89 lines
2 KiB
C
89 lines
2 KiB
C
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#include <stdlib.h>
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#include <string.h>
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#include <stdio.h>
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#include <assert.h>
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#include <ctype.h>
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#include <stdbool.h>
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#include "expand_env.h"
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static bool allowed_env_var_name(char c)
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{
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return c != '\0' &&
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!isblank(c) &&
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!iscntrl(c) &&
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c != '/' &&
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c != '\\' &&
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c != '=' &&
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c != '$';
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}
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#define MAX_LEN (128 * 1024) /* Longest a result can expand to */
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/* Very basic expansion that looks for variable references like $NAME and expands them
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*
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*/
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char *expand_environment(const char *input, const char *src_name, int src_line_no)
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{
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char *result = malloc(MAX_LEN);
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char *out = result;
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const char *in = input;
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while (*in != '\0') {
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// check for buffer overflow
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if (out >= result + MAX_LEN - 1) {
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goto too_long;
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}
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if (*in != '$') {
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// not part of an environment variable name, copy directly
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*out++ = *in++;
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continue;
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}
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// *in points to start of an environment variable reference
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in++;
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const char *env_start = in;
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while (allowed_env_var_name(*in)) { // scan to the end of the name
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in++;
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}
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size_t env_len = in - env_start;
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// make a buffer to hold the environment variable name
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//
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// strndup is not available on mingw32, apparently.
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char *env_name = calloc(1, env_len + 1);
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assert(env_name != NULL);
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strncpy(env_name, env_start, env_len);
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const char *value = getenv(env_name);
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if (value == NULL || strlen(value) == 0) {
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printf("%s:%d: undefined environment variable \"%s\"\n",
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src_name, src_line_no, env_name);
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exit(1);
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}
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free(env_name);
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if (out + strlen(value) >= result + MAX_LEN - 1) {
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goto too_long;
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}
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strcpy(out, value); // append the value to the result (range checked in previous statement)
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out += strlen(value);
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}
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*out = '\0'; // null terminate the result string
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return result;
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too_long:
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printf("%s:%d: Expansion is longer than %d bytes\n",
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src_name, src_line_no, MAX_LEN);
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free(result);
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exit(1);
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}
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void free_expanded(char *expanded)
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{
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free(expanded);
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}
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