Support multiple instances of brep in a single Apache instance

4 files changed, 435 insertions, 89 deletions

diff --git a/web/apache/service b/web/apache/service
index 75c096c..4c0d395 100644
--- a/web/apache/service
+++ b/web/apache/service
@@ -8,6 +8,8 @@
 #include <httpd.h>
 #include <http_config.h> // module, ap_hook_*()
 
+#include <map>
+#include <memory>  // unique_ptr
 #include <string>
 #include <cassert>
 
@@ -19,6 +21,22 @@ 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) module 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 create before the
+    // provided exemplar is initialized. As a result, it is possible to detect
+    // if the module's copy constructor is used to create a "context exemplar"
+    // or a "handling instance".
+    //
     class service: ::module
     {
     public:
@@ -41,6 +59,41 @@ namespace web
       {
         init_directives ();
 
+        // Set configuration context management hooks.
+        //
+        // The overall process of building the configuration hierarchy for a
+        // module is as follows:
+        //
+        // 1. Apache creates directory and server configuration contexts for
+        //    scopes containing module-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 module-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 module exemplar
+        //    for each directory configuration context.
+        //
+        // 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<M>;
+
         // instance<M> () 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
@@ -56,6 +109,7 @@ namespace web
         delete [] cmds;
       }
 
+    private:
       template <typename M>
       static service*&
       instance () noexcept
@@ -88,16 +142,7 @@ namespace web
       config_finalizer (apr_pool_t*, apr_pool_t*, apr_pool_t*, server_rec* s)
         noexcept
       {
-        auto srv (instance<M> ());
-        bool& parsed (srv->options_parsed_);
-
-        if (!parsed)
-        {
-          log l (s, srv);
-          srv->exemplar_.version (l);
-          parsed = true;
-        }
-
+        instance<M> ()->finalize_config (s);
         return OK;
       }
 
@@ -107,44 +152,140 @@ namespace web
       {
         auto srv (instance<M> ());
         log l (s, srv);
-        srv->init_worker (l);
+        srv->template init_worker<M> (l);
       }
 
       template <typename M>
       static int
-      request_handler (request_rec* r) noexcept
+      request_handler (request_rec* r) noexcept;
+
+    private:
+      // 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 module exemplar
+      // during the HTTP request handling phase. We will also use the same
+      // type for both directory and server configuration contexts.
+      //
+      struct context
       {
-        auto srv (instance<M> ());
-        if (!r->handler || srv->name_ != r->handler) return DECLINED;
+        // Outer (server) configuration context for the directory
+        // configuration context, NULL otherwise.
+        //
+        context* server;
 
-        request req (r);
-        log l (r->server, srv);
-        return srv->template handle<M> (req, l);
-      }
+        // 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;
+
+        // Create the server configuration context.
+        //
+        context (): server (nullptr), 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): server (nullptr), special (s) {}
+
+        // Ensure the object is only destroyed by Apache.
+        //
+        ~context () = delete;
+      };
+
+      // Type of the key for configuration options and module exemplar maps.
+      //
+      using context_id = const context*;
+
+      static bool
+      is_null (context_id id) noexcept {return id == nullptr;}
+
+      static context_id
+      make_context_id (const context* c) noexcept {return c;}
+
+      // Convert Apache-provided configuration pointer to the context id.
+      //
+      static context_id
+      make_context_id (void* config) noexcept
+      {return make_context_id (static_cast<const context*> (config));}
 
     private:
       void
       init_directives ();
 
-      void
-      init_worker (log& l) noexcept;
+      // 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 M>
+      static void*
+      merge_server_context (apr_pool_t*, void* enclosing, void* enclosed)
+        noexcept
+      {
+        // Complement the enclosed context with options of the enclosing one.
+        //
+        instance<M> ()->complement (
+          make_context_id (enclosed), make_context_id (enclosing));
+
+        return enclosed;
+      }
 
       static const char*
-      parse_option (cmd_parms* parms, void* mconfig, const char* args) noexcept;
+      parse_option (cmd_parms* parms, void* conf, const char* args) noexcept;
 
       const char*
-      add_option (const char* name, optional<std::string> value);
+      add_option (context_id id, const char* name, optional<std::string> value);
+
+      void
+      finalize_config (server_rec*);
+
+      void
+      clear_config ();
+
+      void
+      complement (context_id enclosed, context_id enclosing);
+
+      template <typename M>
+      void
+      init_worker (log&);
 
       template <typename M>
       int
-      handle (request& r, log& l) noexcept;
+      handle (request&, context_id, log&) const;
 
     private:
       std::string name_;
       module& exemplar_;
       option_descriptions option_descriptions_;
-      name_values options_;
+
+      using options = std::map<context_id, name_values>;
+      options options_;
+
+      using exemplars = std::map<context_id, std::unique_ptr<module>>;
+      exemplars exemplars_;
+
       bool options_parsed_ = false;
+      bool version_logged_ = false;
     };
   }
 }
diff --git a/web/apache/service.cxx b/web/apache/service.cxx
index 96ff855..2ca8cf0 100644
--- a/web/apache/service.cxx
+++ b/web/apache/service.cxx
@@ -4,8 +4,7 @@
 
 #include <web/apache/service>
 
-#include <unistd.h> // getppid()
-#include <signal.h> // kill()
+#include <apr_pools.h>
 
 #include <httpd.h>
 #include <http_config.h>
@@ -51,11 +50,17 @@ namespace web
             i.first->first.c_str (),
             reinterpret_cast<cmd_func> (parse_option),
             this,
-            RSRC_CONF,
+
+            // Allow directives in both server and directory configuration
+            // scopes.
+            //
+            RSRC_CONF | ACCESS_CONF,
+
             // Move away from TAKE1 to be able to handle empty string and
             // no-value.
             //
             RAW_ARGS,
+
             nullptr
           };
       }
@@ -64,21 +69,47 @@ namespace web
       cmds = directives.release ();
     }
 
-    const char* service::
-    parse_option (cmd_parms* parms, void*, const char* args) noexcept
+    void* service::
+    create_server_context (apr_pool_t* pool, server_rec*) noexcept
     {
-      // @@ Current implementation does not consider configuration context
-      //    (server config, virtual host, directory) for directive parsing, nor
-      //    for request handling.
+      // Create the object using the configuration memory pool provided by the
+      // Apache API. The lifetime of the object is equal to the lifetime of the
+      // pool.
+      //
+      void* p (apr_palloc (pool, sizeof (context)));
+      assert (p != nullptr);
+      return new (p) context ();
+    }
+
+    void* service::
+    create_dir_context (apr_pool_t* pool, char* dir) noexcept
+    {
+      // Create the object using the configuration memory pool provided by the
+      // Apache API. The lifetime of the object is equal to the lifetime of
+      // the pool.
+      //
+      void* p (apr_palloc (pool, sizeof (context)));
+      assert (p != nullptr);
+
+      // For the user-defined directory configuration context dir is the path
+      // of the corresponding directive. For the special server directory
+      // invented by Apache for server scope directives, dir is NULL.
       //
+      return new (p) context (dir == nullptr);
+    }
+
+    const char* service::
+    parse_option (cmd_parms* parms, void* conf, const char* args) noexcept
+    {
       service& srv (*reinterpret_cast<service*> (parms->cmd->cmd_data));
 
       if (srv.options_parsed_)
-        // Apache is inside the second pass of its messy initialization cycle
-        // (more details at http://wiki.apache.org/httpd/ModuleLife). Just
-        // ignore it.
+        // Apache have started the second pass of its messy initialization cycle
+        // (more details at http://wiki.apache.org/httpd/ModuleLife). This time
+        // we are parsing for real. Cleanup the existing config, and start
+        // building the new one.
         //
-        return 0;
+        srv.clear_config ();
 
       // 'args' is an optionally double-quoted string. It uses double quotes
       // to distinguish empty string from no-value case.
@@ -91,11 +122,52 @@ namespace web
           ? string (args + 1, l - 2)
           : args;
 
-      return srv.add_option (parms->cmd->name, move (value));
+      // Determine the directory and server configuration contexts for the
+      // option.
+      //
+      context* dir_context (static_cast<context*> (conf));
+      assert (dir_context != nullptr);
+
+      server_rec* server (parms->server);
+      assert (server != nullptr);
+      assert (server->module_config != nullptr);
+
+      context* srv_context (
+        static_cast<context*> (
+          ap_get_module_config (server->module_config, &srv)));
+
+      assert (srv_context != nullptr);
+
+      // Associate the directory configuration context with the enclosing
+      // server configuration context.
+      //
+      context*& s (dir_context->server);
+      if (s == nullptr)
+        s = srv_context;
+      else
+        assert (s == srv_context);
+
+      // If the option appears in the special directory configuration context,
+      // add it to the enclosing server context instead. This way it will be
+      // possible to complement all server-enclosed contexts (including this
+      // special one) with the server scope options.
+      //
+      context* c (dir_context->special ? srv_context : dir_context);
+
+      if (dir_context->special)
+        //
+        // Make sure the special directory context is also in the option lists
+        // map. Later the context will be populated with an enclosing server
+        // context options.
+        //
+        srv.options_.emplace (make_context_id (dir_context), name_values ());
+
+      return srv.add_option (
+        make_context_id (c), parms->cmd->name, move (value));
     }
 
     const char* service::
-    add_option (const char* name, optional<string> value)
+    add_option (context_id id, const char* name, optional<string> value)
     {
       auto i (option_descriptions_.find (name));
       assert (i != option_descriptions_.end ());
@@ -105,47 +177,54 @@ namespace web
       if (i->second != static_cast<bool> (value))
         return value ? "unexpected value" : "value expected";
 
-      options_.emplace_back (name + name_.length () + 1, move (value));
+      options_[id].emplace_back (name + name_.length () + 1, move (value));
       return 0;
     }
 
     void service::
-    init_worker (log& l) noexcept
+    complement (context_id enclosed, context_id enclosing)
     {
-      const string func_name (
-        "web::apache::service<" + name_ + ">::init_worker");
+      auto i (options_.find (enclosing));
 
-      try
+      // The enclosing context may have no options. It can be the context of a
+      // server having no configuration directives in it's immediate scope,
+      // but having ones in it's enclosed scope (directory or virtual server).
+      //
+      if (i != options_.end ())
       {
-        exemplar_.init (options_, l);
+        const name_values& src (i->second);
+        name_values& dest (options_[enclosed]);
+        dest.insert (dest.begin (), src.begin (), src.end ());
       }
-      catch (const exception& e)
+    }
+
+    void service::
+    finalize_config (server_rec* s)
+    {
+      if (!version_logged_)
       {
-        l.write (nullptr, 0, func_name.c_str (), APLOG_EMERG, e.what ());
-
-        // Terminate the root apache process. Indeed we can only try to
-        // terminate the process, and most likely will fail in a production
-        // environment where the apache root process usually runs under root,
-        // and worker processes run under some other user. This is why the
-        // implementation should consider the possibility of not being
-        // initialized at the time of HTTP request processing. In such a case
-        // it should respond with an internal server error (500 HTTP status),
-        // reporting misconfiguration.
-        //
-        ::kill (::getppid (), SIGTERM);
+        log l (s, this);
+        exemplar_.version (l);
+        version_logged_ = true;
       }
-      catch (...)
-      {
-        l.write (nullptr,
-                 0,
-                 func_name.c_str (),
-                 APLOG_EMERG,
-                 "unknown error");
 
-        // Terminate the root apache process.
-        //
-        ::kill (::getppid (), SIGTERM);
-      }
+      // Complement directory configuration contexts with options of the
+      // enclosing server configuration context. By this time virtual server
+      // contexts are already complemented with the main server configuration
+      // context options as a result of the merge_server_context() calls.
+      //
+      for (const auto& o: options_)
+        if (o.first->server != nullptr) // Is a directory configuration context.
+          complement (o.first, o.first->server);
+
+      options_parsed_ = true;
+    }
+
+    void service::
+    clear_config ()
+    {
+      options_.clear ();
+      options_parsed_ = false;
     }
   }
 }
diff --git a/web/apache/service.txx b/web/apache/service.txx
index 300a2a8..b57befc 100644
--- a/web/apache/service.txx
+++ b/web/apache/service.txx
@@ -2,8 +2,12 @@
 // copyright : Copyright (c) 2014-2016 Code Synthesis Ltd
 // license   : MIT; see accompanying LICENSE file
 
+#include <unistd.h> // getppid()
+#include <signal.h> // kill()
+
 #include <http_log.h>
 
+#include <utility>   // move()
 #include <exception>
 
 namespace web
@@ -11,37 +15,147 @@ namespace web
   namespace apache
   {
     template <typename M>
+    void service::
+    init_worker (log& l)
+    {
+      const std::string func_name (
+        "web::apache::service<" + name_ + ">::init_worker");
+
+      try
+      {
+        const M* exemplar (dynamic_cast<const M*> (&exemplar_));
+        assert (exemplar != nullptr);
+
+        // For each directory configuration context create the module exemplar
+        // as a deep copy of the exemplar_ member and initialize it with the
+        // context-specific option list. Note that there can be contexts
+        // having no module options specified for them and no options
+        // inherited from enclosing contexts. Such contexts will not appear in
+        // the options_ map. Meanwhile 'SetHandler <modname>' directive can be
+        // in effect for such contexts, and we should be ready to handle
+        // requests for them (by using the "root exemplar").
+        //
+        for (const auto& o: options_)
+        {
+          const context* c (o.first);
+
+          if (c->server != nullptr) // Is a directory configuration context.
+          {
+            auto r (
+              exemplars_.emplace (
+                make_context_id (c),
+                std::unique_ptr<module> (new M (*exemplar))));
+
+            r.first->second->init (o.second, l);
+          }
+        }
+
+        // Options are not needed anymore. Free up the space.
+        //
+        options_.clear ();
+
+        // Initialize the "root exemplar" by default (with no options). It
+        // will be used to handle requests for configuration contexts having
+        // no options specified, and no options inherited from enclosing
+        // contexts.
+        //
+        exemplar_.init (name_values (), l);
+      }
+      catch (const std::exception& e)
+      {
+        l.write (nullptr, 0, func_name.c_str (), APLOG_EMERG, e.what ());
+
+        // Terminate the root apache process. Indeed we can only try to
+        // terminate the process, and most likely will fail in a production
+        // environment, where the apache root process usually runs under root,
+        // and worker processes run under some other user. This is why the
+        // implementation should consider the possibility of not being
+        // initialized at the time of HTTP request processing. In such a case
+        // it should respond with an internal server error (500 HTTP status),
+        // reporting misconfiguration.
+        //
+        kill (getppid (), SIGTERM);
+      }
+      catch (...)
+      {
+        l.write (nullptr,
+                 0,
+                 func_name.c_str (),
+                 APLOG_EMERG,
+                 "unknown error");
+
+        // Terminate the root apache process.
+        //
+        kill (getppid (), SIGTERM);
+      }
+    }
+
+    template <typename M>
     int service::
-    handle (request& r, log& l) noexcept
+    request_handler (request_rec* r) noexcept
+    {
+      auto srv (instance<M> ());
+      if (!r->handler || srv->name_ != r->handler) return DECLINED;
+
+      assert (r->per_dir_config != nullptr);
+
+      // Obtain the request-associated configuration context id.
+      //
+      context_id id (
+        make_context_id (ap_get_module_config (r->per_dir_config, srv)));
+
+      assert (!is_null (id));
+
+      request rq (r);
+      log lg (r->server, srv);
+      return srv->template handle<M> (rq, id, lg);
+    }
+
+    template <typename M>
+    int service::
+    handle (request& rq, context_id id, log& lg) const
     {
       static const std::string func_name (
         "web::apache::service<" + name_ + ">::handle");
 
       try
       {
-        M m (static_cast<const M&> (exemplar_));
+        auto i (exemplars_.find (id));
+
+        // Use the context-specific exemplar if found, otherwise use the
+        // default one.
+        //
+        const module* exemplar (i != exemplars_.end ()
+                                ? i->second.get ()
+                                : &exemplar_);
+
+        const M* e (dynamic_cast<const M*> (exemplar));
+        assert (e != nullptr);
+
+        M m (*e);
 
-        if (static_cast<module&> (m).handle (r, r, l))
-          return r.flush ();
+        if (static_cast<module&> (m).handle (rq, rq, lg))
+          return rq.flush ();
 
-        if (!r.get_write_state ())
+        if (!rq.get_write_state ())
           return DECLINED;
 
-        l.write (nullptr, 0, func_name.c_str (), APLOG_ERR,
-                 "handling declined while unbuffered content has been written");
+        lg.write (nullptr, 0, func_name.c_str (), APLOG_ERR,
+                  "handling declined while unbuffered content "
+                  "has been written");
       }
       catch (const invalid_request& e)
       {
-        if (!e.content.empty () && !r.get_write_state ())
+        if (!e.content.empty () && !rq.get_write_state ())
         {
           try
           {
-            r.content (e.status, e.type) << e.content;
-            return r.flush ();
+            rq.content (e.status, e.type) << e.content;
+            return rq.flush ();
           }
           catch (const std::exception& e)
           {
-            l.write (nullptr, 0, func_name.c_str (), APLOG_ERR, e.what ());
+            lg.write (nullptr, 0, func_name.c_str (), APLOG_ERR, e.what ());
           }
         }
 
@@ -49,39 +163,39 @@ namespace web
       }
       catch (const std::exception& e)
       {
-        l.write (nullptr, 0, func_name.c_str (), APLOG_ERR, e.what ());
+        lg.write (nullptr, 0, func_name.c_str (), APLOG_ERR, e.what ());
 
-        if (*e.what () && !r.get_write_state ())
+        if (*e.what () && !rq.get_write_state ())
         {
           try
           {
-            r.content (HTTP_INTERNAL_SERVER_ERROR, "text/plain;charset=utf-8")
+            rq.content (HTTP_INTERNAL_SERVER_ERROR, "text/plain;charset=utf-8")
               << e.what ();
 
-            return r.flush ();
+            return rq.flush ();
           }
           catch (const std::exception& e)
           {
-            l.write (nullptr, 0, func_name.c_str (), APLOG_ERR, e.what ());
+            lg.write (nullptr, 0, func_name.c_str (), APLOG_ERR, e.what ());
           }
         }
       }
       catch (...)
       {
-        l.write (nullptr, 0, func_name.c_str (), APLOG_ERR, "unknown error");
+        lg.write (nullptr, 0, func_name.c_str (), APLOG_ERR, "unknown error");
 
-        if (!r.get_write_state ())
+        if (!rq.get_write_state ())
         {
           try
           {
-            r.content (HTTP_INTERNAL_SERVER_ERROR, "text/plain;charset=utf-8")
+            rq.content (HTTP_INTERNAL_SERVER_ERROR, "text/plain;charset=utf-8")
               << "unknown error";
 
-            return r.flush ();
+            return rq.flush ();
           }
           catch (const std::exception& e)
           {
-            l.write (nullptr, 0, func_name.c_str (), APLOG_ERR, e.what ());
+            lg.write (nullptr, 0, func_name.c_str (), APLOG_ERR, e.what ());
           }
         }
       }
diff --git a/web/module b/web/module
index 824551f..85896c3 100644
--- a/web/module
+++ b/web/module
@@ -86,6 +86,9 @@ namespace web
   public:
     using path_type = web::path;
 
+    virtual
+    ~request () = default;
+
     // Corresponds to abs_path portion of HTTP URL as described in
     // "3.2.2 HTTP URL" of http://tools.ietf.org/html/rfc2616.
     // Returns '/' if no abs_path is present in URL.
@@ -120,6 +123,9 @@ namespace web
   class response
   {
   public:
+    virtual
+    ~response () = default;
+
     // Set status code, content type, and get the stream to write
     // the content to. If the buffer argument is true (default),
     // then buffer the entire content before sending it as a
@@ -170,6 +176,9 @@ namespace web
   class log
   {
   public:
+    virtual
+    ~log () = default;
+
     virtual void
     write (const char* msg) = 0;
   };
@@ -188,6 +197,9 @@ namespace web
   class module
   {
   public:
+    virtual
+    ~module () = default;
+
     // Description of configuration options supported by this module. Note:
     // should be callable during static initialization.
     //