server: fix query params lost when proxying requests in multi-model router mode (#19854)

* server: fix query params lost when proxying requests in multi-model router mode

* server: re-encode query params using httplib::encode_query_component in proxy

tools/server/server-http.cpp

@@ -339,6 +339,17 @@ static std::map<std::string, std::string> get_headers(const httplib::Request & r
     return headers;
 }
 
+static std::string build_query_string(const httplib::Request & req) {
+    std::string qs;
+    for (const auto & [key, value] : req.params) {
+        if (!qs.empty()) {
+            qs += '&';
+        }
+        qs += httplib::encode_query_component(key) + "=" + httplib::encode_query_component(value);
+    }
+    return qs;
+}
+
 // using unique_ptr for request to allow safe capturing in lambdas
 using server_http_req_ptr = std::unique_ptr<server_http_req>;
 
@@ -382,6 +393,7 @@ void server_http_context::get(const std::string & path, const server_http_contex
             get_params(req),
             get_headers(req),
             req.path,
+            build_query_string(req),
             req.body,
             req.is_connection_closed
         });
@@ -396,6 +408,7 @@ void server_http_context::post(const std::string & path, const server_http_conte
             get_params(req),
             get_headers(req),
             req.path,
+            build_query_string(req),
             req.body,
             req.is_connection_closed
         });