bind/lib/isc/symtab.c

/*
 * Copyright (C) Internet Systems Consortium, Inc. ("ISC")
 *
 * SPDX-License-Identifier: MPL-2.0
 *
 * This Source Code Form is subject to the terms of the Mozilla Public
 * License, v. 2.0. If a copy of the MPL was not distributed with this
 * file, you can obtain one at https://mozilla.org/MPL/2.0/.
 *
 * See the COPYRIGHT file distributed with this work for additional
 * information regarding copyright ownership.
 */

/*! \file */

#include <stdbool.h>

#include <isc/ascii.h>
#include <isc/magic.h>
#include <isc/mem.h>
#include <isc/string.h>
#include <isc/symtab.h>
#include <isc/util.h>

typedef struct elt {
	char *key;
	unsigned int type;
	isc_symvalue_t value;
	LINK(struct elt) link;
} elt_t;

typedef LIST(elt_t) eltlist_t;

#define SYMTAB_MAGIC	 ISC_MAGIC('S', 'y', 'm', 'T')
#define VALID_SYMTAB(st) ISC_MAGIC_VALID(st, SYMTAB_MAGIC)

struct isc_symtab {
	/* Unlocked. */
	unsigned int magic;
	isc_mem_t *mctx;
	unsigned int size;
	unsigned int count;
	unsigned int maxload;
	eltlist_t *table;
	isc_symtabaction_t undefine_action;
	void *undefine_arg;
	bool case_sensitive;
};

void
isc_symtab_create(isc_mem_t *mctx, unsigned int size,
		  isc_symtabaction_t undefine_action, void *undefine_arg,
		  bool case_sensitive, isc_symtab_t **symtabp) {
	isc_symtab_t *symtab;
	unsigned int i;

	REQUIRE(mctx != NULL);
	REQUIRE(symtabp != NULL && *symtabp == NULL);
	REQUIRE(size > 0); /* Should be prime. */

	symtab = isc_mem_get(mctx, sizeof(*symtab));

	symtab->mctx = NULL;
	isc_mem_attach(mctx, &symtab->mctx);
	symtab->table = isc_mem_cget(mctx, size, sizeof(eltlist_t));
	for (i = 0; i < size; i++) {
		INIT_LIST(symtab->table[i]);
	}
	symtab->size = size;
	symtab->count = 0;
	symtab->maxload = size * 3 / 4;
	symtab->undefine_action = undefine_action;
	symtab->undefine_arg = undefine_arg;
	symtab->case_sensitive = case_sensitive;
	symtab->magic = SYMTAB_MAGIC;

	*symtabp = symtab;
}

void
isc_symtab_destroy(isc_symtab_t **symtabp) {
	isc_symtab_t *symtab;
	unsigned int i;
	elt_t *elt, *nelt;

	REQUIRE(symtabp != NULL);
	symtab = *symtabp;
	*symtabp = NULL;
	REQUIRE(VALID_SYMTAB(symtab));

	for (i = 0; i < symtab->size; i++) {
		for (elt = HEAD(symtab->table[i]); elt != NULL; elt = nelt) {
			nelt = NEXT(elt, link);
			if (symtab->undefine_action != NULL) {
				(symtab->undefine_action)(elt->key, elt->type,
							  elt->value,
							  symtab->undefine_arg);
			}
			isc_mem_put(symtab->mctx, elt, sizeof(*elt));
		}
	}
	isc_mem_cput(symtab->mctx, symtab->table, symtab->size,
		     sizeof(eltlist_t));
	symtab->magic = 0;
	isc_mem_putanddetach(&symtab->mctx, symtab, sizeof(*symtab));
}

static unsigned int
hash(const char *key, bool case_sensitive) {
	const char *s;
	unsigned int h = 0;

	/*
	 * This hash function is similar to the one Ousterhout
	 * uses in Tcl.
	 */

	if (case_sensitive) {
		for (s = key; *s != '\0'; s++) {
			h += (h << 3) + *s;
		}
	} else {
		for (s = key; *s != '\0'; s++) {
			h += (h << 3) + isc_ascii_tolower(*s);
		}
	}

	return h;
}

#define FIND(s, k, t, b, e)                                                   \
	b = hash((k), (s)->case_sensitive) % (s)->size;                       \
	if ((s)->case_sensitive) {                                            \
		for (e = HEAD((s)->table[b]); e != NULL; e = NEXT(e, link)) { \
			if (((t) == 0 || e->type == (t)) &&                   \
			    strcmp(e->key, (k)) == 0)                         \
				break;                                        \
		}                                                             \
	} else {                                                              \
		for (e = HEAD((s)->table[b]); e != NULL; e = NEXT(e, link)) { \
			if (((t) == 0 || e->type == (t)) &&                   \
			    strcasecmp(e->key, (k)) == 0)                     \
				break;                                        \
		}                                                             \
	}

isc_result_t
isc_symtab_lookup(isc_symtab_t *symtab, const char *key, unsigned int type,
		  isc_symvalue_t *value) {
	unsigned int bucket;
	elt_t *elt;

	REQUIRE(VALID_SYMTAB(symtab));
	REQUIRE(key != NULL);

	FIND(symtab, key, type, bucket, elt);

	if (elt == NULL) {
		return ISC_R_NOTFOUND;
	}

	SET_IF_NOT_NULL(value, elt->value);

	return ISC_R_SUCCESS;
}

static void
grow_table(isc_symtab_t *symtab) {
	eltlist_t *newtable;
	unsigned int i, newsize, newmax;

	REQUIRE(symtab != NULL);

	newsize = symtab->size * 2;
	newmax = newsize * 3 / 4;
	INSIST(newsize > 0U && newmax > 0U);

	newtable = isc_mem_cget(symtab->mctx, newsize, sizeof(eltlist_t));

	for (i = 0; i < newsize; i++) {
		INIT_LIST(newtable[i]);
	}

	for (i = 0; i < symtab->size; i++) {
		elt_t *elt, *nelt;

		for (elt = HEAD(symtab->table[i]); elt != NULL; elt = nelt) {
			unsigned int hv;

			nelt = NEXT(elt, link);

			UNLINK(symtab->table[i], elt, link);
			hv = hash(elt->key, symtab->case_sensitive);
			APPEND(newtable[hv % newsize], elt, link);
		}
	}

	isc_mem_cput(symtab->mctx, symtab->table, symtab->size,
		     sizeof(eltlist_t));

	symtab->table = newtable;
	symtab->size = newsize;
	symtab->maxload = newmax;
}

isc_result_t
isc_symtab_define(isc_symtab_t *symtab, const char *key, unsigned int type,
		  isc_symvalue_t value, isc_symexists_t exists_policy) {
	unsigned int bucket;
	elt_t *elt;

	REQUIRE(VALID_SYMTAB(symtab));
	REQUIRE(key != NULL);
	REQUIRE(type != 0);

	FIND(symtab, key, type, bucket, elt);

	if (exists_policy != isc_symexists_add && elt != NULL) {
		if (exists_policy == isc_symexists_reject) {
			return ISC_R_EXISTS;
		}
		INSIST(exists_policy == isc_symexists_replace);
		UNLINK(symtab->table[bucket], elt, link);
		if (symtab->undefine_action != NULL) {
			(symtab->undefine_action)(elt->key, elt->type,
						  elt->value,
						  symtab->undefine_arg);
		}
	} else {
		elt = isc_mem_get(symtab->mctx, sizeof(*elt));
		ISC_LINK_INIT(elt, link);
		symtab->count++;
	}

	/*
	 * Though the "key" can be const coming in, it is not stored as const
	 * so that the calling program can easily have writable access to
	 * it in its undefine_action function.  In the event that it *was*
	 * truly const coming in and then the caller modified it anyway ...
	 * well, don't do that!
	 */
	elt->key = UNCONST(key);
	elt->type = type;
	elt->value = value;

	/*
	 * We prepend so that the most recent definition will be found.
	 */
	PREPEND(symtab->table[bucket], elt, link);

	if (symtab->count > symtab->maxload) {
		grow_table(symtab);
	}

	return ISC_R_SUCCESS;
}

isc_result_t
isc_symtab_undefine(isc_symtab_t *symtab, const char *key, unsigned int type) {
	unsigned int bucket;
	elt_t *elt;

	REQUIRE(VALID_SYMTAB(symtab));
	REQUIRE(key != NULL);

	FIND(symtab, key, type, bucket, elt);

	if (elt == NULL) {
		return ISC_R_NOTFOUND;
	}

	if (symtab->undefine_action != NULL) {
		(symtab->undefine_action)(elt->key, elt->type, elt->value,
					  symtab->undefine_arg);
	}
	UNLINK(symtab->table[bucket], elt, link);
	isc_mem_put(symtab->mctx, elt, sizeof(*elt));
	symtab->count--;

	return ISC_R_SUCCESS;
}

unsigned int
isc_symtab_count(isc_symtab_t *symtab) {
	REQUIRE(VALID_SYMTAB(symtab));
	return symtab->count;
}