Subversion Repositories SvarDOS

/* This file is part of the SvarCOM project and is published under the terms

 * of the MIT license.

 *

 * Copyright (C) 2021-2024 Mateusz Viste

 *

 * 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.

 */

/*

 * routines used to manipulate the environment block

 */

#include <i86.h>

#include <string.h>

#include "env.h"

/* looks for varname in environment block and returns a far ptr to it if

 * found, NULL otherwise. varname MUST be in upper-case and MUST be terminated

 * by either a = sign or a NULL terminator */

char far *env_lookup(unsigned short env_seg, const char *varname) {

  char far *env = MK_FP(env_seg, 0);

  int i;

  for (;;) {

    /* end of environment block? */

    if (*env == 0) return(NULL);

    /* is this it? */

    for (i = 0;; i++) {

      if ((varname[i] == '=') || (varname[i] == 0)) {

        if (env[i] == '=') return(env); /* FOUND! */

        break; /* else look for next string */

      }

      if (varname[i] != env[i]) break;

    }

    /* move env to end of current string */

    while (*env != 0) env++;

    /* move to next variable */

    env++;

  }

}

/* almost identical to env_lookup(), but instead of returning a pointer

 * to the 'NAME=value' string, it returns a pointer to value (or NULL if

 * var not found) */

char far *env_lookup_val(unsigned short env_seg, const char *varname) {

  char far *r = env_lookup(env_seg, varname);

  if (r == NULL) return(NULL);

  /* find '=' or end of string */

  for (;;) {

    if (*r == '=') return(r + 1);

    if (*r == 0) return(r);

    r++;

  }

}

/* locates the value of env variable varname and copies it to result, up to

 * ressz bytes (incl. the NULL terminator). returns the length of the value on

 * success, 0 if var not found or couldn't fit in ressz). */

unsigned short env_lookup_valcopy(char *res, unsigned short ressz, unsigned short env_seg, const char *varname) {

  unsigned short i;

  char far *v = env_lookup_val(env_seg, varname);

  if (v == NULL) return(0);

  for (i = 0;; i++) {

    if (ressz-- == 0) return(0);

    res[i] = v[i];

    if (res[i] == 0) return(i);

  }

}

/* returns the size, in bytes, of the allocated environment block */

unsigned short env_allocsz(unsigned short env_seg) {

  unsigned short far *mcbsz = MK_FP(env_seg - 1, 3); /* block size is a word at offset +3 in the MCB */

  return(*mcbsz * 16); /* return size in bytes, not paragraphs */

}

/* return currently used space (length, in bytes) of the environment */

unsigned short env_getcurlen(unsigned short env_seg) {

  char far *env = MK_FP(env_seg, 0);

  unsigned short envlen;

  for (envlen = 0; env[envlen] != 0; envlen++) {

    while (env[envlen] != 0) envlen++; /* consume a string */

  }

  return(envlen);

}

/* remove a variable from environment, if present. returns 0 on success, non-zero if variable not found */

int env_dropvar(unsigned short env_seg, const char *varname) {

  unsigned short blocksz, traillen;

  unsigned short len;

  char far *varptr = env_lookup(env_seg, varname);

  /* if variable not found in environment, quit now */

  if (varptr == NULL) return(-1);

  for (len = 0; varptr[len] != 0; len++); /* compute length of variable (without trailing null) */

  blocksz = env_allocsz(env_seg);           /* total environment size */

  traillen = blocksz - (FP_OFF(varptr) + len + 1); /* how much bytes are present after the variable */

  _fmemset(varptr, 0, len);               /* zero out the variable */

  if (traillen != 0) {

    _fmemmove(varptr, varptr + len + 1, traillen); /* move rest of memory */

  }

  return(0);

}

/* Writes a variable to environment block. The variable must in the form

 * "VARNAME=value". If variable is already present in the environment block,

 * then the value will be updated. If the new value is empty, then the

 * existing variable (if any) is removed.

 * VARNAME *MUST* be all-uppercase.

 *

 * This function returns:

 *   ENV_SUCCESS = success

 *   ENV_NOTENOM = not enough available space in memory block

 *   ENV_INVSYNT = invalid syntax

 */

int env_setvar(unsigned short env_seg, const char *v) {

  unsigned short envlen;

  unsigned short vlen, veqpos;

  char far *env = MK_FP(env_seg, 0);

  char far *alreadyexists;

  unsigned short alreadyexistslen;

  /* compute v length and find the position of the eq sign */

  veqpos = 0xffff;

  for (vlen = 0; v[vlen] != 0; vlen++) {

    if (v[vlen] == '=') {

      if (veqpos != 0xffff) return(ENV_INVSYNT); /* equal sign is forbidden in value */

      veqpos = vlen;

    }

  }

  /* get length of the current environment */

  envlen = env_getcurlen(env_seg);

  /* does the variable already exist? */

  alreadyexists = env_lookup(env_seg, v);

  alreadyexistslen = 0;

  if (alreadyexists != NULL) {

    while (alreadyexists[alreadyexistslen] != 0) alreadyexistslen++;

  }

  /* do I have enough env space for the new var? */

  if (envlen + vlen + 3 - alreadyexistslen >= env_allocsz(env_seg)) {

    return(ENV_NOTENOM);

  }

  /* remove variable from environment if already set and recompute environment's length */

  env_dropvar(env_seg, v);

  envlen = env_getcurlen(env_seg);

  /* if variable empty, stop here */

  if (veqpos == vlen - 1) return(ENV_SUCCESS);

  /* write the new variable (with its NULL terminator) to environment tail */

  _fmemcpy(env + envlen, v, vlen + 1);

  /* add the environment's NULL terminator */

  env[envlen + vlen + 1] = 0;

  return(ENV_SUCCESS);

}