182 lines
5.9 KiB
C
182 lines
5.9 KiB
C
/*
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* Copyright (c) 2014 Jonas 'Sortie' Termansen.
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*
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* Permission to use, copy, modify, and distribute this software for any
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* purpose with or without fee is hereby granted, provided that the above
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* copyright notice and this permission notice appear in all copies.
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*
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* THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
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* WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
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* MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
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* ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
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* WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
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* ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
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* OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
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*
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* stdlib/setenv.c
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* Set an environment variable.
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*/
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#include <errno.h>
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#include <stdbool.h>
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#include <stdlib.h>
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#include <string.h>
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#include <unistd.h>
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static inline
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bool matches_environment_variable(const char* what,
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const char* name, size_t name_length)
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{
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return !strncmp(what, name, name_length) && what[name_length] == '=';
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}
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static char* create_entry(const char* name, size_t name_length,
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const char* value, size_t value_length)
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{
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size_t result_length = name_length + 1 + value_length;
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size_t result_size = sizeof(char) * (result_length + 1);
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char* result = (char*) malloc(result_size);
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if ( !result )
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return NULL;
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memcpy(result, name, name_length);
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result[name_length] = '=';
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memcpy(result + name_length + 1, value, value_length);
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result[name_length + 1 + value_length] = '\0';
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return result;
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}
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static bool set_entry_at(char** environ, size_t position,
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const char* name, size_t name_length,
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const char* value, size_t value_length)
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{
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char* new_entry = create_entry(name, name_length, value, value_length);
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if ( !new_entry)
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return false;
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free(environ[position]);
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environ[position] = new_entry;
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return true;
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}
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static bool recover_environment(void)
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{
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// It is undefined behavior to change environ to another value (manually
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// taking control of the environment) and reusing any of the pointers from
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// the former environ array. A program that assigns to environ must use its
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// own memory for the environ array and all the strings pointed to by it.
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// TODO: Is that actually undefined behavior?
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// Destroy the old environ array and its entries that we'll assume is no
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// longer used as that would be undefined behavior as said above.
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if ( __environ_malloced )
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{
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for ( size_t i = 0; i < __environ_used; i++ )
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free(__environ_malloced[i]);
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free(__environ_malloced);
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__environ_malloced = NULL;
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__environ_length = 0;
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__environ_used = 0;
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}
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// Prepare a new environ array into which we'll store all the strings.
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size_t environ_length = 0;
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if ( environ )
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while ( environ[environ_length] )
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environ_length++;
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size_t environ_size = sizeof(char*) * (environ_length + 1);
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char** environ_malloced = (char**) malloc(environ_size);
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if ( !environ_malloced )
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return false;
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// Duplicate all the environment variables into the new environment.
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for ( size_t i = 0; i < environ_length; i++ )
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{
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if ( !(environ_malloced[i] = strdup(environ[i])) )
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{
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for ( size_t n = 0; n < i; n++ )
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free(environ_malloced[n]);
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free(environ_malloced);
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return false;
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}
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}
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environ_malloced[environ_length] = NULL;
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// Switch to the newly recovered environment.
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environ = __environ_malloced = environ_malloced;
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__environ_used = environ_length;
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__environ_length = environ_length;
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return true;
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}
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int setenv(const char* name, const char* value, int overwrite)
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{
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if ( !name || !value )
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return errno = EINVAL, -1;
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if ( !name[0] )
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return errno = EINVAL, -1;
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// Verify the name doesn't contain a '=' character.
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size_t name_length = 0;
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while ( name[name_length] )
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if ( name[name_length++] == '=' )
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return errno = EINVAL, -1;
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// Take back control of the environment if the user changed the environ
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// pointer to something the user controls or if the environment has not been
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// initialized yet besides the read-only initial environment.
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if ( (!environ || environ != __environ_malloced) && !recover_environment() )
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return -1;
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size_t value_length = strlen(value);
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// Attempt to locate an existing environment variable with this name.
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for ( size_t i = 0; i < __environ_used; i++ )
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{
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char* previous_entry = environ[i];
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if ( !matches_environment_variable(previous_entry, name, name_length) )
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continue;
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// Report success if the caller doesn't want us to change an existing
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// environment variable, but still set the variable if not set yet.
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if ( !overwrite )
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return 0;
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// Avoid the need to allocate a new string if there is room in the old
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// allocation for the contents of the new string.
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char* previous_value = previous_entry + name_length + 1;
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size_t previous_value_length = strlen(previous_value);
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if ( value_length <= previous_value_length )
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{
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strcpy(previous_value, value);
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return 0;
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}
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// Insert the new entry in the environ array at the same location.
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bool result = set_entry_at(environ, i, name, name_length, value, value_length);
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return result ? 0 : -1;
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}
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// Expand the environ array if it is currently fully used such that we have
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// room to insert the new entry below.
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if ( __environ_used == __environ_length )
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{
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size_t new_length = __environ_length ? 2 * __environ_length : 16;
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size_t new_size = sizeof(char*) * (new_length + 1);
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char** new_environ = (char**) realloc(environ, new_size);
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if ( !new_environ )
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return -1;
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environ = __environ_malloced = new_environ;
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for ( size_t i = __environ_used; i <= new_length; i++ )
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environ[i] = NULL;
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__environ_length = new_length;
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}
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// Append the new entry to the environ array.
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if ( !set_entry_at(environ, __environ_used,
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name, name_length,
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value, value_length) )
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return -1;
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return __environ_used++, 0;
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}
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