Allow responses from image proxy server

servehelper.cpp

@@ -1,12 +1,22 @@
+#include <regex>
+
 #include "config.h"
 #include "servehelper.h"
 
+static std::regex image_proxy_regex(
+    "(https?://)?" // optional scheme
+    "(?:.+?@)?" // optional username and pass
+    "([^/]+(?::\\d+)?)" // host
+    "(?:/.*)?$");
+static inline std::string get_image_proxy_origin(const std::string& url);
+
 void serve(const httplib::Request& req, httplib::Response& res, const Config& config, std::string title, Element element) {
     using namespace std::string_literals;
 
     std::string origin = get_origin(req, config);
     std::string css_url = origin + "/style.css";
-    res.set_header("Content-Security-Policy", "default-src 'none'; img-src 'self'; style-src "s + css_url);
+    res.set_header("Content-Security-Policy", "default-src 'none'; style-src "s + css_url
+        + "; img-src " + get_image_proxy_origin(config.image_proxy_url));
 
     Element html("html", {
         Element("head", {
@@ -68,3 +78,12 @@ std::string get_origin(const httplib::Request& req, const Config& config) {
     }
     return origin;
 }
+
+
+static inline std::string get_image_proxy_origin(const std::string& url) {
+    std::smatch sm;
+    if (!std::regex_match(url, sm, image_proxy_regex)) {
+        return url;
+    }
+    return sm[1].str() + sm[2].str();
+}