include/proxy/ParentSelection.h - trafficserver - Git at Google

 /** @file

   A brief file description

   @section license License

   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.
  */

 /*****************************************************************************
  *
  *  ParentSelection.h - Interface to Parent Selection System
  *
  *
  ****************************************************************************/

 #pragma once

 #include "iocore/eventsystem/ConfigProcessor.h"
 #include "proxy/ControlBase.h"
 #include "proxy/ControlMatcher.h"
 #include "records/RecProcess.h"
 #include "tscore/ConsistentHash.h"
 #include "tscore/Hash.h"
 #include "tscore/Tokenizer.h"
 #include "tscore/ink_apidefs.h"
 #include "proxy/HostStatus.h"

 #include <algorithm>
 #include <memory>
 #include <vector>

 #define MAX_PARENTS           64
 #define DEFAULT_PARENT_WEIGHT 1.0

 struct RequestData;
 struct matcher_line;
 struct ParentResult;
 struct OverridableHttpConfigParams;
 class ParentRecord;
 class ParentSelectionStrategy;

 enum class ParentResultType {
   UNDEFINED,
   DIRECT,
   SPECIFIED,
   AGENT,
   FAIL,
 };

 static const char *ParentResultStr[] = {"ParentResultType::UNDEFINED", "ParentResultType::DIRECT", "ParentResultType::SPECIFIED",
                                         "ParentResultType::AGENT", "ParentResultType::FAIL"};

 enum class ParentRR_t { NO_ROUND_ROBIN = 0, STRICT_ROUND_ROBIN, HASH_ROUND_ROBIN, CONSISTENT_HASH, LATCHED_ROUND_ROBIN, UNDEFINED };

 enum class ParentRetry_t {
   NONE               = 0,
   SIMPLE             = 1,
   UNAVAILABLE_SERVER = 2,
   // both simple and unavailable server retry
   BOTH = 3
 };

 enum class ParentHashAlgorithm { SIPHASH24 = 0, SIPHASH13 };

 struct UnavailableServerResponseCodes {
   UnavailableServerResponseCodes(char *val);
   ~UnavailableServerResponseCodes(){};

   bool
   contains(int code)
   {
     return binary_search(codes.begin(), codes.end(), code);
   }

 private:
   std::vector<int> codes;
 };

 struct SimpleRetryResponseCodes {
   SimpleRetryResponseCodes(char *val);
   ~SimpleRetryResponseCodes(){};

   bool
   contains(int code)
   {
     return binary_search(codes.begin(), codes.end(), code);
   }

 private:
   std::vector<int> codes;
 };

 // struct pRecord
 //
 //    A record for an individual parent
 //
 struct pRecord : ATSConsistentHashNode {
 public:
   char                hostname[MAXDNAME + 1];
   int                 port;
   std::atomic<time_t> failedAt  = 0;
   std::atomic<int>    failCount = 0;
   int32_t             upAt;
   const char         *scheme; // for which parent matches (if any)
   int                 idx;
   float               weight;
   char                hash_string[MAXDNAME + 1];
 };

 using P_table = ControlMatcher<ParentRecord, ParentResult>;

 // class ParentRecord : public ControlBase
 //
 //   A record for a configuration line in the parent.config
 //    file
 //
 class ParentRecord : public ControlBase
 {
 public:
   ~ParentRecord();

   Result Init(matcher_line *line_info);
   bool   DefaultInit(char *val);
   void   UpdateMatch(ParentResult *result, RequestData *rdata);

   void Print() const;

   pRecord *parents               = nullptr;
   pRecord *secondary_parents     = nullptr;
   int      num_parents           = 0;
   int      num_secondary_parents = 0;

   bool
   bypass_ok() const
   {
     return go_direct;
   }

   const char *scheme = nullptr;
   // private:
   void                            PreProcessParents(const char *val, const int line_num, char *buf, size_t len);
   const char                     *ProcessParents(char *val, bool isPrimary);
   bool                            ignore_query                       = false;
   uint32_t                        rr_next                            = 0;
   bool                            go_direct                          = true;
   bool                            parent_is_proxy                    = true;
   ParentSelectionStrategy        *selection_strategy                 = nullptr;
   UnavailableServerResponseCodes *unavailable_server_retry_responses = nullptr;
   SimpleRetryResponseCodes       *simple_server_retry_responses      = nullptr;
   ParentRetry_t                   parent_retry                       = ParentRetry_t::NONE;
   int                             max_simple_retries                 = 1;
   int                             max_unavailable_server_retries     = 1;
   int                             secondary_mode                     = 1;
   bool                            ignore_self_detect                 = false;
   ParentHashAlgorithm             consistent_hash_algorithm          = ParentHashAlgorithm::SIPHASH24;
   uint64_t                        consistent_hash_seed0              = 0;
   uint64_t                        consistent_hash_seed1              = 0;
   int consistent_hash_replicas = 1024; // Number of virtual nodes per host (int to match ATSConsistentHash constructor)
 };

 // If the parent was set by the external customer api,
 //   our HttpRequestData structure told us what parent to
 //   use and we are only called to preserve clean interface
 //   between HttpTransact & the parent selection code.  The following
 ParentRecord *const extApiRecord = (ParentRecord *)0xeeeeffff;

 // used here to set the number of ATSConsistentHashIter's
 // used in NextHopSelectionStrategy to limit the host group
 // size as well, group size is one to one with the number of rings
 constexpr const uint32_t MAX_GROUP_RINGS = 5;

 struct ParentResult {
   ParentResult() { reset(); }
   // For outside consumption
   ParentResultType result;
   const char      *hostname;
   const char      *url;
   int              port;
   bool             retry;
   bool             chash_init[MAX_GROUP_RINGS] = {false};
   bool             use_pristine                = false;
   TSHostStatus     first_choice_status         = TSHostStatus::TS_HOST_STATUS_INIT;
   bool             do_not_cache_response       = false;

   void
   reset()
   {
     ink_zero(*this);
     line_number           = -1;
     result                = ParentResultType::UNDEFINED;
     mapWrapped[0]         = false;
     mapWrapped[1]         = false;
     do_not_cache_response = false;
   }

   bool
   is_api_result() const
   {
     return rec == extApiRecord;
   }

   // Do we have some result?
   bool
   is_some() const
   {
     if (rec == nullptr) {
       // If we don't have a result, we either haven't done a parent
       // lookup yet (ParentResultType::UNDEFINED), or the lookup didn't match
       // anything (ParentResultType::DIRECT).
       ink_assert(result == ParentResultType::UNDEFINED || result == ParentResultType::DIRECT);
       return false;
     }

     return true;
   }

   bool
   parent_is_proxy() const
   {
     // Parents set by the TSHttpTxnParentProxySet API are always considered proxies rather than origins.
     return is_api_result() ? true : rec->parent_is_proxy;
   }

   ParentRetry_t
   retry_type() const
   {
     return is_api_result() ? ParentRetry_t::NONE : rec->parent_retry;
   }

   unsigned
   max_retries(ParentRetry_t method) const
   {
     // There's no API for specifying the retries, so you get 0.
     if (is_api_result()) {
       return 0;
     }

     switch (method) {
     case ParentRetry_t::NONE:
       return 0;
     case ParentRetry_t::SIMPLE:
       return rec->max_simple_retries;
     case ParentRetry_t::UNAVAILABLE_SERVER:
       return rec->max_unavailable_server_retries;
     case ParentRetry_t::BOTH:
       return std::max(rec->max_unavailable_server_retries, rec->max_simple_retries);
     }

     return 0;
   }

   bool
   response_is_retryable(ParentRetry_t retry_type, HTTPStatus response_code) const
   {
     Dbg(dbg_ctl_parent_select, "In response_is_retryable, code: %d, type: %d", static_cast<int>(response_code),
         static_cast<int>(retry_type));
     if (retry_type == ParentRetry_t::BOTH) {
       Dbg(dbg_ctl_parent_select, "Saw retry both");
       return (rec->unavailable_server_retry_responses->contains(static_cast<int>(response_code)) ||
               rec->simple_server_retry_responses->contains(static_cast<int>(response_code)));
     } else if (retry_type == ParentRetry_t::UNAVAILABLE_SERVER) {
       Dbg(dbg_ctl_parent_select, "Saw retry unavailable server");
       return rec->unavailable_server_retry_responses->contains(static_cast<int>(response_code));
     } else if (retry_type == ParentRetry_t::SIMPLE) {
       Dbg(dbg_ctl_parent_select, "Saw retry simple retry");
       return rec->simple_server_retry_responses->contains(static_cast<int>(response_code));
     } else {
       return false;
     }
   }

   bool
   bypass_ok() const
   {
     if (is_api_result()) {
       return false;
     } else {
       // Caller should check for a valid result beforehand.
       ink_assert(result != ParentResultType::UNDEFINED);
       ink_assert(is_some());
       return rec->bypass_ok();
     }
   }

   void
   print()
   {
     printf("ParentResult - hostname: %s, port: %d, retry: %s, line_number: %d, last_parent: %d, start_parent: %d, wrap_around: %s, "
            "last_lookup: %d, result: %s\n",
            hostname, port, (retry) ? "true" : "false", line_number, last_parent, start_parent, (wrap_around) ? "true" : "false",
            last_lookup, ParentResultStr[static_cast<int>(result)]);
   }

   static DbgCtl dbg_ctl_parent_select;

 private:
   // Internal use only
   //   Not to be modified by HTTP
   int           line_number;
   ParentRecord *rec;
   uint32_t      last_parent;
   uint32_t      start_parent;
   uint32_t      last_group;
   bool          wrap_around;
   bool          mapWrapped[2];
   // state for consistent hash.
   int                   last_lookup;
   ATSConsistentHashIter chashIter[MAX_GROUP_RINGS];

   friend class NextHopSelectionStrategy;
   friend class NextHopRoundRobin;
   friend class NextHopConsistentHash;
   friend class ParentConsistentHash;
   friend class ParentRoundRobin;
   friend class ParentConfigParams;
   friend class ParentRecord;
   friend class ParentSelectionStrategy;
 };

 struct ParentSelectionPolicy {
   int32_t ParentRetryTime = 0;
   int32_t ParentEnable    = 0;
   int32_t FailThreshold   = 0;
   ParentSelectionPolicy();
 };

 //
 // API definition.
 class ParentSelectionStrategy
 {
 public:
   int max_retriers = 0;

   ParentSelectionStrategy() { max_retriers = RecGetRecordInt("proxy.config.http.parent_proxy.max_trans_retries").value_or(0); }
   //
   // Return the pRecord.
   virtual pRecord *getParents(ParentResult *result) = 0;
   // void selectParent(bool firstCall, ParentResult *result, RequestData *rdata, unsigned int fail_threshold, unsigned int
   // retry_time)
   //
   // The implementation parent lookup.
   //
   virtual void selectParent(bool firstCall, ParentResult *result, RequestData *rdata, unsigned int fail_threshold,
                             unsigned int retry_time) = 0;

   // uint32_t numParents(ParentResult *result);
   //
   // Returns the number of parent records in a strategy.
   //
   virtual uint32_t numParents(ParentResult *result) const = 0;
   void             markParentDown(ParentResult *result, unsigned int fail_threshold, unsigned int retry_time);
   void             markParentUp(ParentResult *result);

   // virtual destructor.
   virtual ~ParentSelectionStrategy(){};
 };

 class ParentConfigParams : public ConfigInfo
 {
 public:
   explicit ParentConfigParams(P_table *_parent_table);
   ~ParentConfigParams() override;

   bool apiParentExists(HttpRequestData *rdata);
   void findParent(HttpRequestData *rdata, ParentResult *result, unsigned int fail_threshold, unsigned int retry_time);
   void nextParent(HttpRequestData *rdata, ParentResult *result, unsigned int fail_threshold, unsigned int retry_time);
   bool parentExists(HttpRequestData *rdata);

   // implementation of functions from ParentSelectionStrategy.
   void
   selectParent(bool firstCall, ParentResult *result, RequestData *rdata, unsigned int fail_threshold, unsigned int retry_time)
   {
     if (!result->is_api_result()) {
       ink_release_assert(result->rec->selection_strategy != nullptr);
       return result->rec->selection_strategy->selectParent(firstCall, result, rdata, fail_threshold, retry_time);
     }
   }

   void
   markParentDown(ParentResult *result, unsigned int fail_threshold, unsigned int retry_time)
   {
     if (!result->is_api_result()) {
       ink_release_assert(result->rec->selection_strategy != nullptr);
       result->rec->selection_strategy->markParentDown(result, fail_threshold, retry_time);
     }
   }

   void
   markParentUp(ParentResult *result)
   {
     if (!result->is_api_result()) {
       ink_release_assert(result != nullptr);
       result->rec->selection_strategy->markParentUp(result);
     }
   }

   uint32_t
   numParents(ParentResult *result)
   {
     if (result->is_api_result()) {
       return 1;
     } else {
       ink_release_assert(result->rec->selection_strategy != nullptr);
       return result->rec->selection_strategy->numParents(result);
     }
   }

   P_table              *parent_table;
   ParentRecord         *DefaultParent;
   ParentSelectionPolicy policy;
 };

 class HttpRequestData;

 struct ParentConfig {
 public:
   static void startup();
   static void reconfigure();
   static void print();
   static void set_parent_table(P_table *pTable, ParentRecord *rec, int num_elements);

   static ParentConfigParams *
   acquire()
   {
     return (ParentConfigParams *)configProcessor.get(ParentConfig::m_id);
   }

   static void
   release(ParentConfigParams *strategy)
   {
     configProcessor.release(ParentConfig::m_id, strategy);
   }

   static int m_id;
 };

 // Helper Functions
 ParentRecord *createDefaultParent(char *val);

 // Hash utility functions
 ParentHashAlgorithm        parseHashAlgorithm(std::string_view name);
 std::unique_ptr<ATSHash64> createHashInstance(ParentHashAlgorithm algo, uint64_t seed0, uint64_t seed1);

 // Unit Test Functions
 void show_result(ParentResult *aParentResult);
 void br(HttpRequestData *h, const char *os_hostname, sockaddr const *dest_ip = nullptr); // short for build request
 int  verify(ParentResult *r, ParentResultType e, const char *h, int p);

 /*
   For supporting multiple Socks servers, we essentially use the
   ParentSelection infrastructure. Only the initialization is different.
   If needed, we will have to implement most of the functions in
   ParentSection.cc for Socks as well. For right now we will just use
   ParentSelection

   All the members in ParentConfig are static. Right now
   we will duplicate the code for these static functions.
 */
 struct SocksServerConfig {
   static void startup();
   static void reconfigure();
   static void print();

   static ParentConfigParams *
   acquire()
   {
     return (ParentConfigParams *)configProcessor.get(SocksServerConfig::m_id);
   }
   static void
   release(ParentConfigParams *params)
   {
     configProcessor.release(SocksServerConfig::m_id, params);
   }

   static int m_id;
 };
	/** @file

	A brief file description

	@section license License

	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.
	*/

	/*****************************************************************************
	*
	* ParentSelection.h - Interface to Parent Selection System
	*
	*
	****************************************************************************/

	#pragma once

	#include "iocore/eventsystem/ConfigProcessor.h"
	#include "proxy/ControlBase.h"
	#include "proxy/ControlMatcher.h"
	#include "records/RecProcess.h"
	#include "tscore/ConsistentHash.h"
	#include "tscore/Hash.h"
	#include "tscore/Tokenizer.h"
	#include "tscore/ink_apidefs.h"
	#include "proxy/HostStatus.h"

	#include <algorithm>
	#include <memory>
	#include <vector>

	#define MAX_PARENTS 64
	#define DEFAULT_PARENT_WEIGHT 1.0

	struct RequestData;
	struct matcher_line;
	struct ParentResult;
	struct OverridableHttpConfigParams;
	class ParentRecord;
	class ParentSelectionStrategy;

	enum class ParentResultType {
	UNDEFINED,
	DIRECT,
	SPECIFIED,
	AGENT,
	FAIL,
	};

	static const char *ParentResultStr[] = {"ParentResultType::UNDEFINED", "ParentResultType::DIRECT", "ParentResultType::SPECIFIED",
	"ParentResultType::AGENT", "ParentResultType::FAIL"};

	enum class ParentRR_t { NO_ROUND_ROBIN = 0, STRICT_ROUND_ROBIN, HASH_ROUND_ROBIN, CONSISTENT_HASH, LATCHED_ROUND_ROBIN, UNDEFINED };

	enum class ParentRetry_t {
	NONE = 0,
	SIMPLE = 1,
	UNAVAILABLE_SERVER = 2,
	// both simple and unavailable server retry
	BOTH = 3
	};

	enum class ParentHashAlgorithm { SIPHASH24 = 0, SIPHASH13 };

	struct UnavailableServerResponseCodes {
	UnavailableServerResponseCodes(char *val);
	~UnavailableServerResponseCodes(){};

	bool
	contains(int code)
	{
	return binary_search(codes.begin(), codes.end(), code);
	}

	private:
	std::vector<int> codes;
	};

	struct SimpleRetryResponseCodes {
	SimpleRetryResponseCodes(char *val);
	~SimpleRetryResponseCodes(){};

	bool
	contains(int code)
	{
	return binary_search(codes.begin(), codes.end(), code);
	}

	private:
	std::vector<int> codes;
	};

	// struct pRecord
	//
	// A record for an individual parent
	//
	struct pRecord : ATSConsistentHashNode {
	public:
	char hostname[MAXDNAME + 1];
	int port;
	std::atomic<time_t> failedAt = 0;
	std::atomic<int> failCount = 0;
	int32_t upAt;
	const char *scheme; // for which parent matches (if any)
	int idx;
	float weight;
	char hash_string[MAXDNAME + 1];
	};

	using P_table = ControlMatcher<ParentRecord, ParentResult>;

	// class ParentRecord : public ControlBase
	//
	// A record for a configuration line in the parent.config
	// file
	//
	class ParentRecord : public ControlBase
	{
	public:
	~ParentRecord();

	Result Init(matcher_line *line_info);
	bool DefaultInit(char *val);
	void UpdateMatch(ParentResult result, RequestData rdata);

	void Print() const;

	pRecord *parents = nullptr;
	pRecord *secondary_parents = nullptr;
	int num_parents = 0;
	int num_secondary_parents = 0;

	bool
	bypass_ok() const
	{
	return go_direct;
	}

	const char *scheme = nullptr;
	// private:
	void PreProcessParents(const char val, const int line_num, char buf, size_t len);
	const char ProcessParents(char val, bool isPrimary);
	bool ignore_query = false;
	uint32_t rr_next = 0;
	bool go_direct = true;
	bool parent_is_proxy = true;
	ParentSelectionStrategy *selection_strategy = nullptr;
	UnavailableServerResponseCodes *unavailable_server_retry_responses = nullptr;
	SimpleRetryResponseCodes *simple_server_retry_responses = nullptr;
	ParentRetry_t parent_retry = ParentRetry_t::NONE;
	int max_simple_retries = 1;
	int max_unavailable_server_retries = 1;
	int secondary_mode = 1;
	bool ignore_self_detect = false;
	ParentHashAlgorithm consistent_hash_algorithm = ParentHashAlgorithm::SIPHASH24;
	uint64_t consistent_hash_seed0 = 0;
	uint64_t consistent_hash_seed1 = 0;
	int consistent_hash_replicas = 1024; // Number of virtual nodes per host (int to match ATSConsistentHash constructor)
	};

	// If the parent was set by the external customer api,
	// our HttpRequestData structure told us what parent to
	// use and we are only called to preserve clean interface
	// between HttpTransact & the parent selection code. The following
	ParentRecord const extApiRecord = (ParentRecord )0xeeeeffff;

	// used here to set the number of ATSConsistentHashIter's
	// used in NextHopSelectionStrategy to limit the host group
	// size as well, group size is one to one with the number of rings
	constexpr const uint32_t MAX_GROUP_RINGS = 5;

	struct ParentResult {
	ParentResult() { reset(); }
	// For outside consumption
	ParentResultType result;
	const char *hostname;
	const char *url;
	int port;
	bool retry;
	bool chash_init[MAX_GROUP_RINGS] = {false};
	bool use_pristine = false;
	TSHostStatus first_choice_status = TSHostStatus::TS_HOST_STATUS_INIT;
	bool do_not_cache_response = false;

	void
	reset()
	{
	ink_zero(*this);
	line_number = -1;
	result = ParentResultType::UNDEFINED;
	mapWrapped[0] = false;
	mapWrapped[1] = false;
	do_not_cache_response = false;
	}

	bool
	is_api_result() const
	{
	return rec == extApiRecord;
	}

	// Do we have some result?
	bool
	is_some() const
	{
	if (rec == nullptr) {
	// If we don't have a result, we either haven't done a parent
	// lookup yet (ParentResultType::UNDEFINED), or the lookup didn't match
	// anything (ParentResultType::DIRECT).
	ink_assert(result == ParentResultType::UNDEFINED \|\| result == ParentResultType::DIRECT);
	return false;
	}

	return true;
	}

	bool
	parent_is_proxy() const
	{
	// Parents set by the TSHttpTxnParentProxySet API are always considered proxies rather than origins.
	return is_api_result() ? true : rec->parent_is_proxy;
	}

	ParentRetry_t
	retry_type() const
	{
	return is_api_result() ? ParentRetry_t::NONE : rec->parent_retry;
	}

	unsigned
	max_retries(ParentRetry_t method) const
	{
	// There's no API for specifying the retries, so you get 0.
	if (is_api_result()) {
	return 0;
	}

	switch (method) {
	case ParentRetry_t::NONE:
	return 0;
	case ParentRetry_t::SIMPLE:
	return rec->max_simple_retries;
	case ParentRetry_t::UNAVAILABLE_SERVER:
	return rec->max_unavailable_server_retries;
	case ParentRetry_t::BOTH:
	return std::max(rec->max_unavailable_server_retries, rec->max_simple_retries);
	}

	return 0;
	}

	bool
	response_is_retryable(ParentRetry_t retry_type, HTTPStatus response_code) const
	{
	Dbg(dbg_ctl_parent_select, "In response_is_retryable, code: %d, type: %d", static_cast<int>(response_code),
	static_cast<int>(retry_type));
	if (retry_type == ParentRetry_t::BOTH) {
	Dbg(dbg_ctl_parent_select, "Saw retry both");
	return (rec->unavailable_server_retry_responses->contains(static_cast<int>(response_code)) \|\|
	rec->simple_server_retry_responses->contains(static_cast<int>(response_code)));
	} else if (retry_type == ParentRetry_t::UNAVAILABLE_SERVER) {
	Dbg(dbg_ctl_parent_select, "Saw retry unavailable server");
	return rec->unavailable_server_retry_responses->contains(static_cast<int>(response_code));
	} else if (retry_type == ParentRetry_t::SIMPLE) {
	Dbg(dbg_ctl_parent_select, "Saw retry simple retry");
	return rec->simple_server_retry_responses->contains(static_cast<int>(response_code));
	} else {
	return false;
	}
	}

	bool
	bypass_ok() const
	{
	if (is_api_result()) {
	return false;
	} else {
	// Caller should check for a valid result beforehand.
	ink_assert(result != ParentResultType::UNDEFINED);
	ink_assert(is_some());
	return rec->bypass_ok();
	}
	}

	void
	print()
	{
	printf("ParentResult - hostname: %s, port: %d, retry: %s, line_number: %d, last_parent: %d, start_parent: %d, wrap_around: %s, "
	"last_lookup: %d, result: %s\n",
	hostname, port, (retry) ? "true" : "false", line_number, last_parent, start_parent, (wrap_around) ? "true" : "false",
	last_lookup, ParentResultStr[static_cast<int>(result)]);
	}

	static DbgCtl dbg_ctl_parent_select;

	private:
	// Internal use only
	// Not to be modified by HTTP
	int line_number;
	ParentRecord *rec;
	uint32_t last_parent;
	uint32_t start_parent;
	uint32_t last_group;
	bool wrap_around;
	bool mapWrapped[2];
	// state for consistent hash.
	int last_lookup;
	ATSConsistentHashIter chashIter[MAX_GROUP_RINGS];

	friend class NextHopSelectionStrategy;
	friend class NextHopRoundRobin;
	friend class NextHopConsistentHash;
	friend class ParentConsistentHash;
	friend class ParentRoundRobin;
	friend class ParentConfigParams;
	friend class ParentRecord;
	friend class ParentSelectionStrategy;
	};

	struct ParentSelectionPolicy {
	int32_t ParentRetryTime = 0;
	int32_t ParentEnable = 0;
	int32_t FailThreshold = 0;
	ParentSelectionPolicy();
	};

	//
	// API definition.
	class ParentSelectionStrategy
	{
	public:
	int max_retriers = 0;

	ParentSelectionStrategy() { max_retriers = RecGetRecordInt("proxy.config.http.parent_proxy.max_trans_retries").value_or(0); }
	//
	// Return the pRecord.
	virtual pRecord getParents(ParentResult result) = 0;
	// void selectParent(bool firstCall, ParentResult result, RequestData rdata, unsigned int fail_threshold, unsigned int
	// retry_time)
	//
	// The implementation parent lookup.
	//
	virtual void selectParent(bool firstCall, ParentResult result, RequestData rdata, unsigned int fail_threshold,
	unsigned int retry_time) = 0;

	// uint32_t numParents(ParentResult *result);
	//
	// Returns the number of parent records in a strategy.
	//
	virtual uint32_t numParents(ParentResult *result) const = 0;
	void markParentDown(ParentResult *result, unsigned int fail_threshold, unsigned int retry_time);
	void markParentUp(ParentResult *result);

	// virtual destructor.
	virtual ~ParentSelectionStrategy(){};
	};

	class ParentConfigParams : public ConfigInfo
	{
	public:
	explicit ParentConfigParams(P_table *_parent_table);
	~ParentConfigParams() override;

	bool apiParentExists(HttpRequestData *rdata);
	void findParent(HttpRequestData rdata, ParentResult result, unsigned int fail_threshold, unsigned int retry_time);
	void nextParent(HttpRequestData rdata, ParentResult result, unsigned int fail_threshold, unsigned int retry_time);
	bool parentExists(HttpRequestData *rdata);

	// implementation of functions from ParentSelectionStrategy.
	void
	selectParent(bool firstCall, ParentResult result, RequestData rdata, unsigned int fail_threshold, unsigned int retry_time)
	{
	if (!result->is_api_result()) {
	ink_release_assert(result->rec->selection_strategy != nullptr);
	return result->rec->selection_strategy->selectParent(firstCall, result, rdata, fail_threshold, retry_time);
	}
	}

	void
	markParentDown(ParentResult *result, unsigned int fail_threshold, unsigned int retry_time)
	{
	if (!result->is_api_result()) {
	ink_release_assert(result->rec->selection_strategy != nullptr);
	result->rec->selection_strategy->markParentDown(result, fail_threshold, retry_time);
	}
	}

	void
	markParentUp(ParentResult *result)
	{
	if (!result->is_api_result()) {
	ink_release_assert(result != nullptr);
	result->rec->selection_strategy->markParentUp(result);
	}
	}

	uint32_t
	numParents(ParentResult *result)
	{
	if (result->is_api_result()) {
	return 1;
	} else {
	ink_release_assert(result->rec->selection_strategy != nullptr);
	return result->rec->selection_strategy->numParents(result);
	}
	}

	P_table *parent_table;
	ParentRecord *DefaultParent;
	ParentSelectionPolicy policy;
	};

	class HttpRequestData;

	struct ParentConfig {
	public:
	static void startup();
	static void reconfigure();
	static void print();
	static void set_parent_table(P_table pTable, ParentRecord rec, int num_elements);

	static ParentConfigParams *
	acquire()
	{
	return (ParentConfigParams *)configProcessor.get(ParentConfig::m_id);
	}

	static void
	release(ParentConfigParams *strategy)
	{
	configProcessor.release(ParentConfig::m_id, strategy);
	}

	static int m_id;
	};

	// Helper Functions
	ParentRecord createDefaultParent(char val);

	// Hash utility functions
	ParentHashAlgorithm parseHashAlgorithm(std::string_view name);
	std::unique_ptr<ATSHash64> createHashInstance(ParentHashAlgorithm algo, uint64_t seed0, uint64_t seed1);

	// Unit Test Functions
	void show_result(ParentResult *aParentResult);
	void br(HttpRequestData h, const char os_hostname, sockaddr const *dest_ip = nullptr); // short for build request
	int verify(ParentResult r, ParentResultType e, const char h, int p);

	/*
	For supporting multiple Socks servers, we essentially use the
	ParentSelection infrastructure. Only the initialization is different.
	If needed, we will have to implement most of the functions in
	ParentSection.cc for Socks as well. For right now we will just use
	ParentSelection

	All the members in ParentConfig are static. Right now
	we will duplicate the code for these static functions.
	*/
	struct SocksServerConfig {
	static void startup();
	static void reconfigure();
	static void print();

	static ParentConfigParams *
	acquire()
	{
	return (ParentConfigParams *)configProcessor.get(SocksServerConfig::m_id);
	}
	static void
	release(ParentConfigParams *params)
	{
	configProcessor.release(SocksServerConfig::m_id, params);
	}

	static int m_id;
	};