Add Onion-Location header for Tor Browser discovery.

Mirror NullCart's ONION_HOSTNAME env and nginx clearnet header so visitors on HTTPS see ".onion available".

.env.example

@@ -1,2 +1,3 @@
 COMPOSE_PROJECT_NAME=nullcart_promo_prod
 CLEARNET_DOMAIN=nullcart.net
+ONION_HOSTNAME=samplexxxxxxxxx.onion

README.md

@@ -114,6 +114,14 @@ Save and exit the editor. Optional — run once manually to verify:
 ./deploy/scripts/show-onion.sh
 ```
 
+Copy the hostname into `.env.prod` as `ONION_HOSTNAME`, then recreate nginx:
+
+```bash
+docker compose --env-file .env.prod -f docker-compose.prod.yml up -d --force-recreate nginx
+```
+
+Tor Browser will then show ".onion available" when visitors open the clearnet site over HTTPS.
+
 ### 9. Updates
 
 ```bash

nginx/conf.d/clearnet.conf.template

@@ -18,6 +18,8 @@ server {
     ssl_certificate /etc/nginx/certs/live/${CLEARNET_DOMAIN}/fullchain.pem;
     ssl_certificate_key /etc/nginx/certs/live/${CLEARNET_DOMAIN}/privkey.pem;
 
+    ${ONION_LOCATION_HEADER}
+
     root /usr/share/nginx/html;
     index index.html;
 

nginx/docker-entrypoint.sh

@@ -2,7 +2,14 @@
 set -eu
 
 export CLEARNET_DOMAIN
-envsubst '${CLEARNET_DOMAIN}' \
+
+if [ -n "${ONION_HOSTNAME:-}" ]; then
+    export ONION_LOCATION_HEADER="add_header Onion-Location \"http://${ONION_HOSTNAME}\$request_uri\";"
+else
+    export ONION_LOCATION_HEADER=""
+fi
+
+envsubst '${CLEARNET_DOMAIN} ${ONION_LOCATION_HEADER}' \
     < /etc/nginx/templates/conf.d/clearnet.conf.template \
     > /etc/nginx/conf.d/clearnet.conf