%
% (c) The GRASP/AQUA Project, Glasgow University, 1995
%
\subsection[env.lc]{Environment Handling for LibPosix}

Many useful environment functions are not necessarily provided by libc.
To get around this problem, we introduce our own.  The first time that
you modify your environment, we copy the environment wholesale into
malloc'ed locations, so that subsequent modifications can do proper
memory management.  The $environ$ variable is updated with a pointer
to the current environment so that the normal $getenv$ and $exec*$ functions
should continue to work properly.

\begin{code}

#include "rtsdefs.h"
#include "stgio.h"
#include "libposix.h"

/* Switch this on once we've moved the environment to the malloc arena */
int dirtyEnv = 0;

/* 
 * For some reason, OSF turns off the prototype for this if we're _POSIX_SOURCE.
 * Seems to me that this ought to be an ANSI-ism rather than a POSIX-ism,
 * but no matter.
 */

char *
strdup(const char *src)
{
    int len = strlen(src) + 1;
    char *dst;

    if ((dst = malloc(len)) != NULL)
	memcpy(dst, src, len);
    return dst;
}

/* Replace the entire environment */
int
setenviron(envp)
char **envp;
{
    char **old = environ;
    int dirtyOld = dirtyEnv;
    int i;

    /* A quick hack to move the strings out of the heap */
    environ = envp;
    if (copyenv() != 0) {
	environ = old;
	return -1;
    }
    /* Release the old space if we allocated it ourselves earlier */
    if (dirtyOld) {
	for (i = 0; old[i] != NULL; i++)
	    free(old[i]);
	free(old);
    }
    return 0;
}

/* Copy initial environment into malloc arena */
int
copyenv()
{
    char **new;
    int i;

    for (i = 0; environ[i] != NULL; i++);

    if ((new = (char **) malloc((i + 1) * sizeof(char *))) == NULL)
	 return -1;

    new[i] = NULL;

    while (--i >= 0) {
	if ((new[i] = strdup(environ[i])) == NULL) {
	    while (new[++i] != NULL)
		free(new[i]);
	    free(new);
	    return -1;
	}
    }
    environ = new;
    dirtyEnv = 1;
    return 0;
}

/* Set or replace an environment variable */
int
setenv(mapping)
char *mapping;
{
    int i, keylen;
    char *p;
    char **new;

    /* We must have a non-empty key and an '=' */
    if (mapping[0] == '=' || (p = strchr(mapping, '=')) == NULL) {
	errno = EINVAL;
	return -1;
    }
    /* Include through the '=' for matching */
    keylen = p - mapping + 1;

    if (!dirtyEnv && copyenv() != 0)
	return -1;

    if ((p = strdup(mapping)) == NULL)
	return -1;

    /* Look for an existing key that matches */
    for (i = 0; environ[i] != NULL && strncmp(environ[i], p, keylen) != 0; i++);

    if (environ[i] != NULL) {
	free(environ[i]);
	environ[i] = p;
    } else {
	if ((new = (char **) realloc(environ, (i + 1) * sizeof(char *))) == NULL) {
	    free(p);
	    return -1;
	}
	new[i] = p;
	new[i + 1] = NULL;
	environ = new;
    }
    return 0;
}

/* Delete a variable from the environment */
int
delenv(name)
char *name;
{
    int i, keylen;

    if (strchr(name, '=') != NULL) {
	errno = EINVAL;
	return -1;
    }
    keylen = strlen(name);

    if (!dirtyEnv && copyenv() != 0)
	return -1;

    /* Look for a matching key */
    for (i = 0; environ[i] != NULL &&
      (strncmp(environ[i], name, keylen) != 0 || environ[i][keylen] != '='); i++);

    /* Don't complain if it wasn't there to begin with */
    if (environ[i] == NULL) {
	return 0;
    }
    free(environ[i]);

    do {
	environ[i] = environ[i + 1];
	i++;
    } while (environ[i] != NULL);

    return 0;
}

\end{code}