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authorKaren Arutyunov <karen@codesynthesis.com>2020-03-18 22:17:49 +0300
committerKaren Arutyunov <karen@codesynthesis.com>2020-03-27 17:28:44 +0300
commit35359f038f571dc46de3d14af72a2bc911fb0a24 (patch)
treede3e89d678e78b9efc4d395274fd7ccc68f4a213 /web/server/apache/service.hxx
parent8ad672cc7211952716ffe1fbf76c179b4f1149e3 (diff)
Implement brep-monitor
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+// file : web/server/apache/service.hxx -*- C++ -*-
+// license : MIT; see accompanying LICENSE file
+
+#ifndef WEB_SERVER_APACHE_SERVICE_HXX
+#define WEB_SERVER_APACHE_SERVICE_HXX
+
+#include <apr_pools.h> // apr_pool_t
+#include <apr_hooks.h> // APR_HOOK_*
+
+#include <httpd.h> // request_rec, server_rec, HTTP_*, DECLINED
+#include <http_config.h> // module, cmd_parms, ap_hook_*()
+
+#include <map>
+#include <memory> // unique_ptr
+#include <string>
+#include <cassert>
+
+#include <web/server/module.hxx>
+#include <web/server/apache/log.hxx>
+#include <web/server/apache/request.hxx>
+
+namespace web
+{
+ namespace apache
+ {
+ // Apache has 3 configuration scopes: main server, virtual server, and
+ // directory (location). It provides configuration scope-aware modules
+ // with the ability to build a hierarchy of configuration contexts. Later,
+ // when processing a request, Apache passes the appropriate directory
+ // configuration context to the request handler.
+ //
+ // This Apache service implementation first makes a copy of the provided
+ // (in the constructor below) handler exemplar for each directory context.
+ // It then initializes each of these "context exemplars" with the (merged)
+ // set of configuration options. Finally, when handling a request, it
+ // copies the corresponding "context exemplar" to create the "handling
+ // instance". Note that the "context exemplars" are created as a copy of
+ // the provided exemplar, which is never initialized. As a result, it is
+ // possible to detect if the handler's copy constructor is used to create
+ // a "context exemplar" or a "handling instance".
+ //
+ class service: ::module
+ {
+ public:
+ // Note that the module exemplar is stored by-reference.
+ //
+ template <typename H>
+ service (const std::string& name, H& exemplar)
+ : ::module
+ {
+ STANDARD20_MODULE_STUFF,
+ nullptr,
+ nullptr,
+ nullptr,
+ nullptr,
+ nullptr,
+ &register_hooks<H>
+
+#ifdef AP_MODULE_HAS_FLAGS
+ , AP_MODULE_FLAG_NONE
+#endif
+ },
+ name_ (name),
+ exemplar_ (exemplar)
+ {
+ init_directives ();
+
+ // Set configuration context management hooks.
+ //
+ // The overall process of building the configuration hierarchy for a
+ // handler is as follows:
+ //
+ // 1. Apache creates directory and server configuration contexts for
+ // scopes containing handler-defined directives by calling the
+ // create_{server,dir}_context() callback functions. For directives
+ // at the server scope the special directory context is created as
+ // well.
+ //
+ // 2. Apache calls parse_option() function for each handler-defined
+ // directive. The function parses the directives and places the
+ // resulting options into the corresponding configuration context.
+ // It also establishes the directory-server contexts relations.
+ //
+ // 3. Apache calls merge_server_context() function for each virtual
+ // server. The function complements virtual server context options
+ // with the ones from the main server.
+ //
+ // 4. Apache calls config_finalizer() which complements the directory
+ // contexts options with the ones from the enclosing servers.
+ //
+ // 5. Apache calls worker_initializer() which creates handler exemplar
+ // for each directory configuration context that have
+ // 'SetHandler <mod_name>' directive in effect for it.
+ //
+ // References:
+ // http://www.apachetutor.org/dev/config
+ // http://httpd.apache.org/docs/2.4/developer/modguide.html
+ // http://wiki.apache.org/httpd/ModuleLife
+ //
+ create_server_config = &create_server_context;
+ create_dir_config = &create_dir_context;
+ merge_server_config = &merge_server_context<H>;
+
+ // instance<H> () is invented to delegate processing from apache
+ // request handler C function to the service non static member
+ // function. This appoach resticts number of service objects per
+ // specific handler implementation class with just one instance.
+ //
+ service*& srv (instance<H> ());
+ assert (srv == nullptr);
+ srv = this;
+ }
+
+ ~service ()
+ {
+ delete [] cmds;
+ }
+
+ private:
+ template <typename H>
+ static service*&
+ instance () noexcept
+ {
+ static service* instance;
+ return instance;
+ }
+
+ template <typename H>
+ static void
+ register_hooks (apr_pool_t*) noexcept
+ {
+ // The config_finalizer() function is called at the end of Apache
+ // server configuration parsing.
+ //
+ ap_hook_post_config (&config_finalizer<H>, NULL, NULL, APR_HOOK_LAST);
+
+ // The worker_initializer() function is called right after Apache
+ // worker process is started. Called for every new process spawned.
+ //
+ ap_hook_child_init (
+ &worker_initializer<H>, NULL, NULL, APR_HOOK_LAST);
+
+ // The request_handler () function is called for each client request.
+ //
+ ap_hook_handler (&request_handler<H>, NULL, NULL, APR_HOOK_LAST);
+ }
+
+ template <typename H>
+ static int
+ config_finalizer (apr_pool_t*, apr_pool_t*, apr_pool_t*, server_rec* s)
+ noexcept
+ {
+ instance<H> ()->finalize_config (s);
+ return OK;
+ }
+
+ template <typename H>
+ static void
+ worker_initializer (apr_pool_t*, server_rec* s) noexcept
+ {
+ auto srv (instance<H> ());
+ log l (s, srv);
+ srv->template init_worker<H> (l);
+ }
+
+ template <typename H>
+ static int
+ request_handler (request_rec* r) noexcept;
+
+ private:
+
+ // Reflects the allowability of the request handling in the specific
+ // configuration scope.
+ //
+ enum class request_handling
+ {
+ // Configuration scope has 'SetHandler <mod_name>' directive
+ // specified. The handler is allowed to handle a request in the scope.
+ //
+ allowed,
+
+ // Configuration scope has 'SetHandler <other_mod_name>|None'
+ // directive specified. The handler is disallowed to handle a request
+ // in the scope.
+ //
+ disallowed,
+
+ //
+ // Note that if there are several SetHandler directives specified
+ // in the specific scope, then the latest one takes the precedence.
+
+ // Configuration scope has no SetHandler directive specified. The
+ // request handling allowability is established by the enclosing
+ // scopes.
+ //
+ inherit
+ };
+
+ // Our representation of the Apache configuration context.
+ //
+ // The lifetime of this object is under the control of the Apache API,
+ // which treats it as a raw sequence of bytes. In order not to tinker
+ // with the C-style structures and APR memory pools, we will keep it a
+ // (C++11) POD type with just the members required to maintain the
+ // context hierarchy.
+ //
+ // We will then use the pointers to these context objects as keys in
+ // maps to (1) the corresponding application-level option lists during
+ // the configuration cycle and to (2) the corresponding handler exemplar
+ // during the HTTP request handling phase. We will also use the same
+ // type for both directory and server configuration contexts.
+ //
+ struct context
+ {
+ // Outer (server) configuration context for the directory
+ // configuration context, NULL otherwise.
+ //
+ context* server = nullptr;
+
+ // If module directives appear directly in the server configuration
+ // scope, Apache creates a special directory context for them. This
+ // context appears at the same hierarchy level as the user-defined
+ // directory contexts of the same server scope.
+ //
+ bool special;
+
+ // Request handling allowability for the corresponding configuration
+ // scope.
+ //
+ request_handling handling = request_handling::inherit;
+
+ // Create the server configuration context.
+ //
+ context (): special (false) {}
+
+ // Create the directory configuration context. Due to the Apache API
+ // implementation details it is not possible to detect the enclosing
+ // server configuration context at the time of directory context
+ // creation. As a result, the server member is set by the module's
+ // parse_option() function.
+ //
+ context (bool s): special (s) {}
+
+ // Ensure the object is only destroyed by Apache.
+ //
+ ~context () = delete;
+ };
+
+ static context*
+ context_cast (void* config) noexcept
+ {return static_cast<context*> (config);}
+
+ private:
+ void
+ init_directives ();
+
+ // Create the server configuration context. Called by the Apache API
+ // whenever a new object of that type is required.
+ //
+ static void*
+ create_server_context (apr_pool_t*, server_rec*) noexcept;
+
+ // Create the server directory configuration context. Called by the
+ // Apache API whenever a new object of that type is required.
+ //
+ static void*
+ create_dir_context (apr_pool_t*, char* dir) noexcept;
+
+ template <typename H>
+ static void*
+ merge_server_context (apr_pool_t*, void* enclosing, void* enclosed)
+ noexcept
+ {
+ instance<H> ()->complement (
+ context_cast (enclosed), context_cast (enclosing));
+
+ return enclosed;
+ }
+
+ static const char*
+ parse_option (cmd_parms* parms, void* conf, const char* args) noexcept;
+
+ const char*
+ add_option (context*, const char* name, optional<std::string> value);
+
+ void
+ finalize_config (server_rec*);
+
+ void
+ clear_config ();
+
+ // Complement the enclosed context with options of the enclosing one.
+ // If the 'handling' member of the enclosed context is set to
+ // request_handling::inherit value, assign it a value from the enclosing
+ // context.
+ //
+ void
+ complement (context* enclosed, context* enclosing);
+
+ template <typename H>
+ void
+ init_worker (log&);
+
+ template <typename H>
+ int
+ handle (request&, const context*, log&) const;
+
+ private:
+ std::string name_;
+ handler& exemplar_;
+ option_descriptions option_descriptions_;
+
+ // The context objects pointed to by the key can change during the
+ // configuration phase.
+ //
+ using options = std::map<context*, name_values>;
+ options options_;
+
+ // The context objects pointed to by the key can not change during the
+ // request handling phase.
+ //
+ using exemplars = std::map<const context*, std::unique_ptr<handler>>;
+ exemplars exemplars_;
+
+ bool options_parsed_ = false;
+ bool version_logged_ = false;
+ };
+ }
+}
+
+#include <web/server/apache/service.txx>
+
+#endif // WEB_SERVER_APACHE_SERVICE_HXX