Implement easy sliding sync setup

Co-authored-by: h7x4 <h7x4@nani.wtf>

README.MD

@@ -36,3 +36,19 @@ With matrix.YOURDOMAIN pointing at the server:
 ```
 
 is ~enough to get a functional matrix-server running with some workers
+
+## Sliding Sync (Element X)
+
+Just add the following to your config and point `slidingsync.YOURDOMAIN` at the server
+
+```
+services.matrix-synapse-next = {
+  enableSlidingSync = true;
+};
+
+matrix-synapse.sliding-sync.environmentFile = "/some/file/containing/SYNCV3_SECRET=<some secret>";
+
+```
+
+If using well-known delagation make sure `YOURDOMAIN/.well-known/matrix/client` matches
+what's in `matrix.YOURDOMAIN/.well-known/matrix/client`

sliding-sync/default.nix

@@ -15,6 +15,13 @@ in
       description = "What package to use for the sliding-sync proxy.";
     };
 
+    enableNginx = lib.mkEnableOption (lib.mdDoc "autogenerated nginx config");
+    publicBaseUrl = lib.mkOption {
+      type = lib.types.str;
+      description = "The domain where clients connect, only has an effect with enableNginx";
+      example = "slidingsync.matrix.org";
+    };
+
     settings = lib.mkOption {
       type = lib.types.submodule {
         freeformType = with lib.types; attrsOf str;
@@ -98,5 +105,13 @@ in
         WorkingDirectory = "%S/matrix-sliding-sync";
       };
     };
+
+    services.nginx.virtualHosts.${cfg.publicBaseUrl} = lib.mkIf cfg.enableNginx {
+      enableACME = true;
+      forceSSL = true;
+      locations."/" = {
+        proxyPass = lib.replaceStrings [ "0.0.0.0" "::" ] [ "127.0.0.1" "::1" ] "http://${cfg.settings.SYNCV3_BINDADDR}";
+      };
+    };
   };
 }

synapse-module/default.nix

@@ -84,6 +84,8 @@ in
       description = "A yaml python logging config file";
     };
 
+    enableSlidingSync = mkEnableOption (lib.mdDoc "automatic Sliding Sync setup at `slidingsync.<domain>`");
+
     settings = mkOption {
       type = types.submodule {
         freeformType = format.type;
@@ -394,5 +396,19 @@ in
         };
       };
     };
+
+    services.matrix-synapse-next.settings.extra_well_known_client_content."org.matrix.msc3575.proxy" = mkIf cfg.enableSlidingSync {
+      url = "https://${config.services.matrix-synapse.sliding-sync.publicBaseUrl}";
+    };
+    services.matrix-synapse.sliding-sync = mkIf cfg.enableSlidingSync {
+      enable = true;
+      enableNginx = lib.mkDefault cfg.enableNginx;
+      publicBaseUrl = lib.mkDefault "slidingsync.${cfg.settings.server_name}";
+
+      settings = {
+        SYNCV3_SERVER = lib.mkDefault "https://${cfg.public_baseurl}";
+        SYNCV3_PROM = lib.mkIf cfg.settings.enable_metrics (lib.mkDefault "127.0.0.1:9001");
+      };
+    };
   };
 }

synapse-module/nginx.nix

@@ -230,6 +230,9 @@ in
       locations."/_synapse/client" = {
         proxyPass = "http://$synapse_backend";
       };
+      locations."/.well-known/matrix" = {
+        proxyPass = "http://$synapse_backend";
+      };
     };
   };
 }