Add canonical_origin config option

RUNNING.md

@@ -16,6 +16,7 @@ liking. Here's a list of what they are:
 - `bind_host` (string): What address to bind to
 - `bind_port` (zero or positive integer): What port to bind to
 - `image_proxy_url` (string): URL to proxy images to (see https://pixiv.cat/reverseproxy.html), a trailing slash is not needed
+- `canonical_origin` (string or null): A fallback canonical origin if set, useful if you're, say, running Pixwhile behind Ngrok
 
 Pixwhile is intended to be run behind a reverse proxy (e.g. Nginx), so you
 should set your reverse proxy to proxy requests to

config.cpp

@@ -17,4 +17,7 @@ void from_json(const nlohmann::json& j, Config& config) {
         throw std::invalid_argument("Invalid port to bind to: "s + std::to_string(config.bind_port));
     }
     config.image_proxy_url = j.at("image_proxy_url").get<std::string>();
+    if (j.contains("canonical_origin") && j["canonical_origin"].is_string()) {
+        config.canonical_origin = j["canonical_origin"].get<std::string>();
+    }
 }

config.h

@@ -8,6 +8,7 @@ struct Config {
     std::string bind_host = "127.0.0.1";
     int bind_port = 8080;
     blankie::murl::Url image_proxy_url{"https://i.pixiv.cat"};
+    std::optional<std::string> canonical_origin;
 };
 
 Config load_config(const char* path);

example_config.json

@@ -1,5 +1,6 @@
 {
     "bind_host": "127.0.0.1",
     "bind_port": 8080,
-    "image_proxy_url": "https://i.pixiv.cat"
+    "image_proxy_url": "https://i.pixiv.cat",
+    "canonical_origin": null
 }

servehelper.cpp

@@ -79,6 +79,9 @@ std::string get_origin(const httplib::Request& req, const Config& config) {
     if (req.has_header("X-Canonical-Origin")) {
         return req.get_header_value("X-Canonical-Origin");
     }
+    if (config.canonical_origin) {
+        return *config.canonical_origin;
+    }
 
     std::string origin = "http://";
     if (req.has_header("Host")) {