Create ts API functions to change a transaction strategy.

This adds 'c' friendly api calls to get and set strategies,
to get the name of a given strategy and
to get a strategy from the strategy factory by name.

Also includes additions to header_rewrite, regex_remap and lua plugins.

Author: traeak

doc/admin-guide/plugins/header_rewrite.en.rst

@@ -647,6 +647,7 @@ are supported::
 
     %{NEXT-HOP:HOST} Name of the current selected parent.
     %{NEXT-HOP:PORT} Port of the current selected parent.
+    %{NEXT-HOP:STRATEGY} Name of the current strategy (can be "" if not using a strategy)
 
 Note that the ``<part>`` of NEXT-HOP will likely not be available unless
 an origin server connection is attempted at which point it will available
@@ -1083,6 +1084,18 @@ if necessary.
 The header's ``<value>`` may be a literal string, or take advantage of
 `String concatenations`_ to calculate a dynamic value for the header.
 
+set-next-hop-strategy
+~~~~~~~~~~~~~~~~~~~~~
+::
+
+  set-next-hop-strategy <name>
+
+Replaces/Sets the current next hop parent selection strategy with
+the matching strategy specified in `strategies.yaml`
+
+Setting to "" removes the current strategy which will fall back
+to other methods (ie: parent.config or remap to url).
+
 set-redirect
 ~~~~~~~~~~~~
 ::

doc/admin-guide/plugins/lua.en.rst

@@ -1930,6 +1930,50 @@ Here is an example:
 
 `TOP <#ts-lua-plugin>`_
 
+ts.http.get_next_hop_strategy
+-----------------------------
+**syntax:** *ts.http.get_next_hop_strategy()*
+
+**context:** function @ TS_LUA_HOOK_READ_REQUEST_HDR or do_remap()
+
+**description** Returns the name of the current next hop selection strategy, or nil string if no strategy is in use.
+
+Here is an example:
+
+::
+
+    function do_remap()
+		  local strategy = ts.http.get_next_hop_strategy()
+			ts.debug("Using strategy: " .. strategy)
+		end
+
+`TOP <#ts-lua-plugin>`_
+
+ts.http.set_next_hop_strategy
+-----------------------------
+**syntax:** *ts.http.set_next_hop_strategy(str)*
+
+**context:** function @ TS_LUA_HOOK_READ_REQUEST_HDR or do_remap()
+
+**description** Looks for the named strategy and sets the current
+transaction to use that strategy.
+
+Use empty string to clear the strategy and fall back to parent.config
+or the remap to url.
+
+Here is an example:
+
+::
+
+    function do_remap()
+		  local uri = ts.client_request.get_uri()
+			if uri == "otherhost" then
+			  ts.http.set_next_hop_strategy("otherhost")
+			end
+		end
+
+`TOP <#ts-lua-plugin>`_
+
 ts.sha256
 ---------
 **syntax:** *digest = ts.sha256(str)*

doc/admin-guide/plugins/regex_remap.en.rst

@@ -143,6 +143,7 @@ remap.config. The following options are available ::
 
     @caseless                   - Make regular expressions case insensitive
     @lowercase_substitutions    - Turn on (enable) lower case substitutions
+		@strategy                   - Specify a strategy from strategies.yaml
 
 
 This can be useful to force a particular response for some URLs, e.g. ::

doc/developer-guide/api/functions/TSHttpNextHopStrategyNameGet.en.rst

@@ -0,0 +1,49 @@
+.. Licensed to the Apache Software Foundation (ASF) under one or more
+   contributor license agreements.  See the NOTICE file distributed
+   with this work for additional information regarding copyright
+   ownership.  The ASF licenses this file to you under the Apache
+   License, Version 2.0 (the "License"); you may not use this file
+   except in compliance with the License.  You may obtain a copy of
+   the License at
+
+   http://www.apache.org/licenses/LICENSE-2.0
+
+   Unless required by applicable law or agreed to in writing, software
+   distributed under the License is distributed on an "AS IS" BASIS,
+   WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or
+   implied.  See the License for the specific language governing
+   permissions and limitations under the License.
+
+.. include:: ../../../common.defs
+
+.. default-domain:: cpp
+
+TSHttpNextHopStrategyNameGet
+****************************
+
+Synopsis
+========
+
+.. code-block:: cpp
+
+    #include <ts/ts.h>
+
+.. function:: char const* TSHttpNextHopStrategyNameGet(void const* strategy)
+
+Description
+===========
+
+Gets the name associated with the provided strategy.
+This may be nullptr indicating that parent.config is in use.
+
+.. note::
+
+   This returned pointer must not be freed and the contents must not
+   be changed.
+   Strategy pointers held by plugins will become invalid when ATS
+   configs are reloaded and should be reset with :func:`TSRemapNewInstance`
+
+See Also
+========
+
+:func:`TSHttpTxnNextHopStrategyGet`

doc/developer-guide/api/functions/TSHttpTxnNextHopNamedStrategyGet.en.rst

@@ -0,0 +1,52 @@
+.. Licensed to the Apache Software Foundation (ASF) under one or more
+   contributor license agreements.  See the NOTICE file distributed
+   with this work for additional information regarding copyright
+   ownership.  The ASF licenses this file to you under the Apache
+   License, Version 2.0 (the "License"); you may not use this file
+   except in compliance with the License.  You may obtain a copy of
+   the License at
+
+   http://www.apache.org/licenses/LICENSE-2.0
+
+   Unless required by applicable law or agreed to in writing, software
+   distributed under the License is distributed on an "AS IS" BASIS,
+   WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or
+   implied.  See the License for the specific language governing
+   permissions and limitations under the License.
+
+.. include:: ../../../common.defs
+
+.. default-domain:: cpp
+
+TSHttpTxnNextHopNamedStrategyGet
+********************************
+
+Synopsis
+========
+
+.. code-block:: cpp
+
+    #include <ts/ts.h>
+
+.. function:: void const* TSHttpTxnNextHopNamedStrategyGet(TSHttpTxn txnp, const char *name)
+
+Description
+===========
+
+Gets a pointer to the specified :arg:`name` NextHopSelectionStrategy.
+This may be nullptr indicating that no strategy exists with the given name.
+
+This function uses the transaction :arg:`txnp` to get access to the
+NextHopStrategyFactory associated with the current configuration.
+
+.. note::
+
+   This returned pointer must not be freed and the contents must not
+   be changed.
+   Strategy pointers held by plugins will become invalid when ATS
+   configs are reloaded and should be reset with :func:`TSRemapNewInstance`
+
+See Also
+========
+
+:func:`TSHttpTxnNextHopStrategySet`

doc/developer-guide/api/functions/TSHttpTxnNextHopStrategyGet.en.rst

@@ -0,0 +1,49 @@
+.. Licensed to the Apache Software Foundation (ASF) under one or more
+   contributor license agreements.  See the NOTICE file distributed
+   with this work for additional information regarding copyright
+   ownership.  The ASF licenses this file to you under the Apache
+   License, Version 2.0 (the "License"); you may not use this file
+   except in compliance with the License.  You may obtain a copy of
+   the License at
+
+   http://www.apache.org/licenses/LICENSE-2.0
+
+   Unless required by applicable law or agreed to in writing, software
+   distributed under the License is distributed on an "AS IS" BASIS,
+   WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or
+   implied.  See the License for the specific language governing
+   permissions and limitations under the License.
+
+.. include:: ../../../common.defs
+
+.. default-domain:: cpp
+
+TSHttpTxnNextHopStrategyGet
+***************************
+
+Synopsis
+========
+
+.. code-block:: cpp
+
+    #include <ts/ts.h>
+
+.. function:: void const* TSHttpTxnNextHopStrategyGet(TSHttpTxn txnp)
+
+Description
+===========
+
+Gets a pointer to the current transaction :arg:`txnp` NextHopSelectionStrategy.
+This may be nullptr indicating that parent.config is in use.
+
+.. note::
+
+   This strategy pointer must not be freed and the contents must not
+   be changed.
+   Strategy pointers held by plugins will become invalid when ATS
+   configs are reloaded and should be reset with :func:`TSRemapNewInstance`
+
+See Also
+========
+
+:func:`TSHttpTxnNextHopStrategySet`

doc/developer-guide/api/functions/TSHttpTxnNextHopStrategySet.en.rst

@@ -0,0 +1,56 @@
+.. Licensed to the Apache Software Foundation (ASF) under one or more
+   contributor license agreements.  See the NOTICE file distributed
+   with this work for additional information regarding copyright
+   ownership.  The ASF licenses this file to you under the Apache
+   License, Version 2.0 (the "License"); you may not use this file
+   except in compliance with the License.  You may obtain a copy of
+   the License at
+
+   http://www.apache.org/licenses/LICENSE-2.0
+
+   Unless required by applicable law or agreed to in writing, software
+   distributed under the License is distributed on an "AS IS" BASIS,
+   WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or
+   implied.  See the License for the specific language governing
+   permissions and limitations under the License.
+
+.. include:: ../../../common.defs
+
+.. default-domain:: cpp
+
+TSHttpTxnNextHopNameGet
+***********************
+
+Synopsis
+========
+
+.. code-block:: cpp
+
+    #include <ts/ts.h>
+
+.. function:: void TSHttpTxnNextHopStrategySet(TSHttpTxn txnp, void const* strategy)
+
+Description
+===========
+
+Sets the next hop strategy for the transaction :arg:`txnp`
+This :arg:`strategy` pointer must be a valid strategy and can be
+nullptr to indicate that parent.config will be used instead.
+
+Plugins can get a strategy by name by calling
+:func:`TSHttpTxnNextHopStrategyGet` to get the current transaction's
+active strategy or :func:`TSHttpTxnNextHopNamedStrategyGet` to
+look up a strategy by name using the transaction's pointer to the
+NextHopStrategyFactory strategy database.
+
+.. note::
+
+   This strategy pointer must not be freed and the contents must not
+   be changed.
+   Strategy pointers held by plugins will become invalid when ATS
+   configs are reloaded and should be reset with :func:`TSRemapNewInstance`
+
+See Also
+========
+
+:func:`TSHttpTxnNextHopStrategyGet`, :func:`TSHttpTxnNextHopNamedStrategyGet`.

include/proxy/http/HttpTransact.h

@@ -724,11 +724,11 @@ class HttpTransact
     //  able to defer some work in building the request
     TransactFunc_t pending_work = nullptr;
 
-    HttpRequestData                           request_data;
-    ParentConfigParams                       *parent_params     = nullptr;
-    std::shared_ptr<NextHopSelectionStrategy> next_hop_strategy = nullptr;
-    ParentResult                              parent_result;
-    CacheControlResult                        cache_control;
+    HttpRequestData           request_data;
+    ParentConfigParams       *parent_params     = nullptr;
+    NextHopSelectionStrategy *next_hop_strategy = nullptr;
+    ParentResult              parent_result;
+    CacheControlResult        cache_control;
 
     StateMachineAction_t next_action                      = StateMachineAction_t::UNDEFINED; // out
     StateMachineAction_t api_next_action                  = StateMachineAction_t::UNDEFINED; // out

include/proxy/http/remap/NextHopStrategyFactory.h

@@ -45,13 +45,16 @@ class NextHopStrategyFactory
   NextHopStrategyFactory() = delete;
   NextHopStrategyFactory(const char *file);
   ~NextHopStrategyFactory();
-  std::shared_ptr<NextHopSelectionStrategy> strategyInstance(const char *name);
+
+  // The lifetime of this is attached to UrlRewrite which is reference
+  // counted and attached to an HttpSM.
+  NextHopSelectionStrategy *strategyInstance(const char *name) const;
 
   bool strategies_loaded;
 
 private:
   std::string fn;
   void        loadConfigFile(const std::string &file, std::stringstream &doc, std::unordered_set<std::string> &include_once);
   void        createStrategy(const std::string &name, const NHPolicyType policy_type, ts::Yaml::Map &node);
-  std::unordered_map<std::string, std::shared_ptr<NextHopSelectionStrategy>> _strategies;
+  std::unordered_map<std::string, NextHopSelectionStrategy *> _strategies;
 };

include/proxy/http/remap/UrlMapping.h

@@ -112,9 +112,9 @@ class url_mapping
   bool              ip_allow_check_enabled_p = false;
   acl_filter_rule  *filter                   = nullptr; // acl filtering (linked list of rules)
   LINK(url_mapping, link);                              // For use with the main Queue linked list holding all the mapping
-  std::shared_ptr<NextHopSelectionStrategy> strategy = nullptr;
-  std::string                               remapKey;
-  std::atomic<uint64_t>                     _hitCount = 0; // counter can overflow
+  NextHopSelectionStrategy *strategy = nullptr;
+  std::string               remapKey;
+  std::atomic<uint64_t>     _hitCount = 0; // counter can overflow
 
   int
   getRank() const