Switch to openresty to better handle params

Dockerfile

@@ -1,15 +1,11 @@
-FROM nginx:alpine
+FROM openresty/openresty:alpine
 
-# Copy nginx configuration and HTML
-COPY nginx.conf /etc/nginx/nginx.conf
+# Copy config (OpenResty uses this path)
+COPY nginx.conf /usr/local/openresty/nginx/conf/nginx.conf
+# HTML and data dirs (config references /usr/share/nginx/html and /etc/nginx/data)
+RUN mkdir -p /usr/share/nginx/html /etc/nginx/data/cache /etc/nginx/data/temp
 COPY index.html /usr/share/nginx/html/index.html
 
-# Create data directories
-RUN mkdir -p /etc/nginx/data/cache /etc/nginx/data/temp && \
-    chown -R nginx:nginx /etc/nginx/data
-
-# Expose port
 EXPOSE 3000
 
-# Start nginx
-CMD ["nginx", "-g", "daemon off;"]
+CMD ["/usr/local/openresty/bin/openresty", "-g", "daemon off;"]

nginx.conf

@@ -18,21 +18,46 @@ http {
 
     resolver 127.0.0.11 valid=60s;
 
+    # Raw url= value from request (stops at next & so %26 in encoded URLs is preserved)
+    map $request_uri $url_encoded {
+        default "";
+        "~*[?&]url=((?:[^&%]|%[0-9A-Fa-f][0-9A-f])*)(?:&|$)" $1;
+    }
+
     server {
         listen 3000;
 
         location / {
-            # If no url parameter, serve the readme
-            if ($arg_url = "") {
-                rewrite ^ /index.html last;
+            set $backend_base "";
+            # Decode url, build upstream URL, strip our "url=". Force that URI to upstream (variable proxy_pass can send original request URI otherwise)
+            rewrite_by_lua_block {
+                local enc = ngx.var.url_encoded
+                local decoded = (enc and enc ~= "") and ngx.unescape_uri(enc) or ngx.var.arg_url or ""
+                if decoded == "" then
+                    ngx.exec("/index.html")
+                    return
+                end
+                local args = ngx.var.args or ""
+                local rest = args:gsub("^url=[^&]*&?", ""):gsub("&url=[^&]*", ""):gsub("^url=[^&]*$", "")
+                local full = decoded
+                if rest ~= "" then
+                    local sep = decoded:find("?") and "&" or "?"
+                    full = decoded .. sep .. rest
+                end
+                local scheme, host, pathquery = full:match("^(https?)://([^/]+)(.*)$")
+                if not host then
+                    ngx.status = 400
+                    ngx.say("invalid url")
+                    return ngx.exit(400)
+                end
+                if pathquery == "" then pathquery = "/" end
+                local path = pathquery:match("^([^?]*)") or "/"
+                local query = pathquery:match("%?(.*)$") or ""
+                ngx.var.backend_base = scheme .. "://" .. host
+                ngx.req.set_uri(path)
+                ngx.req.set_uri_args((query:gsub("^%?", "")))
             }
-
-            # Forward query string to upstream (? if url has no query, & if it already has ?)
-            set $url_sep "?";
-            if ($arg_url ~ \?) {
-                set $url_sep "&";
-            }
-            proxy_pass $arg_url$url_sep$args;
+            proxy_pass $backend_base$uri$is_args$args;
             proxy_http_version 1.1;
             proxy_set_header Host $proxy_host;
             proxy_ssl_server_name on;