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✏️ Editing: HeaderTable.h

/*
 *  Phusion Passenger - https://www.phusionpassenger.com/
 *  Copyright (c) 2014-2025 Asynchronous B.V.
 *
 *  "Passenger", "Phusion Passenger" and "Union Station" are registered
 *  trademarks of Asynchronous B.V.
 *
 *  Permission is hereby granted, free of charge, to any person obtaining a copy
 *  of this software and associated documentation files (the "Software"), to deal
 *  in the Software without restriction, including without limitation the rights
 *  to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
 *  copies of the Software, and to permit persons to whom the Software is
 *  furnished to do so, subject to the following conditions:
 *
 *  The above copyright notice and this permission notice shall be included in
 *  all copies or substantial portions of the Software.
 *
 *  THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 *  IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 *  FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 *  AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 *  LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 *  OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
 *  THE SOFTWARE.
 */
#ifndef _PASSENGER_SERVER_KIT_HEADER_TABLE_H_
#define _PASSENGER_SERVER_KIT_HEADER_TABLE_H_

#include <boost/cstdint.hpp>
#include <cstring>
#include <cassert>

#include <DataStructures/LString.h>
#include <DataStructures/HashedStaticString.h>
#include <StaticString.h>

namespace Passenger {
namespace ServerKit {

using namespace std;

extern const HashedStaticString HTTP_COOKIE;
extern const HashedStaticString HTTP_SET_COOKIE;

struct Header {
	/** Downcased version of the key, for case-insensitive lookup. */
	LString key;
	/** Original, unmodified key. */
	LString origKey;
	LString val;
	boost::uint32_t hash;
};

/**
 * A hash table, optimized for storing HTTP headers. It assumes the following workload:
 *
 *  * Inserts happen in bulk, soon after hash table creation or clearing.
 *  * Once the bulk insertion phase is over, lookups are frequent, but modifications
 *    are not.
 *  * The hash table does not contain a lot of elements. Maybe 35 or so.
 *
 * The hash table uses open addressing and linear probing for cache friendliness. It
 * supports keys that are non-contigunous in memory, through the use of LString.
 *
 * It supports at most 2^16-1 keys.
 *
 * The hash table automatically doubles in size when it becomes 75% full.
 * The hash table never shrinks in size, even after clear(), unless you explicitly call
 * compact(). This allows you to reuse hash table memory over multiple requests.
 *
 * This implementation is based on https://github.com/preshing/CompareIntegerMaps.
 * See also http://preshing.com/20130107/this-hash-table-is-faster-than-a-judy-array
 */
class HeaderTable {
public:
	#define PHT_FIRST_CELL(hash) (m_cells + ((hash) & (m_arraySize - 1)))
	#define PHT_CIRCULAR_NEXT(c) ((c) + 1 != m_cells + m_arraySize ? (c) + 1 : m_cells)
	#define PHT_CIRCULAR_OFFSET(a, b) ((b) >= (a) ? (b) - (a) : m_arraySize + (b) - (a))

static const unsigned int MAX_KEY_LENGTH = 65535;
	static const unsigned int DEFAULT_SIZE = 64;

struct Cell {
		Header *header;
	};

private:
	Cell *m_cells;
	boost::uint16_t m_arraySize;
	boost::uint16_t m_population;

bool shouldRepopulateOnInsert() const {
		return (m_population + 1) * 4 >= m_arraySize * 3;
	}

OXT_FORCE_INLINE
	bool cellIsEmpty(const Cell * const cell) const {
		return cell->header == NULL;
	}

static boost::uint32_t upper_power_of_two(boost::uint32_t v) {
		v--;
		v |= v >> 1;
		v |= v >> 2;
		v |= v >> 4;
		v |= v >> 8;
		v |= v >> 16;
		v++;
		return v;
	}

OXT_FORCE_INLINE
	static bool isCookieHeader(const Header *header) {
		return header->hash == HTTP_COOKIE.hash()
			&& psg_lstr_cmp(&header->key, HTTP_COOKIE);
	}

OXT_FORCE_INLINE
	static bool isSetCookieHeader(const Header *header) {
		return header->hash == HTTP_SET_COOKIE.hash()
			&& psg_lstr_cmp(&header->key, HTTP_SET_COOKIE);
	}

void repopulate(unsigned int desiredSize) {
		assert((desiredSize & (desiredSize - 1)) == 0);   // Must be a power of 2
		assert(m_population * 4  <= desiredSize * 3);

// Get start/end pointers of old array
		Cell *oldCells = m_cells;
		Cell *end = m_cells + m_arraySize;

// Allocate new array
		m_arraySize = desiredSize;
		m_cells = new Cell[m_arraySize];
		memset(m_cells, 0, sizeof(Cell) * m_arraySize);

if (oldCells == NULL) {
			return;
		}

// Iterate through old array
		for (Cell *oldCell = oldCells; oldCell != end; oldCell++) {
			if (!cellIsEmpty(oldCell)) {
				// Insert this element into new array
				Cell *newCell = PHT_FIRST_CELL(oldCell->header->hash);
				while (true) {
					if (cellIsEmpty(newCell)) {
						// Insert here
						*newCell = *oldCell;
						break;
					} else {
						newCell = PHT_CIRCULAR_NEXT(newCell);
					}
				}
			}
		}

// Delete old array
		delete[] oldCells;
	}

void copyFrom(const HeaderTable &other) {
		m_arraySize  = other.m_arraySize;
		m_population = other.m_population;
		m_cells      = new Cell[other.m_arraySize];
		memcpy(m_cells, other.m_cells, other.m_arraySize * sizeof(Cell));
	}

public:
	HeaderTable(unsigned int initialSize = DEFAULT_SIZE)
	{
		init(initialSize);
	}

HeaderTable(const HeaderTable &other) {
		copyFrom(other);
	}

~HeaderTable() {
		delete[] m_cells;
	}

HeaderTable &operator=(const HeaderTable &other) {
		delete[] m_cells;
		copyFrom(other);
		return *this;
	}

void init(unsigned int initialSize) {
		assert((initialSize & (initialSize - 1)) == 0);   // Must be a power of 2

m_arraySize = initialSize;
		if (initialSize == 0) {
			m_cells = NULL;
		} else {
			m_cells = new Cell[m_arraySize];
			memset(m_cells, 0, sizeof(Cell) * m_arraySize);
		}
		m_population = 0;
	}

const Cell *lookupCell(const HashedStaticString &key) const {
		assert(!key.empty());
		assert(key.size() < MAX_KEY_LENGTH);

if (m_cells == NULL) {
			return NULL;
		}

const Cell *cell = PHT_FIRST_CELL(key.hash());
		while (true) {
			if (cellIsEmpty(cell)) {
				// Empty cell found.
				return NULL;
			} else if (psg_lstr_cmp(&cell->header->key, key)) {
				// Non-empty cell found.
				return cell;
			} else {
				// Keep probing.
				cell = PHT_CIRCULAR_NEXT(cell);
			}
		}
	}

OXT_FORCE_INLINE
	Cell *lookupCell(const HashedStaticString &key) {
		return const_cast<Cell *>(static_cast<const HeaderTable *>(this)->lookupCell(key));
	}

OXT_FORCE_INLINE
	Header *lookupHeader(const HashedStaticString &key) {
		Cell *cell = lookupCell(key);
		if (cell != NULL) {
			return cell->header;
		} else {
			return NULL;
		}
	}

const LString *lookup(const HashedStaticString &key) const {
		const Cell * const cell = lookupCell(key);
		if (cell != NULL) {
			return &cell->header->val;
		} else {
			return NULL;
		}
	}

OXT_FORCE_INLINE
	LString *lookup(const HashedStaticString &key) {
		return const_cast<LString *>(static_cast<const HeaderTable *>(this)->lookup(key));
	}

/**
	 * HeaderTable takes over ownership of `header`. But you must ensure that the pool
	 * that the header was allocated from is not destroyed before the HeaderTable
	 * is destroyed or cleared.
	 */
	void insert(Header **headerPtr, psg_pool_t *pool) {
		Header *header = *headerPtr;
		assert(header->key.size < MAX_KEY_LENGTH);

if (m_cells == NULL) {
			repopulate(DEFAULT_SIZE);
		}

while (true) {
			Cell *cell = PHT_FIRST_CELL(header->hash);
			while (true) {
				if (cellIsEmpty(cell)) {
					// Cell is empty. Insert here.
					if (shouldRepopulateOnInsert()) {
						// Time to resize
						repopulate(m_arraySize * 2);
						break;
					}
					m_population++;

cell->header = header;
					*headerPtr = NULL;
					return;
				} else if (psg_lstr_cmp(&cell->header->key, &header->key)) {
					// Cell matches, so merge value into header.
					if (isCookieHeader(header)) {
						psg_lstr_append(&cell->header->val, pool, ";", 1);
					} else if (isSetCookieHeader(header)) {
						psg_lstr_append(&cell->header->val, pool, "\n", 1);
					} else {
						psg_lstr_append(&cell->header->val, pool, ",", 1);
					}
					psg_lstr_move_and_append(&header->val, pool,
						&cell->header->val);
					psg_lstr_deinit(&header->key);
					psg_lstr_deinit(&header->origKey);
					*headerPtr = NULL;
					return;
				} else {
					cell = PHT_CIRCULAR_NEXT(cell);
				}
			}
		}
	}

Header *insert(psg_pool_t *pool, const StaticString &name,
		const StaticString &value)
	{
		Header *header = (Header *) psg_palloc(pool, sizeof(Header));

char *downcasedName = (char *) psg_pnalloc(pool, name.size());
		convertLowerCase((const unsigned char *) name.data(),
			(unsigned char *) downcasedName, name.size());
		psg_lstr_init(&header->key);
		psg_lstr_append(&header->key, pool, downcasedName, name.size());

psg_lstr_init(&header->origKey);
		psg_lstr_append(&header->origKey, pool, name.data(), name.size());

psg_lstr_init(&header->val);
		psg_lstr_append(&header->val, pool, value.data(), value.size());

header->hash = HashedStaticString(downcasedName, name.size()).hash();
		insert(&header, pool);
		return header;
	}

void erase(Cell *cell) {
		assert(cell >= m_cells && cell - m_cells < m_arraySize);
		assert(!cellIsEmpty(cell));

// Remove this cell by shuffling neighboring cells so there are no gaps in anyone's probe chain
		Cell *neighbor = PHT_CIRCULAR_NEXT(cell);
		while (true) {
			if (cellIsEmpty(neighbor)) {
				// There's no neighbor to move. Go ahead and clear this cell, then return.
				if (cell->header != NULL) {
					// A previous iteration in this loop
					// could have made cell->header NULL.
					psg_lstr_deinit(&cell->header->key);
					psg_lstr_deinit(&cell->header->origKey);
					psg_lstr_deinit(&cell->header->val);
					cell->header = NULL;
				}
				m_population--;
				return;
			}

Cell *ideal = PHT_FIRST_CELL(neighbor->header->hash);
			if (PHT_CIRCULAR_OFFSET(ideal, cell) < PHT_CIRCULAR_OFFSET(ideal, neighbor)) {
				// Erase current cell and move neighbor into this position,
				// then make the now-empty neighbor the new cell to remove.
				if (cell->header != NULL) {
					// A previous iteration in this loop
					// could have made cell->header NULL.
					psg_lstr_deinit(&cell->header->key);
					psg_lstr_deinit(&cell->header->origKey);
					psg_lstr_deinit(&cell->header->val);
				}
				*cell = *neighbor;
				cell = neighbor;
				neighbor->header = NULL;
			}
			neighbor = PHT_CIRCULAR_NEXT(neighbor);
		}
	}

void erase(const HashedStaticString &key) {
		Cell *cell = lookupCell(key);
		if (cell != NULL) {
			erase(cell);
		}
	}

/** Does not resize the array. */
	void clear() {
		if (m_cells != NULL && m_population != 0) {
			memset(m_cells, 0, sizeof(Cell) * m_arraySize);
		}
		m_population = 0;
	}

void freeMemory() {
		delete[] m_cells;
		m_cells = NULL;
		m_arraySize  = 0;
		m_population = 0;
	}

void compact() {
		repopulate(upper_power_of_two((m_population * 4 + 3) / 3));
	}

unsigned int size() const {
		return m_population;
	}

unsigned int arraySize() const {
		return m_arraySize;
	}

void debug(psg_pool_t *pool) const {
		for (unsigned int i = 0; i < m_arraySize; i++) {
			int size = -1;
			int ideal = -1;
			unsigned int hash = 0;
			const char *key = "";
			if (!cellIsEmpty(&m_cells[i])) {
				size = m_cells[i].header->key.size;
				hash = m_cells[i].header->hash;
				ideal = int(PHT_FIRST_CELL(m_cells[i].header->hash) - m_cells);
				if (size > 0) {
					const LString *str = psg_lstr_null_terminate(
						&m_cells[i].header->key, pool);
					key = str->start->data;
				}
			}
			printf("%u: key=(%s), size=%d, hash=%u, ideal index=%u\n",
				i, key, size, hash, ideal);
		}
	}

friend class Iterator;
	class Iterator {
	private:
		HeaderTable *m_table;
		Cell *m_cur;

public:
		Iterator(HeaderTable &table)
			: m_table(&table)
		{
			if (m_table->m_cells != NULL) {
				m_cur = &m_table->m_cells[0];
				if (m_table->cellIsEmpty(m_cur)) {
					next();
				}
			} else {
				m_cur = NULL;
			}
		}

Cell *next() {
			if (m_cur == NULL) {
				// Already finished.
				return NULL;
			}

Cell *end = m_table->m_cells + m_table->m_arraySize;
			while (++m_cur != end) {
				if (!m_table->cellIsEmpty(m_cur)) {
					return m_cur;
				}
			}

// Finished
			return m_cur = NULL;
		}

OXT_FORCE_INLINE
		Cell *operator*() const {
			return m_cur;
		}

OXT_FORCE_INLINE
		Cell *operator->() const {
			return m_cur;
		}
	};

friend class ConstIterator;
	class ConstIterator {
	private:
		const HeaderTable *m_table;
		const Cell *m_cur;

public:
		ConstIterator(const HeaderTable &table)
			: m_table(&table)
		{
			if (m_table->m_cells != NULL) {
				m_cur = &m_table->m_cells[0];
				if (m_table->cellIsEmpty(m_cur)) {
					next();
				}
			} else {
				m_cur = NULL;
			}
		}

const Cell *next() {
			if (m_cur == NULL) {
				// Already finished.
				return NULL;
			}

const Cell *end = m_table->m_cells + m_table->m_arraySize;
			while (++m_cur != end) {
				if (!m_table->cellIsEmpty(m_cur)) {
					return m_cur;
				}
			}

// Finished
			m_cur = NULL;
			return NULL;
		}

OXT_FORCE_INLINE
		const Cell *operator*() const {
			return m_cur;
		}

OXT_FORCE_INLINE
		const Cell *operator->() const {
			return m_cur;
		}
	};
};

} // namespace ServerKit
} // namespace Passenger

#endif /* _PASSENGER_SERVER_KIT_HEADER_TABLE_H_ */

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