used to test this:

events {}
http {
    server {
        listen 127.0.0.1:10001;
        location /gotify/ {
            rewrite ^/gotify/(.*) /$1  break;
            proxy_pass http://127.0.0.1:10000$uri$is_args$args;
        }
        location /gotify/stream {
            rewrite ^/gotify/(.*) /$1  break;
            proxy_pass http://127.0.0.1:10000$uri$is_args$args;
            proxy_set_header Upgrade $http_upgrade;
            proxy_set_header Connection "Upgrade";
        }
    }
}

[jmattheis]

Thanks, there are still some things todo.

The images for applications aren't properly mapped. (See api/application.go:323).

Loading the Swagger UI on the proxy can't load the swagger definition. (http://localhost:8080/gotify/docs)

If the swagger definition is loaded, then it will probably still not work, because no basepath is set inside the definition.

Having a trailing slash at the end redirects wrongly.
http://localhost:8080/gotify/docs/ -> http://localhost:8080/docs

I've used the following config with Caddy:

localhost:8080 

proxy /gotify localhost:80 {
   without /gotify
   transparent
}

proxy /gotify/stream localhost:80 {
	without /gotify
	websocket
	transparent
}

[eternal-flame-AD]

Loading the Swagger UI on the proxy can't load the swagger definition.

I think this is an existing issue because I found that even on my deployment without a reverse proxy I need to manually enter the spec URL to get the swagger definitions.

[codecov]

Codecov Report

Merging #127 into master will not change coverage.
The diff coverage is n/a.

@@          Coverage Diff          @@
##           master   #127   +/-   ##
=====================================
  Coverage     100%   100%           
=====================================
  Files          39     39           
  Lines        1400   1400           
=====================================
  Hits         1400   1400

---

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[codecov]

Codecov Report

Merging #127 into master will not change coverage.
The diff coverage is 100%.

@@          Coverage Diff          @@
##           master   #127   +/-   ##
=====================================
  Coverage     100%   100%           
=====================================
  Files          39     39           
  Lines        1400   1400           
=====================================
  Hits         1400   1400

Impacted Files	Coverage Δ
docs/ui.go	100% <ø> (ø)	⬆️
docs/swagger.go	100% <100%> (ø)	⬆️
api/application.go	100% <100%> (ø)	⬆️

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 09c1516...e1a3d61. Read the comment docs.

[eternal-flame-AD]

I induced an API change that application image URLs are no longer resolved to absolute ones. Resolving URIs relative to the gotify path should be handled by the front-end, not back-end.

For the trailing slash problem I changed my nginx.conf, and now automatic redirects works:

events {}
http {
    server {
        listen 127.0.0.1:10001;
        location = /gotify {
            return 301 /gotify/;
        }
        location /gotify/ {
            rewrite ^/gotify/(.*) /$1  break;
            proxy_pass http://127.0.0.1:10000$uri$is_args$args;
            proxy_redirect ~^/(.*)$ /gotify/$1;
        }
        location /gotify/stream {
            rewrite ^/gotify/(.*) /$1  break;
            proxy_pass http://127.0.0.1:10000$uri$is_args$args;
            proxy_set_header Upgrade $http_upgrade;
            proxy_set_header Connection "Upgrade";
        }
    }
}

For caddy config I guess it should be something like this(I am not very familiar with that, I just translated it from the nginx config and I havn't tested this extensively)
I did not find a way to let caddy rewrite 301/302 URLs from proxy upstream. I can only remove the response Location header to prevent the browser from recording incorrect 301 redirects.

localhost:10001

redir /gotify /gotify/

proxy /gotify/ localhost:10000 {
   without /gotify/
   transparent
   header_downstream -Location
}

proxy /gotify/stream localhost:10000 {
	without /gotify
	websocket
	transparent
}

[jmattheis]

Changing how the images get returned breaks the api and would require an increment of the major version. (It also breaks the images in gotify/android). Tho' I can't think of an other way if we want to support path rewriting with a proxy.

This also breaks images in gotify/android.

[jmattheis]

Thanks! I'll use GitHub "squash" this time.