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421 mateuszvis 1
/* This file is part of the SvarCOM project and is published under the terms
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 * of the MIT license.
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 *
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 * Copyright (C) 2021-2022 Mateusz Viste
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 *
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 * Permission is hereby granted, free of charge, to any person obtaining a
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 * copy of this software and associated documentation files (the "Software"),
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 * to deal in the Software without restriction, including without limitation
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 * the rights to use, copy, modify, merge, publish, distribute, sublicense,
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 * and/or sell copies of the Software, and to permit persons to whom the
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 * Software is furnished to do so, subject to the following conditions:
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 *
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 * The above copyright notice and this permission notice shall be included in
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 * all copies or substantial portions of the Software.
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 *
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 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
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 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
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 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
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 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
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 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
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 * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
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 * DEALINGS IN THE SOFTWARE.
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 */
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/*
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 * routines used to manipulate the environment block
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 */
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#include <i86.h>
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#include <string.h>
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#include "env.h"
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/* looks for varname in environment block and returns a far ptr to it if
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 * found, NULL otherwise. varname MUST be in upper-case and MUST be terminated
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 * by either a = sign or a NULL terminator */
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char far *env_lookup(unsigned short env_seg, const char *varname) {
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  char far *env = MK_FP(env_seg, 0);
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  int i;
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  for (;;) {
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    /* is this it? */
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    for (i = 0;; i++) {
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      if ((varname[i] == '=') || (varname[i] == 0)) {
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        if (env[i] == '=') return(env); /* FOUND! */
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        break; /* else look for next string */
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      }
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      if (varname[i] != env[i]) break;
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    }
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    /* move env to end of current string */
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    while (*env != 0) env++;
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    /* if there's another trailing zero, then that is the end of environment */
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    env++;
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    if (*env == 0) return(NULL);
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  }
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}
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/* almost identical to env_lookup(), but instead of returning a pointer
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 * to the 'NAME=value' string, it returns a pointer to value (or NULL if
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 * var not found) */
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char far *env_lookup_val(unsigned short env_seg, const char *varname) {
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  char far *r = env_lookup(env_seg, varname);
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  if (r == NULL) return(NULL);
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  /* find '=' or end of string */
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  for (;;) {
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    if (*r == '=') return(r + 1);
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    if (*r == 0) return(r);
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    r++;
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  }
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}
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/* locates the value of env variable varname and copies it to result, up to
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 * ressz bytes (incl. the NULL terminator). returns the length of the value on
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 * success, 0 if var not found or couldn't fit in ressz). */
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unsigned short env_lookup_valcopy(char *res, unsigned short ressz, unsigned short env_seg, const char *varname) {
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  unsigned short i;
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  char far *v = env_lookup_val(env_seg, varname);
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  if (v == NULL) return(0);
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  for (i = 0;; i++) {
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    if (ressz-- == 0) return(0);
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    res[i] = v[i];
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    if (res[i] == 0) return(i);
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  }
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}
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/* returns the size, in bytes, of the allocated environment block */
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unsigned short env_allocsz(unsigned short env_seg) {
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  unsigned short far *mcbsz = MK_FP(env_seg - 1, 3); /* block size is a word at offset +3 in the MCB */
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  return(*mcbsz * 16); /* return size in bytes, not paragraphs */
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}
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/* remove a variable from environment, if present. returns 0 on success, non-zero if variable not found */
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int env_dropvar(unsigned short env_seg, const char *varname) {
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  unsigned short blocksz, traillen;
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  unsigned short len;
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  char far *varptr = env_lookup(env_seg, varname);
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  /* if variable not found in environment, quit now */
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  if (varptr == NULL) return(-1);
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  for (len = 0; varptr[len] != 0; len++); /* compute length of variable (without trailing null) */
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  blocksz = env_allocsz(env_seg);           /* total environment size */
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  traillen = blocksz - (FP_OFF(varptr) + len + 1); /* how much bytes are present after the variable */
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  _fmemset(varptr, 0, len);               /* zero out the variable */
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  if (traillen != 0) {
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    _fmemmove(varptr, varptr + len + 1, traillen); /* move rest of memory */
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  }
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  return(0);
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}
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/* Writes a variable to environment block. The variable must in the form
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 * "VARNAME=value". If variable is already present in the environment block,
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 * then the value will be updated. If the new value is empty, then the
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 * existing variable (if any) is removed.
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 * VARNAME *MUST* be all-uppercase.
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 *
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 * This function returns:
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 *   ENV_SUCCESS = success
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 *   ENV_NOTENOM = not enough available space in memory block
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 *   ENV_INVSYNT = invalid syntax
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 */
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int env_setvar(unsigned short env_seg, const char *v) {
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  unsigned short envlen;
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  unsigned short envfree;
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  unsigned short vlen, veqpos;
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  char far *env = MK_FP(env_seg, 0);
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  /* remove variable from environment, if already set */
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  env_dropvar(env_seg, v);
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  /* compute v length and find the position of the eq sign */
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  veqpos = 0xffff;
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  for (vlen = 0; v[vlen] != 0; vlen++) {
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    if (v[vlen] == '=') {
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      if (veqpos != 0xffff) return(ENV_INVSYNT); /* equal sign is forbidden in value */
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      veqpos = vlen;
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    }
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  }
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  /* if variable empty, stop here */
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  if (veqpos == vlen - 1) return(ENV_SUCCESS);
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  /* compute current size of the environment */
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  for (envlen = 0; env[envlen] != 0; envlen++) {
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    while (env[envlen] != 0) envlen++; /* consume a string */
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  }
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  /* compute free space available in environment */
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  envfree = env_allocsz(env_seg);
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  envfree -= envlen;
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  envfree -= 1; /* 1 byte for the environment's NULL terminator */
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  /* do I have enough env space for the new var? */
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  if (envfree < vlen + 1) return(ENV_NOTENOM);
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  /* write the new variable (with its NULL terminator) to environment tail */
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  _fmemcpy(env + envlen, v, vlen + 1);
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  /* add the environment's NULL terminator */
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  env[envlen + vlen + 1] = 0;
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  return(ENV_SUCCESS);
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}