environment.c

/* 
 * Copyright (c) 1998 Michael Smith.
 * All rights reserved.
 *
 * 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 AUTHOR 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 AUTHOR 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.
 */

/*
 * Manage an environment-like space in which string variables may be stored.
 * Provide support for some method-like operations for setting/retrieving
 * variables in order to allow some type strength.
 */

#include "stand.h"

#include <string.h>

struct env_var	*environ = NULL;

/*
 * Look up (name) and return it's env_var structure.
 */
struct env_var	*
env_getenv(const char *name)
{
	struct env_var	*ev;
    
	for (ev = environ; ev != NULL; ev = ev->ev_next)
		if (!strcmp(ev->ev_name, name))
			break;
	return (ev);
}

/*
 * Some notes:
 *
 * If the EV_VOLATILE flag is set, a copy of the variable is made.
 * If EV_DYNAMIC is set, the variable has been allocated with
 * malloc and ownership transferred to the environment.
 * If (value) is NULL, the variable is set but has no value.
 */
int
env_setenv(const char *name, int flags, const void *value,
    ev_sethook_t sethook, ev_unsethook_t unsethook)
{
	struct env_var	*ev, *curr, *last;

	if ((ev = env_getenv(name)) != NULL) {
		/*
		 * If the new value doesn't have NOKENV set, we'll drop the flag
		 * if it's set on the entry so that the override propagates
		 * correctly.  We do this *before* sending it to the hook in
		 * case the hook declines to operate on it (e.g., because the
		 * value matches what was already set) -- we would still want
		 * the explicitly set value to propagate.
		 */
		if (!(flags & EV_NOKENV))
			ev->ev_flags &= ~EV_NOKENV;

		/*
		 * If there's a set hook, let it do the work
		 * (unless we are working for one already).
		 */
		if ((ev->ev_sethook != NULL) && !(flags & EV_NOHOOK))
			return (ev->ev_sethook(ev, flags, value));

		/* If there is data in the variable, discard it. */
		if (ev->ev_value != NULL && (ev->ev_flags & EV_DYNAMIC) != 0)
			free(ev->ev_value);
		ev->ev_value = NULL;
		ev->ev_flags &= ~EV_DYNAMIC;
	} else {

		/*
		 * New variable; create and sort into list
		 */
		ev = malloc(sizeof(struct env_var));
		ev->ev_name = strdup(name);
		ev->ev_value = NULL;
		ev->ev_flags = 0;
		/* hooks can only be set when the variable is instantiated */
		ev->ev_sethook = sethook;
		ev->ev_unsethook = unsethook;

		/* Sort into list */
		ev->ev_prev = NULL;
		ev->ev_next = NULL;
		/* Search for the record to insert before */
		for (last = NULL, curr = environ; curr != NULL;
		    last = curr, curr = curr->ev_next) {

			if (strcmp(ev->ev_name, curr->ev_name) < 0) {
				if (curr->ev_prev) {
					curr->ev_prev->ev_next = ev;
				} else {
					environ = ev;
				}
				ev->ev_next = curr;
				ev->ev_prev = curr->ev_prev;
				curr->ev_prev = ev;
				break;
			}
		}
		if (curr == NULL) {
			if (last == NULL) {
				environ = ev;
			} else {
				last->ev_next = ev;
				ev->ev_prev = last;
			}
		}
	}

	/* If we have a new value, use it */
	if (flags & EV_VOLATILE) {
		ev->ev_value = strdup(value);
		flags |= EV_DYNAMIC;
	} else {
		ev->ev_value = (char *)value;
	}

	ev->ev_flags |= flags & (EV_DYNAMIC | EV_NOKENV);

	return (0);
}

/* coverity[ -tainted_string_return_content ] */
char *
getenv(const char *name)
{
	struct env_var	*ev;

	/* Set but no value gives empty string */
	if ((ev = env_getenv(name)) != NULL) {
		if (ev->ev_value != NULL)
			return (ev->ev_value);
		return ("");
	}
	return (NULL);
}

int
setenv(const char *name, const char *value, int overwrite)
{
	/* No guarantees about state, always assume volatile */
	if (overwrite || (env_getenv(name) == NULL))
		return (env_setenv(name, EV_VOLATILE, value, NULL, NULL));
	return (0);
}

int
putenv(char *string)
{
	char	*value, *copy;
	int	result;

	copy = strdup(string);
	if ((value = strchr(copy, '=')) != NULL)
		*(value++) = 0;
	result = setenv(copy, value, 1);
	free(copy);
	return (result);
}

int
unsetenv(const char *name)
{
	struct env_var	*ev;
	int		err;

	err = 0;
	if ((ev = env_getenv(name)) == NULL) {
		err = ENOENT;
	} else {
		if (ev->ev_unsethook != NULL)
			err = ev->ev_unsethook(ev);
		if (err == 0) {
			env_discard(ev);
		}
	}
	return (err);
}

void
env_discard(struct env_var *ev)
{
	if (ev->ev_prev)
		ev->ev_prev->ev_next = ev->ev_next;
	if (ev->ev_next)
		ev->ev_next->ev_prev = ev->ev_prev;
	if (environ == ev)
		environ = ev->ev_next;
	free(ev->ev_name);
	if (ev->ev_value != NULL && (ev->ev_flags & EV_DYNAMIC) != 0)
		free(ev->ev_value);
	free(ev);
}

int
env_noset(struct env_var *ev __unused, int flags __unused,
    const void *value __unused)
{
	return (EPERM);
}

int
env_nounset(struct env_var *ev __unused)
{
	return (EPERM);
}