Use X-Accel-Redirect for serving ajax-proxy request

uMap allows to use remote URL as data sources, but those URLs
are not always CORS open, so this is why there is this "ajax-proxy"
feature, where the URL is passed to the backend.

Additionally, there is a caching feature, which duration is configurable
through frontend settings. Valid values are: disabled, 5 min, 1 hour,
1 day.

Initially, I wanted this to be totally handled by Nginx, but I never
found a wayt to set the proxy_cache_valid value from a query string.

Since then, at least in OSM France servers, the ajax-proxy is still
handled by a Django view, which then opens the remote URL and transfert
the data. This is not optimal. And I suppose this is what is causing
hicups on the OSM France servers lately.

This PR provides a mix option, where python deals with validating the
URL and parsing the TTL parameter, and then it passes the hand to
nginx which will serve the remote content.

So, roughtly:

- the client calls /ajax-proxy/?url=xxx&ttl=300
- python will validate the URL (not internal calls…)
- if UMAP_SENDFILE_HEADER is set, then the python returns an empty
  response with the path /proxy/http://url plus it will set the
  cache ttl through the header X-Accel-Expires
- this /proxy/ location is then handled by nginx

docs/ubuntu.md

@@ -332,6 +332,7 @@ And then add this new location in your nginx config (before the `/` location):
         alias /path/to/umap/var/data/;
     }
 
+
 ### Configure ajax proxy cache
 
 In Nginx:
@@ -341,28 +342,38 @@ In Nginx:
         proxy_cache_path /tmp/nginx_ajax_proxy_cache levels=1:2 keys_zone=ajax_proxy:10m inactive=60m;
         proxy_cache_key "$args";
 
-- add this location (before the `/` location):
+- add those locations (before the `/` location):
 
-        location /ajax-proxy/ {
+        location ~ ^/proxy/(.*) {
-            valid_referers server_names;
+            internal;
-            if ($invalid_referer) {
-                return 400;
-            }
             add_header X-Proxy-Cache $upstream_cache_status always;
             proxy_cache ajax_proxy;
             proxy_cache_valid 1m;  # Default. Umap will override using X-Accel-Expires
-            gzip on;
+            set $target_url $1;
-            gzip_proxied any;
+            # URL is encoded, so we need a few hack to clean it back.
-            gzip_types
+            if ( $target_url ~ (.+)%3A%2F%2F(.+) ){ # fix :// between scheme and destination
-                application/vnd.google-earth.kml+xml
+              set $target_url $1://$2;
-                application/geo+json
-                application/json
-                application/javascript
-                text/xml
-                application/xml;
-            uwsgi_pass umap;
-            include /srv/umap/uwsgi_params;
             }
+            if ( $target_url ~ (.+?)%3A(.*) ){ # fix : between destination and port
+              set $target_url $1:$2;
+            }
+            if ( $target_url ~ (.+?)%2F(.*) ){ # fix / after port, the rest will be decoded by proxy_pass
+              set $target_url $1/$2;
+            }
+            add_header X-Proxy-Target $target_url; # For debugging
+            resolver 8.8.8.8;
+            proxy_read_timeout 10s;
+            proxy_connect_timeout 5s;
+            proxy_pass $target_url;
+            proxy_intercept_errors on;
+            error_page 301 302 307 = @handle_proxy_redirect;
+        }
+        location @handle_proxy_redirect {
+            resolver 8.8.8.8;
+            set $saved_redirect_location '$upstream_http_location';
+            proxy_pass $saved_redirect_location;
+        }
+
 
 
 

umap/views.py

@@ -351,6 +351,17 @@ class AjaxProxy(View):
             url = validate_url(self.request)
         except AssertionError:
             return HttpResponseBadRequest()
+        try:
+            ttl = int(self.request.GET.get("ttl"))
+        except (TypeError, ValueError):
+            ttl = None
+        if getattr(settings, "UMAP_XSENDFILE_HEADER", None):
+            response = HttpResponse()
+            response[settings.UMAP_XSENDFILE_HEADER] = f"/proxy/{url}"
+            if ttl:
+                response["X-Accel-Expires"] = ttl
+            return response
+
         headers = {"User-Agent": "uMapProxy +http://wiki.openstreetmap.org/wiki/UMap"}
         request = Request(url, headers=headers)
         opener = build_opener()
@@ -375,11 +386,7 @@ class AjaxProxy(View):
             # Quick hack to prevent Django from adding a Vary: Cookie header
             self.request.session.accessed = False
             response = HttpResponse(content, status=status_code, content_type=mimetype)
-            try:
+            if ttl:
-                ttl = int(self.request.GET.get("ttl"))
-            except (TypeError, ValueError):
-                pass
-            else:
                 response["X-Accel-Expires"] = ttl
             return response