/*      $NetBSD: _env.c,v 1.15 2024/01/02 19:27:26 christos Exp $ */

/*-
 * Copyright (c) 2010 The NetBSD Foundation, Inc.
 * All rights reserved.
 *
 * This code is derived from software contributed to The NetBSD Foundation
 * by Matthias Scheler.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 *
 * THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS
 * ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
 * TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
 * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS
 * BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
 * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
 * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
 * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
 * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
 * POSSIBILITY OF SUCH DAMAGE.
 */

#include <sys/cdefs.h>
#if defined(LIBC_SCCS) && !defined(lint)
__RCSID("$NetBSD: _env.c,v 1.15 2024/01/02 19:27:26 christos Exp $");
#endif /* LIBC_SCCS and not lint */

#include "namespace.h"

#include <sys/rbtree.h>

#include <assert.h>
#include <errno.h>
#include <limits.h>
#include <stdlib.h>
#include <stddef.h>
#include <string.h>
#include "csu-common.h"

#include "env.h"
#include "local.h"

/*
 * Red-Black tree node for tracking memory used by environment variables.
 * The tree is sorted by the address of the nodes themselves.
 */
typedef struct {
        rb_node_t       rb_node;
        size_t          length;
        uint8_t         marker;
        char            data[];
} env_node_t;

/* Compare functions for above tree. */
static signed int env_tree_compare_nodes(void *, const void *, const void *);
static signed int env_tree_compare_key(void *, const void *, const void *);

/* Operations for above tree. */
static const rb_tree_ops_t env_tree_ops = {
        .rbto_compare_nodes = env_tree_compare_nodes,
        .rbto_compare_key = env_tree_compare_key,
        .rbto_node_offset = offsetof(env_node_t, rb_node),
        .rbto_context = NULL
};

/* The single instance of above tree. */
static rb_tree_t        env_tree =
    RB_TREE_INITIALIZER(env_tree, &env_tree_ops);

/* The allocated environment. */
static char     **allocated_environ;
static size_t   allocated_environ_size;

#define ENV_ARRAY_SIZE_MIN      16

/* The lock protecting access to the environment. */
#ifdef _REENTRANT
static rwlock_t env_lock = RWLOCK_INITIALIZER;
#endif

/* Compatibility function. */
extern char *__findenv(const char *name, int *offsetp);

__warn_references(__findenv,
    "warning: __findenv is an internal obsolete function.")

/* Our initialization function. */
void __libc_env_init(void);

/*ARGSUSED*/
static signed int
env_tree_compare_nodes(void *ctx, const void *node_a, const void *node_b)
{
        uintptr_t addr_a, addr_b;

        addr_a = (uintptr_t)node_a;
        addr_b = (uintptr_t)node_b;

        if (addr_a < addr_b)
                return -1;

        if (addr_a > addr_b)
                return 1;

        return 0;
}

static signed int
env_tree_compare_key(void *ctx, const void *node, const void *key)
{
        return env_tree_compare_nodes(ctx, node,
            (const uint8_t *)key - offsetof(env_node_t, data));
}

/*
 * Determine the of the name in an environment string. Return 0 if the
 * name is not valid.
 */
size_t
__envvarnamelen(const char *str, bool withequal)
{
        size_t l_name;

        if (str == NULL)
                return 0;

        l_name = strcspn(str, "=");
        if (l_name == 0)
                return 0;

        if (withequal) {
                if (str[l_name] != '=')
                        return 0;
        } else {
                if (str[l_name] == '=')
                        return 0;
        }

        return l_name;
}

/*
 * Free memory occupied by environment variable if possible. This function
 * must be called with the environment write locked.
 */
void
__freeenvvar(char *envvar)
{
        env_node_t *node;

        _DIAGASSERT(envvar != NULL);
        node = rb_tree_find_node(&env_tree, envvar);
        if (node != NULL) {
                rb_tree_remove_node(&env_tree, node);
                free(node);
        }
}

/*
 * Allocate memory for an environment variable. This function must be called
 * with the environment write locked.
 */
char *
__allocenvvar(size_t length)
{
        env_node_t *node;

        node = malloc(sizeof(*node) + length);
        if (node != NULL) {
                node->length = length;
                node->marker = 0;
                rb_tree_insert_node(&env_tree, node);
                return node->data;
        } else {
                return NULL;
        }
}

/*
 * Check whether an environment variable is writable. This function must be
 * called with the environment write locked as the caller will probably
 * overwrite the environment variable afterwards.
 */
bool
__canoverwriteenvvar(char *envvar, size_t length)
{
        env_node_t *node;

        _DIAGASSERT(envvar != NULL);

        node = rb_tree_find_node(&env_tree, envvar);
        return (node != NULL && length <= node->length);
}

/* Free all allocated environment variables that are no longer used. */
static void
__scrubenv(void)
{
        static uint8_t marker = 0;
        size_t num_entries;
        env_node_t *node, *next;

        while (++marker == 0);

        /* Mark all nodes which are currently used. */
        for (num_entries = 0; environ[num_entries] != NULL; num_entries++) {
                node = rb_tree_find_node(&env_tree, environ[num_entries]);
                if (node != NULL)
                        node->marker = marker;
        }

        /* Free all nodes which are currently not used. */
        for (node = RB_TREE_MIN(&env_tree); node != NULL; node = next) {
                next = rb_tree_iterate(&env_tree, node, RB_DIR_RIGHT);

                if (node->marker != marker) {
                        rb_tree_remove_node(&env_tree, node);
                        free(node);
                }
        }

        /* Deal with the environment array itself. */
        if (environ == allocated_environ) {
                /* Clear out spurious entries in the environment. */
                (void)memset(&environ[num_entries + 1], 0,
                    (allocated_environ_size - num_entries - 1) *
                    sizeof(*environ));
        } else {
                /*
                 * The environment array was not allocated by "libc".
                 * Free our array if we allocated one.
                 */
                free(allocated_environ);
                allocated_environ = NULL;
                allocated_environ_size = 0;
        }
}

/*
 * Get a (new) slot in the environment. This function must be called with
 * the environment write locked.
 */
ssize_t
__getenvslot(const char *name, size_t l_name, bool allocate)
{
        size_t new_size, num_entries, required_size;
        char **new_environ;

        /* Search for an existing environment variable of the given name. */
        num_entries = 0;
        if (environ != NULL) {
                while (environ[num_entries] != NULL) {
                        if (strncmp(environ[num_entries], name, l_name) == 0 &&
                            environ[num_entries][l_name] == '=') {
                                /* We found a match. */
                                return num_entries;
                        }
                        num_entries ++;
                }
        }

        /* No match found, return if we don't want to allocate a new slot. */
        if (!allocate)
                return -1;

        /* Does the environ need scrubbing? */
        if (environ != allocated_environ && allocated_environ != NULL)
                __scrubenv();

        /* Create a new slot in the environment. */
        required_size = num_entries + 1;
        if (environ == allocated_environ &&
            required_size < allocated_environ_size) {
                /* Does the environment need scrubbing? */
                if (required_size < allocated_environ_size &&
                    allocated_environ[required_size] != NULL) {
                        __scrubenv();
                }

                /* Return a free slot. */
                return num_entries;
        }

        /* Determine size of a new environment array. */
        new_size = ENV_ARRAY_SIZE_MIN;
        while (new_size <= required_size)
                new_size <<= 1;

        /* Allocate a new environment array. */
        if (environ == allocated_environ) {
                new_environ = environ;
                errno = reallocarr(&new_environ,
                    new_size, sizeof(*new_environ));
                if (errno)
                        return -1;
        } else {
                free(allocated_environ);
                allocated_environ = NULL;
                allocated_environ_size = 0;

                new_environ = NULL;
                errno = reallocarr(&new_environ,
                    new_size, sizeof(*new_environ));
                if (errno)
                        return -1;
                (void)memcpy(new_environ, environ,
                    num_entries * sizeof(*new_environ));
        }

        /* Clear remaining entries. */
        (void)memset(&new_environ[num_entries], 0,
            (new_size - num_entries) * sizeof(*new_environ));

        /* Use the new environment array. */
        environ = allocated_environ = new_environ;
        allocated_environ_size = new_size;

        /* Return a free slot. */
        return num_entries;
}

/* Find a string in the environment. */
char *
__findenvvar(const char *name, size_t l_name)
{
        ssize_t offset;

        offset = __getenvslot(name, l_name, false);
        return (offset != -1) ? environ[offset] + l_name + 1 : NULL;
}

/* Compatibility interface, do *not* call this function. */
char *
__findenv(const char *name, int *offsetp)
{
        size_t l_name;
        ssize_t offset;

        l_name = __envvarnamelen(name, false);
        if (l_name == 0)
                return NULL;

        offset = __getenvslot(name, l_name, false);
        if (offset < 0 || offset > INT_MAX)
                return NULL;

        *offsetp = (int)offset;
        return environ[offset] + l_name + 1;
}

#ifdef _REENTRANT

/* Lock the environment for read. */
bool
__readlockenv(void)
{
        int error;

        error = rwlock_rdlock(&env_lock);
        if (error == 0)
                return true;

        errno = error;
        return false;
}

/* Lock the environment for write. */
bool
__writelockenv(void)
{
        int error;

        error = rwlock_wrlock(&env_lock);
        if (error == 0)
                return true;

        errno = error;
        return false;
}

/* Unlock the environment for write. */
bool
__unlockenv(void)
{
        int error;

        error = rwlock_unlock(&env_lock);
        if (error == 0)
                return true;

        errno = error;
        return false;
}

#endif