added crow

include/crow/middlewares/cors.h

@@ -0,0 +1,237 @@
+#pragma once
+#include "crow/common.h"
+#include "crow/http_request.h"
+#include "crow/http_response.h"
+#include "crow/routing.h"
+
+namespace crow
+{
+    struct CORSHandler;
+
+    /// Used for tuning CORS policies
+    struct CORSRules
+    {
+        friend struct crow::CORSHandler;
+
+        /// Set Access-Control-Allow-Origin. Default is "*"
+        CORSRules& origin(const std::string& origin)
+        {
+            origin_ = origin;
+            return *this;
+        }
+
+        /// Set Access-Control-Allow-Methods. Default is "*"
+        CORSRules& methods(crow::HTTPMethod method)
+        {
+            add_list_item(methods_, crow::method_name(method));
+            return *this;
+        }
+
+        /// Set Access-Control-Allow-Methods. Default is "*"
+        template<typename... Methods>
+        CORSRules& methods(crow::HTTPMethod method, Methods... method_list)
+        {
+            add_list_item(methods_, crow::method_name(method));
+            methods(method_list...);
+            return *this;
+        }
+
+        /// Set Access-Control-Allow-Headers. Default is "*"
+        CORSRules& headers(const std::string& header)
+        {
+            add_list_item(headers_, header);
+            return *this;
+        }
+
+        /// Set Access-Control-Allow-Headers. Default is "*"
+        template<typename... Headers>
+        CORSRules& headers(const std::string& header, Headers... header_list)
+        {
+            add_list_item(headers_, header);
+            headers(header_list...);
+            return *this;
+        }
+
+        /// Set Access-Control-Expose-Headers. Default is none
+        CORSRules& expose(const std::string& header)
+        {
+            add_list_item(exposed_headers_, header);
+            return *this;
+        }
+
+        /// Set Access-Control-Expose-Headers. Default is none
+        template<typename... Headers>
+        CORSRules& expose(const std::string& header, Headers... header_list)
+        {
+            add_list_item(exposed_headers_, header);
+            expose(header_list...);
+            return *this;
+        }
+
+        /// Set Access-Control-Max-Age. Default is none
+        CORSRules& max_age(int max_age)
+        {
+            max_age_ = std::to_string(max_age);
+            return *this;
+        }
+
+        /// Enable Access-Control-Allow-Credentials
+        CORSRules& allow_credentials()
+        {
+            allow_credentials_ = true;
+            return *this;
+        }
+
+        /// Ignore CORS and don't send any headers
+        void ignore()
+        {
+            ignore_ = true;
+        }
+
+        /// Handle CORS on specific prefix path
+        CORSRules& prefix(const std::string& prefix);
+
+        /// Handle CORS for specific blueprint
+        CORSRules& blueprint(const Blueprint& bp);
+
+        /// Global CORS policy
+        CORSRules& global();
+
+    private:
+        CORSRules() = delete;
+        CORSRules(CORSHandler* handler):
+          handler_(handler) {}
+
+        /// build comma separated list
+        void add_list_item(std::string& list, const std::string& val)
+        {
+            if (list == "*") list = "";
+            if (list.size() > 0) list += ", ";
+            list += val;
+        }
+
+        /// Set header `key` to `value` if it is not set
+        void set_header_no_override(const std::string& key, const std::string& value, crow::response& res)
+        {
+            if (value.size() == 0) return;
+            if (!get_header_value(res.headers, key).empty()) return;
+            res.add_header(key, value);
+        }
+
+        /// Set response headers
+        void apply(const request& req, response& res)
+        {
+            if (ignore_) return;
+
+            set_header_no_override("Access-Control-Allow-Methods", methods_, res);
+            set_header_no_override("Access-Control-Allow-Headers", headers_, res);
+            set_header_no_override("Access-Control-Expose-Headers", exposed_headers_, res);
+            set_header_no_override("Access-Control-Max-Age", max_age_, res);
+
+            bool origin_set = false;
+
+            if (req.method != HTTPMethod::Options)
+            {
+                if (allow_credentials_)
+                {
+                    set_header_no_override("Access-Control-Allow-Credentials", "true", res);
+                    if (origin_ == "*")
+                    {
+                        set_header_no_override("Access-Control-Allow-Origin", req.get_header_value("Origin"), res);
+                        origin_set = true;
+                    }
+                }
+            }
+
+            if( !origin_set){
+                set_header_no_override("Access-Control-Allow-Origin", origin_, res);
+            }
+        }
+
+        bool ignore_ = false;
+        // TODO: support multiple origins that are dynamically selected
+        std::string origin_ = "*";
+        std::string methods_ = "*";
+        std::string headers_ = "*";
+        std::string exposed_headers_;
+        std::string max_age_;
+        bool allow_credentials_ = false;
+
+        CORSHandler* handler_;
+    };
+
+    /// CORSHandler is a global middleware for setting CORS headers.
+
+    ///
+    /// By default, it sets Access-Control-Allow-Origin/Methods/Headers to "*".
+    /// The default behaviour can be changed with the `global()` cors rule.
+    /// Additional rules for prexies can be added with `prefix()`.
+    struct CORSHandler
+    {
+        struct context
+        {};
+
+        void before_handle(crow::request& /*req*/, crow::response& /*res*/, context& /*ctx*/)
+        {}
+
+        void after_handle(crow::request& req, crow::response& res, context& /*ctx*/)
+        {
+            auto& rule = find_rule(req.url);
+            rule.apply(req, res);
+        }
+
+        /// Handle CORS on a specific prefix path
+        CORSRules& prefix(const std::string& prefix)
+        {
+            rules.emplace_back(prefix, CORSRules(this));
+            return rules.back().second;
+        }
+
+        /// Handle CORS for a specific blueprint
+        CORSRules& blueprint(const Blueprint& bp)
+        {
+            rules.emplace_back(bp.prefix(), CORSRules(this));
+            return rules.back().second;
+        }
+
+        /// Get the global CORS policy
+        CORSRules& global()
+        {
+            return default_;
+        }
+
+    private:
+        CORSRules& find_rule(const std::string& path)
+        {
+            // TODO: use a trie in case of many rules
+            for (auto& rule : rules)
+            {
+                // Check if path starts with a rules prefix
+                if (path.rfind(rule.first, 0) == 0)
+                {
+                    return rule.second;
+                }
+            }
+            return default_;
+        }
+
+        std::vector<std::pair<std::string, CORSRules>> rules;
+        CORSRules default_ = CORSRules(this);
+    };
+
+    inline CORSRules& CORSRules::prefix(const std::string& prefix)
+    {
+        return handler_->prefix(prefix);
+    }
+
+    inline CORSRules& CORSRules::blueprint(const Blueprint& bp)
+    {
+        return handler_->blueprint(bp);
+    }
+
+    inline CORSRules& CORSRules::global()
+    {
+        return handler_->global();
+    }
+
+} // namespace crow